Experimental Study on Transition Metal Complexes ...

Experimental Study on Transition Metal Complexes

Containing N,S'-, S,S'- and O,O'- Coordinated π

Radicals

Dissertation for the degree of Doktor der Naturwissenschaften in the

Fakultät für Chemie at the Ruhr-Universität Bochum

Presented by

Ruta R. Kapre

Mülheim an der Ruhr, June 2005

This work was independently carried out between August 2002 and May 2005 at the

Max-Planck-Institut für Bioanorganische Chemie, Mülheim an der Ruhr, Germany.

Submitted on: 10- 06 - 2005 Examination: 15-07-2005

Examination Committee:

Prof. Dr. K. Wieghardt (Referent)

Prof. Dr. W. S. Sheldrick (Koreferent)

Prof. Dr. W. Sander (Prüfer)

Acknowledgements

I would like to thank everyone who supported me and help me during the

course of this work. I am especially indebted to:

Prof. Dr. K. Wieghardt, to whom I express my deepest gratitude for giving me an

opportunity to join his group and perform research in this fascinating theme. His

unbridled support and encouragement have contributed a lot in sustaining my efforts.

Prof. Dr. P. Chaudhuri for many helpful suggestions.

Dr. Thomas Weyhermüller and Mrs. Heike Schucht for X-ray crystal structure analyses.

Dr. E. Bothe and Mrs. Petra Höfer for electrochemical measurements.

Dr E. Bill for teaching me the basics of the EPR and magnetochemistry, helping me in

the simulation of EPR spectra and in interpreting my results.

Dr. F. Neese for valuable suggestions regarding the interpretation of XAS data.

I am also thankful to Dr Joris van Slageren, Universität Stuttgart, Germany, for the Far-

IR measurements.

Dr. S. DeBeer George, Stanford Institute, USA, for providing the XAS data and helping

me to the interpretation of the XAS results.

Mr. A. Göbels and Mr. F. Reikowski for measurements of SQUID and EPR.

Mrs. R. Wagner, and Mr. U. Pieper for their help in the laboratory.

Dr. Kil Sik Min for an invaluable help in the lab at the inception of my stay in Muelheim.

Dr. Nuria Aliaga-Alcade, for her useful ideas, checking manuscript and for cheerfulness

throughout my work. For keeping my spirits up and enriching me.

I am very thankful to Dr. John F. Berry for the careful revision of the manuscript, many

fruitful suggestions and honing my final draft.

Special thanks to my colleagues Dr. Krzysztof Chłopek, Dr. Kallol Ray, Dr. Laurent

Benisvy, Dr. Kathrin Merz, Dr. Yufei Song, Dr. Isabelle Sylvestre, Mr. Sumit Khanra,

Mr. Chandan Mukherjee, Mr. Shaon Presow, Dr. Taras Petrenko, Ms. Elham Safaei for

lots of help and a friendly atmosphere in the lab.

Mrs. Jutta Theurich for ordered publications.

I am very much grateful to my mother and father for their motivation and their

immeasurable support and eminent understanding through out the years, and my sister

Reshma and brother Hrishikesh for their love and encouragement.

I am highly indebted to Sachin, for inspiration and many valuable suggestions. I thank

him for invaluable support.

Last but not the least to all my friends, Suchismita, Mamata, Basak family and all my

well-wishers in India for inspirations and friendly help.

I am thankful to the Max-Planck-Gesellschaft (MPG) for financial support.

To my dear parents

Contents and abbr. i

Contents Page

numbers Chapter 1 Introduction

1

1.1 General introduction 1

1.2 Objective of this work 4

1.3 Characterization techniques 7

1.4 References 13

Chapter 2 Cobalt complexes of o-aminothiophenolate [As(Ph)4] [Co(LNS)2] (1) and [N(n-Bu)4] [Co(LNS)2] (2)

15

2.1 Introduction 15

2.2 Synthesis and characterization of 1and 2 18

2.3 Molecular structures of 1and 2 18

2.4 Electrochemistry of 1 21

2.5 Electronic absorption spectra 25

2.6 EPR spectroscopy 26

2.7 Magnetization 28

2.8 Conclusions 32

2.9 References 33

Chapter 3 Cuboidal complexes of chromium with 3,5-di-tert-butyl-aminothiophenol Na[Cr3(tLNS)3(OEt)3(µ-OMe)4(OHEt)4] (3) Na[Cr3(tLNS)3(OMe)3(µ-OMe)4(OHMe)3] (4a) Na [Cr3(tLNS)3(OMe)3(µ-OMe)4(OH2)3] (4b)

35

3.1 Introduction 35 3.2 Synthesis and characterization of 3 and 4 36 3.3 Molecular structures of 3, 4a and 4b 37 3.4 Electrochemistry of 3 43 3.5 Electronic absorption spectra 44

Contents and abbr. ii

3.6 Magnetochemistry 45

3.7 Conclusions 50

3.8 References 51

Chapter 4 Ni, Co and Zn complexes of 2-phenylbenzothiazoline

53

4.1 Introduction 53

4.2 Synthesis and characterization of 5, 5b, 6, 6b and 7 56

4.3 Molecular structures of 5, 5b, 6, 6b and 7 58

4.4 Electrochemistry of 5 and 6 66


4.6 X-band EPR spectroscopy and magnetic susceptibility 73

4.7 Conclusions 81

4.8 References 82

Chapter 5 Cr complexes of 3,5-di-tert-butyl-1,2-benzenedithiol and 3,6-di-tert-butyl-catacholate [N(n-Bu)4][Cr(tLSS)3] (8), [As(Ph)4][CrO(tLSS)2] (9), [Cr(tLCat)3] (10), [Co(Cp)2][Cr(tLCat)3] (10b)

85

5.1 Introduction 85

5.2 Synthesis and characterization of 8, 9, 10 and 10b 88

5.3 Molecular structures of 8, 9 and 10 89

5.4 Electrochemistry of 8, 9 and 10 96


5.6 X-band EPR spectroscopy and magnetic susceptibility 104

5.7 Conclusions 110

5.8 References 111

Contents and abbr. iii

Chapter 6 Mo and W complexes of 2-mercapto-3,5-di-tert-butylaniline and 3,5-di-tert-butyl-1,2-benzenedithiol [Mo(tLNS)3] (11), [Mo(tLSS)3] (12), [N(n-Bu)4][Mo(tLSS)3] (12b), [W(tLSS)3] (13), [N(n-Bu)4] [W(tLSS)3] (13b)

115

6.1 Introduction 115

6.2 Synthesis and characterization of 11, 12, 12b, 13 and 13b 117

6.3 Molecular structures of 11, 12, 12b, 13 and 13b 118

6.4 Electrochemistry 129


6.6 EPR spectroscopy and magnetization 137

6.7 Conclusions 141

6.8 References 142

Chapter 7 XAS of Cr, Mo and W complexes

145

7.1 Introduction 145

7.2 Results and analysis 146

7.3 Conclusions 153

7.4 References 154

Chapter 8 Summary

157

Chapter 9 Experimental

163

9.1 Synthetic procedures 163

9.2 Methods and equipments 187

Appendices 193

1. Magnetochemical data 194

2. Crystallographic data 203

3. Curriculum vitae 213

Contents and abbr. iv

Abbreviations Technical terms:

AF : antiferromagnetic

Ag / AgNO3 : reference electrode

av. : average

B : magnetic field

CT : charge transfer

D : zero-field splitting

deg. : degree (°)

e- : electron

E : total energy

exp. : experimental

Fc/Fc+ : internal electrochemical standard

H : Hamiltonian

J : coupling constant ( cm-1)

m/z : mass per charge

RT : room temperature (293K)

S : electron spin

sim. : simulated

TIP : temperature independent paramagnetism

units:

Å : angstrom (10-10 m)

cm : centimeter

emu : electromagnetic unit

G : gauss

h : hour

K : Kelvin

m : meter

M : molar

min. : minute

Contents and abbr. v

mm : millimeter

nm : nanometer (10-9 m)

s : second

T : tesla

V : volts

µB : bohr magneton

latin expressions:

ca. : around

et a. : and coworkers

e.g. : for example

i.e. : namely

tert- : tertiary

vs. : versus, against

symbols:

λ : wavelength (nm)

ε : extinction coefficient (M-1cm-1)

µeff : magnetic moment (µB)

solvents and reagents:

Cat.: catechol

CH2Cl2 : dichloromethane

CHCl3 : chloroform

Et2O : diethylether

Et3N : triethylamine

EtOH : ethanol

HCl : hydrogen chloride

KBr : potassium bromide

MeOH : methanol

MeCN : acetonitrile

NaOMe : sodium methoxide

Contents and abbr. vi

TBAPF6 : tetrabutylammonium hexafluorophosphate

THF : tetrahydrofuran

techniques:

CV : cyclic voltammetry

EA : elemental analysis

EI : electron ionisation

EPR : electron paramagnetic resonance

ESI : electrospray ionisation

IR : infrared spectroscopy

MS: mass spectroscopy

SQUID : superconducting quantum interface device

SW : square wave voltammetry

UV-Vis : ultraviolet-visible spectroscopy

XAS : X-ray absorption spectroscopy

Chapter 1 1

1.1 General introduction

It is well known that transition metal ions comprise the active sites of

certain enzymes, providing binding sites for substrates and thereby activating the

appropriate bonds of the substrates. Transition metals have a unique accessibility of

variable oxidation states, can act as reservoirs for electrons by accepting and donating

electrons during redox cycles and stabilize otherwise very reactive amino acid radicals,

e.g., phenoxyl radicals in tyrosine residues, thiyl radicals in cysteine residues etc. The

realization of the widespread occurrence of amino-acid radicals in enzyme catalysis has

recently been documented in the literature,1 and the discovery of tyrosine radicals in

various metalloproteins involved in oxygen dependent enzymatic catalysis3 has prompted

continued development in the coordination chemistry of phenol containing ligands.2 The

synthetic analogue of the tyrosine radical is the phenoxyl radical, in which the phenol

groups have the potential ability to form one-electron oxidized phenoxyl radical

complexes. This has led bioinorganic chemists to design and synthesize transition metal

complexes of different phenol-containing ligands for mimicking the structural and/or

functional aspect of metalloenzymes. For example, in order to understand Galactose

oxidase, the coordination chemistry of transition metal ions with radical containing

Chapter 1 Introduction

Introduction 2

ligands such as phenoxyl, anilino and thiyls has been developed in our group. A large

number of transition metal complexes with O,O'-coordinated o-benzosemiquinonate(1-),

N,N'-coordinated o-diiminobenzosemiquinonate(1-), O,N-coordinated o-

iminobezoquinonate(1-), N,S-coordinated o-iminothioenebenzosemiquinonate(1-) and

S,S’-coordinated o-dithiobenzosemiquinonate(1-) π radical ligands have been synthesized

in recent years, characterized by various spectroscopic methods and studied

theoretically.5 The main focus of these studies is the correct description of the electronic

structure of species containing open shell organic ligands and paramagnetic metal ions. In

many cases, the complexes studied have been known since the 1960s, though

characterization at that time was often inadequate to assign unambiguously the proper

oxidation state of the metal. The reason for these discrepancies was the mistreatment of

the terms like formal and physical oxidation state. The formal and physical

(spectroscopic) oxidation states, which are both different concepts, need not always be

identical for a given coordination compound. The formal oxidation state denotes the

charge left on the metal after all ligands have been removed in their normal closed shell

configuration. The physical oxidation state is derived from a known dn configuration.6

Thus, discrepancies arise when an organic radical with an open shell electron

configuration is coordinated to a transition metal ion. At this point, the term non-innocent

ligand is more convenient and is used to emphasize the fact that some ligands do not

possess a closed-shell configuration. This means that these ligands can exist in different

oxidation states while coordinated to metal. It has been shown that these different

oxidation levels can be distinguished by using high quality X-ray crystallography

performed at cryogenic temperatures, and shown below are the significant bond distances

for different ligands. Thus, it is experimentally possible to distinguish between the two

electronic structures A and B by using high quality X-ray crystallography (scheme 1.1.1).

Scheme 1.1.1

X

Y

Mn+

X

Y

M(n-1)+

A B

Chapter 1 3

In general, The C-X/Y bond lengths vary systematically. In the N,S-

coordinated o-aminothiophenolato(1-) [(LNSAP)]1- ligand a C-N bond length of ~1.46 Å is

observed and a C-S bond length of ~1.76 Å. In o-imidothiophenolato(2-) [(LNSIP)]2-, C-N

and C-S bond distances of ~1.40 Å and ~1.75 Å, respectively are observed. The C-N and

C-S bond distances are intermediate between those of a single and double bond i.e. at

~1.36 Å and ~1.72 Å, respectively in the o-iminothiobenzosemiquinonato(1-) [(LNSISQ)]1-

π-radical ligands (scheme 1.1.2).7

Similar trends have been established for O,O-coordinated catecholate(2-)

[(LCat)]2-, benzosemiquinonate(1-) [(LSQ)]1- and benzoquinone [(LBQ)]0 (scheme 1.1.3)4 as

well as in the S,S-coordinated o-dithiolato (2-) [(LSS)]2- and o-dithiobezosemiquinonate

(1-) [(LSSSQ)]1- π-radical ligands (scheme 1.1.4).8

(Lcat)2- (LSQ)1- (LBq)0

Scheme 1.1.3: Redox activity of o-benzoquinone ligands.

Scheme 1.1.2: Redox activity of o-aminothiophenolate ligands.

Introduction 4

In addition to the changes in the C-X bond distances, X,Y-coordinated

(LSQ)1- radicals display a quinoid type distortion of the six-membered ring which is not

observed in closed shell analogues. This distortion involves two alternating short C-C

distances of 1.37 ± 0.01 Å and four longer ones of ~1.415 ± 0.01Å, whereas in the

closed-shell aromatic mono- and dianions, the six C-C bond lengths of 1.39 ± 0.01 Å are

equidistant.

1.2 Objective of this work

As it is possible to determine the true dn configuration of the central metal

ion and measure its physical oxidation state spectroscopically (UV-vis, EPR, X-ray

absorption near edge (XANE) spectroscopy) we decided to reinvestigate the coordination

chemistry of complexes with the above mentioned ligands. In many cases the ligands are

modified by adding tert-butyl substitutents in order to avoid the solubility problems often

encountered in compounds containing un-substituted ligands.

There are about 120 known structures of transition metal complexes

containing at least one N,S-coordinated o-aminothiophenolato derived moiety. Often, the

formal charge or the oxidation level of the moiety was not specified. It is only when

Scheme 1.1.4: Redox activity of o-dithiolele ligands.

Chapter 1 5

Wieghardt et al. found evidence for coordinated radical ligands that the non-innocent

nature of these species was contemplated. Recently the redox non-innocent nature of o-

aminothiophenolate ligands has been established in cobalt and nickel complexes.9

Therefore this work contains the synthesis and characterization of a square-planar cobalt

complex with o-aminothiophenolate, whose electronic structure can now be understood.

Also, in a series of N,S-coordinated nickel and cobalt complexes i.e. [Ni(ddbt)] and

[Co(ddbt)]10 a valence isomer structure was reported, where both forms as shown below

(Fig. 1.2.1) have equal weight. Therefore we resynthesized these complexes in order to

study the redox properties of ligand in the presence of different metal ions.

As compared to the huge number of bis(dithiolene) complexes reported in

the literature, the reports of tris(dithiolene) complexes are fewer (There are roughly 50

homoleptic tris(dithiolene) complexes

reported in the CSDC).11 The electronic

structure and oxidation level of ligands in

bis(dithiolene) complexes has been

explicitly verified for a number of

complexes with the aid of theoretical and

spectroscopic methods,8 however that in

the case of tris(dithiolene) complexes is

still not explicitly clear. The initial

structural report of Re[S2C2(C6H5)2]3,12

and shortly thereafter the reports of

Y

X

M

X

Y

X

YR1

R3

R2

R1

R3

R2

R1

R3

R2

Fig. 1.2.2: Metal tris-chelate complexes.

Fig. 1.2.1: Valence isomer structure suggested by Kushi et al.

N

S

N

S

H H

NiN

S

N

S

H H

Ni

R R R R

Introduction 6

[Mo(edt)3] and [V(S2C2Ph2)3] were the first six-coordinate complexes to exhibit near

trigonal prismatic geometries. Since these reports, the reasons for the preferential

formation of complexes with trigonal prismatic coordination geometry over octahedral

geometry has been discussed extensively13 and the elucidation of the electronic structure

of these species has become a matter of great interest. These are predominantly

complexes of the early transition metal elements, e.g. V, Mo and W. The main features of

these compounds were the assignment of d0 configuration to the central metal centers in

Cr, Mo and W complexes. In our view, as the d3 configuration was well established to the

tris-o-catecholato Cr compounds, the analogous compounds with o-dithiolene are

expected also to possess a +3 oxidation state.

Therefore we undertook the synthesis of tris (o-dithiolato) complexes with

Cr, Mo and W and their characterization is reported in chapters 5 and 6. A schematic

presentation of metallo tris complexes synthesized in this work is shown in Fig. 1.2.2 and

the ligands with their substitutions are displayed in table 1.2.1

Complex X Y R1 R2 R3

11 NH S t-butyl t-butyl H

8, 12, 12b, 13, 13b S S t-butyl t-butyl H

10, 10b O O t-butyl H t-butyl

Table 1.2.1: ligands with their substitutions used for metallo-tris complexes.

Chapter 1 7

1.3 characterization techniques

The spectroscopic methods employed in this work

cover 10 orders of magnitude in photon energy. Different energy

regions provide different and complementary information about

the nature of transition metal complexes. Fig. 1.3.1 illustrates the

various regions into which electromagnetic radiation has been

divided.14,15 The molecular processes associated with each region

are quite different. The descriptions of some of these

spectroscopic techniques are summarized below. Apart from the

spectroscopic techniques, electrochemistry is mainly used to

observe the redox processes of compounds under study.

1) Microwave region

Electron paramagnetic resonance (EPR)

spectroscopy is a branch of spectroscopy in

which radiation of microwave frequency is

absorbed by molecules, ions, or atoms

possessing electrons with unpaired spins. In

EPR, different energy states arise from the

interaction of the unpaired electron spin

moment (given by ms = ± ½ for a free

electron) with the magnetic field (Zeeman

effect, Fig. 1.3.2). The Zeeman

Hamiltonian for the interaction of an

electron with the magnetic field is given by

Fig. 1.3.1: Regions of electromagnetic radiation.

Fig. 1.3.2: The removal of the degeneracyof the electron spin states by magneticfield, and resulting EPR spectrum.

Introduction 8

H = g β H Ŝz where g for a free electron has the value 2.0023193; β is the electron Bohr

magneton, Ŝz is the spin operator; and H is the applied field strength. For a free radical, g

remains close to the free-electron value. In chemical systems, the unpaired electron

occupies an orbital that may be localized on a single atom or may be heavily delocalized

across a molecule or radical. Thus, the g-value reflects the nature of this orbital. In our

systems free electron is often situated on the ligand orbitals, thus g values of very close to

uncoordinated free organic radical are observed. On the other hand, a metal centered free

electron is affected more by spin-orbit coupling and identified by deviation of g values

from free organic radical. An EPR spectrum may show additional fine structure when the

atom on which the unpaired spin is centered has a nuclear spin. In this respect EPR

spectroscopy plays a very important role in our systems to identify the environment of

unpaired electrons.

2) Infrared region

Molecular vibrations occur in the IR region of the spectrum. In order to be

infrared active, there must be a dipole change during the vibration and this change may

take place either along a symmetry axis or at right angles to this axis. A non-linear N-

atomic molecule can have 3N-6 different internal vibrations, if, on the other hand, the

molecule is linear, 3N-5 degrees of vibrational freedom are available. As frequencies are

highly characteristic of functional groups, they are widely used for the analysis of

particular groups. For example, S,S-coordinated o-dithiobezosemiquinonate(1-)

[(LSSSQ)]1- π-radical ligands show an IR stretch at ~ 1106 cm-1, which has proven very

important evidence for identification of radical ligands.

3) Near IR, Visible and UV region

Electronic transitions of molecules cover this region. Both the position and

intensity of the absorption due to an electronic transition are very characteristic of the

molecular group involved. The position of absorption is given at the point of maximum

absorption, λmax (nm). For practical reasons the electronic spectrum is divided into three

regions: (i) the visible region, between 400-750 nm (25,000-13,300 cm-1) (ii) The near

ultra-violet region, between 200-400 nm (50,000-25,000 cm-1) (iii) Near infrared region,

between 750-2000 nm (13,300-5,000 cm-1). Coordination compounds always show d-d

transitions of weak intensity, which are characteristic of involved metal ion. Other than

Chapter 1 9

these weakly allowed transitions, fully allowed transitions occur in strongly covalent

complex with the metal ion and the ligand having complementary redox properties. These

are known as charge-transfer (CT) bands. In our systems these CT bands are dominated

due to the redox non-innocent nature of ligands. The square-planar and octahedral

complexes containing π-radical ligand exhibit characteristic inter valence charge transfer

(IVCT), ligand to ligand charge transfer (LLCT) and ligand to metal charge transfer

bands (LMCT) bands. The intensity of an electronic absorption is given by the simple

equation: ε = A / c l, where c and l are the concentration and path length of the sample, A

is the absorbance and ε is the extinction coefficient.

4) X-ray region

a) X-ray crystallography

Using X-ray crystallography, one can determine the precise composition

and atomic arrangement of any crystalline substance. A single crystal is composed of

some repeating three-dimensional pattern of electron density. The internal arrangements

of the electrons in the crystal lattice determine the directions and intensities of X-ray

beams scattered from it. As shown in scheme 1.1.2, 1.1.3 and 1.1.4, X-ray

crystallography allows identifying the presence of π-radical ligands in coordinated

transition metal complexes due to distinctive features in bond distances of ligands.

b) X-ray absorption spectroscopy (XAS)

XAS probes core electronic energy levels and includes photo dissociation

from core energy levels. The spectrum can be divide into two regions. The edge and the

EXAFS regions. The analysis of the edge region (XANES), i. e. the position of the edge

and the assignment of peaks near the edge give information about oxidation states,

covalency (increasing ligand character of metal d orbitals), molecular symmetry of the

site, and coordination number. The EXAFS provides, local structural information about

the atomic neighborhood of the element being probed. The information consists of the

number of ligands, the identity of these ligand atoms, and precise radial distances. The X-

ray photon absorbed (hν) results in transitions within the atomic energy levels of the

absorbing atom. During the spectroscopic scan absorption occurs when the photon has an

energy equal to the ionization energy of the core electron. At lower X-ray energies, X-ray

induced ionisation of 2p or 2s electrons gives rise to what are called LIII, LII and LI

Introduction 10

absorption edges. At significantly higher energies, photoionization of 1s electrons gives

rise to the K edge. For a given element, K edge energies depend on the chemical

environment of the element. For example, higher oxidation state metals have higher

positive charge, making it slightly more difficult to photodissociate the 1s electron,

shifting the K edge to higher energy. Shifts of 1-2 eV per oxidation state are typical for

first row transition metals. For this reason, in o-dithiolene complexes S K-edge studies

have proven to be very significant for the identification of redox state of ligands.

5) Cyclic voltammetry (CV)

In this technique an "electrochemical spectrum" indicating the potentials at

which chemical processes occur can be rapidly obtained. In CV experiments the cell

current is recorded as a function of the applied potential. It involves sweeping the

electrode potential between limits E1 and E2 at a known scan rate. On reaching the

potential E2 the sweep is reversed and again reaches to the initial potential E1. The scan

rates used range from 50 mV/s up to 1000 mV/s. In the case of a reversible reaction as

described by equation 1.3.1, we assume that only O is initially present and when linear

potential sweep is applied, reduction takes place to produce R.

A reversible CV can only be observed if both O and R are stable and the

kinetics of the electron transfer processes are fast, so that at all potentials and potential

scan rates the electron transfer process on the surface is in equilibrium so that surface

concentrations follow the Nernst equation. For this reason this technique has proven very

important for the identification of radical ligands, which show typical reversible waves in

the CV. Along with CV, controlled potential coulometry is used to determine the overall

number of electrons involved in an electrode process. It is also used to prepare oxidation

and reduction products to enable them to be identified by EPR and electronic absorption

spectroscopy.

RneO ⇔−+ equation 1.3.1

Chapter 1 11

1.4 The ligands used in this work

1) o-aminothiophenol [LNS]

2) 2-phenylbenzothiazoline [LPh]

3) 2-mercapto-3,5-di-tert-butylaniline H2[tLNS]

4) 3,5-di-tert-butyl-1,2-benzenedithiol H2[tLSS]

5) 3,6-di-tert-butylcatacholate H2[tLCat]

Complexes synthesized in this work are:

1) [As(Ph)4] [CoIII(LNS)2] (1)

2) [N(n-Bu)4] [CoIII(LNS)2] (2)

3) [CoIII(LNS)(LISQNS)] (2a)

NH2

SH

HN

S

Ph

H

NH2

SH

SH

SH

OH

OH

(1) H2[LNS] (2) H2[LPh] (3)H2[tLNS]

(4) H2[tLSS] (5) H2[tLCat]

Introduction 12

4) Na [Cr3(tLNS)3(OEt)3(µ-OMe)4(OHEt)4] (3)

5) Na [Cr3(tLNS)3(OMe)3(µ-OMe)4(OHMe)3] (4a)

6) Na [Cr3(tLNS)3(OMe)3(µ-OMe)4(OH2)3] (4b)

7) [Ni(Phbt)2] (5i)

8) [Ni(ddbt)] (5)

9) [Co(Cp)2] [Ni(ddbt)] (5b)

10) [Co(Phbt)2] (6i)

11) [Co(ddbt)] (6)

12) [Co(Cp)2] [Co(ddbt)] (6b)

13) [Zn(Phbt)2] (7)

14) [N(n-Bu)4] [Cr(tLSS)3] (8)

15) [N(n-Bu)4] [CrO(tLSS)2] (9)

16) [Cr(tLCat)3] (10)

17) [Co(Cp)2] [Cr(tLCat)3] (10b)

18) [Mo(tLNS)3] (11)

19) [Mo(tLSS)3] (12)

20) [N(n-Bu)4] [Mo(tLSS)3] (12b)

21) [W(tLSS)3] (13)

22) [N(n-Bu)4] [W(tLSS)3] (13b)

Chapter 1 13

1.5 References

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1990, 90, 1343. (c) Ochiai, E. -I. J. Chem. Ed. 1993, 70, 128. (d) Stubbe, J.; van

der Donk, W. A. Chem. Rev. 1998, 98, 705. (e) Holm, R. H.; Solomon, E. I. Guest

Editors, Chem. Rev. 1996, 96, 7.

2) (a) Bill, E.; Müller, J.; Weyhermüller, T.; Wieghardt, K. Inorg. Chem. 1999, 38,

5795. (b) Wang, Y.; Stack, T. D. P. J. Am. Chem. Soc. 1996, 118, 13097. (c)

Zurita, D.; Gautier-Luneau, I.; Menage, S.; Piere, J. L.; Saint-Aman, E. J. Biol.

Inorg. Chem. 1997, 2, 46. (d) Shimazaki, Y.; Huth, S.; Odani, A.; Yamauchi, O.

Angew. Chem., Int. Ed. 2000, 112, 1666. (e) Halfen, J. A.; Jazdzewski, B. A.;

Mahapatra, S.; Berreau, L. M.; Wilkinson, E. C.; Que, L.; Tolman, W. B. J. Am.

Chem. Soc. 1997, 119, 8217.

3) Goldberg, D. P.; Lippard, S. J. Adv. Chem. Ser. 1995, 246, 59.

4) Pierpont C. G. Coord. Chem. Rev. 2001, 216 and references therein.

5) (a) Bachler, V.; Olbrich, G.; Neese, F.; Wieghardt, K. Inorg. Chem. 2002, 41,

4179. (b) Herebian, D.; Wieghardt, K.; Neese, F. J. Am. Chem. Soc. 2003, 125,

10997. (c) Herebian, D.; Bothe, E.; Weyhermüller, T.; Wieghardt, K. J. Am.

Chem. Soc. 2003, 125, 9116. (d) Sun, X.; Chun, H.; Hildenbrand, K.; Bothe, E.;

Weyhermüller, T.; Neese, F.; Wieghardt, K. Inorg. Chem. 2002, 41, 4295. (e)

Min, K. S.; Weyhermüller, T.; Bothe, E.; Wieghardt, K. Inorg. Chem. 2004, 43,

2922.

6) Jörgensen, C. K. Oxidation Numbers and Oxidation States; Springer: Heidelberg,

Germany, 1969.

7) (a) Bothe, E.; Verani, C. N.; Weyhermüller, T.; Chaudhuri, P.; Wieghardt, K. J.

Inorg. Biochem. 2001, 86, 154. (b) Herebian, D.; Ghosh, P.; Chun, H.; Bothe, E.;

Weyhermüller, T.; Wieghardt K. Eur. J. Inorg. Chem. 2002, 8, 1957. (c)

Herebian, D.; Bothe, E.; Bill, E.; Weyhermüller, T.; Wieghardt K. J. Am. Chem.

Soc. 2001, 123, 10012. (d) Ghosh, P.; Bill, E.; Weyhermüller, T.; Neese, F.;

Wieghardt, K. J. Am. Chem. Soc. 2003, 125, 1293. (e) Ghosh, P.; Bill, E.;

Weyhermüller, T.; Wieghardt, K., J. Am. Chem. Soc. 2003, 125, 3967. (f) Ghosh,

Introduction 14

P.; Begum, A.; Herebian, D.; Bothe, E.; Hildenbrand, K.; Weyhermüller, T.;

Wieghardt, K. Angew. Chem. Int. Ed. 2003, 42, 563.

8) (a) Ray, K.; Weyhermüller, T.; Goossens, A.; Crajé, M. W. J.; Wieghardt, K.

Inorg. Chem. 2003, 42, 4082. (b) Ray, K.; Bill, E.; Weyhermüller, T.; Wieghardt,

K. J. Am. Chem. Soc. 2005, 127, 5641. (c) Ray, K.; Begum, A.; Weyhermüller,

T.; Piligkos, S.; Slageren, J. V.; Neese, F.; Wieghardt, K. J. Am. Chem. Soc. 2005,

127, 4403.

9) Bill, E.; Bothe, E.; Chaudhuri, P.; Chlopek, C.; Herebian, D.; Kokatam, S.; Ray,

K.; Weyhermüller, T.; Neese, F.; Wieghardt, K. Chem. Eur. J. 2005, 11, 204.

10) Kawamoto, T.; Kuma, H.; Kushi, Y. Bull. Chem. Soc. Jpn. 1997, 70, 1599.

11) Stiefel, E. I. editor, Progr. Inorg. Chem. 2004, 111.

12) Eisenberg, R.; Ibers, J. A. J. Am. Chem. Soc. 1965, 87, 3776.

13) (a) Kepert, D. L. Inorganic stereochemistry; Inorganic chemistry concepts 6;

Spinger Verlag: Berlin, 1982, chapter 8. (b) Huheey, J. E.; Keiter, R. L. Inorganic

chemistry: principles of structure and reactivity, 4th ed.; Harper: New York, 1993,

Chapter 13. (c) Schrauzer, V. P.; Mayweg, V. P. J. Am. Chem. Soc. 1966, 88,

3235. (d) Stiefel, E. I.; Eisenberg, R.; Rosenberg, R. C.; Gray, H. B. J. Am. Chem.

Soc. 1966, 88, 2956.

14) Drago, R. S. Physical methods in chemistry, Saunders Company: New York,

1965.

15) Banwell, C. N. Fundamentals of molecular spectroscopy, McGraw-Hill: UK

1972.

Chapter 2 15

2.1 Introduction

Transition metals with a mixed nitrogen-sulfur coordination environment

are often encountered in the active sites of metalloenzymes. Some enzymes such as ATP

sulfurylase1 or nitrile hydratase2 possess a cobalt center, which has been

spectroscopically characterized. A great interest in these biological systems has been

developed and therefore the synthesis of new cobalt complexes containing mixed

nitrogen-sulfur coordination is also of interest.

The majority of CoIII complexes found in the literature have an octahedral

coordination sphere. Only a few square planar complexes are known which are typically

stabilized by four strongly σ-donating ligands. Examples of such monoanionic complexes

with strong donor ligands such as S,S'-dithiolato, 3 N-carboxamido-O-alkyloxo4 have been

reported and characterized. These complexes exist having a spin triplet ground state.

Additionally, complexes such as [Co(bdt)2][N(n-bu)4], [Co(tdt)2][N(n-bu)4] (bdt =

bis(1,2-benzenedithiolato)), (tdt = bis(3,4-toluenedithiolato))5 and [Co(3-Pr(bi))2] (3-

Pr(bi) = [HNCON(C3H7)CONH]2-)6 have been characterized by their magnetic

susceptibility, and a spin triplet ground state was also found. Well-characterized square

planar CoIII complexes having a mixed N2S2 ligand environment are rare: [CoIII(L)]Na,

(L= di-N-carboxamido-di-thiolato, a tetradentate ligand)7a and [CoIII(N2S2)]NEt3 (N2S2 =

Chapter 2 Cobalt complexes of

o-aminothiophenolate

Co complexes 16

N, N'-(2-thioacetyl-isobutyryl)-2-aminobenzylamine).7bRecently, it has been shown that

N,S-coordinated o-aminothiophenolate ligands are redox-non-innocent and they can

exists in four different oxidation and protonation states (Scheme 2.1.1).10

So far, the literature concerning cobalt complexes containing o-

aminothiophenolate ligands is full of ambiguities, which are mostly due to the air

sensitivity of these complexes and the redox non-innocent nature of the ligands. For

example, Livingstone8 reported the first cobalt complex with an o-aminothiophenolate

ligand in 1956 which was blue colored and formulated as [Co(abt)2] (I) (abt = o-

aminobenzenethiol(1-)) though the effective magnetic moment of 2.6 B.M at 294 K

leaves some ambiguity in its description as a low spin, square-planar cobalt (II).

Furthermore, Phillips et al.9 synthesized an orange-brown complex under anaerobic

conditions which has also been formulated as [Co(abt)2] (II) having an effective magnetic

moment of 4.2 B.M. at 292 K. Thus, even though both II and III have been assigned as

having the formula [Co(abt)2], they apparently have either different compositions or

different oxidation states of the metal or the ligands. The magnetic moment of II

decreases gradually as the temperature is lowered; at higher temperatures the Curie-

Weiss law is obeyed, but below 150 K, the reciprocal susceptibility vs. temperature plot

deviated from linearity. From the magnetic behavior of II, the structure was assigned as

an octahedral compound (with bridging sulfur) having antiferromagnetic interactions that

lead to a lowering of the magnetic moment as a function of temperature. Oxidation of

orange-brown II afforded a dark blue substance with an effective magnetic moment of

2.6 B.M. at 293 K, similar to what had been observed before by Livingstone et al. for the

blue complex II. Phillips et al.9 characterized this oxidized dark blue complex as having

the formula [Co(abt)2]OH (III) on account of its elemental analysis.

S

NH

S

NH

S

NH-e+e

-e+e

S

NH2- H+

+ H+

(LNSAP)1- (LNS

IP)2- (LNSISQ)1- (LNS

IBQ)0

Scheme. 2.1.1 Redox activity of o-aminothiophenolate, (abt) (LNS)

Chapter 2 17

With respect to this subject, an orange-brown complex similar to II with

the ligand 6-amino-2,4-di-tert-butylthiophenol [H2(tLNS)], was synthesized under strictly

anaerobic conditions.10 The magnetic moment data fitted well to a dimer model with

SCo=3/2 with g = 2.2, and J = -144cm-1. This result supports an assignment of the formula

of this complex as [CoII(tLNSAP)2]2 (IV). Oxidation of IV in air afforded a black dimeric

compound V, in which each monomeric subunit consists of a five coordinated CoII ion

and two o-iminothiobenzosemiquinonato (1-) π radicals with (S=1/2), weakly

antiferromagnetically coupling to cobalt yielding an ST=0 ground state (Fig.2.1.2).

The magnetic and spectroscopic properties of the orange-brown

compounds II and IV are very similar. This suggests that the compound II, which was

reported to be an octahedral complex, may in fact be a dimer with two CoII ions and four

aminothiophenolato (1-) ligands. Because of their unusual magnetic susceptibility data,

the blue complexes formulated as [CoII(abt)2] (I) and [CoII(abt)2]OH (III) are likely a

mixture of an orange-brown dimer [Co(abt)2]2 (II), and its oxidized blue species.

Besides these neutral complexes, Birkar et al. have reported a

monoanionic cobalt complex with an o-aminothiophenolate ligand i.e. [Co(abt)2][N(n-

bu)4] (VI) (abt = o-aminothiophenolate(2-)). Magnetic susceptibility measurements,

cyclic voltammetry and electronic spectroscopy show that the spin ground state of this

compound is S=1. It should be noted, however, that the neutral and monoanionic

Fig. 2.1.2 Schematic drawing of IV (left) and V(right)

O2, - 4e-

(IV) (V)

Co complexes 18

complexes have not been structurally characterized. All of these results inspired us to

carefully study these systems, in particular the monoanionic complex VI. Therefore VI

have been resynthesized so that it could be characterized by X-ray crystallography and

other spectroscopic techniques.

2.2 Synthesis of [As(Ph)4] [Co(LNSIP)2] (1) and [N(n-bu)4] [Co(LNS

IP)2] (2)

Complexes [As(Ph)4] [Co(LNSIP)2] (1) and [N(n-bu)4][Co(LNS

IP)2] (2) were

synthesized as blue precipitates described by Birker et al.11 To an ethanolic solution of

potassium, the ligand o-aminothiophenol, [H2(LNS)], was added followed by the addition

of CoCl2.6H2O, and [As(Ph)4]Cl respectively. A flow of air was passed for 15 minutes

yielding a blue precipitate of 1, which was isolated by filtration. Compound 2 was

obtained in a similar fashion by adding [N(n-bu)4]+ as a countercation instead of

[As(Ph)4]+. Crystals suitable for X-ray structure analysis were obtained from a mixture

of MeCN and MeOH for both of the complexes. The Infrared spectra of 1 and 2 show a

N-H stretching band at 3238 cm-1. The absence of bands around 1600 cm-1 excludes the

possibility of C=N bond suggesting single bond character for the C-N bond.

2.3 Molecular structures of 1 and 2

The crystal structures of both of the compounds 1 and 2 at 100(2) K have

been determined by X-ray crystallography using Mo Kα radiation. Fig. 2.3.1 and Fig.

2.3.2 show thermal ellipsoid plots of anions in 1 and 2, respectively and table 2.3.1 and

2.3.2 summarize relevant bond lengths.

The complex 1 crystallizes in the tetragonal space group P41. The

geometry of the cobalt center is square planar. Two isomers, cis (20%) and trans (80%)

with respect to the (N, S)- ligand coordination were found disordered in the asymmetric

unit and there is a significant distortion from square-planar geometry (dihedral angle

between N-Co-S planes equal to 5.4º). In the unit cell, the anions are well separated with

an average intermolecular Co....Co distance of 9.916(8) Å and a Co....As distance of

5.678(6) Å. The Co(1)-N(2) distance of 1.873(4) Å is similar to that observed previously

in the structure of compounds [CoIII(L)]Na : (1.872(7) Å) (L= di-N-carboxamido-di-

thiolate)7a and [CoIII(N2S2)]NEt3 : (1.882 (4) Å) (N2S2 = N, N'-(2-thioacetyl-isobutyryl)-2-

Chapter 2 19

aminobenzylamine).7b However, the Co(1)─S(1) distance of 2.176 (1) Å is longer than

the average Co-S distance in [CoIII(N2S2)] (2.134 (2) Å) but similar to that in [CoIII(tdt)2]

(2.167(4) Å) (tdt = bis(3,4-toluenedithiolate)).5 X-ray crystallography is a powerful tool

for differentiating the different oxidized forms of the ligand [H2(LNS)] since the average

C-S and C-N bond lengths are significantly different for the different oxidation states of

the ligand (Scheme 1.1, chapter 1). In the 1, the C(1)-S(1) distances of 1.750(2), and

C(6)-N(2) distance of 1.377(2) Å, are in the single bond range. The six C-C distances of

the phenyl rings are also equidistant within the experimental error (1.398 ± 0.02; 3σ). The

average C-C distances of 1.393(3) Å are typical for aromatic phenyl rings. Both of the

features mentioned above suggest the presence of the dianionic o-iminobenzothiolato

form of both ligands and thus the formal oxidation state for the cobalt centre is +III (d6,

S=1). To reinforce this interpretation, compound 2 was synthesized using [N(n-bu)4]+ as a

countercation .

Bond distance [Å] Co(1)-N(2) S(1)-C(1) C(1)-C(2) C(2)-C(3) C(3)-C(4)

1.873(4) 1.750(4) 1.426(5) 1.384(6) 1.397(8)

Co(1)-S(1) N(2)-C(6) C(1)-C(6) C(4)-C(5) C(5)-C(6)

2.176(1) 1.377(6) 1.402(6) 1.376(7) 1.404(6)

Fig 2.3.1: Thermal ellipsoid drawing of the anion in 1 at the 50%

probability level, and disorder of the ligand with labelling scheme.

Co (1)

S(11)

S(1)

C(1)C(2)

C(6)

C(5)

C(4)

C(3)

N(2)

N(12)

S(11X)

N(12X)

Table 2.3.1: Selected bond distances in [Å] for 1.

Co complexes 20

Compound 2 crystallizes in the monoclinic crystal system in the space group P21/n. In

contrast with 1, in 2, the coordination geometry of the central cobalt atom is perfectly

square-planar, having a dihedral angle between N-Co-S planes equal to 1°. The central

Co ion is coordinated to two nitrogen and two sulfur atoms of both the ligands [H2(LNS)],

in the trans geometry. Two ligands in the molecule are crystallographically identical. The

anions are well separated in the unit cell with average intermolecular Co...Co distances of

6.818(6) Å, and inter-ligand S...S and N...N distances of 4.596(5) and 4.959(7) Å,

respectively. The average Co-N distance (1.845(1) Å) is similar to that observed in 1, and

consistent with those distances in neutral [CoIII(2LN)2] (LN = o-phenylenediamine), and

anionic [CoIII(4LO)2][Co(Cp)2] (LO=2-(2-trifluromethyl)anilino-4,6-di-tert-butylphenol)

complexes.13 In addition, the average Co─S distance (2.1868(4) Å) is similar to the

distances in other sulfur containing cobalt (III) complexes.3d, 5, 7 The C-S (1.7559 ± 0.04

Å) and C-N (1.373± 0.06 Å) average bond distances display single bond character and

the six C-C bonds of the six-membered ring are nearly equidistant within the 3σ error

(1.396± 0.06 Å). These features confirm that the ligands are dianions and that the central

cobalt ion possesses a +3 oxidation state in 8. It is important to note that the ligand

dimensions in 1 and 2 are identical to those observed for the diamagnetic, square-planar

compound [PtII(bpy)(tLNSIP)] . 16

Fig 2.3.2: Thermal ellipsoid plot of 2 with labelling scheme and ellipsoids drawn atthe 50% probability level. Hydrogen atoms have been omitted except aminoprotons.

Co (1)

S(1)

C(1)C(2)

C(6)C(5)C(4)

C(3)

N(1)

Chapter 2 21

2.4 Electrochemistry

The complexes 1 and 2 have been studied by cyclic-voltammetry (CV) in

CH2Cl2 containing 0.10 M [N-(n-bu)4]PF6 as supporting electrolyte. Ferrocene was used

as an internal standard, and all redox potentials were referenced versus the

ferrocenium/ferrocene (Fc+/Fc) couple at room temperature.

The cyclic-voltammograms of 1 and 2 are identical and for simplification

only the one corresponding to 1 is shown in Fig. 2.4.1 (a range of 0.0 to –2.0 V was

used). Two redox processes were observed at E1/2= -0.61V (oxidation) and at E1/2 = -

Bond distance [Å] Co(1)-N(1) Co(1)-S(1) N(2)-C(2) S(1)-C(1)

1.840(1) 2.187(4) 1.371(2) 1.759(2)

C(1)-C(6) C(1)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(5)-C(6)

1.393(2) 1.413(2) 1.406(2) 1.385(2) 1.392(3) 1.390(3)

Table 2.3.2: Selected bond distances in [Å] for 2

Fig. 2.4.1: Cyclic voltammograms of 1 at 25 ºC in CH2Cl2 solution containing 0.10M[(n-bu)4N][PF6], using a glassy carbon working electrode with scan rates of 25, 50, 100,200, 400, 800 mV/s.

-2.0-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.2

E (V)

5µA

Co complexes 22

1.730V (reduction). The oxidation process was found to be reversible over the scan rates

of 25-800 mV/s, however the reduction process was irreversible over the scan rates of 25-

400 mV/s only showing a return wave at the higher scan rate of 800 mV/s. Therefore

controlled potential coulometry was attempted only for the oxidation process. As it is

unlikely that the ligand can be further reduced, the reduction wave is assigned as a metal

centered reduction to CoII. Coulometric oxidation at -5°C and -0.3 V was performed and

the amount of charge passed corresponded to a 1e- oxidation process. The electronic

spectrum (Fig. 2.5.1) recorded after coulometric oxidation (species 1a) was very different

from that of 1. However, on completion of the coulometric oxidation, the cyclic

voltammogram has the current intensities lower than the starting one (Fig. 2.4.2). This

was attributed to the instability of the 1a in CH2Cl2 during the time of the coulometry

leading to some other chemical process. At first glance, we expected that the oxidation

should form an S=1/2 species and that could be recognized by epr; however, 1a was epr

silent. This suggests dimer formation of the oxidized species, which may also explain the

non-reproducibility of cyclic voltammogram after the oxidation process.

Fig. 2.4.2: Cyclic voltammograms of 1 at -25ºC in CH2Cl2 solutioncontaining 0.10M [(n-bu)4N][PF6], using a glassy carbon workingelectrode.

-2.0-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.2

After oxidation before oxidation

E (V)

5µA

Chapter 2 23

Chemical oxidation of 2 was achieved using 1 equivalent of Fc(PF6) in

CH2Cl2 to give transient species 2a. The electronic spectrum of 2a shows a wide band in

the near infrared region between 1600-1200 nm, which was absent in the spectrum of 1a

(Fig.2.5.1). When 2a was exposed to air for few minutes at room temperature, it changes

its color from green to brown giving a electronic spectrum similar to that of 1a. This

again indicates that both the electrochemically-oxidized species, and chemically oxidised

species 2a, were short-lived, and during the time of the coulometry, it is not stable as a

monomer, having a tendency to dimerise (1a). Based on the observations above, the

redox activity of complexes 1 and 82 can be best described as shown in scheme 2.4.1,

where the monoanionic species is formulated as [CoIII(LNSIP)2]1-.

DFT calculations on the spin triplet [Co(1LN)2]1- have shown that the

HOMO is a 2b2g orbital, which has almost equal contributions from the metal and the

ligand (Fig. 2.4.2) and thus, the explicit assignment of electron configuration at the metal

ion (i.e. to determine the dn (n = 6 or 7)) is not possible.13 But in contrast to this situation,

the geometry of the ligands in [Co(LNSIP)2]1- as determined by X-ray crystallography for

compounds 1 and 2 clearly suggest a CoIII (d6, S=1) spectroscopic oxidation state over a

[CoII(LNSISQ)(LNS

IP)] mixed-valence configuration.

Scheme 2.4.1: Redox activities of complexes 1 and 2

[CoIII(LNSIP)2] -e

+e[CoIII(LNS

ISQ)(LNSIP)]-e

+e[CoII(LNS

IP)2]2

[CoIII(LNSISQ)(LNS

IP)]2

FcPF6-e

[CoIII(LNSISQ)(LNS

IP)]Unstable

Unstable(S=1) (S=1/2)

(S=1/2) (S=0)

fast

slow

(2a) (1a)

Co complexes 24

Fig. 2.4.2: MO scheme of

[Co(1LN)2]1-

Chapter 2 25

2.5 Electronic absorption spectra

The electronic absorption spectrum of compound 1 shows absorption

maxima at 666 nm (ε ≈ 1.25 × 104 M-1 cm-1), 569 nm (ε ≈ 2 × 104 M-1 cm-1), and at 380

nm (ε ≈ 1 × 104 M-1 cm-1). Because of their high absorption coefficients these bands may

be assigned as charge transfer bands. The spectrum

of 1 is similar to the compound [CoIII(LBu)2]1-, in

which the assignment of the physical oxidation state

to the cobalt center has been shown by spectroscopy

and theory to be CoIII.3d Moreover, 1 does not

present any band in the near infrared region, typical

for an intervalence charge transfer band as the one

found in the spectra of [AuIII(LBu)(LBu●)] 17, in

which one of the ligands is a radical ligand and the

other one is dianionic. This confirms the

[CoIII(LNSIP)2]1- assignment for the complex. The

molecular orbital scheme of [CoIII(LBu)2]1-,3d

obtained from the DFT calculations (Fig. 2.5.2),

have shown that the CoIII intermediate spin (d6)

central metal ion contains two singly occupied dxz

and dyz orbitals and one vacant d orbital (dxy). The

vacant dxy orbital was placed very high in energy in

the case of D2h symmetry; therefore the high-energy

band at 380 nm may be assigned as the LMCT to

this orbital.

The chemically oxidized species 2a, shows a broad absorption band in the near IR region

(1180 nm, ε ≈ 2 × 103 M-1 cm-1), which does not appear in the spectrum of the

electrochemically-oxidized species (1a, presumably a dimer). Due to its high intensity,

this band is not likely an electric-dipole-forbidden d-d transition, but may be a spin

allowed ligand-to-ligand intervalence charge transfer band (LLIVCT). Several square-

planar complexes of Ni, Pd, and Pt with one o-iminothionebenzosemiquinonate (1-)

S

S

S

SM X

Y

2b2g

1ag (dx2

-y2)

2ag(dz2)

1b3g

1au

1b2g

1b1u

2b3g(dyz)

1b1g (dxy)

Fig. 2.5.2: Mo scheme of

[CoIII(LBu)2]1-

Co complexes 26

radical ligand exhibit similar bands in the near infrared region.18 This suggests the

presence of a (LNSISQ) ligand radical in the 2a, denoting ligand-centered oxidation.

2.6 X-band EPR

The X-band EPR spectrum of 2a, in frozen CH2Cl2 at 8.5 K is shown in

Fig. 2.6.1. The spectrum indicates an S=1/2 signal with an eight-line hyperfine splitting

due to the coupling of the 59Co (I=7/2) nucleus to the unpaired spin. The following

parameters have been obtained from a simulation: gx = 2.002, gy = 2.0071, gz = 2.01, and

A (59Co): (Ax = 124, AZ = 49.17) * 10-4 cm-1. The spectrum shows slight anisotropy,

which is commonly observed for delocalized organic radicals. The observed g values in

the spectrum are very close to the free electron value but the hyperfine-coupling constant

for 59Co nucleus is very strong compared to reported values for CoIII low spin octahedral

Fig. 2.5.1: Electronic absorption spectra of 1, 1a and 2a in CH2Cl2 at –50 C.

400 600 800 1000 1200 1400 16000.0

0.5

1.0

1.5

2.0

2.5

ε X

104 c

m-1

M-1

wavelength (nm)

1

2a

1a

Chapter 2 27

complexes containing a single ligand radical.14 Thus there are two ways to explain the

observed simulation parameters. In one case it is possible that, CoIII (d6, S=1)

antiferromagnetically couples with the unpaired electron from a radical ligand to give

SCo=1/2, which can explain the eight line hyperfine splitting with large hyperfine splitting

parameter. On the other hand, this spectrum is very similar to what observed for the

oxidized species of [Co(LBu)2]-, for which theoretical studies have suggested the presence

of a hydrated octahedral [CoIII(LBu)(LBu●)(H2O)2] species in solution.3d Thus during the

oxidation of complex 1, it is possible that water molecules from the solvent can occupy

the 5th and the 6th coordination sites of the cobalt, modifying its geometry from square

planar to octahedral and therefore changing the spin state of the CoIII center from

intermediate spin to low spin. Such coordination by water molecules during oxidation is

also observed in the oxidation of square planar [CoIII(LNO(ISQ))(LNO)] in CH2Cl2 solution,

which results in the formation of [CoII(LNO(IBQ))2(H2O)2]2+, (LNO represents o-

aminophenolato (2-) ligand, LNO(ISQ) represents o-iminobenzosemiquinonato (1-) ligand

and LNO(IBQ) represents o-iminobenzoquinonato(0) ligand).15 This result suggests that,

during the oxidation of complex 7, the species [CoIII(LIPNS)(LAP

NS)(H2O)2] may be

formed in solution which would explain the observed anisotropic g values (near to free

electron) in the EPR spectrum of 2a.

300 320 340 360 380

dχ"/d

B

B [mT]

Simulated

Experimental

Fig. 2.6.1: X-band epr spectrum of 2a. Exp: T = 8.5K, freq = 9.63GHz, power = 0.10mw.

Co complexes 28

2.7 Magnetic susceptibility

Magnetic susceptibility data of 1 and 2 were collected in the temperature

ranges 2 to 290 K in an applied magnetic field of 1T and are similar; only the data for 2 is

shown in the Fig. 2.7.1. Above T=50 K the complex shows a temperature independent

µeff value of 2.90 µB, indicating the presence of two unpaired electrons (ST=1) in the

complex. However, at temperatures lower than 50 K the µeff value decreases

monotonically with a decrease of the temperature reaching a value of 0.8 µB at 2 K. As

the intermolecular Co....Co and Co....S distances in the crystals of 2 are found to be too

long for any kind of exchange coupling interactions, this magnetic behavior may be

explained by a large zero field splitting value. This results in the splitting of the S=1

ground state into Ms = 0 and Ms= ±1 levels, leading to an increased population of the Ms

= 0 level at lower temperatures (Fig.2.7.4). The experimental magnetic susceptibility data

were simulated with a D (zero field splitting) value of ⏐47⏐cm-1 and a g value of 2.153

which are in agreement with similar results found for [Co(LBu)2]-, and [Co(LMe)2]1-

(g=2.17; D = 34 cm-1). 5

Fig. 2.7.1: Plot µeff vs. T for 1. The solid line represents the best least squares fitting for the experimental data (squares).

0 50 100 150 200 250

1.0

1.5

2.0

2.5

3.0

3.5

g = 2.153 D = 47.11 cm-1

TIP =0.417E-03 emu/mol

µ eff /

µB

T/K

Chapter 2 29

The sign of D was determined from variable field/ variable temperature

measurements and spin Hamiltonian simulations of the experimental data (Fig. 2.7.2).

The best fit for the magnetization behaviour is obtained for D = +41.2 cm-1 (fixed; from

far-infrared measurements), g = 2.003.

Far-infrared experiments have been reported for [(n-Bu4N)][Co(L)2] and

[(n-Bu4N)][Co(LMe)2] 5 to determine the zero field splitting parameters of the complexes

spectroscopically. A band at 34 cm-1 is observed in each case and is assigned to the intra-

triplet transition between the Ms = 0 and Ms = ± 1 components of the triplet ground state,

on the basis of the temperature dependence of the band. A far-infrared transmission

spectrum for 8 was measured over the frequency range of 10-50 cm-1. The measurements

were performed at variable fields in order to distinguish the electronic transition bands

from the normal phonon bands. The temperature was kept constant at 1.8 K and the field

was varied from 0 to 7 T. A very sharp band (1cm-1 width) is observed at 41 cm-1, the

position of which is found to be field dependent. Whereas all other bands remain

Figure 2.7.2: Magnetization measurements at 1, 4 and 7 T for 1. The solid lines represent the simulation. (D = +41.2 cm-1, g = 2.003).

0.0 0.5 1.0 1.5 2.00.00

0.05

0.10

0.15

0.20

MM

OL / N

gβ

βH/kT

1 T

4 T

7 T

Co complexes 30

unaffected on application of the magnetic field, the band at 41 cm-1 moves to lower

frequency with increasing field strength (Fig. 2.7.3), and hence, clearly arises from a low-

frequency electronic transition. The field dependence of the band may be accounted for

by the following: In axial symmetry, when the magnetic field and principal molecular

axis (z) and parallel, the effect of zero field splitting on the S=1 electron states is as

shown in Fig. 2.7.4 (a), where the Zeeman splitting of Ms = ± 1 states is of the magnitude

of ~10cm-1. However, when the magnetic field is perpendicular to the principle axis (z),

the Zeeman interaction is very weak (~1cm-1) (Fig. 2.7.4 (b)). In a solid sample there will

be very few molecules with principle axis parallel to field, and far more perpendicular.

The result is a weakening of the Zeeman interaction, and consequently a shift of ~1 cm-1

of the band at 41 cm-1 to the lower frequency.

The D value obtained from the susceptibility measurements is in

agreement with the zero field splitting parameter obtained from the far-infrared spectrum.

Thus, 1 and 2 possess a spin triplet ground state and a zero field splitting of +41 cm-1

lifts the degeneracy of the ground state.

Figure 2.7.3: Far-infrared transmission spectrum of 2 at 1.8 K and at fields varied between 0 and 7 T.

10 15 20 25 30 35 40 45 501E-3

0.01

0.1

1

Tr.

frequency (cm-1)

40.0 40.5 41.0 41.5 42.0 42.5 43.0

0 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T

Chapter 2 31

Fig. 2.7.4 Splitting of S=1 in magnetic field with zero field splitting, (a) Magnetic field is parallel to molecular axis.

(b) Magnetic field is perpendicular to molecular axis.

H increasing

0

H increasing

0

ms= 0

ms= +1

ms= -1

ms= 0

ms= ±1

D D

10 cm-11 cm-1

(a) (b)

Co complexes 32

2.8 Conclusions

The complexes 1 and 2 have been fully characterized structurally,

electrochemically and also by magnetic measurements in order to show that these species

contain a central CoIII (d6, S=1) metal ion. The cyclic voltammograms of 1 and 2 show

reversible one-electron waves corresponding to oxidation of a ligand and irreversible

waves corresponding to one electron reduction of the cobalt. The absorption spectra of

the complexes contain intense LMCTs occurring in the visible region (< 700 nm). The

ground state of the complexes has been shown to be a spin triplet, in which the

degeneracy is lifted by large positive zero field splitting. A zero field splitting (+41 cm-1)

for complex 2 has been measured independently by magnetic moment measurement,

variable-temperature and variable field and SQUID magnetometry, and far-infrared

absorption. These studies have clarified the ambiguity for the proper formalism of the

monoanionic cobalt complex VI, and therefore it is possible to assign this complex

properly as [CoIII(LNSIP)2]1-. As was pointed out in the introduction, compounds I, and III

were likely not pure, i.e. they were most probably mixtures of monoanion 2 (S=1) and the

neutral dimer 1a (S=0). This altogether led to the observed magnetic moment of 2.6

B.M., which is less than a value of 2.73 B.M. expected for S=1. And therefore the

assignment of the oxidation state to the cobalt as +2 was likely in error.

Chapter 2 33

2.9 References

1) Gavel, O. Y.; Bursakov, S.A.; Calvete, J. J.; George, J. J.; Moura, G; Moura, I.

Biochemistry 1998, 37, 16225.

2) Kobayashi, M.; Shimizu, S. Eur. J. Biochem. 1999, 261, 1.

3) (a) Eisenberg, R.; Dori, Z.; Gray, H. B.; Ibers, J. A. Inorg. Chem. 1968, 7, 741 (b)

Fikar, R.; Koch, S. A.; Miller, M. M. Inorg. Chem. 1985, 24, 1985. (c) Mrkvova,

K.; Kamenicek, J.; Sindelar, Z.; Kvitek, L. Trans. Metal Chem. 2004, 29, 238. (d)

Ray, K.; Begum, A.; Weyhermüller, T.; Piligkos, S.; Slageren, J. V.; Neese, F.;

Wieghardt, K. J. Am. Chem. Soc. 2005, 127, 4403.

4) Collins, T. J.; Richmond, T. G.; Santarsiero, B. D.; Treco, B. G. R. T. J. Am.

Chem. Soc. 1986, 108, 2088.

5) van der Put, P. J.; Schilperoord, A. A. Inorg. Chem. 1974, 13, 2476.

6) Birker, P. J. M. W. L.; Bour, J. J.; Steggerda, J. J. Inorg. Chem. 1973, 12, 1254.

7) (a) Heirich, L.; Li, Y.; Provost, K.; Michalowicz, A.; Vaissermann, J.; Chottard, J.

C. Inorg. Chim. Acta. 2001, 318, 117. (b) Chatel, S.; Rat, M.; Dijols, S.; Leduc,

P.; Tuchagues, J. P.; Mansuy, D.; Artaud, I. J. Inorg. Biochem. 2000, 80, 239.

8) Livingstone, S. E. J. Am. Chem. Soc. 1956, 1042.

9) Larkworthy, L. F.; Murphy, J. M.; Phillips, D. J. Inorg. Chem. 1968, 7, 1436.

10) Herebian, D.; Ghosh, P.; Chun, H.; Bothe, E.; Weyhermüller, T.; Wieghardt, K.

Eur. J. Inorg. Chem. 2002, 1957.

11) Birker, P. J. M. W. L.; De Boer, E. A.; Bour, J. J. J. Coord. Chem. 1973, 3, 175.

12) Forbes, C. E.; Gold, A.; Holm, R. H. Inorg. Chem. 1971, 11, 2479.



14) (a) Jung, O. S.; Pierpont, C. G. Inorg. Chem. 1994, 33, 2227. (b) Adams, D. M.;

Noodelman, L.; Hendrickson, D. N. Inorg. Chem. 1997, 36, 3966. (c) Min, K. S.;

Weyhermüller, T.; Wieghardt, K. Dalton Trans. 2003, 6, 1126. (d) Dutta, S. K.;

Beckmann, U.; Bill, E.; Weyhermüller, T.; Wieghardt, K. Inorg. Chem. 2000, 39,

3355.

15) Kokatam, S.; Wieghardt, K. Unpublished results.

Co complexes 34

16) Ghosh, P.; Begum, A.; Herebian, D.; Bothe, E.; Hildenbrand, K.; Weyhermüller,

T.; Wieghardt, K. Angew. Chem. Int. Ed. 2003, 42, 563.

17) Ray, K., Weyhermüller, T.; Goossens, A.; Craje, M. W. J.; Wieghardt, K. Inorg.

Chem. 2003, 42, 4082.

18) Herebian, D.; Bothe, E.; Bill, E.; Weyhermüller, T.; Wieghardt K. J. Am. Chem.

Soc. 2001, 123, 10012.

Chapter 3 35

3.1 Introduction

The reactivity of CrIII with ligands containing sulfur donor atoms (soft

bases) has not been as extensively studied as the coordination with nitrogen and oxygen

donor ligands (hard bases). A small number of CrIII complexes have been reported in the

literature with N,S- coordination: the neutral complex with N,N'-diphenylthiourea;

Cr[SC(NPh)(NHPh)]3,1 [(en)Cr(SCH2CH2NH2)2]ClO4 2 where, en = ehtylenediamine and

both neutral [Cr(SCN3H4)3] and ionic [Cr(SCN3H5)3]Cl3·3H2O complexes with

thiosemicarbazide.3

With the exception of work of Phillips et al., 4 in which the synthesis of an

impure and insoluble (in most organic solvents) [Cr(abt)2] (abt=aminothiophenolato(2-))

complex has been described, there is hardly any account on chromium complexes

coordinated to o-aminothiophenolate or derivatives forming either square planar or

octahedral complexes. Therefore, we decided to synthesize CrIII complexes with the 2-

mercapto-3,5-di-tert-butyl-aniline ligand (H2[tLNS]). However, the reaction of CrIICl2

with 3 equivalents of (H2[tLNS]) in different solvents resulted at each attempt, in the

formation of cuboidal compounds, Na[CrIII3(LISQ)3(µ-OMe)4(OEt)3(OHEt)3] (3),

Chapter 3 Cuboidal complexes of

chromium with 2-mercapto-3,5-di-tert-

butylaniline

Cuboidal Cr complexes 36

Na[CrIII3(LISQ)3(µ-OMe)4(OMe)3(OHMe)3] (4a) and Na[CrIII

3(LISQ)3(µ-

OMe)4(OMe)3(OH2)3] (4b). Even though these results were unexpected, cuboidal

clusters have generally been of a great interest, especially concerning their magnetic

properties. Oligo- and polynuclear group 6 transition-metal alkoxides have been the

subject of intensive study as they provide versatile substrates to mimic processes which

are relevant for both homogeneous and heterogeneous catalysis.5 Hence, over the years a

number of oligo- and polynuclear CrIII clusters with, O2-, 6-9 OH2,9 RCO2-,10-12 HO-,10,14

CO, 14,15, RO- 16 bridging ligands have been reported. In this chapter, the structural,

electrochemical and magnetic properties of the above-mentioned CrIII cuboidal

complexes have been characterized to provide an insight into the properties of these

compounds.

3.2 Synthesis and characterization

Na[CrIII3(LISQ)3(µ-OMe)4(OEt)3(OHEt)3] (3)

Complex 3 was synthesized by reaction of CrIICl2 and Na2[tLNS], in

MeOH under anaerobic conditions. The color of the reaction mixture turned from

yellow-brown to light blue in 1 h. A flow of air was then allowed to pass through the

mixture for 2 minutes and as a consequence, the color of the reaction changed to dark

brown. A brown solid obtained by evaporation of solvent was dissolved in a mixture of

EtOH/ Ether(1:1), from which green crystals of compound 3 suitable for X-ray crystal

analysis were obtained by slow evaporation of solvents. The infrared spectrum of this

complex shows O-H stretching peak (from coordinated MeOH) at 3283 cm-1,

characteristic of the presence of bonded OH groups rather that free OH groups and the

C-O stretching at 1079 cm-1, authenticates the presence of methoxy groups.

Chapter 3 37

Na[CrIII3(LISQ)3(µ-OMe)4(OMe)3(OHMe)3] (4a)

Na[CrIII3(LISQ)3(µ-OMe)4(OMe)3(OH2)3] (4b)

Compound 4 was synthesized in similar fashion as 3, but MeOH was

used instead of EtOH as a solvent of crystallization. Crystals suitable for X-ray structure

analysis of compound 4, were obtained by slow evaporation of mixture of MeOH/DCM.

3.3 Molecular structures of 3 and 4

The crystal structures of compounds 3 and 4 at 100(2) K have been

determined using Mo Kα radiation.

The structure of compound 3 is presented in Fig. 3.3.1, and tables 3.3.1

and 3.3.2 summarize the bond angles and bond lengths, respectively. The 3 crystallizes

in the trigonal crystal system in a space group R3c. It contains three Cr atoms positioned

at the vertices of an equilateral triangle and connected by a triply bridging µ3-methoxide

and three µ2-methoxide ligands shaping a cuboidal structure. Each chromium ion has a

distorted octahedral coordination geometry, three of the coordination sites being

occupied by oxygen atoms of bridging methoxide ligands with Cr-O distances of

2.005(4) Å. The nitrogen and sulfur atoms of the tLNS ligand (Cr-N; 1.959(6) Å, Cr-S;

(2.345(2) Å) and one oxygen atom from terminal monodentate ethoxide group (Cr-O;

1.905(4) Å) occupy the rest of the coordination sites of the chromium. The resulting

mononegative Cr3III(LNS

ISQ)3(µ-OMe)4(OEt)3 moiety is coordinated to Na ion through

the oxygens of µ2-OCH3 groups. There is a C3 axis passing through the Na ion and

through O(21). The Na ion is coordinated to three EtOH groups (Na-O(21); 2.289(6)).

There is a hydrogen-bonding interaction (2.643(5) Å, 150.79 (1)°) between the hydrogen

atom from EtOH group (coordinated to Na), and an O(31) from a terminal OEt group.

The bond angles O-Cr-S and N-Cr-O vary from 165.8(2) to 175.26(14)°, showing

significant distortion from octahedral geometry at the Cr centers. The average Cr-O-Cr

and O-Cr-O bond angles in the Cr3O4 core are 107.3(4) and 90.4(5)°, indicating also

distortions from cubic geometry.


Bond angles (deg) Cr(1)# 2-O(25)-Cr(1) 98.2(2) Cr(1)#2-O(25)-Cr(1) 105.4(2) Cr(1)-O(25)-Na(40) 109.2(4) N(2)-Cr(1)-O(25)#1 166.1(2) O(25)#1-Cr(1)-O(25) 90.4(3) O(25)-Cr(1)-O(21) 78.0(2) O(25)-Cr(1)-S(1) 175.2(1) O(31)-Cr(1)-O(21) 165.8(2)

Bond distances [Å] Cr(1)-O(31) 1.905(4) C(1)-C(2) 1.433(10) Cr(1)-O(25) 2.005(4) C(1)-C(6) 1.401(9) Cr(1)-O(21) 2.107(4) C(2)-C(3) 1.405(9) Cr(1)-N(2) 1.959(6) C(3)-C(4) 1.352(10) Cr(1)-S(1) 2.345(2) C(4)-C(5) 1.450(12) S(1)-C(1) 1.741(7) C(5)-C(6) 1.373(10) N(2)-C(2) 1.364(8)

Table 3.3.2: Selected bond distances [Å] for 3

Table 3.3.1: Selected bond angles in deg. for 3

Chapter 3 39

The Cr....Cr distances among the three metallic centers are similar within

the experimental error. This Cr....Cr average distance of 3.185 ± 0.01 Å is longer than the

typical range of Cr-Cr single bonds (2.67-2.97 Å), 6,15,17 and therefore is consistent with a

nonbonding M....M distance (~3.241(1) Å) observed in polynuclear carbonyl

complexes.18, 19 This, along with the paramagnetism of the complexes indicates the

absence of direct Cr-Cr bonding. The Cr(1)-O(25) distance of 2.005(4) Å is intermediate

between the one observed in the oxo bridged [(η-C5R5)Cr(µ3-O)4] 7(1.941(6) Å) cluster

and the one observed in methoxy bridged [Cr4(CO)12(µ3-OCH3)4]6 (2.114(6) Å) cluster.

The Cr-N and Cr-S average distances of 1.939(6) and 2.345(2) Å are similar with the

previously reported distances in CrIII complexes.1,2,13,20-21

C (5 )

C r(1 )

N (2 )

S (1 )

C (1 )

C (2 )

C (6 )

C (3 ) C (4 )

O (2 5 )O (3 1 )

H (4 1 )O (2 1 ) N a (4 0

)

Fig. 3.3.1: Ball and stick diagram and atom labeling scheme for 3.


In the ligand tLNS, the C-S (1.737 ± 0.02 Å) and C-N (1.351 ± 0.02 Å)

bond distances display significant double bond character, and the six-membered rings

exhibit distortions typical of a quinoid type structure, namely two shorter C=C and four

longer ones (1.362 ± 0.03 and 1.422 ± 0.03Å) (Scheme 1.1, chapter 1). These features are

characteristic of N,S-coordinated o-iminothiobezosemiquinonate (1-) π–radical ligands

and have been systematically illustrated in the series of square planar transition metal

complexes of Ni, Pd, Pt, Co and Fe.22-24 Thus, this complex is a classic example of non-

innocent o-aminothiophenolato ligands coordinated to CrIII centers in an octahedral

geometry.

The 4 also crystallizes in space group R3c with an identical intramolecular

arrangement to compound 3. The main structural difference between clusters 3 and 4 is

the terminal groups: OEt for 3 and OMe for 4. The coordination of terminal ethoxide

groups to chromium and sodium atoms in 3 was a consequence of the ethanol used during

recrystallization. Using methanol instead of ethanol has proved this and as expected,

methoxide groups were found in the place of the terminal ethoxide groups in 4. In

crystals of 4, there are two crystallographically independent molecules 4a and 4b, having

different composition. They are shown in Fig. 3.3.2 and Fig. 3.3.3 respectively. The

difference between these two clusters arises from the coordination of the Na ion where, in

4a, the sodium is coordinated to three MeOH groups (Na(40)-O(41); 2.293(3) Å); while

in 4b, Na is coordinated to three OH2 groups (Na(40)-O(91); 2.319(3) Å). Characteristic

bond angles and bond distances for compounds 4a and 4b are presented in table 3.3.3 and

table 3.3.4, respectively. The average Cr....Cr distances in 4a and 4b are 3.177 ± 0.09Å

and 3.182 ± 0.09Å, respectively. The Cr-O-Cr angles in the Cr3O4 core are 98.8(1) and

107(1)° in 4a, and 98.6(1) and 105.4(1)° in 4b. The Average O-Cr-O bond angles are

88.17(9) and 89.53(9)° in 4a and 4b, correspondingly. The Cr(1)-O(25) and Cr(1)-O(31)

distances are 2.0035 (4) and 1.882(2) Å, respectively. The average Cr-N and Cr-S

distances of 1.930(3) and 2.3476(9) Å are comparable with the reported distances in CrIII

compounds.1,2,13, 20-21As observed in 3, in the ligand, the average C-S (1.733 ± 0.009 Å)

and C-N (1.344 ± 0.01 Å), bond lengths display substantial double bond character and the

six-membered rings exhibit distortions typical of quinoid type structures, namely two

Chapter 3 41

shorter C=C and four longer ones (1.374 ± 0.01 and 1.420 ± 0.01 ) and therefore indicate

the presence of o-iminothiobenzosemiquinonato (1-) π–radical ligands.

Bond angles (deg) for 4a Cr(1)# 2-O(21)-Cr(1) 98.8(1) Cr(1)#2-O(25)-Cr(1) 105.41(9) Cr(1)-O(25)-Na(40) 97.85(8) N(2)-Cr(1)-O(25)#1 166.78(9) O(25)#1-Cr(1)-O(25) 89.9(1) O(25)-Cr(1)-O(21) 77.67(7) O(25)-Cr(1)-S(1) 174.82(6) O(31)-Cr(1)-O(21) 164.2(1)

Bond angles (deg) for 4b Cr(2)# 4-O(71)-Cr(2) 98.6(1) Cr(2)#4-O(75)-Cr(2) 105.35(9) Cr(2)-O(75)-Na(90) 98.82(8) N(52)-Cr(2)-O(75) 167.1(1) O(75)-Cr(2)-O(75)#3 89.9(1) O(75)#3-Cr(2)-O(71) 77.66(8) O(25)#3-Cr(2)-S(51) 175.45(7) O(81)-Cr(2)-O(71) 163.9(1)

Bond distances [Å] Cr(1)-O(31) Cr(2)-O(81)

1.888(2) 1.897(2)

C(1)-C(2) C(51)-C(52)

1.433(4) 1.434(4)

Cr(1)-O(25) Cr(2)-O(75)

2.003(1) 1.987(2)

C(1)-C(6) C(51)-C(56)

1.412(4) 1.427(4)

Cr(1)-O(21) Cr(2)-O(71)

2.095(2) 2.096(1)

C(2)-C(3) C(52)-C(53)

1.422(4) 1.421(4)

Cr(1)-N(2) Cr(2)-N(52)

1.931(2) 1.929(3)

C(3)-C(4) C(53)-C(54)

1.368(5) 1.370(4)

Cr(1)-S(1) Cr(2)-S(51)

2.3459(8) 2.3493(9)

C(4)-C(5) C(54)-C(55)

1.414(5) 1.416(4)

Cr(1)-Na(40) Cr(2)-Na(90)

3.412(2) 3.461(2)

C(5)-C(6) C(55)-C(56)

1.380(5) 1.386(4)

S(1)-C(1) S(51)-C(51)

1.738(3) 1.728(3)

N(2)-C(2) N(52)-C(52)

1.343(4) 1.346(4)

Table 3.3.4: Selected bond distances [Å] for 4a and 4b.

Table 3.3.3: Selected bond angles in deg. for 4a and 4b.


C(55)

Cr(2)

N(52)

S(51)

C(51)

C(52)C(56)

C(53)

O(81A) H(91B)

C(54)

Fig. 3.3.3: Thermal ellipsoid plot of 4b with labeling scheme and ellipsoids drawn at the 50% probability level. Hydrogen atoms have been omitted.

C(5)

Cr(1)

N(2)

S(1)C(1)

C(2)

C(6)

C(3)

C(4)

O(25)

O(31A)H(41B)

O(21) Na(40)

Fig. 3.3.2: Ball and stick diagram and atom labeling scheme for 4a.

Chapter 3 43


The electrochemical behaviour of both of the cuboidal complexes 3 and 4

has been studied by cyclic voltammetry (CV) in dichloromethane containing [N(n-

bu)4]PF6 (0.10M) as supporting electrolyte. Ferrocene was used as an internal standard,

and all redox potentials have been referenced versus the ferrocenium/ferrocene (Fc+/Fc)

couple. As one might expect, clusters 3 and 4 show identical redox behaviour and for

simplification only the result with 3 is presented.

Fig. 3.4.1 displays the CV of complex 3 over the potential range of 1.0 V

to –2.0 V at room temperature. It shows two successive, reversible one electron processes

at -0.884 V (E11/2) and at -1.094 V (E2

1/2), plus one irreversible process at 0.46 V (E31/2).

The reversible processes correspond to the expected electron transfer series known for

many square-planar complexes containing o-iminothiobenzosemiquinonato radical

ligands, 22 where they correspond to ligand centered reductions. Thus the redox activity of

the compound 2.1 can be explained as shown below in scheme 3.4.1.

[CrIII3(OR)7(tLNS

ISQ)3]1- [CrIII3(OR)7(tLNS

ISQ)2(tLNSIP)]2-

[CrIII3(OR)7(tLNS

ISQ)(tLNSIP)2]3-

+e

+e

Scheme 3.4.1 redox activity of 3 and 4


3.5 Electronic absorption spectrum

The electronic spectrum of compound 3, as shown in Fig. 3.5.1, displays a broad band in

the near infrared region between 1000 to 1400 nm (ε = 2.5 × 103 mol-1 cm-1). This band

may be a spin and dipole allowed ligand-to-ligand charge transfer transition (LLCT),

which is observed in all square-planar complexes of NiII, PdII, and PtII containing two

bidentate benzosemiquinonato type ligands.22 In the visible region appear two intense

bands at 696 nm (ε = 6 ×103 M-1 cm-1) and at 476 nm (ε = 6 × 103 M-1 cm-1). The higher

values of extinction coefficients indicate that they are charge transfer bands and most

probably ligand to metal charge transfer bands to the two unoccupied metal d orbitals.

Fig. 3.4.1: Cyclic voltammogram of 3 at 22ºC in CH2Cl2 solution, at the scanrate of 100 mV/s containing 0.10M[(n-bu)4N]PF6 with glassy carbon workingelectrode.

-2.0-1.5-1.0-0.50.00.51.0

E (V)

10 µ

A

Chapter 3 45

3.6 Magnetochemistry

Magnetic susceptibility data of cuboidal 3 and 4 were collected in the

temperature range 2 to 290 K in an applied magnetic field of 1T. Both of these

compounds show identical magnetic behaviors. Fig. 3.6.1 displays the magnetic moment

vs. temperature plot of 3. The analysis of the magnetic data was performed using

Heisenberg-Dirac-Van Vleck (HDVV) model. The least square fitting computer program

JULIUS-F and a full matrix diagonalization approach was employed to fit the

experimental data. The program uses the spin Hamiltonian operator, Htotal = HZ + HHDVV

in which the Zeeman interaction are given by HZ = µBBgiSi , and the exchange coupling is

described by HHDVV = -2J [S1S2+S2S3+S1S3].

400 600 800 1000 1200 14000.0

0.5

1.0

1.5ε

X 10

4 M-1

cm-1

λ nm

696

476

Fig. 3.5.1: Electronic absorption spectrum of the 3 in CH2Cl2 solution at 25ºC.


The magnetization curve displays an effective magnetic moment of 4.93µB

in the region of 100 to 290 K. This value corresponds to the expected spin-only value for

three uncoupled S = 1 units ( 3)1( +SSg = 4.9µB). This leads to the consideration that

each CrIII (S=3/2) is strongly antiferromagnetically coupled to a radical (S=1/2) in order

to achieve a local S=1 spin state. The magnetic moment µeff /molecule of 4.93µB at 290 K

decreases monotonically with decrease of the temperature reaching the final value of 1.52

µB at 2 K, indicating antiferromagnetic exchange coupling between the three S=1 units.

The best fit (solid line in the Fig. 3.6.1) of the experimental data resulted in the following

parameters: gCr = 1.987, J = -2.164 cm-1, χTIP = 0.617 × 10-3 e.m.u.

Comparisons with other oxo bridged cubane complexes like [(η-

C5Me5)Cr(µ3-O)]4 (SCr=3/2) (J = -211cm-1),6 indicate that the exchange coupling

between the Cr atoms in 3 and 4 is very weak (J = -2.164cm-1). This can be attributed to

the presence of methoxy bridges. In the oxo-bridged complexes, oxygen has “sp” hybrid

orbitals and therefore, two of the filled p orbitals of the oxygen are available for the π

Fig. 3.6.1: Plot of µeff vs T for compound 3. The solid line represents the best least squares fitting for the experimental data (circles).

0 50 100 150 200 2502

3

4

5

Sim. Exp.

µ eff

/ µB

T/K

Chapter 3 47

interactions with the dxz and dyz orbitals of chromium. However in 3, and 4, the oxygen

from the methoxy bridges is involved in “sp2” hybridization and only one "p" orbital is

available for the π interactions with d orbitals in chromium. Consequently, a weak

antiferromagnetic exchange interaction is present between the three Cr metal centers, thus

leading to smaller J values. The methoxy ligand is commonly used as a bridge in oligo-

and polynuclear transition metal clusters25-29 including chromium clusters.16

K[Fe3(OCH3)7(dbm)3]4CH3OH19 (dbm = dibenzoylmethane), is an analogous cuboidal

cluster to 3 and 4, in which three high-spin iron(III) metal centers are

antiferromagnetically coupled with an S = 1/2 spin ground state with J = -10.6cm-1.

Similarly, in methoxy bridging oligo- and polynuclear chromium clusters, the

antiferromagnetic exchange couplings between chromium ions are in a similar range of (J

= -1.9 to10 cm-1).16 The magnetic properties of reported clusters were studied using the

Hamiltonian of type Hex = -2 J S1S2 (S1 and S2 are intrinsic spins of chromium), where in

the case of compounds 3 and 4 a simple model was used to describe what is actually a

more complex situation. This may be understood by considering that the intrinsic spin of

S = 1 is partially delocalized on the chromium and the radical ligand. Values of these

delocalized spins are obtained by projection technique and the rest of the couplings are

obtained by considering a full Hamiltonian so obtained as described below in Fig. 3.6.2

and scheme 3.6.1.

S 1=1 S

2 =1

J

J'

J"

J'

S1Cr S2

Cr

S1rad S2

rad

Fig. 3.6.2: exchange coupling interactions between two Cr centers and coordinated

radical ligands in the 3


As described in scheme 3.6.1, the exchange coupling constant JCr, is a

major contributor to the antiferromagnetic exchange between chromium centers (-25/16

J). In addition, a smaller contribution from ferromagnetic exchange coupling between

chromium and radical (5/8 J'), and negligible contributions from radical-radical

antiferromagnetic exchange coupling (-1/16 J") were also needed in order to get the total

J. Therefore, the total value of the coupling constant J is different than the one that

should expected if only a chromium-chromium exchange would have been taken into

account.

Fig. 3.6.3 shows the energy ladder calculated for 3 and 4 by using the

program ENERGY. This program calculates the energies of the different spin states using

the equation 3.6.2, in which, the J value obtained from previous fits are applied.

The energy ladder plot shows the ST = 0 spin ground state of 3 and 4 as a single non-

degenerate level. On the other hand, non-integer spin systems arranged in an equilateral

triangle exhibit spin frustration i.e. orbitally degenerate ground state. Equilateral triangles

Hex = - 2 JCr SCr.SCr - [2 J'Cr.rad SCr.Srad ]2 – 2 J"

rad Srad.Srad

By applying the spin projection technique for energetically well-

isolated total spin manifolds, for S1 = S2 =1

SCr = 5/4 S1

Srad = -1/4 S1

Hex = (-25/8 JCr + 5/4 J'Cr.rad –1/8 J"

rad.rad) S1S2

Comparing this with hamiltonian, Hex = -2 J S1S2

J = -25/16 JCr + 5/8 J'Cr.rad –1/16 J"

rad.rad

Scheme 3.6.1

E(ST) = - J [ST(ST+1) –3S(S+1)] eq. 3.6.2 Where, S* = S2+S3, ST= S1+S*, S1=S2=S3=S

Chapter 3 49

with local S = 1 spin states are very uncommon in the literature. Hence these clusters are

very exceptional examples of S = 1 spin-triangles having three equal J values.

Ene

rgy

(cm

-1)

Field (T)

S = 0

S = 1

S = 2

S = 3

Fig. 3.6.3: Energy level scheme for a spin-spin interaction of the formH = - 2J [S1S2+S2S3+S1S3] with S1 = S2 = S3 = 1 for 3.


3.7 Conclusions

The reported compounds 3, 4a and 4b are archetypal CrIII cuboidal

clusters with a N,S- coordination. Methoxy bridges are also an additional feature of these

cuboidal complexes. The structural features of 3, 4a, and 4b demonstrated that the ligand,

2-mercapto-3, 5-di-tert-butylaniline exists in o-iminothiobenzosemiquinonato (1-) π–

radical form, which verifies the noninnocent nature of o-aminothiophenolato ligands.

Magnetic behaviour of these complexes show antiferromagnetic exchange coupling

between three S = 1 spins giving a singly non-degenerate S = 0 ground state, and thus

making these clusters very exceptional examples of S = 1 spin-triangles having three

equal J values.

Chapter 3 51

3.8 References

1) Bodensieck; W., Carraux, Y.; Stoeckli-Evans, K.; Süss-Fink, G. Inorg. Chim.

Acta 1992, 195, 135.

2) Stein, C.; Bouma, S.; Carlson, J.; Cornelius, C.; Maeda, J.; Weschler, C.; Deutsch,

E.; Hodgson, K. O. Inorg. Chem. 1976, 15, 1183.

3) Shibutani, Y.; Shinra, K.; Matsumoto, C. J. Inorg. Nucl. Chem. 1981, 43, 1345.

4) Larkoworthy, L. F.; Murphy, J. M.; Phillips, D. J. Inorg. Chem. 1968, 7, 1436.

5) (a) Schrock, R. R.; Listemann, M. L.; Sturgeoff, L. G. J Am. Chem. Soc. 1982,

104, 4291. (b) Chisholm, M. H.; Kelly, R. L., Inorg. Chem. 1979, 18, 2266 (c)

Chisholm, M. H.: Huffman, J. C.; Marchant, N. S., Polyhedron 1984, 3, 1033.

6) Allen, D. P.; Bottomley, F.; Day, R. W.; Decken, A.; Sanchez, V.; D. Summers,

A.; Thompson, R. C. Organometallics 2001, 20, 1840.

7) Bottomley, F.; Paez, D. E.; White, P.S. J. Am. Chem. Soc. 1981, 103, 5581.

8) Bottomley, F.; Paez, D. E.; Sutin, L.; White, P.S.; Kohler, F.H.; Thompson, R.C.;

Westwood, N. P. C. Organometallics 1990, 9, 2443.

9) Bottomley, F.; Paez, D. E.; White, P.S. J. Am. Chem. Soc. 1982, 104, 5651.

10) Eshel, M.; Bino, A. Inorg. Chim. Acta. 2002, 329, 45.

11) Coxall, R. A.; Parkin, A.; Parsons, S.; Smith, A. A.; Timco, G.A.; Winpenny, R.

E. P. J. Solid State Chem. 2001, 159, 321.

12) Parsons, S.; Smith, A. A.; and Winpenny, R. E. P. Chem. Commun. 2000, 579.

13) Elder, R. C.; Florian, L.; Lake, R. E.; Yacynych, A. M. Inorg. Chem. 1973, 12,

2690.

14) MacNeese, T. J.; Muller, T. E.; Wierda, D. A.; Darensbourge, D. J. Inorg. Chem.

1985, 24, 3465.

15) MacNeese, T. J.; Cohen, M. B.; and Foxman, B. M. Organometallics 1984, 3,

552.

16) (a) Fischer, H. R.; Glerup, J.; Hodgson, D. J.; Pedersen, E., Inorg. Chem. 1982,

21, 3063. (b) Paine, T. K.; Weyhermüller, T.; Wieghardt, K.; Chaudhuri, P.,

Inorg. Chem. 2002, 41, 6538.

17) Bottomley, F.; Chen, L.; and MacIntosh, S. M. Organometallics 1991, 10, 906.


18) Herrmann, W. A.; Alberto, R.; Bryan, J. C.; Sattelberger, A. P. Chem. Ber. 1991,

124, 1107.

19) Caneschi, A.; Cornia, A.; Fabretti, A.C.; Gatteschi, D.; Malavasi, W. Inorg.

Chem. 1995, 34, 4660.

20) De Meester, P.; Hodgson, D. J.; Freeman, H. C.; Moore, C. J. Inorg. Chem. 1977,

16, 1494.

21) Pattanayak, S.; Das, D. K.; Chakraborty, P.; Chakravorty, A. Inorg. Chem. 1995,

34, 6556.

22) Herebian, D.; Bothe, E.; Bill, E.; Weyhermüller, T.; Wieghardt, K. J. Am. Chem.

Soc. 2001, 123, 10012.

23) Herebian, D.; Ghosh, P.; Chun, H.; Bothe, E.; Weyhermüller, T.; Wieghardt, K.

Eur. J. Inorg. Chem. 2002, 1957.

24) Ghosh, P.; Bill, E.; Weyhermüller, T.; Neese, F.; Wieghardt, K. J. Am. Chem. Soc.

2003, 125, 1293.

25) Burlitch, J. M.; Hayes, S. E.; Whitwell, G. E. Organometallics 1982, 1, 1074.

26) Papaefthy, G. C.; Lippard, S. J. J. Am. Chem. Soc. 1993, 115, 11753.

27) Andrew, J. E.; Black, A. B. J. Chem. Soc. A 1969, 1456.

28) Pence, L. E.; Canesci, A.; Lippard, S. J. Inorg. Chem. 1996, 35, 3069.

29) Brechin, E. K.; Harris, S. G.; Parsons, S.; Winpenny, R. E. P. Chem. Commun.

1996. 1439.

Chapter 4 53

4.1 Introduction:

Large discrepancies exist in the literature about nickel complexes

containing two bidentate N,S-coordinated o-aminothiophenolate ligands,1-3 mostly due to

the overly strict treatment of the oxidation states of the metal without a complete analysis

involving the ligand, which is also redox active. Recently a more detailed study of the

structures4 together with theoretical analysis5 has shown that contributions of the ligand to

the properties of such compounds are important. Accordingly, the physical oxidation

level of these ligands is often best evaluated as an open shell, monoanionic π radical (o-

iminothiobenzosemiquinonato), which may lead to a singlet diradical ground state for

neutral NiL2 complexes. Nickel complexes with cyclic tetradentate N2S2-coordinated

ligands, falls in to two different categories (Fig. 4.1.1): (a) Compounds containing a

ligand derivative where the amino nitrogen

atoms form C=N double bonds (Schiff

bases). (b) Compounds containing a C-N

single bond between the amino nitrogen and

the carbon. As examples of the complexes

that are included in the family of compounds

(a), [Ni(PEX)] (S,S-o-xylyl-2,3-pentanedione

bis(mercaptoethylimine)nickel(II)),6 [Ni(BMAX)] (PEX = S,S-o-xylyl-2,3-butanedione

bis(mercaptoanil)), and [Ni(CAMX)] (CAMX = S,S-o-xylyl-1,2-cyclohexanedione

bis(mercaptoanil))7 and [Ni(gma)]8 (gma = glyoxal-bis(2-mercaptoaniline), which all

S

N

M

R2R1

S

N

M

H R2

R1

Fig. 4.1.1(a) (b)

Chapter 4 Ni, Co and Zn complexes of

2-phenylbenzothiazoline

Ni, Co and Zn complexes 54

contain an sp2 hybridized nitrogen donor. The physical oxidation state of the central metal

can be unambiguously established in these compounds as NiII close shell (d8) by making

use of the structural information of the ligand, where the C=N bond length of the Schiff

base is short at 1.29 ± 0.02 Å and the N-CPhenyl bond is found at 1.41 ± 0.02 Å. However,

discrepancies arise when these compounds are reduced by one electron. Recently DFT

calculations have clarified the appropriate description of the electronic structure for

[Ni(gma)]1- as containing a closed shell NiII ion bound to a (gma•)3- trianionic radical

ligand.10

In the case of complexes that fall in to the category (b), the physical oxidation state and

the electronic configuration are not clearly understood due to the absence of high quality

crystal structures of such complexes. The complex [Ni(H2gma)] (a bridge-saturated

derivative of [Ni(gma)], where gma = glyoxal bis(2-mercaptoaniline)), is one of the key

examples included in this category of compounds, since it has been described in the

literature having two different models of its electronic structure which have been

critically and controversially discussed. On one hand Gray et al.11 have proposed that

N

S

N

S

H H

Ni

R R

Fig.4.1.2a (above): diradical structure proposed by Gray and 4.1.2b (below): resonance structure proposed by Holm and

Kushi et al.

N

S

N

S

H H

NiN

S

N

S

H H

Ni

R R R R

Chapter 4 55

these species are diradicals with a singlet ground state (Fig. 4.1.2a) On the other hand,

Holm et al.12 proposed that two resonance structures (Fig. 4.1.2b) describe the ground

state. In this case, [Ni(H2gma)]- (S = 1/2) may be described in a purely formal sense as

NiIII with a (d7) configuration, where unpaired electron will be nickel based, which in turn

result in large g value anisotropies. On the contrary, Gray et al.11 proposed that the

anisotropy in the g tensor is not a reliable criterion of metal d orbital involvement,

particularly in complexes with ligands containing atoms with large spin-orbit coupling

constants (e.g. Sulfur). The crystal structure of [Ni(H2gma)]- is not available, but Gray et

al. have reported the crystal structure of the related complex, diacetyldihydrobis (2-

mercaptoanil)nickel monoanion, [NEt4][Ni(H2dma)].11 The C-S and C-N bond distances

of this complex are an arithmetic average of mono- and dianionic (LNSISQ)1- and (LNS

IP)2-

forms of ligands. At this point, Wieghardt et al.13 (scheme 4.1.1.) have proposed the

existence of a single radical delocalized over both the ligands (H2LNS). Similar properties

were found in [Ni(ddbt)] and [Co(ddbt)] (ddbt = bis-2,2'-(1,2-

diphenylethelylediimine)benzenethiolato), formed via a ring opening reaction of the 2-

phenylbenzothiazoline ligand.14 In both complexes the assignment of the oxidation state

of each metal was made considering the resonance forms of the ligand; thus the central

metal is assigned as MII.

Wieghardt et al.13 have recently established a series of cobalt and nickel

complexes containing two bidentate non-innocent ligands. It has been possible to

differentiate the oxidation states of the ligand by low temperature (100 K)

crystallography. For the neutral nickel complex, the ground state is a singlet diradical

S

HN

[M(LNSIP)2]n

M

S

HN

M

S

HN

M

[M(LNSISQ)2]n [M(LNS

IP)(LNSISQ)]n

1.35

1.72

1.411.36

1.42

1.38 1.431.76

1.37

Av. 1.39 1.365

1.741.42

1.411.385

1.40

5

1.375 1.40

Av.1.405

Scheme 4.1.1


(NiII; d8), however in the analogues cobalt complex the situation is more complicated.

Spectroscopic oxidation states describing a CoIII (d6) or CoII (d7) electron configuration

cannot be unambiguously assigned. The structures of [Ni(ddbt)] and [Co(ddbt)]14 were

obtained at room temperature, with an average experimental error of a given C-C, C-N or

C-S bond lengths of ≅ ±0.03Å (= 3σ), which may not have allowed a correct assignment

of the oxidation level of ligands. To obtain more insight into these complexes, the one

electron reduced forms of these complexes are described here.

Kochin et al. have reported a Zn complex which was formed via a ring

opening reaction of 2-phenylbenzothiazoline ligand and formulated as [Zn(ddbt)].15

Corbin et al. pointed out that it should be possible that the bridging ligand present in Zn

complex, could be removed by reduction of the complex with sodium borohydride,

removing the Zn as Zn(OH)2.16 But as this was not successful, the formulation of this

complex was doubtful. Therefore we decided to synthesis Zn complex and to

characterize it by X-ray structure analysis.


Complexes [Ni(Phbt)2] (5i), [Ni(ddbt)] (5), [Co(Phbt)2] (6i), [Co(ddbt)]14

(6) and [Zn(Phbt)2]16 (7) (where, Phbt = bis-(2-phenylmethyleneamino)benzenethiolato,

and ddbt = Bis-2,2'-(1,2-diphenylethylenediimine)benzenethiolato) were synthesized as

described in the literature. The general synthetic procedure for all the compounds is

demonstrated in scheme 4.2.1.

Scheme 4.2.1: Synthesis of [M(Phbt)] and [M(ddbt)]

M 2+

MeOH Toluene[M(Phbt)2] [M(ddbt)]LPh

RefluxNH2

SH

PhCHO

MeOHLNS

HN

S

H

PhN

S S

NM

PhPh

N

S S

NM

PhPhH H

Chapter 4 57

[Ni(ddbt)] (5):

[Ni(Phbt)2] (5i), was obtained in ethanol by 2:1 reaction of the 2-phenylbenzothiazoline

with nickel(II) acetate tetrahydrate. Heating for 10 minutes afforded deep brown crystals

of [Ni(Phbt)2]. Black crystals of [Ni(ddbt)] (5) were obtained by heating 5i for 1 h in

toluene. In all the [M(ddbt)] compounds the carbon-carbon bond formation takes place

between two imino carbon atoms in ligands. Crystals of 5 suitable for X-Ray analysis

were obtained by slow evaporation of a mixture of CHCl3 and MeOH.

[Co(ddbt)2] (6):

6i was obtained in a better yield than previously reported14 by dissolving the ligand 2-

phenylbenzothiozoline in ethanol, with cobalt acetate tetrahydrate, in presence of 4 eq. of

base (NaOMe). Heating for 20 minutes afforded deep brown crystals of 6i. Complex

[Co(ddbt)2] (6) was formed by heating 6i for 1 h in toluene under inert atmosphere,

resulting in the greenish blue solution of 6. Crystals of 6 suitable for X-ray analysis were

obtained by slow evaporation of a mixture of MeCN and MeOH.

[Zn(Phbt)2] (7):

An orange solid of [Zn(Phbt)2] (7) was obtained after the addition of zinc acetate to a

solution of 2-phenylbenzothiazoline in methanol. Further heating in toluene for more

than 2 hours did not result in any change contrary to the case of the [Ni(ddbt)] and

[Co(ddbt)] complexes. Crystals suitable for X-ray structure analysis were obtained from a

mixture of CH2Cl2 and MeOH.

[Co(Cp2)][Ni(ddbt)] (5b) and [Co(Cp2)][Co(ddbt)] (6b):

The one-electron reduced forms of [Ni(ddbt)] and [Co(ddbt)] were

obtained by using 1 equivalent of cobaltocene as a reducing agent resulting in two new

compounds [Co(Cp2)][Ni(ddbt)] (5b) and [Co(Cp2)][Co(ddbt)] (6b), subsequently. Dark

green and dark violet crystals of 5b and 6b were obtained by slow evaporation of

mixture of acetonitrile and hexane.


4.3 Molecular Structures

The crystal structures of compound 5, 6, 7, 5b, and 6b at 100(2) K have

been determined using Mo Kα radiation.

Fig. 4.3.1 shows a thermal ellipsoid plot of [Ni(ddbt)] (5) and table 4.3.1

displays the most important bond distances. 5 crystallizes in the monoclinic crystal

system with a space group P21/n. The coordination geometry of NiII is square planar and

the dihedral angle between N-Ni-S planes is 7.7°. The phenyl groups on carbon atoms

C(8) and C(9) are staggered and trans to each other with a torsion angle of 144°. The

average intramolecular Ni-S and Ni-N distances of 2.1270(4) and 1.8194(10) Å are

consistent with the reported values for this complex.14 These distances are also

comparable to the Ni-S and Ni-N distances in several NiII complexes having N2S2 chelate

ligand coordination.17

The C-S (1.7185 ± 0.009Å) and C-N (1.3515 ± 0.009 Å), bond distances

show a substantial double bond character and the phenyl rings exhibit distortions typical

of quinoid type structures: two shorter C=C and four longer ones (1.3723 and 1.4197 Å).

Fig. 4.3.1: Thermal ellipsoid plot of 5 at the 50% probability level with atom labelling scheme.

Ni (1)

S(12)S(1)

C(1)C(2)

C(12) C(13)

C(14)

C(6)

C(5)C(4)

C(3)

C(15)

C(16)

C(11)N(7)

N(10)

C(8)C(9)

Chapter 4 59

As per the criterion developed by Wieghardt et al.4 for the identification of radical ligands

in 3,5-di-tert-butyl-aminothiophenolates, these features in the bond distance of the ligand

indicate the presence of o-iminothiobenzosemiquinonato (1-) π–radical ligands instead of

the suggested resonance structures. Thus, based on this thorough analysis of the ligand

oxidation levels, 5 can be assigned as having a singlet diradical ground state (NiII, d8).

The structure of 6 is isostructural with that of compound 5; therefore it is

not shown separately. Selected bond lengths are represented in table 4.3.2. In the

structure of 6, both of the ligands exhibit deprotonation of the nitrogen and sulfur atoms

coordinated to metal. The complex has a square planer configuration, with the dihedral

angle in the N-Co-S planes of 8.8°. The phenyl groups on carbons C(8) and C(9) are

staggered with a torsion angle of 142.77°. The average intra molecular Co-S and Co-N

distances at 2.1386(6) and 1.815(2) Å, respectively are identical to the reported distances

for the same complex; (2.139(2) Å and (1.815(4) Å, respectively).14 The Co-N distances

are similar to the distances observed in CoIII complexes, [Co(2LN)2] (1.862(2)) and

[Co(4LO)2] (1.822(2)) (2LN represents o-phenylenediamine, and 4LO represents 2-(2-

trifluromethyl)anilino-4,6-di-tert-butylphenol)). The C-S (1.736 ± 0.02Å) and C-N (1.368

± 0.02Å), bond lengths display intermediate character between a single and a double

Bond distance [Å]

Ni(1)-N(7)

Ni(1)-S(1)

S(1)-C(1)

N(7)-C(6)

C(1)-C(2)

C(1)-C(6)

C(2)-C(3)

C(3)-C(4)

C(4)-C(5)

C(5)-C(6)

1.818(1)

2.1268(4)

1.719(1)

1.351(1)

1.409(2)

1.432(2)

1.375(2)

1.420(2)

1.369(2)

1.420(2)

Ni(1)-N(10)

Ni(1)-S(12)

S(12)-C(12)

N(10)-C(11)

C(11)-C(12)

C(11)-C(16)

C(12)-C(13)

C(13)-C(14)

C(14)-C(15)

C(15)-C(16)

1.820(1)

2.1271(4)

1.718(1)

1.352(1)

1.432(2)

1.419(2)

1.405(2)

1.379(2)

1.410(2)

1.379(2)

Table 4.3.1: Selected distances [Å] for (5)


bond and the six C-C bonds of the six-memberd ring are nearly equidistant within the 3σ

level (1.390 ± 0.02 Å) as shown in scheme 4.1.1. This suggests a formal oxidation state

of +3 for the cobalt centre with a charge distribution of this species as

[CoIII(LNSIP)(LNS

ISQ)], with delocalization of the charge over both of the ligands. Thus, the

valence isomerisation picture of ligand, demonstrated by Kushi et al., which leads to CoII

formalism is erroneous and [Co(ddbt)] can be more correctly formulated as described

above with CoIII oxidation state of central metal.

Fig. 4.3.3 displays a thermal ellipsoid plot of [Zn(pdbt)2] (7) and selected

bond lengths are presented in table 4.3.3. The structure of 7 belongs to the P21/n space

group. As is apparent from the Fig. 4.3.3, the zinc atom is four coordinate with two

sulfur and the two imine nitrogen atoms of the two 2-phenylbenzothiazoline ligands. The

Zn ion has a distorted tetrahedral geometry, with a dihedral angle of 88.54(4)º between

the S-Zn-N planes. The Zn-S and Zn-N average distances of 2.2687(5) and 2.1028(13) Å

are in the expected range of these distances.18 The S(1)-Zn(1)-S(21) angle (121.01(2)º) is

slightly larger than expected for a tetrahedral geometry, while N(7)-Zn(1)-N(27) ,

(111.51(5)º) angle is close to the tetrahedral angle of 109º. The C-S (1.760 ± 0.006 Å)

and C-N (1.432 ± 0.004 Å) average bond lengths clearly display only single bond

Bond distance [Å]

Co(1)-N(7)

Co(1)-S(1)

S(1)-C(1)

N(7)-C(6)

C(1)-C(2)

C(1)-C(6)

C(2)-C(3)

C(3)-C(4)

C(4)-C(5)

C(5)-C(6)

1.816(2)

2.1384(6)

1.738(2)

1.365(3)

1.398(3)

1.417(3)

1.379(3)

1.407(3)

1.372(3)

1.411(3)

Co(1)-N(10)

Co(1)-S(12)

S(12)-C(12)

N(10)-C(11)

C(11)-C(12)

C(11)-C(16)

C(12)-C(13)

C(13)-C(14)

C(14)-C(15)

C(15)-C(16)

1.815(2)

2.1388(6)

1.735(2)

1.371(3)

1.413(3)

1.411(3)

1.397(3)

1.377(3)

1.395(3)

1.390(3)

Table 4.3.2: Selected distances [Å] for 6.

Chapter 4 61

character. In addition the six C-C (1.402 ± 0.006 Å) bonds of the six-membered ring do

not show quinoid type distortion being equidistant within 3σ, confirming the normal

closed shell form of the ligands with [ZnII(Phbt)2] formalism of the complex.

Bond distance [Å]

Zn(1)-N(7)

Zn(1)-S(1)

N(7)-C(8)

S(1)-C(1)

C(6)-N(7)

C(1)-C(2)

C(1)-C(6)

C(2)-C(3)

C(3)-C(4)

C(4)-C(5)

C(5)-C(6)

2.093(1)

2.2646(5)

1.293(2)

1.762(2)

1.429(2)

1.402(2)

1.407(2)

1.384(2)

1.391(3)

1.389(2)

1.400(2)

Zn(1)-N(27)

Zn(1)-S(21)

N(27)-C(28)

S(21)-C(21)

C(26)-N(27)

C(21)-C(22)

C(21)-C(26)

C(22)-C(23)

C(23)-C(24)

C(24)-C(25)

C(25)-C(26)

2.113(1)

2.2728(5)

1.291(2)

1.758(2)

1.435(2)

1.403(2)

1.405(2)

1.381(3)

1.386(3)

1.386(3)

1.395(2)

Table 4.3.3 Selected distances [Å] for 7

Zn (1) S(21)S(1)

C(1)C(2)

C(22)

C(23)

C(24)

C(6)

C(5)C(4)

C(3)

C(25)

C(26)

C(21)

N(7)

N(27)

C(8)

C(9)

Fig. 4.3.2 A thermal ellipsoid plot of 7 at the 50% probability level with labelling scheme.


The thermal ellipsoid plot of [Co(Cp)2][Ni(ddbt)] (5b) with the labelling

scheme as well as the most relevant bond distances are shown below in Fig. 4.3.4 and

table 4.3.4, respectively. The crystal structure of the complex consists of the packing of

discrete Co(Cp2)+ cations and approximately planar Ni(ddbt)- anions (dihedral angle

between N-Ni-S planes is 2.7°). Molecule possesses idealized C2 symmetry. The

crystallographic data show that the Ni-S and Ni-N distances of 2.1444(3) and 1.8216(10)

Å are identical to those of the neutral complex [Ni(ddbt)] (5) within the experimental

error (±0.03Å), suggesting a similar oxidation state of the central Ni in both the neutral

(5) and reduced form (5b) thus confirming the ligand centered reduction. These distances

are consistent with those of the monoanionic nickel complexes [Ni(H2dma)]11 (where

dma represents diacetyldihydrobis(2-mercaptoanil)), and [Ni(-SC6H4-o-NH-)2]-.2,3 The C-

S (1.747 ± 0.004 Å) and C-N (1.371 ± 0.005 Å) average bond distances are intermediate

between a single and a double bonds as it was observed in the [Co(ddbt)] (6). These

distances are precisely the arithmetic mean of a single and a double bond length. In

addition, the six C-C (1.402 ± 0.006 Å) bonds of the aromatic ring do not show the

already discussed quinoid distortion being intermediate between a single and a double

bonds as it is depicted in scheme 4.1.1, thus confirming the presence of a radical ligand

where the charge is delocalized over both of the ligands.

Bond distance [Å]

Ni(1)-N(7)

Ni(1)-S(1)

S(1)-C(1)

N(7)-C(6)

1.822(1)

2.1444(3)

1.747(1)

1.370(1)

C(1)-C(2)

C(1)-C(6)

C(2)-C(3)

C(3)-C(4)

C(4)-C(5)

C(5)-C(6)

1.398(2)

1.425(2)

1.388(2)

1.400(2)

1.389(2)

1.410(2)

Table 4.3.4: Selected distances [Å] for 5b

Chapter 4 63

The thermal ellipsoid plot and labelling scheme of 6b is shown in Fig.

4.3.5 and relevant bond distances are reported in table 4.3.5. The structure belongs to the

space group P21/c. Each molecule in the unit cell possesses square planar geometry with a

dihedral angle of 2.2° between N-Co-S planes. The Co(1)-N(7) and Co(1)-S(1) distances

of 1.825(10) Å and 2.170 (3) Å, respectively are identical within the experimental error

(±0.03Å) to the corresponding neutral compound [Co(ddbt)] (6) indicating a ligand

centered reduction. It is important to note that the average C-S bond lengths for both

ligands are quite long in the range of 1.76(1) Å. The six C-C distances of the aromatic

rings (1.403 ± 0.05; 3σ) are also equidistant within the range of experimental error. The

average C-C distance at 1.393(3) Å is typical for an aromatic phenyl ring. In particular,

the long C-S bonds indicate the presence of N,S-coordinated aromatic 1,2-

imidothiophenolate(2-) ligands, implying an assignment of a +3 oxidation state to the

Fig. 4.3.4: A thermal ellipsoid plot of 5b at the 50% probability level with atom labelling scheme.

Ni (1)

S(12)S(1)

C(1)C(2) C(12) C(13)

C(14)

C(6)

C(5)C(4)

C(3)

C(15)

C(16)

C(11)N(7)

N(10)

C(8) C(9)

Co(1)


central cobalt atom. coordinated aromatic 1,2-imidothiophenolate(2-) ligands, implying

an assignment of a +3 oxidation state to the central cobalt atom.

Bond distance [Å]

Co(1)-N(7)

Co(1)-S(1)

S(1)-C(1)

N(7)-C(6)

C(1)-C(2)

C(1)-C(6)

C(2)-C(3)

C(3)-C(4)

C(4)-C(5)

C(5)-C(6)

1.83(1)

2.173(3)

1.76(1)

1.37(1)

1.40(2)

1.42(2)

1.39(2)

1.40(2)

1.39(2)

1.41(2)

Co(1)-N(10)

Co(1)-S(12)

S(12)-C(12)

N(10)-C(11)

C(11)-C(12)

C(11)-C(16)

C(12)-C(13)

C(13)-C(14)

C(14)-C(15)

C(15)-C(16)

1.83(1)

2.168(3)

1.76(1)

1.38(1)

1.407(2)

1.404(2)1.

389(2)

1.39(2)

1.38(2)

1.398(2)

Co (1)

S(12)

S(1)

C(1)C(2)

C(12)

C(14)

C(6)

C(5)C(4)

C(3)

C(15)

C(16)

C(11)

N(7)

N(10)

C(8)

C(9)

C(13)Co (2)

Fig. 4.3.5:A thermal ellipsoid plot of 6b at the 50% probability level with atom labelling scheme.

Table 4.3.5: Selected distances in [Å] for 6b

Chapter 4 65

DFT calculations on the nickel complexes namely [Ni(1LN)2] and

[Ni(1LN)2]1- show that (Fig. 4.3.6) the central nickel ions in both complexes have a +2

oxidation state. The HOMO in the monoanion is 2b2g, which have 26% 3dxz character thus

making this redox active SOMO predominantly ligand based. The reason of predominant

ligand character in 2b2g orbital in case of nickel is the higher effective nuclear charge of

Ni relative to cobalt that brings the 3d orbitals much lower in energy relative to the ligand

orbitals for Ni.

In contrast, the spin triplet [Co(1LN)2]1- have shown that the HOMO is a

2b2g orbital, which has almost equal contributions from the metal and the ligand and thus,

the explicit assignment of electron configuration at the metal ion (i.e. to determine the dn

(n = 6 or 7)) is not possible. But in contrast to this situation, the geometry of the ligands

Fig. 4.3.6: MO schemes of [Co(1LN)2]1- and [Ni(1LN)2]1-


in [Co(ddbt)]1- as determined by X-ray crystallography clearly suggest a CoIII (d6, S=1)

spectroscopic oxidation state over a mixed-valence configuration.13

4.4. Electrochemistry of 5 and 6

The redox properties of 5 and 6 have been studied in CH2Cl2 and MeCN,

respectively by cyclic voltammetry (CV). [N(n-Bu)4][PF6] (0.10M) was used as a

supporting electrolyte, glassy carbon as working electrode and Ag/AgNO3 as the

reference electrode. Ferrocene was used as internal standard, and all redox potentials are

referenced vs. the ferrocene/ferrocenium (Fc/Fc+) couple at room temperature. Fig. 4.4.1

and 4.4.2 show the cyclic voltammograms of 5 and 6 from +2.0 V to -2.0 V and +0.5 V to

–2.0 V, respectively. For 5, four reversible electron-transfer waves were observed and

three reversible electron-transfer waves were observed for 6. Table 4.4.1 and 4.4.2

summarizes the redox potentials (E1/2) of electron transfer waves for compounds 5 and 6

vs. (Fc / Fc+), respectively.

According to coulometric measurements at appropriate fixed potentials,

two waves in 5 namely; E31/2, and E4

1/2 correspond to two reversible oxidation processes

and the other two waves, E11/2 and E2

1/2 correspond to two reversible reduction processes.

This behavior for 5 correspond exactly to that reported4 for [NiII(LISQ)2] (LISQ = 3,5-di-

tert-butyl-iminothiobenzosemiquinone) (table 4.4.1), where it was shown that these

processes are ligand centered rather than metal centered as explained in scheme 4.4.1.

Such complete (or incomplete) electron transfer series have been reported for many

Compound E11/2(2-/1-) E2

1/2(1-/0) E31/2(0/1+) E4

1/2(1+/2+)

[NiII(LISQ)2] -1.714 -0.826 +0.284 0.896(irr.)

[Ni(ddbt)] (13) -1.509 -0.658 +0.574 +1.017

Table 4.4.1: Redox potentials [V] of 5 and [NiII(LISQ)2] vs. Fc/Fc+ at 22° C.

Chapter 4 67

square-planar NiII, PdII and PtII complexes containing two catecholate, phenylenediamide,

benzodithiolate, or o-iminothiophenolate ligands. 8, 12a, 20

For 6, two reversible reduction processes, E11/2 and E2

1/2 and one oxidation process E31/2

are observed. Similar cyclic voltammograms and redox potentials (table 4.4.2) have been

reported for [CoIII(1LN)2],12a [CoIII(2LN)2],13 and [CoIII(4LO)2] (2LN represents o-

-e+e[NiII(ddbt)]

-e+e

+e -e -e +e

[NiII(ddbt)]1-

[NiII(ddbt)]2-

[NiII(ddbt)]1+

[NiII(ddbt)]2+

Scheme 4.4.1: Redox activity of 5

Fig. 4.4.1: Cyclic Voltammogram of 5 in CH2Cl2 solution containing 0.10M[(n-bu)4N][PF6], at 22°C and scan rates of 50, 100, 200, 400, 1000 mV/s usingglassy carbon working electrode.

-2.0-1.5-1.0-0.50.00.51.01.5

10 µ

A

I (µA

)

E (mV)


phenylenediamine, and 4LO represents 2-(2-trifluromethyl)anilino-4,6-di-tert-

butylphenol)),13 showing the similar redox activity in all of these complexes as explained

by scheme 4.4.2, reinforcing the +3 oxidation state of cobalt in 6.

Although, the peak height of E31/2 is half as intense compard with the other two reversible

reduction processes, controlled potential coulometry has shown that the three processes

consumed same amount of current, indicating that each of them correspond to one

electron transfer process. Interestingly, the redox potentials for the reduction waves E21/2

are found to be similar in both of compounds, 5 and 6 irrespective of the nature of the

central metal ion (nickel or cobalt). However, the oxidation potentials differ in both of

them.

Compound E11/2(2-/1-) [V] E2

1/2(1-/0) [V] E31/2(0/1+) [V]

[Co(1LN)2] -1.98 -0.95 -0.32

[Co(2LN)2] -1.03 -0.50

[Co(4LO)2] -0.85 -0.20

[Co(ddbt)] (3.2) -1.81 -0.61 -0.027

Table 4.4.1- Redox potentials [V] of 6 and other complexes vs. Fc/Fc+ at 22° C.

N

S

N

S

HPhH

Ni

N

S

N

S

H HPh

Ni

Ph

N

S

N

S

H HPh

Ni

Ph Ph

[Ni(ddbt)]1-

[Ni(ddbt)]2-

[Ni(ddbt)]1+

N

S

N

S

H HPh

Ni

Ph

[Ni(ddbt)]2+

N

S

N

S

H HPh

Ni

Ph

[Ni(ddbt)]

+e

+e

+e

+e

Fig. 4.4.1: relevant structures for the redox series of [Ni(ddbt)]

Chapter 4 69


Controlled-potential coulometry allows the selective generation of the

stable monocation as well as the mono- and dianions of 5 of which the respective

electronic spectra have been recorded. The electronic spectra for all these species are

shown in Fig. 4.5.1. The neutral complex 5 shows an intense band in the near infrared

region at 820 nm (ε = 4.2 × 104 M-1 cm-1), that likely corresponds to a spin and dipole

allowed ligand-to-ligand charge transfer transition (LLCT), which is observed in all

square-planar complexes of NiII, PdII, and PtII containing two bidentate o-

Scheme. 4.4.2- redox activity of 6.

[CoIII(ddbt)]-e+e[CoIII(ddbt)]+

-e+e

[CoIII(ddbt)]--e+e [CoII(ddbt)]2-

Fig. 4.4.2: Cyclic Voltammogram of 6 in MeCN solution containing 0.10M[(n-bu)4N][PF6] at 22°C and scan rates of 50, 100, 200, 400 mV/s using glassycarbon working electrode.

-2.0-1.5-1.0-0.50.0

E (V)

10 µ

A


iminothiobenzosemiquinonato ligands (Scheme. 4.5.1, LISQ = o-

iminothiobezosemiquinonate(1-), LAP = o-aminothiophenolate(1-), LIBQ = o-

iminothiobezoquinonate).4

For the neutral species [Ni(1LNISQ)2] (1LN

ISQ = o-

diiminobenzosemiquinonate(1-), NiII; d8 ), it has been established that within the D2h

point group, the HOMO (1b1u) and the LUMO (2b2g) correspond to the symmetric and

antisymmetric combinations of the SOMO of the free bezosemiquinonate (1-) ligand. The

HOMO-LUMO transition 1b1u -2b2g corresponds to a LLCT band and no other LMCT

[NiII(LAP)(LIBQ)]*

Excited singlet state

[NiII(LISQ)2]h.ν

(S=0), µ=0 (S=0), µ≠0

Scheme. 4.5.1

Singlet ground state

hν

Fig. 4.5.1: Electronic absorption spectra of 5, 5a, 5b and 5c in CH2Cl2 solution (0.10M [(n-Bu)4N] PF6) at –5 °C.

500 1000 1500 20000.0

0.5

1.0

1.5

2.0

2.5 [Ni(ddbt)]1+ (5a) [Ni(ddbt)] (5) [Ni(ddbt)]1- (5b) [Ni(ddbt)]2- (5c)

ε X1

04 M-1 c

m-1

λ (nm)

5

5a

5b

5c

Chapter 4 71

band is observed in the visible region. Upon one electron oxidation (species 5a), the

former HOMO 1b1u (π*) becomes SOMO, which cannot mix with d-orbitals of the nickel

ion due to symmetry reason.5 Thus, the spectrum of the 5a exhibits an intense absorption

at 840 nm (ε = 2 × 104 mol-1 cm-1) which may be assign as an intraligand π-π *charge

transfer band of a coordinated o-iminothiobezoquinonato ligand, (LIBQ). In addition a

broad absorption at ≈ 1100 nm is observed with ε = 7000 M-1cm-1 which is assigned as an

intervalence charge transfer band (IVCT), and which confirms ligand mixed valency.

Thus, an electronic structure of type [NiII (LISQ)(LIBQ)]+ with S=1/2 ground state is

proposed for 5a.

The spectrum of monoanion (5b) shows an intense absorption band at 910

nm (ε = 1.5 × 104 M-1 cm-1) and a weak absorption band at 700 nm. In this case, the

former LUMO (2b2g) becomes the SOMO, which has ~15% Ni 3dxz character, thus the

transition 1b1u-2b2g is spin and dipole allowed and represents ligand-to-ligand

intervalence charge transfer band (LLIVCT). The nature of these bands in 5b suggest the

presence of at least one radical ligand as in the [NiII(LISQ)(LIP)]-. 5b also shows a broad

charge transition band in the near infrared region (1750 nm, ε = 6 × 103 mol-1 cm-1),

which corresponds to IVCT of the type as shown in Scheme 4.5.2.

In the spectrum of the dianionic species (5c), both of these strong LLCT and IVCT bands

are quenched, confirming the presence of the dianionic o-imidothiophenolato (LIP) forms

of the ligand. The spectral and electrochemical behavior so confirms that the redox

activity of this complex is predominantly ligand based as shown in Scheme. 4.4.1.

The electronic spectrum of neutral 6 (Fig. 4.5.2) shows a broad ligand-to-ligand charge

transfer band (LLCT) in the near infrared at 1400 nm (ε = 4.2 ×103 M-1 cm-1) similar to

the one observed for [Ni(ddbt)]1- (5b), suggesting that the origin of this band is the same

as in the [Ni(ddbt)]1- species. This broad band in the near infrared region is absent in the

spectra of the monocation (6a), the monoanion (6b) and dianion (6c). The spectra of

monoanion (6b) and monocation (6a) present similar features: In the spectrum of the 6b,

[NiII(LPhISQ)(Lph

IP)] [NiII(LPhIP)](LPh

ISQ)] Scheme 4.5.2


an absorption band at 550 nm with an extinction coefficient of, ε = 1.5 × 104 M-1cm-1 and

a weak absorption at 680 nm (ε = 1 × 104 M-1cm-1) are present, while 6a displays a strong

absorption band at 600 nm (ε =1 .5 × 104 mol-1cm-1) and a weaker band at 780 nm (ε =1 ×

104 mol-1cm-1). This pattern is very similar to the spectrum of [CoIII(LNSIP)2]- (1) (chapter

2), where they were assigned as ligand to metal (LMCT) bands. In the spectrum of the

dianionic species (6c), both of these strong LLCT and LMCT bands are quenched.

The electronic spectrum of [Zn(pdbt)2] (7) (Fig. 4.5.3) was recorded in

dichloromethane. It exhibits a transition at 450 nm (ε = 3000 M-1cm-1), which is likely a

LMCT band.

Fig. 4.5.2: Electronic spectra of 6, 6a, 6c and 6c in CH2Cl2 solution (0.10M)[(n-Bu)4N] PF6 at –5 °C.

400 600 800 1000 1200 1400 1600 18000

1

1

2

3

3

4

5 [Co(ddbt)] (6) [Co(ddbt)]- (6b) [Co(ddbt)]+ (6a) [Co(ddbt)]2- (6c)

ε M

-1cm

-1X

104

λ nm

6

6b

6a

6c

Chapter 4 73

4.6 X-band EPR spectra and magnetic susceptibility

X-band EPR spectra and magnetic susceptibility data were recorded for 5,

5a, 6, 7, 5b and 6b. As expected compounds 5 and 7 were diamagnetic. X-band EPR

spectra of the 5b and 5a in frozen CH2Cl2 solutions at 10 K is shown below in Fig 4.6.1

and Fig. 4.6.2, respectively. Both of these spectra are indicative of an S = ½ ground state.

The EPR spectrum of 5b displays a rhombic signal with anisotropic g values (gx = 2.124,

gy = 2.024, gz = 1.997), whereas 5a shows an isotropic EPR signal at giso = 1.9968. These

spectra closely resemble those reported for analogous monoanionic and monocationic

species in the literature.4,21

As mentioned in the introduction of this chapter, two controversial

approaches have been discussed in the literature25 about the observed g anisotropies for

the [Ni(H2dma)]1- and similar complexes. Holm et al.12 believed that in such complexes

the large g value anisotropies can be explained by considering NiIII (d7) configuration,

with appreciable admixture of d orbitals of metal in the wave function of an odd electron.

Fig. 4.5.3: Electronic absorption spectrum of the neutral 7 in CH2Cl2 at 22°C.

400 500 6000

1

2

3

4

[Zn(phbt)2]

ε Μ

−1 c

m−1

X 1

03

λ nm


On the contrary, Gray et al.11 believe that the monoanion can de described as NiII (d8),

coordinated to monoradical ligand and that the anisotropy in the g tensor is a

consequence of the larger spin-orbit coupling. Indeed, previous DFT calculations in our

group21,22 have shown that, [MII(LISQ)2] complexes are singlet diradical species and that

the monoanionic species contain one coordinated ligand π radical. In the neutral species,

the two molecular orbitals shown in Fig. 4.6.3 are highest in energy. These two MOs are

the symmetric and antisymmetric combination of the singly occupied molecular orbital

(SOMO) of the free semiquinonate ligand. In the neutral species, two electrons occupy

the two close lying au and bg orbitals. In the monocation, the ground state is 2Au with the

au MO in fig. 4.6.3, containing a single unpaired electron. Due to symmetry reasons, the

au orbital cannot mix with any metal d orbital. Consequently metal hyperfine coupling

cannot be expected and is not observed experimentally. The lack of metal character in the

au SOMO causes mixing of the excited states with the ground state to be inefficient, and

therefore, g anisotropy is expected to be very small in agreement with the experiment.

Fig. 4.6.1: X band EPR spectra of 5b Exp : T = 9.94 K, ν = 9.52GHz , P = 1.0060 x 10-4 mW , MA = 10 G

300 320 340 360

dχ"/d

B

B [mT]

2.3 2.2 2.1 2 1.9

Experimental

Simulated

g-factor

gx = 2.13 gy = 2.024 gz = 1.997

Chapter 4 75

In contrast, in the monoanion, two electrons occupy the au orbital and the

bg orbital is the SOMO. As this orbital can mix with the metal d orbitals, it acquires some

metal character. Since the ground state 2Bg mixes with low-lying d-d states, it has a

sizable orbital angular momentum, which manifests itself experimentally in g anisotropy.

M

a1u

b2g

Fig. 4.6.3: HOMOs of [ML2]0, [ML2]1-, and [ML2]1+

Fig. 4.6.2: X band EPR spectra of 5a Exp : T = 9.94 K, ν = 9.52 GHz , P = 1.0060 x 10-4 mW , MA = 10 G

280 320 360 400

dχ"/d

B

B [mT]

2.6 2.4 2.2 2 1.8 1.6

g-factor

Experimental

Simulated

giso = 1.997


Magnetic susceptibility data of 5b was collected in the temperature range from 2 to 290

K. This data is shown below in Fig. 4.6.4 as µeff vs. temperature. It shows a temperature

independent magnetic moment of 1.70 µB corresponding to an S = 1/2 ground state.

Following simulation parameters yield the best fit of experimental data: g = 2.049, χTIP =

0.343*10-4 emu mol-1, θ = -0.596 K, where g value is kept fix from the EPR spectrum

parameters.

The X-band EPR spectrum for the neutral complex 6 is shown in Fig.

4.6.5. The monocation (6a) and the monoanion (6b) are both EPR silent. 6 shows a

rhombic EPR signal with following simulation parameters: gx = 2.0160, gy = 2.0457 and

gz = 2.7022, and a hyperfine coupling of the unpaired electron with the 59Co nucleus (I =

7/2) is observed with Axx = 18.00, Ayy = 0, and Azz = 28.36G. These spectrum and fitting

parameters closely resemble to those reported for [Co(2LN)2],13 (2LN represents o-

phenylenediamine) where the simulation parameters are as following : gx = 1.9906, gy =

2.058, gz = 2.8100 with 59Co hyperfine coupling constants Axx= 24.0, Ayy = 0, Azz= 42 G.

0 50 100 150 200 2500,0

0,4

0,8

1,2

1,6

2,0

µ eff/µ

B

T/K

Fig. 4.6.4: Plot of µeff vs. temperature for 5b. The solid line represents thebest least squares fitting for the experimental data (squares).

µeff = 1.73 µB g = 2.049 χTIP = 0.343×10-4 emu mol-1

θ = -0.596 K

Chapter 4 77

The observed g values in the spectrum clearly show that the unpaired

electron must be located on the metal d orbital, which can be achieved by two possible

ways: 1) A square-planar low spin CoII (d7) complex possessing a SCo=1/2 ground state.

Similar simulation parameters have been reported for other related complexes.23 2)

Alternatively, a CoIII (d6) ion in a square-planar ligand field possessing an SCo=1 local

spin. This may allow antiferromagnetic exchange coupling within the radical ligand to

give a SCo =1/2 ground state. It is not possible to discern between these two possibilities

using only EPR spectroscopy. However, based on the X-ray structure analysis, the bond

distances in the ligand point towards the second possibility i.e. CoIII (d6), assignment to

the central metal.

6 shows a temperature independent magnetic moment of 1.93 µB

corresponding to an S = 1/2 ground state (Fig. 4.6.6, g = 2.28 (fixed from EPR

parameters), χTIP = 0.3*10-4 emu mol-1, θ = -0.119 K). It is still not possible to discern

between the above mentioned two possibilities for the S = 1/2 ground state from magnetic

susceptibility measurements.

Fig. 4.6.5- X band epr spectrum of 6 exp:T = 9.90 K, ν = 9.64 GHz , P = 6.3462 x 10-5 mW, MA = 10 G

240 260 280 300 320 340 360 380

Experimental

Simulated

dχ"

/dT

B [mT]

2.8 2.6 2.4 2.2 2 1.8g-factor

gx = 1.9906 gy = 2.058 gz = 2.8100


The compound 6b is EPR silent but shows a temperature independent

magnetic moment of 3.0 µB corresponding to S = 1 ground state (Fig. 4.6.7, g = 2.15, χTIP

= 0.277×10-4 emu mol-1, D = 37.0 cm-1). The zero-field splitting of a high magnitude, D =

|36| cm1- is known for the CoIII spin triplet compounds.19 Taking into account these

parameters and previous data, the ground state of 6b can be assigned as CoIII (d6), which

in turn confirms the CoIII, physical oxidation state for the cobalt center for compound 6

assuming ligand centered reduction takes place. The sign of D was determined from

variable field / variable temperature measurements and spin Hamiltonian simulations of

the experimental data (Fig. 4.6.8). The best fit of the magnetization behaviour is obtained

for D = +31 cm-1, g = 2.1, E/D= -0.385.

Fig.4.6.6: Plot µeff vs. µB for 6. The solid line represents the best least squaresfitting for the experimental data (squares).

50 100 150 200 250

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

µ eff/

µ Β

T/K

µeff = 1.93 µB g = 2.28 χTIP = 0.3×10-4 emu mol-1

θ = -0.119 K

Chapter 4 79

Fig. 4.6.7: Plot µeff vs. µB for 6b. The solid line represents the bestleast squares fitting for the experimental data (squares).

0 50 100 150 200 250

1.0

1.5

2.0

2.5

3.0

3.5

µ ef

f / µ

B

T / K

µeff = 3 µB g = 2.15 χTIP = 0.277×10-4 emu mol-1

D = 37.0 cm-1

0.0 0.5 1.0 1.5 2.0 2.50.0

0.1

0.2

0.3

Mm

ol/N

gβ

βH/kT

1 T

4 T

7 T

Figure 4.6.8: Magnetization measurements at 1, 4 and 7 T for complex 6b. Thesolid lines represent the simulation. (D = +31 cm-1, g = 2.1)


Far-infrared transmission spectrum for complex 6b has been measured

over the frequency range of 10-50 cm-1. The measurements were performed at variable

fields in order to distinguish the electronic transition bands from the normal phonon

bands. The temperature was kept constant at 1.8 K and the field was varied from 0 to 7 T.

A very sharp band (1 cm-1 width) is observed at 36.67 cm-1, which is found to be field

dependent. Whereas all other bands remain unaffected on application of the magnetic

field, the band at 36.67 cm-1 moves to higher frequency with increasing field strength

(Fig. 4.6.9), and hence, clearly arises from a low-frequency electronic transition

(Fig.2.7.4, chapter 1). The D value obtained from the susceptibility measurements (37

cm-1) is in agreement with zero field splitting parameter obtained from the far-infrared

spectrum. Thus, compound 6 possesses a spin triplet ground state with a zero field

splitting of +36.67 cm-1.

Fig. 4.6.9: Far-infrared transmission spectrum of 6b at 1.8 K and at fields varied between 0 and 7 T.

34 35 36 37 38

0 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T

10 15 20 25 30 35 40 451E-3

0.01

0.1

1

Tr

Chapter 4 81

4.7 Conclusions

In this study, the crystal structures properties as well as the

electrochemical, spectroscopic and magnetic behavior of 5, 6, 7, 5b and 6b have been

fully characterized. As pointed out in the introduction, it has been verified that the metal

ions in analogous tetra coordinated cobalt and nickel complexes exist in different

oxidation levels; by low temperature crystallography of 5, 6, 5b and 6b . Thus, in the

neutral and monoanionic nickel complexes, 5 and 5b the central nickel has a NiII (d8)

electron configuration, where the HOMO are predominantly ligand centered. On the other

hand, in the case of the neutral cobalt complex (6), the observed ligand bond lengths

clearly suggest a CoIII (d6) electron configuration. In the monoanion 6b, the ligand bond

distances indicate dianionic form of ligands leading to a spin triplet ground state for 6b.

Even though the DFT calculations on the similar compounds suggest the two possibilities

namely: CoIII (d6), or CoII (d7) coordinated to ligand radical, the structural features of 6b

point toward CoIII (d6) configuration. The degeneracy of the ground state of 6b is lifted

by large positive zero field splitting of 36.67 cm-1, which has been measured

independently by magnetic moment measurement, variable-temperature and variable

field, and far-infrared absorption.

The absorption spectra of the neutral and electrochemically-generated species show

several charge transfer bands. Intense LLCT bands occurring in the visible region are a

significant feature of the spectra of complexes containing two radical ligands. Spectra of

complexes containing only one radical ligand contain IVCT bands in the near infrared

region. The EPR parameters for 6 and 5b show that the spin-orbit coupling plays a role in

the deviation of g value from free radical value. These radical stabilized complexes have

proved the noninnocent nature of the o-aminothiophenolate ligands, thus disproving the

proposed valence isomer structure in the literature,12,14 for the proper assignment of

oxidation level of ligand.


4.8 References

1) Larkworthy, L. F.; Murphy, J. M.; Phillips, D. J. Inorg. Chem. 1968, 7, 1436

2) Liaw, M. -C.; Lee, G. -H.; Peng, S. -M. Bull. Inst. Chem. Academia Sinica, 1993,

40, 23

3) Hsieh, C. -H.; Hsu, I. -J.; Lee, C. -M.; Ke, S. -C.; Wang, T. -Y.; Lee, G. -H.;

Chen, J. -M.; Lee, J. -F.; Liaw, W. F. Inorg. Chem. 2003, 42, 3925.

4) Herebian, D.; Bothe, E.; Bill, E.; Weyhermüller, T.; Wieghardt, K. J. Am. Chem.

Soc. 2001, 123, 10012.

5) (a) Bachler, V.; Olbrich, G.; Neese, F.; Wieghardt, K. Inorg. Chem. 2002, 41,

4179. (b) Herebian, D.; Wieghardt, K.; Neese, F. J. Am. Chem. Soc. 2003, 125,

10997. (c) Herebian, D.; Bothe, E.; Weyhermüller, T.; Wieghardt, K. J. Am.

Chem. Soc. 2003, 125, 9116.

6) Thompson, M. C.; Busch, D. H. J. Am. Chem. Soc. 1964, 86, 3651.

7) Elder, M. S.; Prinz, G. M.; Thornton, P.; Busch, D. H. Inorg. Chem. 1968, 7,

2426.

8) Stiefel, E. I.; Waters, J. H.; Billig, E.; Gray, H. B. J. Am. Chem. Soc. 1965, 87,

3016.

9) Holm, R. H.; Balch, A. L.; Davison, A. A.; Maki, H.; Berry, T. E. J. Am. Chem.

Soc. 1967, 89, 2866.

10) Ghosh, P.; Bill, E.; Weyhermüller, T.; Neese, F.; Wieghardt, K., J. Am. Chem.

Soc. 2003, 125, 1293.

11) Dori, Z.; Eisenberg, R.; Stiefel, E. I.; Gray, H. B. J. Am. Chem. Soc. 1970, 92,

1506

12) (a) Balch, A. L.; Holm, R. H. J. Am. Chem. Soc. 1966, 88, 5201. (b) Holm, R. H.

Progress. Inorg. Chem. 1971, 14, 241



14) Kawamoto, T.; Kuma, H.; Kushi, Y. Bull. Chem. Soc. Jpn. 1997, 70, 1599.

15) Kochin, S. G.; Garnovskii, A. D.; Kogan, V. A.; Osipov, O. A.; Sushko, T. G.

Russ. J. Inorg. Chem. 1969, 14, 748.

16) Corbin, J. L.; Work, D. E. Can. J. Chem. 1974, 52, 1054.

Chapter 4 83

17) Yamamura, T.; Tadokoro, M.; Hamaguchi, M.; Kuroda, R. Chem. Lett. 1898,

1481.

18) López-Torres, E.; Mendiola, M. A.; Pastor, C. J.; Pérez, B. S. Inorg. Chem. 2004,

43, 5222.

19) (a) van der Put, P. J.; Schilperoord, A. A. Inorg. Chem. 1974, 13, 2476. (b) Ray,

K.; Begum, A.; Weyhermüller, T.; Piligkos, S.; Slageren, J. V.; Neese, F.;

Wieghardt, K. J. Am. Chem. Soc. 2005, 127, 4403.

20) Holm, R. H.; Balch, A. L.; Davison, A. A.; Maki, H.; and Berry, T. E. J. Am.

Chem. Soc. 1967, 89, 2866.

21) (a) Sun, X.; Chun, H.; Hildenbrand, K.; Bothe, E.; Weyhermüller, T.; Neese, F.;

Wieghardt, K. Inorg. Chem. 2002, 41, 4295. (b) Min, K. S.; Weyhermüller, T.;

Bothe, E.; and Wieghardt, K. Inorg. Chem. 2004, 43, 2922.

22) Herebian, D.; Wieghardt, K.; Neese, F. J. Am. Chem. Soc. 2003, 125, 10997.

23) Daul, C.; Schläpfer, C. W.; Zelewski, A. V. Struct. Bonding, 1979, 36, 12.

24) (a) Corwin, D. T.; Koch, S. A. Inorg. Chem. 1988, 27, 493. (b) Hu, W. J.; Barton,

D.; Lippard, S. J. J. Am. Chem. Soc. 1973, 95, 1170. (c) Kawamoto, T.; Kushi, Y.

J. Chem. Soc., Dal. Trans. 1992, 3137.

25) (a) Schmitt, R. D.; Maki, A. H. J. Am. Chem. Soc. 1968, 90, 2288. (b) Maki, A.

H.; Berry, T. E.; Davison, A.; Holm, R. H.; Balch, A. L. J. Am. Chem. Soc. 1966,

88, 1080. (c) Maki, A. H.; Edelstein, N.; Davison, A.; Holm, R. H. J. Am. Chem.

Soc. 1964, 86, 4580

.

Chapter 5 85

5.1 Introduction

As it is known that the sulfur donors are essential constituents of the

coordination spheres of transition metals that form the active centers of numerous

oxidoreductases such as hydrogenases or nitrogenases,1 four and six coordinate

complexes with sulfur donor ligands have been studied in detail for many years.2

Recently the non-innocent nature of S,S'-coordinated benzene-1,2-ditholato(2-) ligands

has been established on the basis of crystallography as well as magnetic and

spectroscopic features in a series of square-planar complexes, where different redox

forms of the ligand exhibit different structural features (scheme 1.1.4 (chapter1), and

scheme 5.1.1).3 Taking into account the ligand centered redox activity observed in these

four coordinate complexes, six coordinate compounds are also expected to show similar

redox behavior. However, the redox properties of such compounds reported so far are

vague.

Chapter 5 Cr complexes of

3,5-di-tert-butyl-1,2-benzenedithiol and

3,6-di-tert-butyl-catacholate

Scheme 5.1.1

S

S

-e+e

-e+e

(tLSS)2- (tLSS)1- (tLSS)0

MS

SM

S

SM

Cr complexes 86

Maki et al. have reported the synthesis and characterization of series of

tris-(o-benzenedithiolato)chromium complexes: [(C6H5)4As][CrS6C6(CF3)6],

[(C6H5)4As]2[CrS6C6(CN)6], [(C6H5)4As]3[CrS6C6(CN)6].4 In this series the +5 and +6

oxidation states were claimed to the monoanionic and to the neutral compound,

respectively. Nevertheless, except for the structure of [(NEt4)2][Cr(S2C6Cl4)3],5 no

square-planar or octahedral chromium complex coordinated by o-benzenedithiolato

ligands have been structurally characterized. Therefore, we aim to synthesize [Cr(tLSS)3]n

(n = 0, -1) complexes (tLSS = 3,5-di-tert-butyl-1,2-benzenedithiol), which is reported here

with the X-ray crystallographic and spectroscopic characterizations. XAS studies are

reported in chapter 7.

Attempts to synthesize tris-(o-toluenedithiolato)chromium complex have

been reported to lead to the formation of [(n-C4H9)4N][CrVO(tdt)2], which was

characterized by an isotropic epr signal at g = 1.994. In our efforts to synthesize tris-

(tLss)3-chromium, [(n-C4H9)4N][CrVO(tLSS)2] was also the result. Characterization and X-

ray structure analysis of this compound is discussed in this chapter. The preparation of

stable CrV compounds is of considerable importance. The presence of oxochromium bond

(O=Cr) is the most common feature of the metal in this higher oxidation state. However,

the chemistry associated with it is largely unexplored. The possibility of effecting a direct

transfer of the oxygen atom from the O=Cr functionality to a donor such as olefin

(scheme 5.1.2) poses an interesting challenge, which has been realized with series of CrV

complexes.6

Roćek et al.7 have reported a first stable crystalline chromium (V)

compound, potassium bis(2-hydroxy-2-methylbutyrato)oxochromate (V) monohydrate,

K[OCr(O2CCOMeEt)2]ּH2O. Afterwards, Groves and Kruper achieved a oxochromium

C C + M

O

C C

O

+ M

Scheme 5.1.2

Chapter 5 87

(V) derivative of chloro(tetraphenylporphyrinato)chromium(III), which was capable of

hydroxylating and epoxidizing hydrocarbons under catalytic and stoichiometric

conditions.8 Synthesis of various oxochromium(V) cations ligated with salen [N,N’-

ethylenebis(salicylideneaminato)], i.e. O=Cr(salen)+ was reported in the literature.9,10 A

series of chromium(V) model complexes that mimic the binding of Cr(V) to peptide

backbone have been prepared and reported.11 Relatively stable Cr(V/IV)–ehba (ehbaH2 =

2-ethyl-2-hydroxybutanoic acid) complexes are extensively used as models for

understanding the Cr(V/IV) reactions with biomolecules.12 In this regard our compound

which contains Cr=O bond along with S,S'-coordinated benzene dithiolene environment

is very interesting.

The non-innocent nature of O, O'-coordinated o-benzoquinone ligands was

well established in the series of tris(quinone) complexes of Cr, Mn, Fe, Co etc.13 Three

different oxidation levels of O,O'-coordinated o-benzoquinone can be unequivocally

identified by the structural parameters of these compounds as shown in schemes 5.1.3

and 1.1.3(chapter1).

The reaction between an o-benzoquinone and Cr(CO)6 has been reported

to give tris(quinone) complexes of general form CrQ3.14, 15 The view of these complexes

as consisting of radical SQ (semiquinone) ligands coordinated to CrIII, [CrIII(SQ•)3], is

based on the observation of diamagnetic behavior and structural features. The spins of the

radical ligands couple antiferromagnetically with the metal dπ (t2g3) electrons that show

diamagnetic behavior.14,16 Mössbauer spectra recorded on the related complexes of iron,

[FeIII(SQ•)3],17 verify that the metal ion is in the form of high spin FeIII. Electrochemical

Scheme 5.1.3

O

O

-e+e

-e+e

(tLCat)2-(tLSQ)1- (tLBQ)0

MO

OM

O

OM

Cr complexes 88

characterization of the [CrIII(SQ•)3] series have shown three membered oxidation and

reduction series. This, with other structural, magnetic and spectral properties obtained for

various members of the redox series, has led to the view that the redox couples are ligand

based, with the metal remaining in the form of CrIII through the series.15,18 Structural

features of the members of the reduction series support this view by having the metal-

oxygen bond lengths of typical CrIII, and the structural features of the quinone ligands

support the catecholate and semiquinonate charges of [CrIII(Cat)3]3-, [CrIII(Cl4SQ)3], and

[CrIII(3,5-DBSQ)3] (DBSQ = di-tert-butyl-semiquinonato).15,19,20 Nevertheless a recent

report on the electronic structure of K[Cr(3,5-DBQ)3] concludes that the Cr is in the +5

oxidation state, with the ligands all being catecholate.21 This view, which was based on

the position and intensity of the Cr-K-edge and pre edge peaks in the X-ray absorption

spectrum, is contradictory to the established non-innocent nature of o-benzeoquinone

ligands. In this regard we have synthesized a six coordinated [Cr(tLcat)3] (tLcat = 3,6 di-

tert-butyl-catacholate) and characterized it thoroughly by X-ray structure analysis, and

spectroscopy. The related XAS results are reported in chapter 7.


[N(n-bu)4][Cr(tLss)3] (8)

To obtain a compound, to a solution of the ligand 3,5-di-tert-butyl-1,2-

benzenedithiol H2[tLSS] in MeCN, CrCl3(THF)3 was added followed by the addition of

Et3N under anaerobic conditions. After 1 h, [N(n-bu)4]Br was added and air was passed

through this solution for 10 minutes. Violet crystals of 8 were obtained from the solution

at low temperature (-200C). Infrared spectrum of this compound shows an intense peak at

1108 cm-1 corresponding to C-S•. The 8i, having [As(Ph)4] as countercation was prepared

in the similar way by using [As(Ph)4]Br instead of [N(n-bu)4]Br.

[As(Ph)4] [CrO(tLss)2] (9)

When a solution of 8i was exposed to air for a long time (6-7 hours), the

color of the solution changed from violet to red brown and upon evaporation of solvent,

Chapter 5 89

red-brown crystals were obtained. This compound shows an intense peak in its infrared

spectrum at 967cm-1, corresponding to a Cr=O stretch.

[Cr(tLcat)3] (10)

To a solution of the ligand 3,6-di-tert-butyl-catacholate in MeCN,

CrCl3(THF)3 was added, followed by the addition of Et3N. The reaction mixture was

heated for 1 hour in air. Crystalline 10 was obtained by the slow evaporation of solvent.

The IR spectrum of this compound shows sharp bands at 1432 and 1416 cm-1,

characteristic of the SQ ligand.16

[Co(Cp)2][Cr(tLcat)3] (10b)

To a deep red-brown solution of 10 in CH2Cl2, cobaltocene was added

under anaerobic conditions. A blue precipitate formed was isolated by filtration and

washed with diethyl ether.

5.3 Molecular structures

The crystal structures of compounds 8, 9, and 10 at 100(2) K have been

determined using Mo Kα radiation.

The crystal structure of 8 consists of discrete [Cr(tLss)3]1- anions and

[N(n-bu)4]1+ cations. 8 crystallizes in the monoclinic crystal system with a space group

P21/c. The units of [Cr(tLss)3]- and [N(n-bu)4]+ are well separated from each other by a

distance of 8.24 (4) Å, in which the Cr ions adopt a distorted octahedral geometry. The

coordination sphere of the chromium is composed of three bidentate ligands. The ligands

coordinate through the deprotonated sulfur atoms. Intermolecular interactions in the

crystal are weak, due to the large tert-butyl groups, which preclude the π-stacking

interactions. A schematic representation of the bond lengths and angles for the three

independent o-benzodithiolene rings and S-Cr-S planes are displayed in Fig. 5.3.1. The

average S-Cr-S angle of 84.37(5)° is less than the ideal 90° angle for an octahedron. The

dihedral angles between the planes of the o-dithiolene rings and the S-Cr-S planes are

12.9, 23.6 and 6.5° for rings one through three, respectively. The o-benzodithiolene rings

are almost planar; the mean deviation from the planes being 0.0088, 0.0174, and 0.0147

Cr complexes 90

Å for one to three planes respectively. The thermal ellipsoid plot of anion in 8 with atom

labeling scheme is shown in Fig. 5.3.2 and table 5.3.1 and 5.3.2 display the relevant bond

angles and distances respectively.

One descriptor of distortion in the tris-chelate complexes is the chelate

projection (twist) angle.16 These angles should be 0˚ in the trigonal prismatic limit and

60˚ in the octahedral limit. The individual values observed here are Ф(S(1), Cr, S(2)) =

46.0˚, Ф(S(21), Cr, S(22)) = 37.7˚, and Ф(S(41), Cr, S(42)) = 33.7˚. The mean S-M-S

angle involving trans sulfur atoms is 136 ± 1˚ in known trigonal prismatic structures.4,5,9

The mean value of 162.55(6) observed in 8 is much closer to octahedral geometry.

The average Cr-S distances of 2.299(5) Å are in agreement with the

reported distances for S-CrIII.22 The average C-S bond distance of 1.750 ± 0.001 Å is

intermediate between typical single and double bond lengths. In square-planar complexes

containing two radical ligands, the C-S• distance is in between 1.723 ± 0.01 Å and 1.731

± 0.01 Å (3σ). In the compounds, containing one radical ligand and one dianionic ligand,

this distance is in the range of 1.744 ± 0.015 to 1.752 ± 0.015 Å (scheme 1.1.4, chapter

1). Since 8 is an octahedral complex with three ligands, if one ligand is a radical ligand

and the other two are dianionic, the average C-S bond distance is expected to show

almost single bond character (C-S = 1.755 ± 0.01 to 1.77± 0.01 Å). On the other hand, if

all three of the ligands are radical ligands then the average C-S bond length should show

double bond character with C-S• distance of ∼1.723 ± 0.01 Å. Consequently, the

structural features of 8 suggest the presence of two radical ligands and one dianionic

ligand, the average C-S distance (1.750 ± 0.001 Å) being intermediate of single and

Fig. 5.3.1: Schematic presentation of the bond distances and angles for 8.

S(2)(1)S

Cr

S(22)(21)S

Cr

S(42)(41)S

Cr

2.283

(1)

2.290(1)

2.291(5)2.303

(1)

2.301

(1) 2.327(1)

1.754(5)

1.74

6(5)

1.756(5)

1.75

3(5)

1.757(5)

1.73

8(5)

1.408(7)

1.411(7)

1.401

(7)

1.363(7)

1.410(7)

1.397

(7)

1.412(7)

1.422(7)1.39

9(7)

1.38

5(7)

1.374(7)

1.404(7)

1.406(7)

1.432(7)1.40

9(7)

1.364(7)

1.408(7)

1.386

(7)

84.49(5) 84.37(5)83.85(5)

di. Angle12.9

di. Angle23.6

di. Angle6.5

Chapter 5 91

double bond lengths leading to the assignment of +3 (d3, S = ½) oxidation state to the

chromium. It is known from square-planar complexes containing one radical ligand and

one dianionic ligand, that the charge is delocalized over the ligands and the assignment of

redox states of individual ligands is difficult.23 In 8 also the three ligands show nearly

identical features in bond distances, thus disallowing the assignment of redox states of

individual ligands unequivocally. Along with these characteristic C-S bond distances, the

phenyl rings of the ligand exhibit distortions typical of quinoid type structures, namely

two shorter C=C and four longer ones (1.372(7) and 1.408(7) Å), also indicating the

presence of radical ligands.

Bond angles (deg) S(1) -Cr(1)-S(2) 84.49(5) S(1) -Cr(1)-S(21) 163.11(6) S(21) -Cr(1)-S(22) 83.85(5) S(2) -Cr(1)-S(41) 164.97(6) S(42) -Cr(1)-S(41) 84.37(3) S(42) -Cr(1)-S(22) 159.58(6)

Cr(1)S(1)

S(2)

C(1)

C(2)

C(3)C(4)

C(5)

C(6)S(22)S(21)

S(42)

S(41)

Fig. 5.3.2: A thermal ellipsoid plot of the anion in 8 at the 50% probability level with atom labeling scheme.

Table 5.3.1: Selected bond angles [deg] for 8

Cr complexes 92

Fig. 5.3.3 shows the thermal ellipsoid plot of the anion in 9 with atom

labeling scheme and table 5.3.3 displays the relevant bond distances and bond angles.

The structure consists of anions of [CrO(tLss)2]- and [As(Ph)4]+ cations arranged in the

monoclinic crystal system. The chromium atom is bonded to an oxo group and two

bidentate 3,5-di-tert-butylbenzenedithiolate ligands through deprotonated sulfur atoms.

The geometry about the Cr atom is distorted square pyramidal. The deviation from the

square pyramidal geometry lies in the difference between the angles S(1)-Cr(1)-S(21)=

140.07(11)° and S(2)-Cr(1)-S(22) = 145.99(11)° which then yields τ = 0.098°, (a perfect

pyramidal yields τ = 0) where τ is determined by the formula τ = (β-α)/60 (where β and

α are the two largest S-Cr-S angles in degrees).24 There is a disorder in the Cr and O

atoms making the bond distances less relevant. The five membered chelate rings are

almost planar, the average deviation from planes being 0.0097 Å. The Cr(1) atom is

displaced above the square plane defined by four sulfur atoms by 0.720 Å. The Cr(1)-

O(1) distance of 1.572(7) Å is ~0.02 Å longer than those reported 7,10,25 for CrV-O double

bonds. The Cr(1)-S average distance of 2.274(2) Å is less than that observed in 8

(2.2994(5)), where chromium has a +3 oxidation state. The average C-S (1.786 ± 0.02Å)

bond distance indicates single bond character and the six C-C bonds of the aromatic ring

are equidistant within the 3σ error (1.390± 0.02 Å). Thus, both of the ligands are o-

Bond Distance [Å] Cr(1)-S(1) 2.283(1) Cr(1)-S(21) 2.301(1) Cr(1)-S(41) 2.304(1) Cr(1)-S(2) 2.290(1) Cr(1)-S(22) 2.327(1) Cr(1)-S(42) 2.291(1) S(1)-C(1) 1.754(5) S(21)-C(21) 1.756(5) S(41)-C(41) 1.757(5) S(2)-C(2) 1.746(5) S(22)-C(22) 1.753(5) S(42)-C(42) 1.738(5) C(1)-C(2) 1.408(7) C(21)-C(22) 1.412(7) C(41)-C(42) 1.406(7) C(1)-C(6) 1.411(7) C(21)-C(26) 1.422(7) C(41)-C(46) 1.432(7) C(2)-C(3) 1.401(7) C(22)-C(23) 1.399(7) C(42)-C(43) 1.409(7) C(3)-C(4) 1.363(7) C(23)-C(24) 1.374(7) C(43)-C(44) 1.364(7)

C(4)-C(5) 1.410(7) C(24)-C(25) 1.404(7) C(44)-C(45) 1.408(7)

C(5)-C(6) 1.397(7) C(25)-C(26) 1.385(7) C(45)-C(46) 1.386(8)

Table 5.3.2: Selected distances [Å] for 8

Chapter 5 93

benzodithiolate (2-) dianions that in together with dianionic oxygen leads to (+5)

oxidation state to the chromium. As there are no structural evidences of CrV complexes

coordinated to sulfur ligands, this complex is a unique model in this case.

Bond Distance [Å] Bond angles (deg) Cr(1)-O(1) 1.572(7) Cr(1)-S(21) 2.267(2) O(1)-Cr(1)-S(21) 112.5(3) Cr(1)-S(1) 2.278(3) Cr(1)-S(22) 2.274(2) O(1)-Cr(1)-S(22) 107.2(7) Cr(1)-S(2) 2.276(3) S(21)-C(21) 1.759(8) O(1)-Cr(1)-S(2) 106.8(3) S(1)-C(1) 1.787(8) S(22)-C(22) 1.758(8) O(1)-Cr(1)-S(1) 107.3(3) S(2)-C(2) 1.785(8) C(21)-C(22) 1.42(1) S(22)-Cr(1)-S(2) 146.0(1) C(1)-C(2) 1.42(1) C(21)-C(26) 1.41(1) S(21)-Cr(1)-S(1) 140.1(1) C(1)-C(6) 1.40(1) C(22)-C(23) 1.39(1) S(21)-Cr(1)-S(22) 85.51(9) C(2)-C(3) 1.40(1) C(23)-C(24) 1.38(1) S(21)-Cr(1)-S(2) 81.45(9)

C(3)-C(4) 1.38(1) C(24)-C(25) 1.39(1) S(22)-Cr(1)-S(1) 84.96(9)

C(4)-C(5) 1.40(1) C(25)-C(26) 1.41(1) S(2)-Cr(1)-S(1) 85.20(1)

C(5)-C(6) 1.39(1)

Table 5.3.3: Selected bond distances [Å] and angles[deg] for 9.

Cr(1) S(21)

S(22)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

S(2)

S(1)

O(1)

Fig. 5.3.3: A thermal ellipsoid plot of anion in 9 at the 50% probability level with atom labeling scheme.

Cr complexes 94

The complex 10 crystallizes in the monoclinic crystal system with a space

group C2/c. The three bidentate ligands [(tLcat)] coordinate through the deprotonated

oxygen atoms and the chromium ion adopts a distorted octahedral geometry. Figure 5.3.4

shows the thermal ellipsoid plot of 10 with atom labeling scheme and table 5.3.4 and

5.3.5 display the important bond distances and bond angles, respectively. Molecule is

crystallographically symmetric.

The O(1)-Cr-O(2) angle of 81.41(9)° is less than the 90° for an ideal

octahedron. In addition, the bond angle between O(2)-Cr(1)-O(2)#1 of 177.74(14)°, that

should be 180° for an octahedron, signify a slight distortion from an octahedral geometry.

The angle C(1)-O(1)-Cr(1) (114.14 (19)°), indicate a sp2 hybridised oxygen with angle

close to 120°, that in turn indicates the C=O character with semiquinone nature of the

ligand. This is reinforced by the C-O average bond distances, which fall in the double

bond range of 1.305(4)-1.310(5) Å (Scheme 1.1.3, chapter 1). The average intra

molecular Cr-O distances of 1.936(2) Å is in agreement with the reported distances for

O-CrIII.26 In the aromatic rings of ligand, two alternate bonds are shorter (1.372 ± 0.01)

and other four are longer (1.430± 0.01). Similar distances of C-O and Cr-O bonds along

with quinoid type ring distortions are reported for [CrIII(LSQ)3] complexes containing

semiquinonate (1-) π-radical ligand suggesting a +3 oxidation state of the chromium (d3)

for 10.

Bond Distance [Å] Cr(1)-O(1) 1.929(2) C(1)-C(2) 1.440(4) Cr(1)-O(2) 1.934(2) C(1)-C(6) 1.431(4) Cr(1)-O(21) 1.947(2) C(2)-C(3) 1.433(4) O(1)-C(1) 1.310(4) C(3)-C(4) 1.372(4) O(2)-C(2) 1.305(4) C(4)-C(5) 1.420(5) O(21)-C(21) 1.303(4) C(5)-C(6) 1.372(4)


Chapter 5 95

Bond angles (deg) O(1) -Cr(1)-O(2) 81.41(9) O(21)#1-Cr(1)-O(21) 81.4(1) O(1)# -Cr(1)-O(2)#1 81.41(9) O(1)#1-Cr(1)-O(21) 169.25(9) O(1) -Cr(1)-O(21)#1 169.25(9) O(2)-Cr(1)-O(2) #1 177.7(1)


Cr(1)

O(1)

O(2)

C(1)

C(2)C(3)

C(4)

C(5)

C(6)

O(21)

O(21)#1

O(1)#1O(2)#1

Fig. 5.3.4: A thermal ellipsoid plot of 10 at the 50% probability level with atom labeling scheme.

Cr complexes 96


The Electrochemistry of 8, 9, and 10 has been studied in CH2Cl2 by cyclic

voltammetry (CV). 0.10M [N(n-Bu)4][PF6] was used as a supporting electrolyte, a glassy

carbon as working electrode and Ag/AgNO3 as reference electrode. Ferrocene was used

as internal standard, and all redox potentials are referenced versus the

ferrocenium/ferrocene (Fc+/Fc) couple at room temperature. The redox potentials (vs.

Fc+/Fc) are presented in the table 5.4.1. The cyclic voltammogram of 8 (Fig. 5.4.1) and

10 (Fig. 5.4.2) exhibit 4 and 5 membered electron transfer series, respectively. This kind

of redox processes are observed in many metallo-tris (o-benzodithiolato) 27 (M= Mo, W,

Re, Tc) and tris(o-catacholato) (M= Fe, Ru, Os, Re, Mn) complexes.28 It correspond to

species with charge of –3, -2, -1, 0, and +1. The redox potentials in general reflect the

stabilization of the more highly charged species (-2 or –3) species for 8 than 10. The

waves corresponding to reduction are reversible in both of the compounds, whereas the

oxidation processes are reversible in 10, but display irreversible character in 8.

In the case of metallo-tris (o-benzodithiolato)2 complexes, the nature of the

redox activity is vague till now, but in case of compounds of type, [M(Lcat)3] (M= Fe, Ru,

Os, Re, Mn; Lcat = 3,5 di-tert-butylcatecholate, or 3,6 di-tert-butylcatecholate)28 these

redox processes are known to be ligand centered rather than metal centered. Thus the

redox activity of 8 and 10 can be described analogously as presented in scheme 5.4.1.

Compound E11/2 (3-/2-) E2

1/2 (2-/1-) E31/2 (-1/0) E4

1/2 (0/+1) E51/2 (+1/+2)

8 -1.574 -0.944 -0.25 +0.46

9 -0.958 +0.150

10 -1.934 -1.289 -0.634 +0.578 +0.966

Table 5.4.1: Redox potentials (V) of compound 8, 9 and 10 Vs. Fc / Fc+ at 22° C.

Chapter 5 97

[CrIII(tL0SS)(tLSS)2]+

-e+e

[CrIII(tLSS)3]+e-e -e

[CrIII(LSS)2(LSS)] - +e [CrIII(LSS)(LSS)2]2-

[CrIII(tLbq)(tLsq)2]+-e+e

[CrIII(tLsq)3]+e-e -e

[CrIII(Lsq)2(LCat)] -+e [CrIII(Lsq)(LCat)2]2-

-e+e

[CrIII(tLbq)2(tLsq)]2+

Scheme 5.4.1: Redox activity of 8 and 10.

Fig. 5.4.1: Cyclic voltammogram of 8 in CH2Cl2 solution containing 0.10M [(n-bu)4N][PF6] at 22°C with scan rates of 50, 100, 200, 400, mV/s.

-2.0-1.5-1.0-0.50.00.5

10µA

E (V)

Cr complexes 98

Chronoamperometry is a technique in which current is recorded as a

function of time at a fixed applied potential. This has been proved an important technique

for bis-o-benzodithiolene complexes,3 which can be used in conjunction with

spectroscopy to monitor spectroscopic changes during oxidation or reduction. In case of

8, the changes in infrared frequency upon oxidation and one and two electron reductions

at appropriate fixed potential were monitored (Fig.5.4.3). In 8 there is a sharp band at

1106 cm-1 and a weak peak at 1041 cm-1. The strong peak at 1106 cm-1 is observed in all

metallo-bis-(o-dithiolene) complexes containing C-S• bond3 and the peak at 1039 cm-1

correspond to C-S stretching. Upon one electron oxidation (8a), the intensity of a peak at

1106 cm-1 has not change but it has shifted to frequency of 1109 cm-1. Upon one electron

reduction (8b), the intensity of the peak at 1106 cm-1 decreases, and upon two-electron

reduction (8c), this peak is totally absent with increase in the intensity of the peak at 1042

Fig. 5.4.2: Cyclic voltammogram of 10 in CH2Cl2 solution containing 0.10M [(n-bu)4N][PF6] at 22°C with scan rates of 50, 100, 200, 400, mV/s.

-2.5-2.0-1.5-1.0-0.50.00.51.01.5

10µA

E (V)

Chapter 5 99

cm-1. Thus, the peak at 1106 cm-1, characteristic of the C-S• radical, becomes less intense

after one electron reduction (8b) due to reduction of one of the radical ligands to the

dianionic form. In 8c, both of the radical ligands are reduced and no more radical ligand

is present, which is reflected in the disappearance of the peak at 1106 cm-1. The reason

for the unchanged intensity after oxidation is ambiguous. In general, these results are

consistent with the observations from the X-ray crystal structure analysis for 8, where the

C-S bond distances in the ligand illustrate the presence of two radical ligands among the

three with the remaining one having dianionic character. In 8c, the peak intensity at 1041

cm-1 is increased, which correspond to C-S single bond stretching, confirming the

assignment of these species as [CrIII(tLSS)3]3-.

The cyclic voltammogram of 9 (Fig. 5.4.4) displays two irreversible

electron transfer waves at - 0.958V (reduction) and at +0.150V (oxidation). Due to their

irreversible nature, generation of one electron oxidized or reduced species are not

possible by controlled potential coulometry.

Fig. 5.4.3: Changes in the infrared spectra upon oxidation

and reduction for 8 in the range 1250-1000 cm-1.

10001050110011501200

[Cr(LSS)3]3- (8c)

[Cr(LSS)3]2 (8b)

[Cr(LSS)3] (8a)

[Cr(LSS)3]- (8)

cm-1

1109

1106

1042

1039

1200

1202

rel.

tran

smis

sion

Cr complexes 100


It was possible to generate the mono-, di- and trianionic species of 8 and

10 by coulometry at appropriate fixed potentials. The electronic absorption spectra of 8,

and 10 are displayed in Fig.5.5.1 and 5.5.2 respectively. Spectra of the neutral complexes

display one intense band at ~570 nm (ε = 2 × 104 M-1 cm-1) and two weak electronic

transitions at ~750 nm (ε = 7.5 × 103 M-1 cm-1) and ~1000 nm (ε = 5 × 103 M-1 cm-1).

This pattern in 8 and 10 does not resemble those of the corresponding metallo-tris- (o-

dithiolato) (metal = Mo, W, Re) complexes, which generally have two strong bands at

~400 nm (1.5 ×104 M-1 cm-1) and ~700 nm (2.5 × 104 M-1 cm-1), indicating a difference in

the electronic structure of 8 and 10 from other metallo-tris- (o-dithiolato) compounds,

and may indicate that the formal oxidation state of Cr in 8 and 10 is different from the

metals in other metallo-tris- (o-dithiolato) compounds. The similarity of the electronic

absorption spectra for the neutral complexes leads to the conclusion that, both of them

possess a similar electronic structure. The high-energy transitions in 8a (neutral form of

8) and 10 may correspond to the ligand to metal charge transfer (LMCT) bands. In the

Fig. 5.4.4: Cyclic Voltammogram of 9 in CH2Cl2 solution containing 0.10M [(n-bu)4N][PF6] at 22°C with scan rate of 50 mV/s using glassy carbon working electrode.

-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.4

E (V)

5 µA

Chapter 5 101

mono-, and dianionic species intensity of this LMCT is decreased with the formation of a

new wide band in the near infrared region for both of 8 and 10. This is suggestive that the

electronic structure of mono-, and dianionic species of both the compounds are

correspondingly analogous. Such band has been observed for a series of complexes of

Mn and Co containing o-catecholate ligands.17, 27 These wide bands in the near infrared

region are assigned as intramolecular intervalence charge transfer band (IVCT) of

catecholate to semiquinonate. These bands suggest the presence of both forms of ligands

in these species. From the spectra, the degree of electric coupling, Hab, can be estimated

using the well-known Hush formula30 for mixed valence complexes. (eq. 5.5.1).

Where, εmax is the maximum extinction coefficient of the absorption band

in M-1 cm-1, ∆ν1/2 is the bandwidth at half εmax, νmax is the energy of the absorption in cm-

1, rL-L is the shortest distance between ligand S-S or O-O atoms. The calculated values are

similar to that observed in literature for identical Cr compounds,17 indicating strong

coupling interaction between SQ and Cat through the chromium atom (table 5.5.1).

The spectra of trianionic species do not exhibit any strong absorption band

for both 8 and 10. It is indeed possible to see the Laporte-forbidden d-d bands for CrIII in

these species. For CrIII, in an octahedral environment, splitting of the spin quartet terms is

as shown in Fig. 5.5.2. Three transitions, 4A2g→4T2g, 4A2g →4T1g (F), 4A2g →4T1g (P) are

expected in this case and are experimentally observed. From the low energy transition the

value of Dq can be estimated.

∆E (4A2g→4T2g) =10 Dq = 12,500 cm-1 (for [Cr(tLSS)3]3), and therefore Dq = 1,250 cm-1

And for [Cr(tLCat)3]3-, Dq = 1430 cm-1

Compound λmax(nm) ν max(cm-1) ε (M-1 cm-1) ν ½ (cm-1) R = dO O/S S Hab(cm-1)

8 1767 5659 3269 6878 3.001 2436

10 1700 5882 7447 1372 2.765 1817

Table 5.5.1: The IVCT band shape data and estimated Hush coupling energy Hab for 8 and 10 at 25ºC.

Hab= (2.05 x 10-2) [εmax ∆ν1/2/νmax]1/2 νmax / rLL equation 5.5.1

Cr complexes 102

Fig.5.5.1: Electronic absorption spectra of the neutral and the electrochemicallyreduced forms of [Cr(tLSS)3][N(n-bu)4] (8) in CH2Cl2 solution, (0.10M[(n-Bu)4N]PF6) at –5 0C.

400 600 800 1000 1200 1400 1600 1800 20000.0

0.5

1.0

1.5

2.0

2.5ε

X 10

4 M-1

cm-1

λ (nm )

[CrIII(L•ss)3]0

[CrIII(L•ss)(Lss)2]2-

[CrIII(Lss)3]3- [CrIII(L•ss)2(Lss)]1-

Fig.5.5.2: Electronic absorption spectra of the neutral and the electrochemically reduced forms of [Cr(tLCat)3] (10) in CH2Cl2 solution, (0.10M[(n-Bu)4N] PF6) at –5 ºC.

4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 00 .0

0 .5

1 .0

1 .5

2 .0

ε X

104 M

-1 c

m-1

λ (n m )

[Cr(III)(LSQ)( Lcat)2]2- [Cr(III)(LSQ)2( Lcat)]1-

[Cr(III)(LSQ)3]

[Cr(III)(Lcat)3]3-

Chapter 5 103

The electronic absorption spectrum of 9 is displayed in Fig. 5.5.4. It shows

two intense bands in the visible region. They are most likely the ligand to metal charge

transfer bands.

Fig.5.5.4: Electronic absorption spectra of 9 at 25ºC.

400 600 800 1000 12000

1

2

3

ε x

103 M

-1 c

m-1

λ (nm)

731

498

4F

4P

4A2g

4T2g

4T1g

4T1g

I

II

III

400 600 8000

50

100

150

ε (

M-1

cm-1

)

λ (nm)

I I

III

Fig. 5.5.3: quartet terms of 3d3 in an octahedral field, and corresponding d-d absorption spectrum of [Cr(tLcat)3]3-.

Cr complexes 104

5.6 X band EPR and magnetic susceptibility

X-band EPR spectra were recorded for 8, 9 and electrochemically

generated monocation and monoanion species of 10 in frozen CH2Cl2 solutions at 10 K.

The magnetic susceptibility data of complexes 8, 9, 10 and 10b were collected in the

temperature range 2 to 290 K. As expected compounds 8, 9 and 10b are paramagnetic

and 10 is diamagnetic. The EPR spectrum of 8 (Fig. 5.6.1) displays an axial signal with

g⊥ =1.9947, g║ = 2.0074, (S=1/2) in accord with the spin coupling model involving

antiferromagnetic coupling between two ligand based radicals and the CrIII center (S =

3/2). The EPR spectrum can also be interpreted as arising from a d1 system (CrV), or an

exchange coupled d2(CrIV)-ligand radical system. But the structural features indicate that

the CrIII exchange coupled with two ligand-based radicals is more likely model.

Moreover, unlike the sharp EPR signals that are observed for CrV, those of CrIII are

broad.31 The observed g values which are very close to free electron g value of 2.0023

indicate a small spin orbit contribution and thus the excited state are well separated from

the ground state. An estimate of spin-orbit contribution can be known from equation

5.6.1:33

where ∆xz, ∆yz, and ∆x2-y2 correspond to the energy separation between the ground state

and the indicated excited state. Knowing the value of ∆xz =12,500 cm-1, from the

electronic absorption spectra, and g value from the EPR fitting parameter, the spin-orbit

coupling value (λ) obtained is, 47.5 cm-1.

Fig. 5.6.2 displays the magnetic moment vs. temperature plot for the

complex 8. It shows a temperature independent magnetic moment of 1.72 µB at 250 K,

corresponding to spin-only value for an S=1/2 ground state (g = 1.990, χTIP = 0.17*10-3

emu mol-1, θ = -1.38 K, where g value is fixed from the parameters of EPR spectrum.).

gx = ge - 2λ/∆xz, gy = ge- 2λ/∆yz, gz = ge- 2λ/∆x2-y2 equation 5.6.1

Chapter 5 105

Fig. 5.6.1: X-band EPR spectrum of 8 Exp: T = 10.0 K, ν = 9.63 GHz, P = 6.362 x 10-4 mW, MA = 10 G

330 340 350 360-0.3

-0.2

-0.1

0.0

0.1

0.2

0.31.9522.05

dX"/

dB

B (mT)

Exp. Sim.

g-factor

50 100 150 200

1.2

1.4

1.6

1.8

µ ef

f / µ

B

T (K)

Fig. 5.6.2: Plot µeff vs. temp. for 8. The solid line represents the best least squares fitting for the experimental data (circles).

Cr complexes 106

The room temperature (298 k) X-band epr spectrum of 9 (Fig. 5.6.3) in

CH2Cl2 displays a sharp isotropic signal for (S = 1/2) with hyperfine interaction due to 53Cr (I = 3/2) nucleus. Simulation yielded following fitting parameters: giso=1.996, (Axx =

35 MHz. A similar EPR signal and hyperfine splitting parameter was observed in a CrV-

Alanine complex having a Cr = O double bond.32

The magnetization curve of 9 displays an effective magnetic moment of

1.70µB in the region of 100 to 225 K. This value corresponds to the expected spin-only

value for an S=1/2 ground state. The best fit (solid line in the Fig. 5.6.4) of the

experimental data resulted in the following parameters: gCr = 1.996, χTIP = 0.38 × 10-3

e.m.u. θ = -4.20 K, where g value is fixed from the fit-parameters of EPR spectrum.

Fig. 5.6.3: X-band EPR spectra of 9 Exp: T = 298 K, ν = 9.63 GHz, P = 6.362 x 10-4 mW, MA = 10 G

340 342 344 346 348 350-60

-40

-20

0

20

40

601.971.981.9922.012.02

dX"/

dB

B (mT)

g factor

SimulatedExperimental

Chapter 5 107

The EPR spectra of 10a (one electron oxidized form of 10, Fig. 5.6.5) and

10b (Fig. 5.6.6) displayed axial and isotropic signals respectively. The simulation of the

experimental data resulted in the following parameters, for 10a: g⊥ = 1.973, g║ = 1.984

and for 10b: giso = 1.976. Similarity in the EPR spectra of both compounds indicate that

in both of them the metal possesses an identical oxidation state that is in accord with the

spin coupling model involving antiferromagnetic coupling between two ligand based

radicals and the CrIII center (S = 3/2). The EPR spectrum can also be interpreted as arising

from a d1 system (CrV), or an exchange coupled d2(CrIV)-ligand radical system. But the

structural features point towards the CrIII exchange coupled with two ligand-based

radicals.

50 100 150 200

1.0

1.2

1.4

1.6

1.8µ e

ff / µ

Β

T (K)

Fig. 5.6.4: Plot µeff vs. temp. for 9. The solid line represents the best least squares fitting for the experimental data (circles).

Cr complexes 108

342 344 346 348 350 352 354 356

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.941.961.9822.02

dX" /d

B

B (mT)

g factor


Fig. 5.6.6: X-band EPR spectra of 10b Exp: T = 10.04 K, ν = 9.64 GHz, P = 5.0289 x 10-3 mW, MA = 5 G

330 340 350 360 370

-4

-3

-2

-1

0

1

2

3

4

1.901.952.002.052.10

dX" /d

B

B (mT)


g factor

Fig. 5.6.5: X-band EPR spectra of 10a Exp T = 9.93 K, ν = 9.63 GHz, P = 1.003 x 10-3 mW, MA = 10 G

Chapter 5 109

Fig. 5.6.7 displays the magnetic moment vs. temperature plot for 10b. It

shows a temperature independent magnetic moment of 1.73 µB corresponding to spin-

only value for an S=1/2 ground state (g = 1.976, χTIP = 0.5*10-3emu, θ = -0.25 K, where g

value is fixed from the parameters of EPR spectrum.).

50 100 150 200 250

1.55

1.60

1.65

1.70

1.75

µ ef

f/ µB

T (K)

Fig. 5.6.7: Plot µeff vs. temp. for 10b. The solid line represents the best least squares fitting for the experimental data (squares).

Cr complexes 110

5.7 Conclusions

Thus we have shown in this chapter that oxidation states of higher than

+III for the central chromium ion are not present in the tris-(o-benzene-dithiolato) and

tris-(o-benzocatacholato) chromium complexes. In contrast to earlier literature reports,21

we have not found spectroscopic evidences for the occurrence of chromium(IV),

chromium(V) and chromium(VI). The electronic structures of the resulting complexes are

often complicated and were elucidated by a combination of electronic, EPR, X-ray

crystallography and magnetic susceptibility measurements.

In complex 9, chromium was found in the higher oxidation state of (+5)

which was confirmed by the epr parameters, and existence of Cr=O bond was confirmed

by the infrared spectrum and X-ray crystallography.

Chapter 5 111

5.8 References

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Cr complexes 112

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Dalton Ttrans., 1966, 2945.

28) (a) Bhattacharya, S.; Boone, S. R.; Fox, G. A.; and Pierpont, C. G. J. Am. Chem.

Soc. 1990, 112, 1088. (b) Attia, A. S.; Pierpont, C. G. Inorg. Chem. 1998, 37,

3051.

29) (a) Jung, O. S.; Jo. D. H.; Lee, Y. –A.; Conklin, B. J. Pierpont, C. G. Inorg. Chem.

1997, 36, 19. (b) Attia, A. S.; Pierpont, C. G. Inorg. Chim. Acta. 1998, 37, 3051.

30) Hush, N. S. Prog. Inorg. Chem. 1967, 8, 357.

31) Lay, P. Prog. Inorg. Chem. 2003, 51, 145.

32) Headlam, H. A.; Weeks, C. L.; Turner, p.; Hambley, T. W.; Lay, P. A. Inorg.

Chem. 2001, 40, 5097.

33) Ballhausen, C. J. Introduction to ligand field theory; McGraw-Hill: New York.

Chapter 6 115

6.1 Introduction

The aim of this chapter is to establish the electronic structures of the tris(o-

benzenedithiolato)molybdenum and tungsten, which have been previously described in

most cases as MoVI and WVI implying thereby a d0 electron configuration of the central

metal ion,1 and their one-electron reduced monoanionic forms are typically considered as

having a MV configuration thus assuming metal centered reductions. Most of these

complexes possess an unusual trigonal prismatic (TP) geometry. The crystal structure of

[MoVI(Lss)3 ] was reported2 with short average C-S bonds of 1.73Å and with visible

distortions of the rings from the normal aromatic behaviour. Knowing the non-innocent

nature of o-benzenedithiolate ligands3 along with the structural features of the ligand in

different oxidation states, the observed short C-S bond lengths in above mentioned

compounds provide ambiguity in assigning these complexes as [MVI(Lss)3]. Due to the

large experimental errors in the C-C and the C-S bond lengths in above mentioned and

other related compounds; an unambiguous assignment of the oxidation level of ligand

could not be made.

Gray et al.4 and Schrauzer and co-workers5 have employed molecular

orbital theory (MO theory) to understand the electronic structures and electronic

absorption spectra of six coordinate metallo-tris(dithiolenes). However, only the former

Chapter 6 Mo and W complexes of 2-mercapto-3,5-di-tert-

butylaniline and 3,5-di-tert-butyl-1,2-

benzenedithiol

Mo and W complexes 116

researcher made concrete attempts to describe the electronic structure that stabilize the

TP geometry over the more common octahedral arrangement. Moreover, the MO

description of Gray and co-workers has been more accepted due to its ability to explain

the salient features of their electronic absorption spectra. On the other hand Schrauzer et

al.6 proposed the +4 oxidation state in the neutral complexes [M(S6C6R6)] with M = Cr,

Mo, and W. They represent the neutral compounds as shown in scheme 6.1.1, where the

three canonical forms have equal weight. They assumed that this type of ground state

delocalization is important with such ligands and is largely responsible for their unusual

chemical properties.

In comparison with metallo-tris(dithiolenes), tris compounds with o-

aminothiophenolate ligands are limited and only the structure of [Mo(abt)3] (abt = o-

aminothiophenolate, 2-) has been reported.7 In this case also the central metal ion has

been assigned a formal oxidation state of +6. As o-aminothiophenolate ligands have

proven to be redox noninnocent8 (i.e. they can exist in different oxidation levels) the

assigned +6 oxidation state of the metal ion is therefore ambiguous since redox

noninnocent nature of ligand was ignored. To study these systems carefully, we have

synthesized tris molybdenum complex with 2-mercapto-3,5-di-tert-butylaniline H2[tLNS]

and a series of neutral and monoanionic complexes of Mo and W with 3,5-di-tert-butyl-

1,2-benzenedithiol H2[tLSS] and have characterized these with X-ray crystallography and

other spectroscopic methods.

S

SM S

S

SS

S

SM S

S

SS

S

SM S

S

SS

Scheme 6.1.1: Resonance forms of [M(Lss)3] complexes suggested by Schrauzer et al.

Chapter 6 117


[Mo(tLNS)3] (11):

To a solution of the ligand 2-mercapto-3,5-di-tert-butylaniline H2[tLNS] in MeOH, a

solution of MoO2(acac)2 in MeOH was added. After one hour, a green precipitate of

[Mo(tLNS)3] was filtered of and recrystallized from a mixture of dichloromethane and

diethyl ether (1:1).

[Mo(tLSS)3] (12)

It was obtained similarly and was recrystallized from a mixture of MeCN/diethyl ether.

The infrared spectrum of 12 shows an intense peak at 1107 cm-1 corresponding to a C-S●

stretch and weak bands at 1023, 1040 cm-1, corresponding to the C-S stretches. A band at

1585 cm-1 indicates the presence of a C=C double bond in the aromatic ring of the ligand.

[N(n-Bu)4][Mo(tLSS)3] (12b)

To a CH2Cl2 solution of [Mo(tLss)3] was added [N(n-Bu)4]SH. The olive green air

sensitive mixture was concentrated under vacuum and the resulting solid was

recrystallized from a mixture of DCM and MeCN. The strong peak at 1107 cm-1, which

was present in the infrared spectrum of the 12, is absent in the spectrum of 12b, thus

suggesting the absence of an intense C-S● mode.

[W(tLSS)3] (13)

A CCl4 solution of tungstenhexachloride and 3,5-di-tert-butyl-1,2-benzenedithiol was

heated under anaerobic conditions and allowed to cool to room temp. A blue-green

powder obtained after evaporation of the solvent was recrystallized from EtOH and

diethyl ether. The infrared spectrum of 13 is identical to that of 12. The IR spectrum

shows a strong peak at 1110 cm-1 corresponding to C-S● and weak peaks at 1023 and

1040 cm-1 that correspond to C-S stretching frequencies.

[N(n-Bu)4][W(tLSS)3] (13b)

To a solution of [W(tLss)3] in CH2Cl2, was added [N(n-Bu)4]SH under anaerobic

conditions. The olive green air sensitive mixture was concentrated under vacuum and the

resulting solid was recrystallized from mixture of DCM and MeCN. In the infrared

spectrum of 13b, no peak at 1110 cm-1 is observed.


6.3 Molecular structures

The X-ray crystal structures of compounds 11, 12, 12b, 13 and 13b at

100(2) K have been determined using Mo Kα radiation.

The complex 11 crystllizes in the monoclinic crystal system in the space

group p21/n. The molybdenum atom is six coordinate and bonded to the sulfur and

nitrogen atoms from the three 2-aminothiophenolate ligands. The coordinated atoms are

arranged in roughly trigonal-prismatic geometry about the molybdenum atom with the

two triangular faces defined by the three sulfur atoms and by the three nitrogen atoms.

The S3N3 polyhedron is distorted from ideal trigonal-prismatic geometry. One kind of

distortion arises from the different dimensions of the triangular faces. The triangle

defined by the sulfur atoms has an average S....S distance of 3.149(30)Å, while the

smaller triangle has an N....N side of 2.214(6) Å. Thus, the polyhedron is severely

tapered.

One descriptor of the distortion in the tris-chelate complexes is the chelate

projection (twist) angle.16 Fig. 6.3.1a shows a projection along the approximate C3 axis

normal to the mean plane defined by the above pair of triangular faces and gives the

individual chelate projection angles (Ф'). This

angles should be 0˚ in the trigonal prismatic

limit and 60˚ in the octahedral limit. The

individual values observed here are Ф(S(1),

Mo, N(2)) = 2.6˚, Ф(S(21), Mo, N(22)) = 1.9˚,

and Ф(S(41), Mo, N(42)) = 1.3˚. It is clear

that the compound has nearly ideal trigonal

prismatic geometry. In [Mo(abt)]3,7 these

distortion is on average 12.4˚. A thermal

ellipsoid plot with the atom labeling scheme is

shown in Fig. 6.3.1b. Table 6.3.1 and 6.3.2

display the relevant bond distances and bond angles, respectively. A solvent molecule of

diethyl ether is crystallized in the unit of the crystal providing a hydrogen bonding

interaction between N(1)-H(1)…..O(43) (3.019(4) Å, 161.5(2)˚). The average Mo-N

distance of 2.025(4) Å is almost identical to that of 1.997(8) Å found in [Mo(abt)3]. The

L1

L2 L3

L'1

L'2

L'3

M

Ø

Fig. 6.3.1a

Chapter 6 119

average Mo-S distance of 2.3867(9) Å is shorter than the distance at 2.418(6) Å found in

[Mo(abt)3], but is identical with the distance at 2.367(6) Å in [Mo(bdt)3]2 (bdt =

benzenedithiolato). The average C-S distance of 1.740(3) Å is intermediate between

typical single and double bond values. The average C-N distance of 1.364(4) is also

shorter than normal C-N single bond distance. Both of these C-S and C-N distances

clearly indicate the presence of o-iminothiobenzosemiquinonato(1-) radical ligands. The

individual C-C distances in each phenyl ring show quinoid type distortions with two

alternate short bonds (1.376(4), 1.387(4) Å) and four longer ones (1.423(4) Å). As

discussed in the case of 8 ([N(n-bu)4][Cr(tLSS)3], Chaper 5), the estimation of number of

radical ligands is difficult for six-coordinated complexes from the structural features.

Thus X-ray crystal structure analysis alone is not sufficient to confirm the physical

oxidation state of metal in this complex.

Bond distances [Å] Mo(1)-N(2) 2.026(3) Mo(1)-N(22) 2.026(3) Mo(1)-N(42) 2.024(3) Mo(1)-S(1) 2.397(9) Mo(1)-S(21) 2.385(9) Mo(1)-S(41) 2.378(9) S(1)-C(1) 1.741(3) S(21)-C(21) 1.744(3) S(41)-C(41) 1.737(3) N(2)-C(2) 1.363(4) N(22)-C(22) 1.370(4) N(42)-C(42) 1.360(4) C(1)-C(2) 1.421(4) C(21)-C(22) 1.428(5) C(41)-C(42) 1.427(5)

C(1)-C(6) 1.433(4) C(21)-C(26) 1.435(4) C(41)-C(46) 1.427(4) C(2)-C(3) 1.416(4) C(22)-C(23) 1.418(4) C(42)-C(43) 1.410(5) C(3)-C(4) 1.376(4) C(23)-C(24) 1.367(5) C(43)-C(44) 1.380(5) C(4)-C(5) 1.422(4) C(24)-C(25) 1.418(5) C(44)-C(45) 1.415(5) C(5)-C(6) 1.387(4) C(25)-C(26) 1.380(5) C(45)-C(46) 1.379(5)

Bond angles (deg) N(42) -Mo(1)-S(41) 77.68(8) N(22) -Mo(1)-S(21) 73.99(8) N(2) -Mo(1)-S(1) 77.27(8) N(2) -Mo(1)-S(41) 132.93(8) N(22) -Mo(1)-S(41) 136.14(9) N(42) -Mo(1)-S(21) 134.36(9)




The complex 12 crystallizes in the monoclinic crystal system in the space

group P21/n. The three bidentate ligands [H2(tLSS)] coordinate to the molybdenum ion

through the deprotonated sulfur atoms in

order to form a polyhedron which is not

close to either the trigonal prismatic (TP) or

octahedral geometry. The structure consists

of two S3 triangles, with an average side of

3.18(6) Å. The individual chelate projection

(twist) angles for each ligand are Ф(S(1),

Mo, S(2)) = 4.7˚; Ф(S(21), Mo2, S(22)) =

1.9˚ and Ф(S(41), Mo, S(42)) = 1.6˚ (Fig. Fig. 6.3.2a

S2

S21

S1

S42

S22

S41

M

Ø=4.7

Ø=1.9

Ø=1.6

Fig. 6.3.1b: Thermal ellipsoid plot of 11 with ellipsoids drawn at the 50% probability level with atom labeling scheme.

Mo(1)

S(1)C(1)

C(2)C(3)

C(4)

C(5)C(6)

N(1)

O(43)

N(2)S(2)

C(22)

C(23)

C(24)C(25)

C(26)

C(21)

Chapter 6 121

6.3.2a). Hence the triangles are twisted from each other by an averaged angle of 2.7˚,

very close to the ideal TP value of 0˚. The mean S-M-S angle involving trans sulfur

atoms is 136 ± 1˚ in known trigonal prismatic structures.4,5,9 The mean value of 134.94(2)

observed in 12 is similar to that observed in [Mo(bdt)3]2 and is clearly consistent with

trigonal prismatic geometry. The intra- and interligand S-Mo-S angles (81.42(2),

81.65(2), 81.33(2)˚) are similar and agree with those found in TP structures. The average

Mo-S distance of (2.364(5) Å) is similar to the corresponding distance in [Mo(bdt)3].2 A

thermal ellipsoid plot of 12 with the labelling scheme is shown below in Fig. 6.3.2b.

Table 6.3.3 and 6.3.4 display the important bond distances and bond angles.

There is a disorder in the sulfur atoms leading to uncertainty in the C-S

and Mo-S distances. The sulfur–carbon distance (average 1.737(3) Å) is shorter than that

observed in 8 ([N(n-bu)4][Cr(tLss)3]; 1.75 Å). In 8, it was concluded that the metal is in

the +3 oxidation state and two monoanionic-monoradical ligands are present. In 12, the

C-S bond distance (average 1.737(3) Å) is intermediate of single and double bond

distance. The individual C-C distances in each phenyl ring show quinoid type distortions

with two alternate short bonds (1.376(2), 1.381(2) Å) and four longer ones (1.418(5) Å).

Thus even though the quinoid type distortions in phenyl rings suggest the presence of

radical ligands, disorders in the sulfur atoms prevent the unambiguous assignment for the

oxidation level of ligands and metal from the structural characterization

.

Bond distances [Å] Mo(1)-S(1) 2.3600(5) Mo(1)-S(21) 2.3709(5) Mo(1)-S(41) 2.3645(6) Mo(1)-S(2) 2.3677(5) Mo(1)-S(22) 2.3602(5) Mo(1)-S(42) 2.3582(6) S(1)-C(1) 1.745(2) S(21)-C(21) 1.748(2) S(41)-C(41) 1.743(2) S(2)-C(2) 1.738(2) S(22)-C(22) 1.715(2) S(42)-C(42) 1.733(2) C(1)-C(2) 1.410(3) C(21)-C(22) 1.414(3) C(41)-C(42) 1.413(3) C(1)-C(6) 1.433(2) C(21)-C(26) 1.431(3) C(41)-C(46) 1.436(3) C(2)-C(3) 1.414(2) C(22)-C(23) 1.404(3) C(42)-C(43) 1.410(3) C(3)-C(4) 1.376(2) C(23)-C(24) 1.369(3) C(43)-C(44) 1.371(3)

C(4)-C(5) 1.415(4) C(24)-C(25) 1.413(3) C(44)-C(45) 1.417(3)

C(5)-C(6) 1.381(2) C(25)-C(26) 1.373(3) C(45)-C(46) 1.384(3)



12b crystallizes in the monoclinic crystal system in space group P21/c. The

molybdenum atom is coordinated to the sulfur atoms of the three 3,5-di-tert-butyl-1,2

benzenedithiolato ligands. The geometry around the molybdenum is again intermediate

between octahedral and trigonal prismatic (twist angles: Ф(S(1), Mo, S(2)) = 39.9˚,

Bond angles (deg) S(1)-Mo(1)-S(2) 81.42(2) S(21) -Mo(1)-S(22) 81.33(2) S(41) -Mo(1)-S(42) 81.65(2) S(1) -Mo(1)-S(41) 136.27(2) S(22) -Mo(1)-S(41) 132.92(2) S(42) -Mo(1)-S(21) 135.63(2)

Table 6.3.4: Selected angles [deg] for 12

Fig. 6.3.2b: The thermal ellipsoid drawing of the 12 at the 50% probability level with atom-labeling scheme is shown.

Mo(1)

S(1)C(1)

C(2)C(3)

C(4)

C(5)C(6)

S(2)

S(21)

S(22)

C(21)C(22)

C(23)C(24)

Chapter 6 123

Ф(S(41), Mo, S(42)) = 25.4˚, and Ф(S(21), Mo, S(22)) = 29.7˚; average = 31.67˚). The

average twist angle (31.67˚) is identical to that observed in the [N(n-bu)4][Mo(bdt)3],10

where the twist angle was 33.5˚. A schematic representation of the bond lengths and

dihedral angles between the three independent o-benzodithiolene rings and S-Mo-S

planes are displayed in Fig. 6.3.3. The dihedral angles between the planes of the o-

dithiolene rings and the S-Cr-S planes are 13.6, 23.9 and 3.3° for rings one through three,

respectively.

The average intramolecular Mo-S distances of 2.3775(7) Å is similar to

that found in the neutral complex 12 suggesting that the oxidation state of the metal is the

same in both of these complexes. The average C-S bond distance of 1.758 ± 0.009Å

indicates single bond character, and the C-C distances in the phenyl ring are almost

equidistant within the experimental error (1.402(4) Å). These bond distances are reliable

as there is no disorder problem in this structure and lead to the conclusion that all the tree

ligands are closed-shell dianionic o-dithiolate (2-) and the metal ion is in the +5 oxidation

state. Considering the ligand centered reduction leading to unchanged metal oxidation

state in neutral (12) and monoanionic (12b), the presence of one radical ligand in the

neutral 12 with +5 oxidation state of metal is suggested. Fig. 6.3.4 shows the thermal

ellipsoids of the anion in 12b with labelling scheme and table 6.3.5 and 6.3.6 display the

important bond angles and bond distances respectively.

Fig. 6.3.3: Schematic representation of the bond distances and dihedral angles for 12b

S(2)(1)S

Mo

S(22)(21)S

Mo

S(42)(41)S

Mo

2.373

3(7) 2.3818(8) 2.3

824(8

) 2.3911(7) 2.373

3(7) 2.3560(7)

av. 1.399(4) av. 1.402(4) av. 1.403(4)

di. angle= 13.6 °

di. angle= 23.9 °

di. angle= 3.3 °

1.765(3)

1.75

1(3) 1.759(3)

1.76

4(3) 1.759(3)

1.74

4(3)


Bond angles (deg) S(1)-Mo(1)-S(2) 81.21(2) S(21) -Mo(1)-S(22) 81.11(2) S(41) -Mo(1)-S(42) 81.69(3) S(1) -Mo(1)-S(21) 158.08(3) S(2) -Mo(1)-S(41) 159.37(3) S(42) -Mo(1)-S(22) 152.21(3)

Bond distance [Å] Mo(1)-S(1) 2.3733(7) Mo(1)-S(21) 2.3824(7) Mo(1)-S(41) 2.3733(7) Mo(1)-S(2) 2.3818(8) Mo(1)-S(22) 2.3911(7) Mo(1)-S(42) 2.3560(7) S(1)-C(1) 1.765(3) S(21)-C(21) 1.759(3) S(41)-C(41) 1.759(3) S(2)-C(2) 1.751(3) S(22)-C(22) 1.764(3) S(42)-C(42) 1.744(3) C(1)-C(2) 1.404(4) C(21)-C(22) 1.407(4) C(41)-C(42) 1.411(4) C(1)-C(6) 1.417(4) C(21)-C(26) 1.416(4) C(41)-C(46) 1.430(4) C(2)-C(3) 1.388(4) C(22)-C(23) 1.401(4) C(42)-C(43) 1.400(4) C(3)-C(4) 1.387(4) C(23)-C(24) 1.386(4) C(43)-C(44) 1.373(4)

C(4)-C(5) 1.404(4) C(24)-C(25) 1.404(4) C(44)-C(45) 1.412(4)

C(5)-C(6) 1.396(4) C(25)-C(26) 1.399(4) C(45)-C(46) 1.392(4)

Table 6.3.6: Selected bond distances [Å] for 12b

Table 6.3.5: Selected bond angles [deg] for 12b

Chapter 6 125

The structure of 13 is isostructural to that of compound 12; therefore it is

not shown separately. This complex also crystallizes in space group P21/n with an

identical intramolecular arrangement to compound 12. Similar to 12, sulfur atoms of the

ligand exhibit disorder leading to inaccuracy in the C-S and Mo-S bond distances. Table

6.3.7 and 6.3.8 display the important bond angles and bond distances, respectively.

The individual chelate projection (twist) angles for each ligand are Ф(S(1),

W(1), S(2)) = 4.2˚; Ф(S(21), W(1), S(22)) = 0.6˚ and Ф(S(41), W(1), S(42)) = 9.9˚.

Hence the triangles are twisted from each other by an average angle of 4.9˚ an exact

intermediate of octahedral (60˚) and TP value of (0˚). The similar complex with un-

substituted ligand, [W(C6H4S2-1,2)3]11 shows a (0˚) twist angle, implying a perfect TP

geometry. The intra molecular M-S and C-S distances are very similar to that observed in

12, 2.361(1), and 1.747(8) Å, respectively. Thus the oxidation level of ligands and metal

should be similar in both of these compounds.

Mo(1)

S(1)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

S(2)S(42)

S(41)

C(42)

C(41)C(46)

S(22)

S(21)

Fig. 6.3.4: The thermal ellipsoid drawing of the 12b at the 50% probability level with atom-labeling scheme.


Bond distance [Å] W(1)-S(1) 2.361(1) W(1)-S(21) 2.360(1) W(1)-S(41) 2.363(1) W(1)-S(2) 2.374(1) W(1)-S(22) 2.352(1) W(1)-S(42) 2.357(1) S(1)-C(1) 1.748(4) S(21)-C(21) 1.773(4) S(41)-C(41) 1.763(4) S(2)-C(2) 1.738(4) S(22)-C(22) 1.723(4) S(42)-C(42) 1.739(4) C(1)-C(2) 1.411(5) C(21)-C(22) 1.391(6) C(41)-C(42) 1.412(5) C(1)-C(6) 1.428(5) C(21)-C(26) 1.437(5) C(41)-C(46) 1.429(45 C(2)-C(3) 1.411(5) C(22)-C(23) 1.413(6) C(42)-C(43) 1.402(5) C(3)-C(4) 1.375(5) C(23)-C(24) 1.380(6) C(43)-C(44) 1.371(5)

C(4)-C(5) 1.410(5) C(24)-C(25) 1.408(6) C(44)-C(45) 1.411(5)

C(5)-C(6) 1.377(5) C(25)-C(26) 1.378(6) C(45)-C(46) 1.380(5)

Bond angles (deg) S(1)-W(1)-S(2) 81.11(3) S(21) -W(1)-S(22) 81.18(4) S(41) -W(1)-S(42) 81.39(3) S(1) -W(1)-S(21) 134.22(4) S(22) -W(1)-S(41) 133.86(4) S(1) -W(1)-S(41) 135.25(4)

Table 6.3.8: Selected distances [Å] for 13


Chapter 6 127

The structure of 13b is isostructural with that of compound 12b; therefore

it is not shown separately. This complex also crystallizes in the space group P21/m with

an identical intramolecular arrangement to compound 12b. Table 6.3.9 and 6.3.10 display

important bond angles and bond distances, respectively. The individual chelate projection

(twist) angles for each ligand are Ф(S(1), W(1), S(2)) = 37.9˚; Ф(S(21), W(1), S(22)) =

26.3˚ and Ф(S(21X), W(1), S(22X)) = 30.3˚. The average twist angle of 31.5˚ is similar

to that observed in 12b. The average twist angle of 33˚ observed in [PHMe2Ph][W(1,2-

C6H4S2)3]12 is similar to that observed in 13b. A schematic representation of the bond

lengths and dihedral angles between the three independent o-benzodithiolene rings and S-

W-S planes are displayed in Fig. 6.3.5. The dihedral angles between the planes of the o-

dithiolene rings and the S-W-S planes are 11.9, 21.2 and 4.4° for rings one through three,

respectively. The average intramolecular M-S (2.370(2) Å) and C-S (1.760(7) Å)

distances are identical within the experimental error with the 12b, where all the C-S

distances clearly show single bond character.

The C-C distances in the phenyl ring are also almost equidistant within the

experimental error (1.39(1)) implying a dianionic o-dithiolate (2-) form of ligands and

thus the similar +5 oxidation state of metals in 12b and 13b.

S(2)(1)S

W

S(22)(21)S

W

S(42)(41)S

W

2.373

(2)

2.376(2) 2.380

(2)

2.381(2) 2.381

(2)

2.365(2)

av. 1.399(4) av. 1.402(4) av. 1.403(4)

di. angle= 11.9 °

di. angle= 21.2 °

di. angle= 4.4 °1.763(7)

1.74

3(8) 1.763(7) 1.

775(

8) 1.769(8) 1.75

4(8)

Fig. 6.3.5: schematic representation of the bond distances and dihedral angles for 13b.


An overview of the twist angles for all these complexes is shown below in

table 6.3.11. Almost all of these compounds show intermediate of ideal TP and

octahedral geometry. The most important electronic structure factors that have been

suggested to stabilize the TP geometry in metallo-tris(dithiolenes) are strong metal sulfur

π bonding as well as very effective interligand (S-S) bonding interactions.13,14 Indeed, the

ligand-ligand repulsions are maximized in the TP geometry and minimized in the

Bond angles (deg) S(1)-W(1)-S(2) 81.59(7) S(21) -W(1)-S(22) 81.36(7) S(41) -W(1)-S(42) 81.61(8) S(1) -W(1)-S(21) 158.27(7) S(2) -W(1)-S(41) 159.62(7) N(42) -W(1)-S(22) 153.91(7)

Bond distance [Å] W(1)-S(1) 2.373(2) W(1)-S(21) 2.380(2) W(1)-S(1) 2.373(2) W(1)-S(2) 2.376(2) W(1)-S(22) 2.373(2) W(1)-S(2) 2.376(2) S(1)-C(1) 1.763(7) S(21)-C(21) 1.763(7) S(41)-C(41) 1.769(8) S(2)-C(2) 1.743(8) S(22)-C(22) 1.775(8) S(42)-C(42) 1.754(8) C(1)-C(2) 1.39(1) C(21)-C(22) 1.40(1) C(41)-C(42) 1.37(1) C(1)-C(6) 1.41(1) C(21)-C(26) 1.41(1) C(41)-C(46) 1.43(1) C(2)-C(3) 1.41(1) C(22)-C(23) 1.41(1) C(42)-C(43) 1.41(1) C(3)-C(4) 1.38(1) C(23)-C(24) 1.40(1) C(43)-C(44) 1.35(1)

C(4)-C(5) 1.40(1) C(24)-C(25) 1.38(1) C(44)-C(45) 1.42(1)

C(5)-C(6) 1.39(1) C(25)-C(26) 1.39(1) C(45)-C(46) 1.36(1)

Table 6.3.10: Selected distances [Å] for 13b.

Table 6.3.9: Selected bond angles [deg] for 13b.

Chapter 6 129

octahedral geometry. Understanding both the π donor and π-acceptor properties of

coordinated dithiolenes provides a basis for understanding how electron delocalization

can stabilize TP geometry. Considering a noncovalent (ionic) bonding model involving

high-valent metal centers and reduced unsaturated dithiolates, in the dianionic limit,

ligand-ligand repulsions are more, and the distortions of metallo-tris(dithiolenes) will

tend toward an octahedral geometry in order to minimize interligand S-S interactions. If

one now allows for metal-ligand covalency, the ligand electron density is delocalized

over the half filled or empty metal d orbitals, resulting in a reduction of interligand S-S

repulsions and increased stabilization of TP geometry.15


The electrochemistry of [Mo(tLNS)3] (11), [Mo(tLSS)3] (12) and [W(tLSS)3]

(13), have been studied in CH2Cl2 solution by cyclic voltammetry (CV), with 0.10M

[N(n-Bu)4][PF6] as a supporting electrolyte, a glassy carbon as working electrode and

Ag/AgNO3 as reference electrode. Ferrocene was used as an internal standard, and all

redox potentials are referenced versus the ferrocene/ferrocenium (Fc/Fc+) couple at room

temperature. Fig. 6.4.1, 6.4.2 and 6.4.3 show the cyclic voltammograms of 11, 12, and 13

over the potential range from +2.0 V to -2.0 V and +0.5 V to –2.0 V, respectively. For 11,

three reversible electron-transfer waves were observed and for 12 and 13 two reversible

and one irreversible electron-transfer waves were observed. Table 6.4.1 summarizes the

redox potentials (E1/2) for compounds 11, 12 and 13 vs. (Fc/Fc+), respectively.

According to coulometric measurements at appropriate fixed potentials,

two reversible processes in 11, 12 and 13 namely; E21/2, and E3

1/2 correspond to reduction

and the one E41/2 correspond to oxidation. The redox potentials for the -2/-1 and –1/0

Compound 11 12 12b 13 13b

Av. Α (deg) 1.7 26.1 31.6 30 31.5

Table 6.3.11: Comparison of trigonal prismatic angles in 11, 12, 12b, 13 and 13b.


couple in 11 are quite higher than that in 12 and 13, indicating that these redox couples

are highly dependent on the ligand. In addition, the redox potential for -2/-

1 and –1/0 couple in [Mo(bdt)]2 are about 0.5 V higher than that in 12 and

13. These redox potentials in general reflect that the electron donating groups stabilize

the highly negatively charged species. The redox potential of the 0/+1 couple is very high

in 12 and 13, and the wave is irreversible; therefore coulometry was not done. The cyclic

Compound E21/2(2-/1-) E3

1/2(1-/0) E41/2(0/1+)

[Mo(tLNS)3] (11) -1.595 -0.823 +0.133

[Mo(tLSS)3] (12) -0.994 -0.482 +0.91

[W(tLSS)3] (13) -1.109 -0.474 +0.951

[Mo(bdt)3]2 -0.390 +0.20

Table 6.4.1: Redox potentials (V) of 11, 12 and 13 vs. Fc/Fc+ at 22° C.

Fig. 6.4.1: Cyclic Voltammogram of 11 in CH2Cl2 solution containing 0.10M [(n-bu)4N][PF6] at scan rates of 25, 50, 100, 200, 400, mV/s at 22°C.

-2.5-2.0-1.5-1.0-0.50.00.51.0

10µA

I (µA

)

E (V)

Chapter 6 131

voltammograms do not change after coulometric reduction, indicating effective stability

of the reduced products. The redox reactions, monitored spectroelectrochemically,

proceed with well-defined isobestic points and stoichiometric conversions.

Fig. 6.4.2: Cyclic Voltammogram of 12 in CH2Cl2 solution containing 0.10M [(n-bu)4N][PF6] at scan rates of 25, 50, 100, 200 mV/s at 22°C.

-1.5-1.0-0.50.00.51.0

10µA

E (V)

Fig. 6.4.3: Cyclic Voltammogram of 13 in CH2Cl2 solution containing 0.10M [(n-bu)4N][PF6] at scan rates of 25, 50, 100, 200 mV/s at 22°C.

-2.0-1.5-1.0-0.50.00.51.0

10µA

E (mV)


Chronoamperometry was utilized to monitor the changes in infrared

frequencies upon one and two electron reductions at appropriate fixed potential for 12

and 13. In the neutral species, there is a sharp band at ~1106 cm-1 (corresponding to C-S●

radical ligand) and a weak band at 1041 cm-1(correspond to C-S single bond stretching).

Upon one electron reduction, the peak at 1106 cm-1 disappears in both 12 and 13. This is

an evidence for presence of a single π-radical ligand in the neutral species, and three non-

radical ligands in the monoanionic species suggesting the +5 oxidation state of metal in

both of these species. This result together with X-ray crystal structure analysis of 12, 12b,

13 and 13b confirms the ligand centered redox activities as demonstrated below in

scheme 6.4.1.

[MV(tL0SS)(tLSS)2]+

-e+e

[MV(tLSS)(tLSS)2]+e-e -e[MV(tLSS)3]1- +e [MIV(tLSS)3]2-

Scheme 6.4.1 redox activity of 12 and 13

Fig. 6.4.3: Infrared spectra of 12 and 12b.

1050110011501200

[Mo(tLSS)3]-

[Mo(tLSS)3]

cm -1

rel.

tran

smita

nce

1106 cm-1

(C=S●)

Chapter 6 133

6.5 Electronic spectra

The electronic absorption spectra of 11, 12 and 12b along with their

electrochemically generated mono-, and dianionic species are displayed in Fig.6.5.1,

6.5.2 and 6.5.3, respectively. The general similarity of the electronic absorption spectra

for neutral as well as mono-and dianionic forms leads to the proposition that they all

possess a similar electronic structure. Electronic absorption spectra for the neutral

complexes exhibit two intense electronic transition bands in the visible region: ~ 400 nm

(1.5 × 104 M-1 cm-1) and ~700 nm (2.5 × 104 M-1 cm-1). According to a MO scheme

developed by Gray et al.4a for [M(S2C2Ph2)3] (M = Re, Mo, W) (Fig. 6.5.4) the band at

~700 nm is assigned to the 2a2'(3πv) → 5e' (3πv, dxy, dx2-y2) transition and the ~400 nm

band to the 3e'(πh), 2a2''(πh) → 3a'(dz2) transitions. The 5e' and 3a' both have considerable

ligand character. Thus these and similar transitions in 11, 12 and 13 are L→ M in

character. The LMCT nature of transitions is evident from the fact that in [W(tLss)3]

10001050110011501200

[W(tLSS)3]-

rel.

tran

mita

nce

cm-1

[W(tLSS)3]

Fig. 6.4.4: Infrared spectra of 13 and 13b.

1106 cm-1 (C=S●)


transitions always occur at higher energies (lower wavelengths) than the their

corresponding [Mo(tLss)3] counterparts. Thus, predominantly metal-based MOs of W are

stabilized relative to those of Mo and are located at deeper binding energies.

The electronic absorption spectra of monoanionic species exhibit four

bands in the visible region (table 6.5.1). In contrast to the spectrum of [Cr(tLss)3]1- (8)

and [Cr(tLCat)3]1- (10b) (chapter 5), they do not exhibit any charge transfer band in the

near infrared region, which are known as intervalence ligand to ligand charge transfer

bands. Absence of IVLLCT bands for 11b, 12b and 13b suggest that three of the ligands

in these species are closed shell, aromatic o-dithiolate (2-). In the electronic absorption

spectra of dianionic species (11c, 12c and 13c), two intense bands in the visible region

are present, which may correspond to ligand to metal charge transfer bands. Thus, redox

activities of these compounds are predominantly ligand centered and redox behavior can

be explained as shown in scheme 6.5.1 for 11 and scheme 6.4.1 for 12, and 13.

400 600 800 1000 12000.0

0.5

1.0

1.5

2.0

2.5

3.0 [MoV(tLNS)3]1-

[MoIV(tLNS)3]2-

[MoV(tLNS)3]1+

[MoV(tLNS)3]

ε X

104 M

-1 c

m-1

λ nm

Fig. 6.5.1: Electronic absorption spectra of the neutral and the electrochemically reduced forms of 11 in CH2Cl2 solution, (0.10M[(n-Bu)4N] PF6) at –5 0C

Chapter 6 135

λ1(ε) λ2 (ε) λ3 (ε) λ4 (ε) [Mo(tLNS)3] (11) 408 (2.04) 719 (1.83)[Mo(tLNS)3]+ (11a) 402 (1.42) 477 (1.38) 767 (1.60) [Mo(tLNS)3]1- (11b) 329 (1.87) 438 (1.31) 581 (0.64) 663 (0.51) [Mo(tLNS)3]2- (11c) 347 (1.75) 486 (1.88) 649 (0.13) [Mo(tLss)3] (12) 430 (2.14) 693 (2.48) 881 (0.32) [Mo(tLss)3]1- (12b) 413 (1.57) 479 (1.16) 638 (0.88) 701 (0.80) [Mo(tLss)3]2- (12c) 353 (2.5) 413 (0.33) 575 (1.71) 628 (0.64) [W(tLss)3] (13) 353 (1.25) 390 (1.90) 649 (2.53) 790 (0.35) [W(tLss)3]1- (13b) 360 (1.91) 537 (1.17) 632 (0.613) [W(tLss)3]2- (13c) 344 (1.84) 384 (0.40) 468 (2.45) 539 (0.90)


400 600 800 10000.0

0.5

1.0

1.5

2.0

2.5

3.0

[MoV(tLSS)3]1-

[MoIV(tLSS)3]2-

[MoV(tLSS)2(L.SS)]

ε X

104

M-1

cm-1

λ nm

Table 6.5.1: wavelength [nm] and extinction coefficients (104 M-1 cm-1) for neutral and electrochemically generated species of 11, 12 and 13.

[MoV(tL0NS)(tLNS)2]+

-e+e

[MoV(tLNS)(tLNS)2]+e-e -e[MoV(tLNS)3]1- +e [MoIV(tLNS)3]2-

Scheme 6.5.1: Redox activity of 11


5 d

6 s

π hπ h

π h

3 π v

3 π v

3 π vdx2-y2 , xy

π h

3 π v

dx2-y2 , xy

dz2

dxz,yz

2a2"3e'3e"

4e'2a2'3a1'5e'

Fig. 6.5.4: A diagram showing the orbital levels of interest informulating the ground state of [M(S2C2Ph2)3]4a.

Metal

Ligand


400 600 800 10000.0

0.5

1.0

1.5

2.0

2.5

3.0 [ WV(Lss)3]

1-

[ WIV(Lss)3]2-

[ WV(Lss)2(L.SS)2]

ε X

104 M

-1 c

m-1

λ nm

Chapter 6 137

6.6 X-band EPR spectra and magnetic susceptibility

The X-band EPR spectra are recorded for electrochemically generated

monocation and monoanion species of 11, 12 and 13 in frozen CH2Cl2 solutions at 10 K.

Magnetic susceptibility data of complexes 11, 12, 12b, 13 and 13b were collected in the

temperature range 2 to 290 K. As expected compounds 11, 12 and 13 are diamagnetic and

12b, 13b are paramagnetic. The EPR spectrum of electrochemically generated reduced

form of 11 i.e 11b displayed a 16 line hyperfine pattern due to the coupling of 95Mo (I =

5/2) nucleus along with the superhyperfine splitting due to 14N (I = 1), 1H (I=1/2) at 221

K. This superhyperfine was absent in the frozen solution (at the 10 K) or at room

temperature. It is reported that the temperature at which highest resolution is obtained is

above the freezing point of the solvent.19 The fitting parameters obtained from simulation

are: giso = 1.996, Ax = ( 14N = 8, 1H = 21), AY = ( 14N = 6, 1H = 8) G and 95,97Mo = 34G.

Similar g value and hyperfine splitting constants have been reported for [Mo(abt)3]1-(g =

1.988, A95,97Mo = 38, A14N = 2.1 and A1H = 6.3)G.17 The EPR spectrum of the monocation

species (denoted as 11a henceforward) shows the similar 16-line hyperfine splitting due

to 95,97Mo (I = 5/2) nucleus along with the superhyperfine splitting due to 14N (I = 1), 1H

(I = 1/2) at 194 K. The similarity between the EPR spectral parameters of 11a and 11b

imply in the identical metal oxidation state in both of these species.

The S=1/2 state thus observed for 11a and 11b in the EPR spectrum can

342 344 346 348-0,4

-0,2

0,0

0,2

0,4

0,6

0,8 Sim

Exp

B (mT)343 344 345 346 347

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

B (mT)

Fig. 6.6.1: X-band EPR spectra of 11a and 11b 11b(left) Exp: T = 221.9 K, ν = 9.64GHz, P = 2.007 mW, MA = 0 G

11a(right) Exp: T = 193.8 K, ν = 9.64GHz, P = 2.002 mW, MA = 0 G


be interpreted as arising from a d1 system (MoV), or an exchange coupled d2(MoIV)-ligand

radical system. But the structural features favour the MoV configuration. The presence of

MoV in both 11a and 11b clearly suggests that the neutral compound 11 also possesses

MoV oxidation state that undergoes ligand centered redox processes.

The X band EPR spectrum of 12b is shown in Fig. 6.6.2. It shows an axial

signal with hyperfine splitting due to interaction of 95,97Mo (I = 5/2, 9.5% natural

abundance) nucleus, which leads to 6-line hyperfine pattern. This hyperfine interaction

was not observable at 10K but only at 230K it was observable. The simulation yields

following fitting parameters: g║ = 2.0021, g┴ = 2.0191.

Fig. 6.6.3 displays the magnetic moment vs. temperature plot for 12b. It

shows a temperature independent magnetic moment of 1.70 µB corresponding to spin-

only value for an S = 1/2 ground state (g = 2.007, χTIP = 0.394*10-2emu, θ = -0.3 K,

where g value is fixed from the parameters of EPR spectrum).

330 335 340 345 350 355 360

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

dX"/d

B

Exp Sim

B (mT)

335 340 345 3501

0

1

B (mT)

Fig. 6.6.2: X-band EPR spectrum of 12b Exp: T = 9.5 K, ν = 9.64GHz, P = 5.0289 x 10-3 mW, MA = 10 G

Insert, Exp: T = 231.6 K, ν = 9.63GHz, P = 5.028 x 10-3 mW, MA = 1 G. gx= gy = 2.0021, gz = 2.0191.

Chapter 6 139

The X band EPR spectrum of 13b shows an axial signal as shown in Fig.

6.6.4. The simulation yields the following fitting parameters: g║ = 1.9869, g┴ = 2.00.

Lower g values than free radical value and corresponding Mo complex are a consequence

of higher spin-orbit coupling constants. The reason for high spin orbit coupling constants

for heavy elements is due to the higher nuclear charge. The higher spin orbit-coupling

constant also manifests the lowering of the magnetic moment than the expected spin only

value for one unpaired electron.18 Thus, as shown in Fig. 6.6.5 magnetic moment of 1.69

µB in the temperature range of 0 to 130 K is observed for 13b. Other fitting parameters

after simulation are g = 1.99 (fixed from the EPR parameters), χTIP = 0.394*10-2 emu, θ =

-0.22 K. The magnetic moment along with EPR spectrum suggests the S = 1/2 (d1, WV)

ground state to the 13b.

50 100 150 200 250 300

1.3

1.4

1.5

1.6

1.7

1.8

Exp. Sim.

µ eff/

µ B

T (K)

Fig.6.6.3: Plot µeff vs. temp. for 12b. The solid line represents the best least squares fitting for the experimental data (circles).


320 340 360 380-0,06

-0,04

-0,02

0,00

0,02

0,04

0,06

0,081,81,922,12,2

dX"/d

B

Exp. Sim.

B (mT)Fig. 6.6.4: X-band EPR spectra of 13b

Exp: T = 9.97 K, ν = 9.63GHz, P = 1.006 x 10-3 mW, MA = 10 G gx= gy = 1.9869, gz = 2.00

Fig.6.6.5: Plot µeff vs. temp. for 13b. The solid line represents the best least squares fitting for the experimental data (circles).

50 100 150 200

1,2

1,4

1,6

1,8

Exp Sim

µ eff

/ µ B

T (K)

Chapter 6 141

6.7 Conclusions

In this chapter [M(tLSS)3]n (M = Mo, W; n = 0, 1) complexes along with

[Mo(tLNS)3] have been studied and it has been found that the oxidation state of +5 is

present for the central metal ion for all these compounds. In contrast to the previous

literature reports viewing the neutral complexes as MVI (d0) configuration, we have found

that the neutral species are MV (d1), which undergo ligand centered redox activities to

produce corresponding monoanionic and monocation species with unchanged oxidation

state of metal ion. The electronic spectra of all compounds contain characteristic ligand to

metal charge transfer bands. The electronic structures of these complexes were elucidated

by a combination of electronic, EPR, X-ray crystallography and magnetic susceptibility

measurements.

As compared to [Cr(tLSS)3]1- (8), the electronic spectra of monoanionic

compounds 11b, 12b and 13b are different. The X-ray structure analyses of these

compounds also show significant differences in bond distances for 8 than other

[M(tLSS)3]1- complexes. Thus, in contrast to the previous suggestions of considering Cr,

Mo and W having a similar oxidation state in similar ligand atmosphere, we conclude that

the metal oxidation states is different in case of 8 than other [M(tLSS)3]1- complexes (M =

Mo, W).


6.8 References

1) (a) McCleverty, J. A.; Locke, J.; Wharton, E. J.; Gerloch, M. J. Chem. Soc. (A)

1968, 817. (b) Wharton, E. J.; McCleverty, J. A. J. Chem. Soc. (A) 1969, 2258.(c)

Eisenberg, R. Progr. Inorg. Chem. 1970, 12, 295. (d) Hoyer, E.; Dietzsch, W.;

Schroth, W. Z. Chem. 1971, 11, 41.

2) Cowie, M.; Bennett, M. J. Inorg. Chem. 1976, 15, 1584.




T.; Piligkos, S.; Slageren, J. V.; Neese, F.; Wieghardt, K. J. Am. Chem. Soc. 2005,

127, 4403.

4) (a) Stiefel, E. I.; Eisenberg, R.; Rosenberg, R.; Gray, H. J. Am. Chem. Soc. 1966,

88, 2956.(b) Eisenberg, R.; Stiefel, E. I.; Rosenberg, R.; Gray, H. B. J. Am. Chem.

Soc. 1966, 88, 2874.

5) Smith, A. E.; Schrauzer, G. N.; Mayweg, V. P.; Heinrich, W. J. Am. Chem. Soc.

1965, 87, 5798.

6) Schrauzer, G. N.; Mayweg, V. P. J. Am. Chem. Soc. 1966, 88, 3235.

7) Yamanouchi, K.; Enemark, J. H. Inorg. Chem. 1978, 17, 2911.

8) (a) Herebian, D.; Bothe, E.; Bill, E.; Weyhermüller, T.; Wieghardt, K. J. Am.

Chem. Soc. 2001, 123, 10012. (b) Herebian, D.; Ghosh, P.; Chun, H.; Bothe, E.;

Weyhermüller, T.; Wieghardt, K. Eur. J. Inorg. Chem. 2002, 1957. (c) Ghosh, P.;

Bill, E.; Weyhermüller, T.; Neese, F.; Wieghardt, K. J. Am. Chem. Soc. 2003,

125, 1293.

9) (a) Eisenberg, R.; Ibers, J. A. J. Am. Chem. Soc. 1965, 87, 3776. (b) Pierpont,

C.G.; Eisenberg, R. J. Chem. Soc. (A) 1971, 2285.

10) Cervilla, A.; Llopis, E.; Marco, D.; Pérez, F. Inorg. Chem. 2001, 49, 6525.

11) Huynh, H, V.; Lügger, T.; Hahn, F. E. Eur. J. Inor. Chem. 2002, 3007.

12) Burrow, T.; Morris, R. H. Acta. Cryst. 1993, C49, 1591.

13) Campbell, S.; Harris, S. Inorg. Chem. 1996, 35, 3285.

14) Trogler, W. C. Inorg. Chem. 1980, 19, 697.

Chapter 6 143

15) Kirk, M.; Mcnaughton, R. L.; Helton, M. E. Progr. Inorg. Chem. 2004, 52, 111.

16) Stiefel, E. I.; Brown, G. F. Inorg. Chem. 1972, 11, 434.

17) Gardner, J. K.; Pariyadath, N.; Corbin, J. L.; Stiefel, E. I. Inorg. Chem. 1978, 17,

897.

18) Earnshaw, A. Introduction to magnetochemistry, Acadamic Press; 1968.

19) (a) Marov, I. N.; Balyaeva, V. K.; Ermakov, A. N.; Dubrov, Y. N. Russ. J. Inorg.

Chem. 1969, 14, 1391. (b) Duglav, I. N.; Usmanov, Z. I. Zh. Strukt. Khim. 1975,,

16, 312.

Chapter 7 145

7.1 Introduction

As described in the chapter 1, X-ray absorption spectroscopy (XAS) involves the

excitation of core electrons to valence orbitals and to the continuum.1 The resultant

spectrum is typically divided into two regions: 1) the edge region, which is characterized

by a sharp discontinuity resulting from the ionization of a core electron and provides

electronic structural information; and 2) the EXAFS region which occurs after the

electron has been excited to the continuum and is able to interact with neighboring atoms,

thus providing detailed metrical information. In this section, we will focus on the XAS

edge region. Specifically, a combination of metal K- (or metal L-) and ligand K-edge

XAS will be used to provide electronic structural information on a series of Cr, Mo and

W benzodithiolates and Cr catecholates.

The metal K-edge is characterized by an intense electric dipole allowed 1s to 4p

transition. To lower energy, a weak 1s to 3d transition occurs, which is formally electric

dipole forbidden, but may gain intensity through 3d-4p mixing in appropriate

symmetry.2,3 The pre-edge and edge region show oxidation state dependent shifts, and

hence the transition energies may be used to assess oxidation state changes.3,4 The metal

L-edge results from dipole allowed 2p to 3d transition, which will be split into L3 and L2

Chapter 7 XAS of Cr, Mo and W

complexes

XAS

146

edges due to the spin orbit coupling of the 2p hole.5 The energies of the L3 and L2

transitions will vary depending on the electronic structure of the site.6-9 A change in Zeff,

due to a change in oxidation state or in coordination number, will affect the energy of

both the 2p and the 3d orbitals, while a change in the ligand field (which results in a

change in the spitting of the d-manifold) will only affect the 3d orbital energies. The

ligand K-edge, results from a dipole allowed transition from a ligand 1s orbital to a ligand

4p orbital.10,11 In cases where the ligand is bound to an open shell transition metal the

covalent interaction between the ligand 3p orbitals and the metal 3d orbitals, produces

ligand 3p hole character, resulting in a pre-edge transition, the intensity of which will

reflect the covalency of the metal-ligand bond. The energy of a ligand K-edge transition

can provide further electronic structural information. The pre-edge energy is affected by

the energy of the unoccupied (or partially occupied) 3d orbitals (which will have

contributions from the ligand field and Zeff) and the energy of the ligand 1s core. In

addition, the ligand K-edge rising edge energy reflects the chemical shifts in the ligand 1s

core. Thus, by evaluating changes in edge and pre-edge energies, changes in the 3d

orbital energies may be obtained.

7.2 Results and Analysis

Figure 7.1 shows a comparison of the Mo L2 XAS data for [Mo(Lss)3]1-

(12b) and [Mo(Lss)3]0 (12). The essentially identical L2-edge energies reflect a very

similar charge on the Mo in these two complexes. (Note the rise in the background is due

to the fact that the Mo L-edge sits on a strong sulfur background). In contrast, the S K-

edge data (Figure 7.2) show that on going from the monoanionic (12b) to the neutral (12)

complex the sulfur ligand has been oxidized, as evidenced by the shift in the rising edge

energy. In addition, the pre-edge feature splits, going from a single feature at ~2470.8 eV

in the monoanion to two features at 2470.2 eV and 2471.3 eV in the neutral complex.

Based on the similarity of the Mo L-edge data for these two complexes, it is most

reasonable to assume that the higher energy feature in the neutral complex corresponds to

a S 1s transition to a primarily Mo 4d based orbital. The transition is higher in energy in

Chapter 7 147

the neutral 12 than in the monoanionic 12b because the increased effective nuclear charge

on the sulfur moves the sulfur 1s orbital to deeper binding energy and thus increases the

overall transition energy. The lower energy feature at 2470.2 eV is then assigned as a S

1s to S 3p transition, reflecting ligand radical character.

Figure 7.3 shows a comparison of the S K-edge data for [Mo(Lss)3]0 (12) and

[W(Lss)3]0 (13). W L-edge data were obtained, however, no appropriate comparisons are

currently available, and therefore only the S K-edge data are shown. The similar pre-

edge and rising edge structures of the two neutral complexes may argue for a similar

electronic structural description of these two complexes, but this is difficult to judge from

the S K-edge data in isolation. Due to the extreme air sensitive nature of [W(Lss)3]1-

(13b), it was not possible to record its XAS. However the essential similarity in infrared,

X-ray structure and electronic absorption spectra of 12 and 13, and 12b and 13b

respectively, suggest the similarity in the electronic structure of corresponding Mo and W

complexes.

Fig. 7.1: Comparison of the MoL2-edges [Mo(tLSS)3] (12) and [Mo(tLSS)3]1- (12b)

2622 2624 2626 2628 2630 2632 26341.0

1.2

1.4

[Mo(tLSS)3]0

[Mo(tLSS)3]1-

Nor

mal

ized

Abs

orpt

ion

Energy (eV)

XAS

148

Fig. 7.2: Comparison of the S K-edges for [Mo(tLSS)3] (12) and [Mo(tLSS)3]1- (12b)

2464 2466 2468 2470 2472 2474 2476 2478-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Nor

mal

ized

Abs

orpt

ion

Energy (eV)

[Mo(tLSS)3]0

[Mo(tLSS)3]1-

Fig. 7.3: Comparison of the S K-edges for [W(tLSS)3] (13) and [Mo(tLSS)3] (12)

2464 2466 2468 2470 2472 2474 2476 2478

0.0

0.5

1.0

1.5

2.0

Nor

mal

ized

Abs

orpt

ion

Energy (eV)

[W(tLSS)3]

[Mo(tLSS)3]

Chapter 7 149

A comparison of the S K-edge XAS data for 12b and [Cr(Lss)3]1- (8) is

shown in Figure 7.4. The appearance of a lower energy pre-edge feature in 8 argues for

the formation of a ligand based radical in the Cr complex that is absent in the Mo

complex.

Figure 7.5 shows a comparison of the Cr K-edge data for [Cr(Lcat)3]0 (10),

[Cr(Lcat)3]1- (10b), [Cr(Lss)3]1- (8), and [CrO(Lss)2]1- (9) with references K2CrO4 (CrVI)

and CrCl3(H2O)6 (CrIII). The similar pre-edge and rising edge positions for the neutral 10

and monoanionic 10b complexes indicate that the effective nuclear charge in these two

complexes is similar. Comparison to Cr K-edge data of known oxidation state (Figure

7.5) appear to be most consistent with an oxidation state assignment of Cr(III). At this

point, Lay et al.13 have different judgment. They have recorded XANES in the spectra of

[Cr(LCat)3]n- complexes (n = 1-3) during the in situ electrochemical XAS (295K). They

have noticed small increase in the edge energies (6002.9 vs 6002.4 eV) and in the

Fig. 7.4: Comparison of S K-edges for [Cr(tLSS)3]1- (8) and [Mo(tLSS)3]1- (12b)

2464 2466 2468 2470 2472 2474 2476 2478

0.0

0.5

1.0

1.5

Nor

mal

ized

Abs

orpt

ion

Energy (eV)

[Cr(tLSS)3]1-

[Mo(tLSS

)3]1-

XAS

150

intensities of pre-edge peaks for [Cr(LCat)3]2-/1- relative to the [Cr(LCat)3]3-. This shift in

the edge position by about 0.5eV has been attributed to metal centered oxidations. Thus

in their point of view the oxidation state of metal changes from +3 to +5, going from

[Cr(LCat)3]3- to [Cr(LCat)3]1- which lead to the +6 oxidation state to the neutral compound.

As we have clearly seen in our case that there is no change in the Cr K-edges in neutral

and monoanionic species and they are consistent with the reference CrIII species, the +6

assignment done by Lay et al. is erroneous.

The metal K-edge for [Cr(Lss)3]1- (8) appears at 0.5 eV lower in energy

than the reference CrIII, 10 and 10b, indicating a less effective nuclear charge (+2

oxidation state). The comparison of Cr K- pre-edge and edge data for 9 and 8 indicate

that 9 has a greater effective nuclear charge than 8 based on the pre-edge energy position.

A comparison of Cr K-edge data of 9 is similar to that reported in the literature for CrV

complexes,14 which is in agreement with the infrared and X-ray crystallographic

assignment of +5 oxidation state to this compound. Note that due to shakedown

contributions to the rising edge region (which will generally be more significant for sulfur

based ligands than for oxygen ligands) are difficult to compare.

Chapter 7 151

5980 5990 6000 6010 6020 60300.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4N

orm

aliz

ed A

bsor

ptio

n

Energy (eV)

[Cr(tLSS)3]1-

[CrO(tLSS)3]1-

[Cr(tLCat)3]

[Cr(tLCat)3]1-

K2CrO4

CrCl3(H2O)6

Fig. 7.5: Comparison of Cr K-edges for 8, 9, 10 and 11 with references K2CrO4 and CrCl3(H2O)6

5988 5990 5992 5994 5996 59980.0

0.2

0.4

0.6

0.8

1.0 [Cr(tLSS)3]

1-

[CrO(tLSS)3]1-

[Cr(tLCat)3]

[Cr(tLCat)3]1-

K2CrO4

CrCl3(H2O)6

Nor

mal

ized

Abs

orpt

ion

Energy (eV)

XAS

152

Figure 7.6 compares the S K-edge XAS data for [Cr(Lss)3]1- and

[CrO(Lss)2]1-. Based on the rising edge energies, the sulfur is clearly more oxidized in the

[Cr(Lss)3]1- complex than in the [CrO(Lss)2]1- complex. This is consistent with the

formation of a ligand radical in the former, but not in the latter.

2464 2466 2468 2470 2472 2474 2476 24780.0

0.5

1.0

1.5

Nor

mal

ized

Abs

orpt

ion

Energy (eV)

[CrO(tLSS)3]1-

[Cr(tLSS

)3]1-

Fig. 7.6: Comparison of S K-edges for [Cr(tLSS)3]1- (8) and [CrO(tLSS)2]1- (9)

Chapter 7 153

7.3 Conclusions

The XAS studies on the neutral Mo and W complexes coordinated to tris-

o-dithiolene clearly show the presence of one dithiobezosemiquinonate (1-) radical and

its absence in the monoanionic Mo complex in agreement with the results of the other

spectroscopic studies done on these complexes (chapter 6). Comparison of the

monoanionic species of Cr and Mo reveals that the electronic structures of these species

are different: in the first case a dithiobezosemiquinonate (1-) radical ligand is present and

in the second case it is not.

However, the situation is a little more complicated for the [Cr(LSS)3]1- (8),

[Cr(tLCat)3] (10) and [Cr(LCat)3]1- (10b) species. While the metal K-edge for 8 appears at

0.5 eV less than the reference CrIII compound, the metal K-edges of 10 and 10b appear

almost at the same position as compared to the reference CrIII. In contrast with this, the

electronic absorption spectra of electrochemically oxidized and reduced forms of 8 and

10 are correspondingly identical (chapter 5). Thus, while the metal K-edge data for the 8

points toward a CrII assignment, IR spectroscopy, X-ray crystallography and electronic

absorption spectroscopy (chapter 5) correlate best with that of a CrIII assignment. In the

case of 9, the metal is clearly more oxidized than 8, consistent with the +5 oxidation state

of the metal and absence of a ligand radical.

XAS

154

7.4 References

1) Koningsberger, D. C.; Prins, R. X-ray Absorption: Principles, Applications,

Techniques of EXAFS, SEXAFS, and XANES; John Wiley and Sons Inc.: New

York, 1988.

2) Shadle, S. E.; Penner-Hahn, J. E.; Schugar, H. J.; Hedman, B.; Hodgson, K. O.;

Solomon, E. I. J. Am. Chem. Soc. 1993, 115, 767.

3) Westre, T. E.; Kennepohl, P.; DeWitt, J. G.; Hedman, B.; Hodgson, K. O.;

Solomon, E. I. J. Am. Chem. Soc. 1997, 119, 6297.

4) DuBois, J. L.; Mukherjee, P.; Solomon, E. I.; Stack, T. D. P.; Hodgson, K. O. J.

Am. Chem. Soc. 2000, 122, 5775.

5) Fuggle, J. C. Phys. Scrp. 1987, T17, 64.

6) George, S. J.; Lowery, M. D.; Solomon, E. I.; Cramer, S. P. J. Am. Chem. Soc.

1993, 115, 2968.

7) Cramer, S. P.; deGroot, F. M. F.; Ma, Y.; Chen, C. T.; Sette, F.; Kipke, C. A.;

Eichhorn, D. M.; Chan, M. K.; Armstrong, W. H. J. Am. Chem. Soc. 1991, 113,

7937.

8) DeBeer George, S.; Basumallick, L.; Szilagyi, R. K.; Randall, D. W.; Hill, M. G.;

Nersissian, A. M.; Valentine, J. S.; Hedmann, B.; Hodgson, K. O.; Solomon, E. I.

2003, submitted for publication.

9) Wasinger, E. C.; deGroot, F. M. F.; Hedman, B.; Hodgson, K. O.; Solomon, E. I.

J. Am. Chem. Soc. 2003, 125, 12894.

10) Solomon, E. I.; Hedman, B.; Hodgson, K. O.; Dey, A.; Szilagyi, R. K. Coord.

Chem. Rev. 2004, in press.

11) Glaser, T.; Hedman, B.; Hodgson, K. O.; Solomon, E. I. Acc. Chem. Res. 2000,

33, 859.

Chapter 7 155

12) Hedman, B.; Frank, P.; Gheller, S. F.; Roe, A. L.; Newton, W. E.; Hodgson, K. O.

J. Am. Chem. Soc. 1988, 110, 3798.

13) Levina, A.; Foran, G. J.; Pattison, D. I.; Lay, P. A. Angew. Chem. Int. Ed. 2004,

43, 462.

14) Pattison, D. I.; Levina, A.; Davies, M. J.; G. J.; Lay, P. A. Inorg. Chem. 2001, 40,

214.

Chapter 8 157

The coordination chemistry of transition metals with bidentate ligands

derived from o-aminothiophenolate, o-dithiolate and o-catacholate has been studied in

this work. The ligands used were:

1) o-aminothiophenol [LNS]

2) 2-Phenylbenzothiazoline [LPh]

3) 2-mercapto-3,5-di-tert-butylaniline H2[tLNS]

4) 3,5-di-tert-butyl-1,2-benzenedithiol H2[tLSS]

5) 3,6-di-tert-butylcatacholate H2[tLCat]

Twenty-two transition metal complexes of these ligands have been

synthesized and characterized spectroscopically. Seventeen complexes among them have

been structurally characterized. These ligands were readily one-electron oxidized yielding

N,S-, S,S- and O,O-coordinated π radical anions. In this work, we have shown that the

spectroscopic oxidation states in transition metal complexes coordinated to these ligands

could be assigned by the combination of crystallographic and spectroscopic methods. The

main outcomes of the study are listed below:

Chapter 8 Summary

Summary

158

Chapter 2

The complexes [As(Ph)4] [Co(LNS)2] (1) and [N(n-Bu)4] [Co(LNS)2] (2)

have been fully characterized structurally, electrochemically and by magnetic

measurements in order to show that these species contain a central CoIII (d6, S=1) metal

ion. The cyclic voltammograms of 1 and 2 show reversible one-electron waves

corresponding to oxidation of a ligand and irreversible waves corresponding to a one

electron reduction of the cobalt. The absorption spectra of the complexes contain intense

LMCT bands occurring in the visible region (< 700 nm). The ground state of the

complexes has been shown to be a spin triplet, in which the degeneracy is lifted by large

positive zero field splitting. A zero field splitting (+41 cm-1) for complex 2 has been

measured independently by magnetic moment measurement, variable-temperature and

variable field SQUID magnetometry, and far-infrared absorption. These studies have

clarified the ambiguity surrouding the proper formalism of the monoanionic cobalt

complex, and therefore it is possible to assign this complex properly as [CoIII(LNSIP)2]1-.

Chapter 3

The reported compounds Na[Cr(tLNS)3(OEt)3(µ-OMe)4(OHEt)4] (3),

Na[Cr(tLNS)3(OMe)3(µ-OMe)4(OHMe)3] (4a) and Na [Cr(tLNS)3(OMe)3(µ-

OMe)4(OH2)3] (4b) are archetypal CrIII cuboidal clusters with a N,S- coordination.

Methoxy bridges are an additional feature of these cuboidal complexes. The structural

features of 3, 4a, and 4b demonstrate that the ligand, 2-mercapto-3, 5-di-tert-butylaniline

exists in o-iminothiobenzosemiquinonato (1-) π–radical form, which verifies the

noninnocent nature of o-aminothiophenolato ligands. Magnetic behaviour of these

complexes show antiferromagnetic exchange coupling between three S = 1 spins, giving

a singly non-degenerate S = 0 ground state and thus making these clusters very

exceptional examples of S = 1 spin-triangles having three equal J values.

Chapter 4

In this study the crystal structure properties as well as the electrochemical,

spectroscopic and magnetic behavior of [Ni(ddbt)] (5), [Co(Cp)2][Ni(ddbt)] (5b),

[Co(ddbt)] (6), [Co(Cp)2][Co(ddbt)] (6b) and [Zn(phbt)2] (7) have been fully

Chapter 8 159

characterized. As pointed out in the introduction, it has been verified by low temperature

crystallography of 5, 6, 5b and 6b that the metal ions in analogous tetra coordinated

cobalt and nickel complexes exist in different oxidation levels. Thus, in the neutral and

monoanionic nickel complexes 5 and 5b, the central nickel has a NiII (d8) electron

configuration, where the HOMO are predominantly ligand centered. On the other hand, in

the case of the neutral cobalt complex (6), the observed ligand bond lengths clearly

suggest a CoIII (d6) electron configuration. In the monoanion 6b, the ligand bond

distances indicate dianionic form of ligands leading to a spin triplet ground state for 6b.

The DFT calculations on the similar compounds suggested two possibilities, namely:

CoIII (d6), or CoII (d7) coordinated to a ligand radical, though the structural features of 6b

point toward CoIII (d6) configuration. The degeneracy of the ground state of 6b is lifted

by large positive zero field splitting of 36.67 cm-1, which has been measured

independently by magnetic moment measurement, variable-temperature and variable field

and far-infrared absorption.

The absorption spectra of the neutral and electrochemically-generated

species show several charge transfer bands. Intense LLCT bands occurring in the visible

region are a significant feature of the spectra of complexes containing two radical

ligands. Spectra of complexes containing only one radical ligand contain IVCT bands in

the near infrared region. The EPR parameters for 6 and 5b show that spin-orbit coupling

plays a role in the deviation of the g value from the free radical value. These radical

stabilized complexes have proven the non-innocent nature of the o-aminothiophenolate

ligands, thus disproving the proposed valence isomer structure reported in the literature

for the assignment of the oxidation level for ligands.

Chapter 5

We have shown in this chapter that oxidation states of higher than +3 for

the central chromium ion are not present in the tris-(o-benzene-dithiolato) [N(n-

Bu)4][Cr(tLSS)3] (8) and tris-(o-benzocatacholato) chromium [Cr(tLCat)3] (10)

[Co(Cp)2][Cr(tLCat)3] (10b) complexes. In contrast to earlier literature reports, we

Summary

160

have not found spectroscopic evidence for the occurrence of chromium(IV),

chromium(V) and chromium(VI). The electronic structures of the resulting complexes are

often complicated and were elucidated by a combination of electronic, EPR, X-ray


In the complex [N(n-Bu)4] [CrO(tLSS)2] (9), chromium was found in the

higher oxidation state of (+5) which was confirmed by the EPR parameters, and the

existence of the Cr=O bond was confirmed by infrared spectroscopy and X-ray

crystallography.

Chapter 6

In this chapter [M(tLSS)3]n (M = Mo, W; n = 0, 1) (12, 12b, 13, 13b)

complexes along with [Mo(tLNS)3] (11) have been studied and it has been found that the

oxidation state of +5 is present for the central metal ion for all these compounds. In

contrast to the previous literature reports viewing the neutral complexes as MVI (d0)

configuration, we have found that the neutral species are MV (d1), which undergo ligand

centered redox activities to produce corresponding monoanionic and monocation species

with an unchanged oxidation state of the metal ion. The electronic spectra of all

compounds contain characteristic ligand to metal charge transfer bands. The electronic

structures of these complexes were elucidated by a combination of electronic, EPR, X-ray


As compared to [Cr(tLSS)3]1- (8), the electronic spectra of monoanionic

compounds 11b, 12b and 13b are quite different. The X-ray structure analyses of these

compounds also show significant differences in bond distances for 8 than other

[M(tLSS)3]1- complexes. Thus, in contrast to previous suggestions considering Cr, Mo and

W as having a similar oxidation state in a similar ligand atmosphere, we conclude that the

metal oxidation states is different in the case of 8 than other [M(tLSS)3]1- complexes (M =

Mo, W).

Chapter 8 161

Chapter 7

The XAS studies on the neutral Mo and W complexes coordinated to tris-

o-dithiolene clearly showed the presence of dithiobezosemiquinonate (1-) radical and its

absence in the monoanionic Mo complex; in agreement with the results of the other

spectroscopic studies done on these complexes (chapter 6). Comparison of the

monoanionic species of Cr and Mo reveal that the electronic structures of these species

are different: in the first case dithiobezosemiquinonate (1-) radical ligand is present and

in second case it is not.

However, the situation is a little more complicated for the [Cr(LSS)3]1- (8),

[Cr(tLCat)3] (10) and [Cr(LCat)3]1- (10b) species. While the metal K-edge for 8 appears at

0.5 eV less than the reference CrIII compound, the metal K-edges of 10 and 10b appear

almost at the same position as compared to the reference CrIII. In contrast with this, the

electronic absorption spectra of electrochemically oxidized and reduced forms of 8 and

10 are correspondingly identical (chapter 5). Thus, while the metal K-edge data for the 8

points toward a CrII assignment, IR spectroscopy, X-ray crystallography and electronic

absorption spectroscopy (chapter 5) correlate best with that of a CrIII assignment. In the

case of 9, the metal is clearly more oxidized than 8, consistent with the +5 oxidation state

of the metal and the absence of a ligand radical.

Chapter 9 163

9.1 Synthetic procedures

The ligand 3,6-di-tert-butylcatacholate H2[LCat]1 and [MoO2(acac)2]2 were synthesized as

described in the literature. 2-Aminobenzenethiol; H2[LNS] is commercially available.

Ligand synthesis:

1) 2-mercapto-3,5-di-tert-butylaniline H2[tLNS]3

a) 3,5- di- tert-butylaniline (L1.1)

3,5-di-tert-butylbenzoic acid (5 g, 22 mmol) was dissolved in conc. H2SO4 (15 ml) and

CHCl3 (15 ml). At 45 °C, over a period of an hour, NaN3 (1.5 g, 23 mmol) was added and

the reaction mixture was then stirred for 5 hours. The CHCl3 was removed by evaporation

(rotary evaporator). The residue was cooled (0 °C) and ice water (150 ml) was added. The

precipitate was filtered and washed with water (100 ml). This precipitate of 3,5-di- tert-

butylanilinesulphate was dissolved in MeOH (25 ml) and KOH (5 g in 100 ml H2O) was

NH2COOH HN

SNH2

NH2

SH

(L1.1) (L1.2) H2[tLNS]

a b c

Chapter 9 Experimental

Experimental

164

added. The precipitate was filtered and washed with large amount of water. The product

was dried in air.

Yield: 4.3 g (98%)

Molecular weight: 205 g /mol

b) 5,7-di- tert-butyl-2-benzothiazolamine (L1.2)

3,5-di- tert-butylaniline (L1.1) (4.5 g, 22 mmol) and KSCN (3.9 g, 40 mmol) were

dissolved in conc. CH3COOH (40 ml). 1 ml of Br2 (3.1 g, 22 mmol) in acetic acid (10

ml) was added dropwise and the reaction mixture was stirred for 2 hours. The acetic acid

was removed by evaporation with water suction. The residue was suspended in MeOH

(75 ml) and made alkaline with KOH (4 g in 25 ml water). The product precipitated on

addition of H2O (100 ml). The product was filtered, washed with water and dried under

air.

Yield: 4.6 g (80.7 %)

Molecular weight: 262 g/mol

c) 2-mercapto-3,5-di- tert-butylaniline H2[tLNS]

5,7-di- tert-butyl-2-benzothiazolamine (L1.2) (4.5 g, 17 mmol) and KOH (30 g, 550

mmol) were dissolved in 2,3-butanediol (40 ml). This mixture was refluxed under an

argon atmosphere for 3 hours at 200 °C. To the hot reaction mixture acetic acid (50 ml)

and H2O (100 ml) were added and the solution was allowed to cool to room temperature.

The reaction mixture was extracted with Et2O (ca. 150 ml) and the solvent was removed

under reduced pressure. The yield was a yellow/brown oil, which is 2-mercapto-3,5-di-

tert-butyl-aniline. It has been used for the synthesis of complexes without further

purification.

Yield: 3.9 g (95.6%)


Chapter 9 165

Infrared spectrum:

2) 2-Phenylbenzothiazoline (Lph)4

2-Aminobenzenethiol (1.25 g, 10 mmol) was added to a solution of benzaldehyde (1.06 g,

10 mmol) in ethanol (20 ml) and stirred at ca. 70°C for 20 minutes. After cooling to room

temperature a yellowish product precipitated, which was collected by filtration.

Yield: 1.50 g (70 %)


NH2

SH S H

HN Ph

500100015002000250030003500

3476

2925

2591

1603

1459

1244

1054853

661

w aven u m b er (cm -1 )

rel.

Tran

smis

sion

Fig. 9.1: IR spectrum of 2-mercapto-3,5-di-tert-butylaniline H2[tLNS]

Experimental

166

Infrared spectrum:

3) 3,5-di-tert-butyl-1,2-benzenedithiol, H2[tLSS]5

a) 3,5-di- tert-butyl-2-nitrobenzoic acid (L3.1)

3,5 di-tert-butylbenzoic acid (10 g, 42.6mmol) was dissolved in 70 ml of conc. H2SO4

and cooled in an ice bath. To the solution a mixture of 14 ml of conc. HNO3, NaNO2 (120

COOHCOOH

S

S

NO2

COOH

NH2

H

BF4 SH

SH

a b

c d

Fig. 9.2: IR spectrum of 2-Phenylbenzothiazoline (Lph)

500100015002000250030003500

3382

3063

1584

1471

1255

1027

697

rel.

Tran

smis

ion

w avenum ber (cm -1)

Chapter 9 167

mg, 17.4 mmol) and 14 ml conc. H2SO4 were added dropwise with constant stirring. The

temperature was kept below 0 oC during the addition. Stirring was continued below 0 oC

for 15 minutes and afterwards at room temperature for 30 minutes. Then the mixture was

poured into ice and the precipitate that formed was collected by filtration, washed with

water and air-dried.

Yield: 11.8 g (98.6%)

Molecular weight: 280.34 g/mol

b) 3,5-di- tert-butylanthranilic acid (L3.2)

Dry 3,5-di- tert-butyl, 2-nitrobenzoic acid (L3.1) (11.8 g, 42 mmol) was dissolved in 100

ml methanol. Pd/C catalyst (1.2 g) and HCOONH4 (9 g, 142 mmol) were added under an

argon atmosphere. The reaction mixture was stirred for 4 hrs and then the solution was

filtered through celite. The filtrate was put under rotary evaporator and then 10 ml of

water was added, the product was extracted with ether. The ether layer was concentrated

giving a yellow crystalline compound.

Yield: 6.5g. (64%)


c) 3,5-di-tert-butylanthranilic acid (L3.2) (6.5 g, 26 mmol) was dissolved in a mixture of

THF (2ml) dioxane (10ml) and added dropwise to a refluxing solution of 1,2

dichloroethane (70 ml), distilled CS2 (13 ml), isoamylalcohol (4.6 ml), and

isopentylnitrite (4 ml) at 40°C. The solution was refluxed from 40-80°C for 0.5 hour. The

solvent was removed under vacuum. The resulting yellowish brown oil was dissolved in a

minimum amount of ether, treated with charcoal and filtered. The filtrate was treated with

HBF4 (7.6 ml 50% in ether, 42 mmol) solution at -30°C in absence of light. A white

precipitate of compound L3.3 formed after 2-3 hours which was filtered off, washed with

ether, stored in the dark and was used immediately.

Experimental

168

d) 3,5-di-tert-butyl-1,2-benzenedithiol, H2[tLSS]

Ammonia (250 ml) was liquefied at –78°C. To it compound L3.3 was added while the

ammonia was warming up to room temperature. Sodium pieces were added until the blue

color of the solution persisted. The solution was kept stirring under argon until the

ammonia is evaporated. The residue was treated with ice-cold water and conc. HCl, and

the pH of the solution was adjusted to 2. This solution was extracted with diethyl ether

and the ether was evaporated under vacuum. A yellowish oily residue was obtained as the

final product.

Yield: 2.6 g (40 %)


Infrared spectrum:

Fig. 9.3: IR spectrum of 3,5-di-tert-butyl-1,2-benzenedithiol

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

2 9 6 3

2 5 2 6

1 3 9 5

1 2 6 01 0 4 4 7 9 9

re

l. Tr

ansm

issi

on

w a v e n u m b e r (c m -1 )

Chapter 9 169

[As(Ph)4] [Co(LNS)2] (1)

Potassium metal (600 mg, 15 mmol) was carefully dissolved in absolute ethanol (25 ml).

Under argon 2-aminobenzenethiol (920 mg, 7 mmol) was added, followed by the addition

of a solution of CoCl2.6H2O (0.80 g, 3.5 mmol) in ethanol (5 ml) and the [As(Ph)4]Cl

(1.46 g, 3.5 mmol). The reaction mixture was stirred in air for 15 minutes. The dark blue

precipitate was filtered off and washed with absolute ethanol and dry diethyl ether.

Yield: 1.27 g (50.19 %)

Molecular weight: 688.15

Elemental analysis:

Infrared spectrum:

C36 H30 As Co N2 S2 % C % H % N

Calculated 62.79 4.36 3.94

Found 62.55 4.60 4.06

Fig. 9.4: IR spectrum of [As(Ph)4] [Co(LNS)2](1)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

10 0 8

4 8 9

1 0 7912 9 9

16 3 3

74 51 4 41

rel.

Tran

smis

sion


Experimental

170

[N(n-Bu)4] [Co(LNS)2] (2)

Potassium metal (600 mg, 15 mmol) was dissolved in absolute ethanol (25 ml). Under

argon 2-aminobenzenethiol (920 mg, 7 mmol) was added, followed by the addition of a

solution of CoCl2.6H2O (0.80 g, 3.5 mmol) in absolute ethanol (5 ml) and [N(n-Bu)4]Br

(1.12 g, 3.5mmol). The reaction mixture was stirred in air for 15 minutes. The dark blue

precipitate was filtered off and washed with absolute ethanol and dry diethyl ether.

Yield: 2.1g (52.15 %)

Molecular weight: 547.73

Elemental analysis:

Infrared spectrum:

C28 H46 Co N3 S2 % C % H % N % Co

Calculated 61.39 8.46 7.67 10.75

Found 61.26 8.72 7.74 10.65

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

rel.

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sion

W a v e n u m b e r (c m -1)

1 46 7

7 52

1 12 1

15 81

3 03 932 38

Fig. 9.5: IR spectrum of [N(n-Bu)4][Co(LNS)2] (2)

Chapter 9 171

Na[Cr(tLNS)3(OEt)3(µ-OMe)4(OHEt)4] (3)

Na (46 mg, 2mmol) was dissolved in distilled MeOH (25ml) under argon. To this

solution, the ligand 2-mercapto-3,5-di- tert-butylaniline (237 mg, 1 mmol) was added and

the mixture was stirred for 10 minutes under argon. Vacuum dried CrIICl2 ( 625 mg, 0.5

mmol ) was added and stirring continued for 1 hour. A flow of air was passed through

this reaction mixture for 2 minutes. The color of the reaction changed from green to

brown. The reaction mixture was filtered off and the solvent was removed under vacuum.

The brown compound was redissolved in EtOH.. Dark green crystals of the product

appeared after the slow evaporation of the solvent.

Yield: 1.08 g (50 %)


Elemental analysis:

Infrared spectrum:

C58 H105 Cr3 N3 Na O10 S3 % C % H % N

Calculated 54.31 8.48 3.27

Found 54.18 8.40 3.26

Fig. 9.6: IR spectrum of Na [Cr(tLNS)3(OEt)3(µ-OMe)4(OHEt)4]

5 0 01 00 015 0 02 0 0 02 5 003 0 003 50 040 0 0

3439

2962

1458 1079

703

526

rel.

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w aven u m b er (cm -1)

3283

2787

Experimental

172

Na[Cr3(tLNS)3(OMe)3(µ-OMe)4(OHMe)3] (4a)

Na[Cr3(tLNS)3(OMe)3(µ-OMe)4(OH2)3] (4b)

Na (46 mg, 2 mmol) was dissolved in distilled MeOH (25 ml) under argon. To this

solution, the ligand 2-mercapto-3,5-di- tert-butyl-aniline (237 mg, 1 mmol) was added

and the mixture was stirred for 10 minutes under argon. Vacuum dried CrIICl2 (625 mg,

0.5 mmol) was added and the stirring was continued for 1 hour. A flow of air was then

passed through the reaction mixture for 2 minutes. The reaction mixture was filtered off

and the solvent was removed under vacuum. The brown compound was redissolved in

MeOH. Dark brown crystals of product appeared after slow evaporation of the solvent.

Yield: 1.00 g (50 %)


Elemental analysis:

Infrared spectrum:

C101 H186 Cr6 N6 Na2 O20 S6 % C % H % N % Cr

Calculated 51.47 7.89 3.57 13.25

Found 51.28 7.76 3.47 13.15

500100015002000250030003500

rel.

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w aven u m b er (cm -1 )

2966

1026

1632

528

797

3444

Fig. 9.7: IR spectrum of 4a and 4b

Chapter 9 173

[Ni(ddbt)] (5)

[Ni(phbt)2] (phbt = bis-(2-phenylmethyleneamino)benzenethiolato) was synthesized as

described in the literature.5 A suspension of [Ni(phbt)2] (960 mg, 20 mmol) in toluene (30

ml) was heated for 20 minutes and then cooled to room temperature. After filtering the

solvent was removed on the rotary evaporator. The black crystalline product was

dissolved in CH2Cl2 (ca. 15 ml) and filtered. The filtrate was purified by chromatography

on silica gel (230-400 mesh) column eluting with CH2Cl2. A dark violet crystalline

[Ni(ddbt)], (ddbt = bis-2,2'-(1,2-diphenylethylenediimine)benzenethiolato) was obtained

by evaporation of the solvent.

Yield: 540 mg (56%)


Elemental analysis:

Infrared spectrum:

C26 H20 N2 Ni S2 % C % H % N

Calculated 64.61 4.17 5.80

Found 63.81 3.91 5.57

Fig. 9.8: IR spectrum of [Ni(ddbt)] (5)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

11 43

74 5

1 0511 31 2

14 23

rel.

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w a ve n u m b e r (c m -1 )

1 5 9 7

Experimental

174

[Co(Cp)2][Ni(ddbt)] (5b)

To a deep violet solution of [Ni(ddbt)] (242 mg, 0.5 mmol) in CH2Cl2 (25 ml)

cobaltocene (95 mg, 0.5 mmol) was added under argon atmosphere. The solution was

then stirred at room temperature for 3 hours; a green precipitate was isolated by filtration

and washed with diethyl ether. Crystals suitable for X-ray crystal structure analysis were

grown by the slow evaporation of mixture of MeCN and MeOH.

Yield: 230 mg (70%)


Elemental analysis:

Infrared spectrum:

C36H30Co N2 Ni S2 % C % H % N

Calculated 64.30 4.49 4.16

Found 63.88 4.51 5.14

Fig. 9.9: IR spectrum of [Co(Cp)2][Ni(ddbt)] (5b)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1413

738

1306

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W a ven u m b er (c m -1 )

Chapter 9 175

[Co(ddbt)] (6)

[Co(phbt)2] (phbt = bis-(2-phenylmethyleneamino)benzenethiolato) was synthesized as

described in the literature.5 A suspension of [Co(phbt)2] (215 mg, 0.45 mmol) in toluene

(30 ml) was heated for 30 minutes. The solution turned dark greenish blue. The solution

was filtered and the solvent was removed on the rotary evaporator. The dark blue solid

was dissolved in CH2Cl2 and filtered. Then the product was purified by chromatography

on silica gel (230-400 mesh) column with CH2Cl2. The complex was eluted as a first blue

band. Removal of CH2Cl2 under reduced pressure yielded the metallic red-purple

powdery product of [Co(ddbt)], (ddbt = bis-2,2'-(1,2-

diphenylethylenediimine)benzenethiolato). X-ray quality crystals were grown by slow

evaporation of mixture of CH2Cl2 and MeOH.

Yield: 110 mg (50%)


Elemental analysis:

Infrared spectrum:

C26 H20Co N2 S2 %C %H %N %Co

Calculated 64.58 4.17 5.80 12.25

Found 64.38 4.06 5.59 12.20

Fig. 9.10: IR spectrum of [Co(ddbt)](6)

4 0 08 0 01 2 0 01 6 0 02 0 0 02 4 0 02 8 0 0

1 0 9 75 3 6

7 4 7

1 6 3 11 4 2 6

1 2 6 1

1 0 3 7

rel.

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W a v e n u m b e r (c m -1 )

Experimental

176

[Co(Cp)2]( [Co(ddbt)] (6b)

To a deep blue solution of [Co(ddbt)] (242 mg, 0.5 mmol) in CH2Cl2 (25 ml) under an

argon atmosphere was added cobaltocene (95 mg, 0.5 mmol). After the solution was

stirred at room temperature for 1 hour, a violet precipitate formed, which was isolated by

filtration. Single crystals suitable for X-ray crystal structure analysis were grown by the

solvent evaporation from a mixture of MeCN and MeOH.

Yield: 260 mg (80%)


Elemental analysis:

Infrared spectrum:

C36 H30 Co2 N2 S2 %C %H %N

Calculated 64.29 4.46 4.17

Found 64.18 4.42 4.16

Fig.9.11: IR spectrum of [Co(ddbt)][Co(Cp)2](6b)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1 5 6 2

1 0 3 7

7 4 51 2 9 9

1 4 4 8

rel.

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Chapter 9 177

[Zn(phbt)2] (7)

Zinc acetate (1.09 g, 5 mmol) was added to a refluxing solution of 2-

phenylbezothiazoline (2.13 g, 10 mmol) in MeOH (50ml). After stirring for 0.5 hour, an

orange precipitate was filtered off and washed with MeOH and diethyl ether. X-ray

quality crystals of [Zn(phbt)2] (phbt = bis-(2-phenylmethyleneamino)benzenethiolato)

were obtained by re-dissolving this complex in a mixture of dichloromethane and

methanol and slow evaporation of the solvents.

Yield: 1.71g (70%)


Elemental analysis:

Infrared spectrum:

C26 H20 N2 S2 Zn % C % H % N

Calculated 63.68 4.08 5.71

Found 63.74 4.15 5.78

Fig. 9.12: IR spectrum of [Zn(phbt)] (7)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

2 9 6 4

1 5 6 1

1 4 3 8

1 0 8 1

7 4 5

rel.

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Experimental

178

[N(n-Bu)4][Cr(tLSS)3] (8)

To a solution of the ligand 3,5-di-tert-butyl-1,2-benzenedithiol, H2[tLSS] (0.126 g, 0.5

mmol) in 25 ml MeCN, CrCl3(THF)3 (46 mg, 0.125 mmol) was added followed by the

addition of Et3N (0.3 ml, 3mmol) under argon. After one hour, air was passed through the

solution for 10 minutes. As a consequence color of the reaction mixture turned to violet

from green. [N(n-Bu)4]Br was added and the reaction mixture was stirred for another one

hour. Violet crystals of [N(n-Bu)4] [Cr(tLSS)3] were obtained from the solution at low

temperature (-20 °C) which were separated by filtration.

Yield: 71 mg (55%)


Elemental analysis:

Infrared spectrum:

C58 H96 Cr N S6 %C %H %S %Cr

Calculated 66.96 9.20 18.29 4.94

Found 65.96 9.10 18.33 4.87

Fig.9.13: IR spectrum of [N(n-Bu)4][Cr(tLSS)3] (8)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

8 6 3

1 0 3 4

1 3 8 41 4 7 9

1 1 1 71 6 3 7

2 9 6 6


rel.

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Chapter 9 179

[As(Ph)4] [CrO(tLSS)2] (9)

To a solution of the ligand 3,5-di-tert-butyl-1,2-benzenedithiol (126 mg, 0.5 mmol) in 25

ml MeCN, CrCl3(THF)3 (93 mg, 0.25 mmol) was added followed by the addition of Et3N

(0.3 ml, 3mmol) under argon. After one hour stirring, air was passed through reaction

mixture for 1 hour. During this time color of the reaction mixture changed from green to

red-brown. Subsequently [As(Ph)4]Br was added and reaction mixture stirred for another

one hour. The solvent was evaporated by slow evaporation. During this time brown

crystalline [As(Ph)4] [CrO(LSS)2] was obtained.

Yield: 85mg (60%)


Elemental analysis:

Infrared spectrum:

C56 H66AsCrN2OS4 %C %H %S % Cr

Calculated 64.78 6.41 12.35 5.00

Found 64.01 5.82 12.21 4.89

Fig. 9.14: IR spectrum of [As(Ph)4] [CrO(tLSS)2] (9)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1 3 8 4 9 6 6

1 6 3 7

7 3 9

2 9 5 3


rel.

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Experimental

180

[Cr(tLcat)3] (10)

To a solution of the ligand 3,6-di-tert-butyl-catacholate (110 mg, 0.5 mmol) in 25 ml

MeCN, CrCl3(THF)3 (62 mg, 0.166 mmol) was added, followed by the addition of Et3N

(0.2 ml, 2mmol). Reaction mixture was refluxed for 1 hour in air. In the course of

reaction the color of the reaction mixture turned to red-purple. The reaction mixture was

kept for slow evaporation through which crystalline complex [Cr(tLCat)3] was obtained.

Yield: 106 mg (90%)


Elemental analysis:

Infrared spectrum:

C42H60 CrO6 %C %H %N

Calculated 70.75 8.48 7.29

Found 70.65 8.48 7.37

Fig. 9.15: IR spectrum of [Cr(tLcat)3] (10)

50010001500200025003000

2947

1555

1413

646823

966

re

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issi

on

w avenum ber (cm -1)

Chapter 9 181

[Co(Cp)2][Cr(tLcat)3] (10b)

To a deep violet solution of [Cr(tLcat)3] (178 mg, 0.25 mmol) in CH2Cl2 (25 ml) under

argon atmosphere was added cobaltocene (48 mg, 0.25 mmol). After the solution was

stirred at room temperature for 3 hours, a blue precipitate formed was isolated by

filtration and washed with diethyl ether. Crystals suitable for X-ray crystal structure

analysis were grown by the evaporation of mixture of MeCN and MeOH.

Yield: 185 mg (85%)


Elemental analysis:

Infrared spectrum:

C52H70 CrO6Co % C % H % O % Cr

Calculated 69.24 7.82 10.64 5.76

Found 69.07 7.14 10.45 5.73

Fig. 9.16: IR spectrum of [Co(Cp)2] [Cr(tLcat)3] (10b)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1 5 5 3

1 6 5 2

1 2 6 27 9 9

1 0 9 7

2 9 5 9


rel.T

rans

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Experimental

182

[Mo(tLNS)3] (11)

To a solution of the ligand 2-mercapto-3,5-di-tert-butylaniline (365 mg, 1.5 mmol) in 15

ml MeOH, a filtered solution of [MoO2(acac)2] (164 mg, 0.5 mmol) in 10 ml of MeOH

was added . Color of the reaction mixture immediately turned to dark green. After one

hour, green precipitate of [Mo(tLNS)3] was filtered and recrystallized from the mixture of

dichloromethane and diethyl ether.

Yield: 320 mg (80%)

Molecular weight: 801g/mol

Elemental analysis:

Infrared spectrum:

C46 H71 Mo N3 O S3 % C % H % N % Mo

Calculated 62.89 7.92 5.23 11.96

Found 62.75 7.88 5.17 12.08

Fig. 9.17: IR spectrum of [Mo(tLNS)3] (11)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1 3 5 6

1 4 5 5 1 1 0 01 0 1 5 8 0 2

1 6 3 3

2 9 6 1


rel.

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Chapter 9 183

[Mo(tLSS)3] (12)

To a solution of the ligand 3,5-di-tert-butyl-1,2-benzenedithiol (127 mg, 0.5 mmol) in 15

ml MeOH, a filtered solution of [MoO2(acac)2] (54 mg, 0.17 mmol) in 10 ml of MeOH

was added . The color of the reaction mixture immediately turned to dark green. After

one hour, green precipitate of [Mo(tLSS)3] was filtered and recrystallized from the mixture

of MeCN/diethyl ether.

Yield: 119 mg (85%)


Elemental analysis:

Infrared spectrum:

C42 H60 Mo S6 % C % H % S % Mo

Calculated 59.12 7.08 22.54 11.24

Found 58.94 6.93 21.54 10.86

Fig. 9.17: IR spectrum of [Mo(tLSS)3] (12)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

8 7 1

1 3 6 3

1 5 9 6

1 6 6 4 8 6 3

1 0 3 4

1 1 1 7

2 9 6 6

re

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Experimental

184

[N(n-Bu)4][Mo(tLSS)3] (12b)

To 50 ml of a CH2Cl2 solution of [Mo(tLss)3] (85 mg, 1mmol) was added N(n-Bu)4SH

(28 mg, 1 mmol). The color immediately changed from green to olive green. The air

sensitive mixture was concentrated under vacuum and resultant solid was recrystallized

from mixture of DCM and MeCN.

Yield: - 94 mg (87%)


Elemental analysis:

Infrared spectrum:

C6 H99 Mo N2 S6 % C % H % S % Mo

Calculated 59.12 7.08 22.54 11.24

Found 58.94 6.93 21.54 10.86

Fig. 9.18: IR spectrum of [N(n-Bu)4] [Mo(tLSS)3] (12b)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1 0 1 41 1 3 7

8 7 7

1 3 9 01 4 7 9

1 6 4 4

2 9 7 3

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Chapter 9 185

[W(tLSS)3] (13)

Tungsten hexachoride (56 mg, 0.13 mmol) was dissolved in 20 ml of CCl4 and filtered

under argon. The filtrate was then added to a solution of ligand 3,5-di-tert-butyl-1,2-

benzenedithiol (100 mg, 0.39 mmol) dissolved in about 10 ml of CCl4. As a result, a deep

blue-green color appeared to the reaction mixture. This solution was refluxed under argon

for 3 hr. and allowed to cool to room temp. The solution was filtered and filtrate was

concentrated. The residue was washed with n-pentane and vacuum dried to give a blue-

green powder. The recrystallization was done in the mixture of EtOH and diethyl ether.

Yield: 92 mg (70%)


Elemental analysis:

C42 H60 S6 W % C % H % S %W

Calculated 53.60 6.42 20.43 19.53

Found 53.46 6.53 20.38 19.67

Infrared spectrum:

Fig. 9.19: IR spectrum of [W(tLSS)3] (13)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

1 3 9 7 1 2 6 0

1 6 6 4

8 0 11 0 1 4

1 1 1 7

2 9 5 2

re

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Experimental

186

[N(n-Bu)4] [W(tLSS)3] (13b)

To a solution of [W(tLss)3] (96 mg, 1 mmol) in 50 ml CH2Cl2, was added N(n-Bu)4SH

(28 mg, 1 mmol) under anaerobic conditions. The color of the reaction mixture

immediately changed from green to olive green. The air sensitive mixture was

concentrated under vacuum and resulting solid compound was recrystallized from

mixture of DCM and MeCN.

Yield: 102 mg (85%)


Elemental analysis:

Infrared spectrum:

C58H96NS6W % C % H % S %W

Calculated 58.85 8.17 16.25 15.37

Found 58.91 8.23 16.47 15.55

Fig. 9.20: IR spectrum of [N(n-Bu)4] [W(tLSS)3] (13b)

5 0 01 0 0 01 5 0 02 0 0 02 5 0 03 0 0 0

2 9 6 6

1 4 7 31 6 3 7

8 0 1

1 0 2 81 1 1 0rel.

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Chapter 9 187

9.2 Methods and Equipment

Unless otherwise specified, all measurements were performed at the Max

Planck Institut für Bioanorganische Chemie, Mülheim an der Ruhr, Germany.

Commercial grade chemicals were used for the synthetic purposes and solvents were

distilled and dried before use.

Crystallography

Frau H. Schucht collected x-ray diffraction data, on a Siemens SMART

CCD diffractometer, or on an Enraf-Nonius Kappa CCD diffractometer (with or without

rotating anode). Graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) was

employed. Data were collected by the 2θ-ω scan method. The data were corrected for

absorption and Lorenz polarization effects. The structures were solved by Dr. T.

Weyhermüller, by direct methods and subsequent Fourier-difference techniques, and

refined anisotropically by full-matrix least squares on F2 with the program SHELXTL

PLUS. Hydrogen atoms were included at calculated positions with U < 0.08 Å2 in the last

cycle of refinement.

Electrochemistry

Cyclic voltammograms and square wave voltammograms were recorded

by using a EG&G potentiostat/galvanostat 273 A. A three-electrode cell was employed

with a glassy carbon working electrode, a platinum-wire auxiliary electrode and a

Ag/AgNO3 reference electrode (0.01 M AgNO3 in MeCN).

UV-vis-assisted controlled-potential coulometries were performed with

the same potentiostat, in a thermostatic 5 mm quartz cell equipped with a Pt grid as work

electrode, a Pt brush separated from the work electrode compartment by a Vycor frit as

counter-electrode, and a Ag/AgNO3 electrode (0.01 M, MeCN) as reference.

IR-assisted controlled-potential coulometries were performed, with the same potentiostat,

in an Optically Transparent Thin Layer Electrode (OTTLE) cell, built by H. Schmidt and

Dr. E. Bothe. The OTTLE cell consists of glassy carbon walls used as counter-electrode,

with CaF2 windows. In-between is a 160 µm PEEK spacer, in which are embedded a Pt

grid used as working electrode, and a silver wire used as pseudo-reference electrode.

Experimental

188

Elemental Analysis

Elemental analyses were performed by the “Microanalytisches Labor H.

Kolbe”, in Mülheim an der Ruhr, Germany.

EPR Spectroscopy

First derivative X-band EPR spectra of frozen solution samples were

recorded on a Bruker ESP 300 equipped with a Bruker ER 041 XK-D microwave bridge

and a Oxford Instruments 910 EPR-cryostat. The simulation of the spectra was performed

with help of the programs “ESIM/GFIT” from Dr. E. Bill and “EPR” from Dr. F. Neese.

Far-Infrared Spectroscopy

The measurements were done by the group of Dr Joris van Slageren in

Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany. The

measurements were performed on a Bruker IFS113v spectrometer equipped with a

mercury lamp as a light source, a 50 micron mylar beamsplitter, an Infrared Labs pumped

Si bolometer and a 5 mm aperture. The sample was put into an Oxford Instruments

Spectromag 4000 8 T split coil magnetic cryostats with specially enlarged mylar

windows. The spectra (typically 32 scans) were recorded on a 1 cm diameter pressed

powder pellet of the compound (160 mg) at various temperatures from 4.2 to 150 K and

magnetic fields from 0 to 7 T.

Infrared Spectroscopy

The infrared spectra were measured on a ‘Perkin-Elmer FT-IR-

Spectrophotometer 2000.’ Powder IR spectra were measured in KBr pellets with a

spectral resolution of 2 cm-1. Solution spectra were measured between NaCl windows

with different path-length spacers, or in an OTTLE cell with CaF2 windows.

Magnetic Susceptibility Measurements

The measurements of the temperature or field dependent magnetization of

the samples were performed in the range 2 to 400 K at 1, 4 or 7 T on a Quantum Design

SQUID Magnetometer. The samples were encapsulated in gelatine capsules and the

Chapter 9 189

response function was measured four times for each given temperature, yielding a total of

32 measured points. The resulting volume magnetization from the samples had its

diamagnetic contribution compensated and was recalculated as volume susceptibility.

Diamagnetic contributions were estimated for each compound with the help of

Pascal’sconstants. The experimental results were fitted with the programme JULIUS

calculating through full matrix diagonalization of the Spin-Hamiltonian.

Mass Spectrometry

All mass spectra were recorded by the group of Dr. W. Schrader at the

Max-Planck-Institut Für Kohlenforschung, Mülheim an der Ruhr, Germany.

Mass spectra in the electron impact mode (EI; 70eV) were recorded on a

Finnigan MAT 8200 mass spectrometer. Electron Spray Interface (ESI) mass spectra

were recorded on either a Finnigan MAT 95 or a HP 5989 mass spectrometer.

UV-vis Spectroscopy

UV-Vis spectra were recorded on a HP 8452A diode array

spectrophotometer, or on a PE Lambda 19 spectrophotometer. Near-IR measurements

were performed on a Lambda 19 spectrophotometer, using Hellma Quartz Suprasil 3000

cells. The program “PeakFit-4”was used to deconvolute the spectra in Gaussian-shaped

lines. The oscillator strengths fosc were calculated by

X-ray Absorption Spectroscopy

All data were measured at the Stanford Synchrotron Radiation Laboratory

under ring conditions of 3.0 GeV and 60-100 mA. All S K-edge data were measured

using the 54-pole wiggler beam line 6-2 in high magnetic field mode of 10 kG with a Ni-

coated harmonic rejection mirror and a fully tuned Si(111) double crystal

monochromator. Details of the optimization of this setup for low-energy studies have

Experimental

190

been described previously.6 Data were measured at room temperature by fluorescence,

using a Lytle detector. To check for reproducibility, 2-3 scans were measured for each

sample. The energy was calibrated from S K-edge spectra of Na2S2O3·5H2O, run at

intervals between sample scans. The maximum of the first pre-edge feature in the

spectrum was fixed at 2472.02 eV. A step size of 0.08 eV was used over the edge region.

Data were averaged, and a smooth background was removed from all spectra by fitting a

polynomial to the pre-edge region and subtracting this polynomial from the entire

spectrum. Normalization of the data was accomplished by fitting a flattened polynomial

or straight line to the post-edge region (2490-2740 eV) and normalizing the post-edge to

1.0. For samples containing Mo, the Mo L-edge data were collected by extending the

region file to 2810 eV and fine stepping over the Mo L3 and L2-edge regions.

Cr K-edge XAS data were measured on unfocused bend magnet beam line

2-3 or focused 16-pole wiggler beam line 9-3. A Si(220) monochromator was utilized for

energy selection. The monochromator was detuned 50% (for beam line 2-3) to minimize

higher harmonic components in the X-ray beam (for beam line 9-3 a harmonic rejection

mirror was present). All samples were prepared as solids in boron nitride, pressed into a

pellet and sealed between 38 µm Kapton tape windows in a 1 mm aluminum spacer. The

samples were maintained at 10 K during data collection using an Oxford Instruments

CF1208 continuous flow liquid helium cryostat. Data were measured in transmission

mode. Internal energy calibrations were performed by simultaneous measurement of a Cr

reference foil placed between a second and third ionization chamber. The first inflection

point was assigned to 5989.0 eV. Data represent three to five scan averages and were

processed by fitting a second order polynomial to the pre-edge region and subtracting this

background from the entire spectrum. A three-region cubic spline was used to model the

smooth background above the edge. The data were normalized by subtracting the spline

and normalizing the post-edge 1.0.

Chapter 9 191

9.3 References

1) Belostotskaya, I. S.; Komissarova, N. L.; Dzhuaryan, E. V.; Ershov, V. V. Isv.

Akad. Nauk SSSR 1984, 1610.

2) Kawamoto T., Kuma H., and Kushi Y., Bull. Chem. Soc. Jpn., 1997, 1599.

3) Sellmann, D.; emig, S.; Heinmann, F. W.; Knoch, F. Z. Naturforsch. 1998, 53b,

1461.

4) Chikashita, H.; Miyazaki, M.; Itoh, K. J. Chem. Soc. Perkin Trans. 1, 1987, 699.

5) (a) Sellmann, D.; Freyberger, G.; Eberlein, R.; Böhlen, E.; Huttner, G.; Zsolnai,

L. J. Organomet. Chem. 1987, 323, 21. (b) Sellmann, D.; Käppler, O. Z. Natur-

forsch. 1987, 42b, 1291

6) Hedman, B.; Frank, P.; Gheller, S. F.; Roe, A. L.; Newton, W. E.; Hodgson, K. O.

J. Am. Chem. Soc. 1988, 110, 3798.

Appendices

193

Appendices 1. Magnetochemical data 2. Crystallographic data

3. Curriculum Vitae

Appendices

194

1) Magnetochemical data

[As(Ph)4] [Co(LNS)2] (1)

MW = 688.15 g/mol, χdia = -364.0 x 10-6 cm3 mol-1

No T(K) µexp µcalc

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

1.967 5.121 10.245 15.067 20.009 30 40.003 50.026 60.07 70.109 80.15 90.148 100.23 110.25 120.28 130.32 140.34 150.37 160.39 170.44 180.41 190.4 200.41 210.58 220.41 230.39 240.4 250.4 260.4 270.41 280.39 290.38

0.79047 1.25546 1.746 2.07378 2.3205 2.63495 2.80582 2.90374 2.96214 2.99946 3.02519 3.02987 3.05505 3.06359 3.06974 3.07378 3.07597 3.07886 3.07944 3.0806 3.08109 3.08119 3.08164 3.08151 3.08108 3.08085 3.07958 3.08008 3.07894 3.07836 3.07859 3.07905

0.76411 1.22064 1.72858 2.05117 2.32407 2.66171 2.83012 2.91945 2.97082 3.0025 3.02325 3.03744 3.04769 3.05519 3.06089 3.06531 3.0688 3.07161 3.0739 3.07579 3.07737 3.0787 3.07983 3.08082 3.08165 3.08238 3.08303 3.08359 3.08409 3.08454 3.08494 3.0853

Appendices

195

Na [Cr3(tLNS)3(OEt)3(µ-OMe)4(OHEt)4] (3)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

1.957 5.08 10.137 15.041 20.004 30.001 40.001 50.007 60.021 70.06 80.076 90.107 100.13 110.14 120.13 130.16 140.18 150.19 160.14 170.22 180.22 190.24 200.24 210.24 220.25 230.25 240.27 250.25 260.27 270.25 280.26 290.28

2.03631 2.70312 3.31341 3.68513 3.93726 4.24369 4.41975 4.53109 4.60588 4.66161 4.70327 4.73634 4.76008 4.77903 4.79362 4.80516 4.81401 4.8132 4.82836 4.83558 4.83909 4.84172 4.84469 4.84499 4.84844 4.84883 4.84872 4.84994 4.84957 4.84879 4.84775 4.84723

1.51737 2.67159 3.37342 3.76056 4.00655 4.28975 4.44363 4.53941 4.60453 4.65168 4.68721 4.71502 4.73733 4.75561 4.77085 4.78382 4.79494 4.80459 4.81298 4.8205 4.82713 4.83308 4.8384 4.84325 4.84766 4.85168 4.85537 4.85875 4.86189 4.86479 4.86748 4.86999

Appendices

196

[Co(Cp)2] [Ni(ddbt)](5b)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

1.966 5.182 10.084 15.013 20.004 30.002 40.001 50.008 60.038 70.049 80.048 90.096 100.1 110.13 120.15 130.16 140.07 150.18 160.19 170.2 180.2 190.23 200.23 210.23 220.24 230.23 240.24 250.24 260.26 270.25 280.26 290.08

1.492 1.63908 1.68302 1.69637 1.70455 1.71098 1.71452 1.7181 1.72107 1.72196 1.72176 1.7213 1.72156 1.72187 1.72244 1.72241 1.72251 1.72282 1.72326 1.72344 1.72383 1.72419 1.72438 1.7249 1.72503 1.72582 1.72547 1.72577 1.72728 1.7298 1.72876 1.73107

1.49762 1.63318 1.67827 1.69442 1.70276 1.71118 1.71542 1.71797 1.71968 1.72089 1.72181 1.72252 1.72309 1.72355 1.72394 1.72427 1.72455 1.72479 1.72501 1.7252 1.72537 1.72552 1.72565 1.72577 1.72588 1.72599 1.72608 1.72616 1.72624 1.72631 1.72638 1.72644

Appendices

197

[Co(Cp)2] [Co(ddbt)] (6b)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

1.95 5.08 10 15.04 20 30 40 50 60.04 70.06 80.08 90.08 100.1 110.13 120.1 130.17 140.18 150.18 160.2 170.21 180.23 190.24 200.25 210.23 220.26 230.15 240.26 250.25 260.26 270.25 280.25 290.24

0.79212 1.26434 1.75559 2.11387 2.36558 2.66535 2.81447 2.89294 2.93992 2.96888 2.9906 3.00535 3.01555 3.02508 3.03211 3.03864 3.04421 3.04927 3.05542 3.06018 3.06535 3.06953 3.07518 3.07872 3.08274 3.08747 3.09259 3.09573 3.09954 3.10609 3.10804 3.11332

0.79010 1.26345 1.75523 2.11377 2.36543 2.66531 2.81444 2.89292 2.93989 2.96881 2.99004 3.00514 3.01521 3.02502 3.03207 3.03864 3.04421 3.04927 3.05542 3.06007 3.06425 3.06953 3.07518 3.07872 3.08274 3.08747 3.09257 3.09561 3.09823 3.10586 3.10792 3.11237

Appendices

198

[N(n-Bu)4] [Cr(tLSS)3] (8)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1.921 5.172 9.996 15.013 20.005 30.003 39.999 50.007 60.034 70.057 80.047 90.087 100.12 110.13 120.17 130.17 140.18 150.19 160.14 170.22 180.23 190.24 200.24 210.24 220.25 230.16 240.26 250.26 260.27 270.26 280.26

1.16357 1.55078 1.63885 1.6578 1.66901 1.68636 1.68862 1.71254 1.71898 1.72532 1.73132 1.73605 1.73932 1.74211 1.7438 1.74501 1.74563 1.74617 1.74639 1.74693 1.74647 1.74595 1.74588 1.74449 1.74352 1.74422 1.74475 1.74644 1.75079 1.6997 1.73588

1.26441 1.55078 1.63828 1.67313 1.69123 1.70992 1.71948 1.72529 1.7292 1.732 1.73411 1.73575 1.73708 1.73816 1.73906 1.73982 1.74048 1.74105 1.74154 1.74198 1.74237 1.74272 1.74304 1.74332 1.74359 1.74382 1.74404 1.74424 1.74442 1.74459 1.74475

Appendices

199

[N(n-Bu)4] [CrO(tLSS)2] (9)

MW = 572 g/mol, χdia = -350.0 x 10-6 cm3 mol-1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1.998 4.979 10.04 15.039 20.006 30.001 39.999 50.003 60.039 70.044 80.083 90.077 100.13 110.13 120.1 130.17 140.18 150.19 160.19 170.2 180.22 190.22 200.22 210.15 220.24 230.25 240.25 250.26 260.28 270.27 280.25 290.24

1.28456 1.41275 1.48522 1.52072 1.54941 1.59745 1.63507 1.66616 1.68848 1.70132 1.71437 1.72317 1.73034 1.73453 1.73747 1.73903 1.74016 1.73994 1.74066 1.73999 1.74047 1.74109 1.74273 1.74561 1.75079 1.75781 1.76557 1.76789 1.77124 1.77548 1.7804 1.79664

1.19313 1.38963 1.47105 1.5492 1.59309 1.64133 1.66716 1.68326 1.69428 1.70226 1.70833 1.71307 1.71692 1.72007 1.7227 1.72496 1.72689 1.72856 1.73003 1.73134 1.7325 1.73354 1.73447 1.73532 1.7361 1.7368 1.73745 1.73805 1.7386 1.73911 1.73959 1.74003

Appendices

200

[Co(Cp)2] [Cr(tLCat)3] (10b)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

2.001 5.003 10.016 15.014 20.006 29.998 40 50.01 60.037 70.033 80.081 90.093 100.15 110.13 120.16 130.17 140.04 150.19 160.21 170.21 180.23 190.23 200.22 210.26 220.15 230.22 240.25 250.27 260.08 270.26 280.25 290.25

1.55684 1.66063 1.71827 1.72622 1.73145 1.73482 1.73478 1.73588 1.73588 1.73714 1.74138 1.73908 1.73832 1.73726 1.73664 1.73584 1.73502 1.73484 1.7348 1.73461 1.73487 1.73509 1.73538 1.73709 1.73748 1.73922 1.73926 1.73940 1.73942 1.73944 1.73947 1.73950

1.61756 1.69384 1.71775 1.72541 1.72919 1.73292 1.73478 1.73588 1.73662 1.73714 1.73754 1.73784 1.73809 1.73829 1.73845 1.73859 1.73871 1.73882 1.73891 1.73899 1.73906 1.73912 1.73918 1.73923 1.73928 1.73932 1.73936 1.73942 1.73943 1.73946 1.73949 1.73952

Appendices

201

[N(n-bu)4] [Mo(tLSS)3] (12b)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1.951 5.079 9.996 15.056 20.004 30 40.005 50.014 60.037 70.061 80.068 90.1 100.11 110.12 120.14 130.16 140.18 150.19 160.2 170.21 180.22 190.24 200.24 210.23 220.25 230.04 240.25 250.25 260.28 270.26 280.26 290.27

1.50923 1.66185 1.68516 1.69501 1.6996 1.70508 1.71042 1.71202 1.71485 1.7177 1.7207 1.72381 1.72526 1.72707 1.72788 1.7287 1.72729 1.72642 1.72292 1.71936 1.71805 1.71638 1.7164 1.71776 1.71785 1.71645 1.71573 1.71550 1.71397 1.71298 1.71444 1.71533

1.57368 1.66132 1.68761 1.69656 1.7009 1.70526 1.70743 1.70873 1.7096 1.71022 1.71068 1.71104 1.71133 1.71156 1.71176 1.71192 1.71206 1.71219 1.71229 1.71239 1.71247 1.71255 1.71262 1.71268 1.71273 1.71278 1.71345 1.71301 1.71324 1.71317 1.71356 1.71408

Appendices

202

[N(n-Bu)4] [W(tLSS)3] (13b)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1.927 5.144 9.985 15.012 20.005 29.998 40.003 50.015 60.037 70.045 80.074 90.113 100.13 110.13 120.16 130.17 140.18 150.19 160.21 170.22 180.23 190.24 200.25 210.24 220.25 230.25 240.25 250.28 260.26 270.25 280.25 290.16

1.57899 1.6299 1.6621 1.66635 1.67189 1.67725 1.68248 1.68687 1.6887 1.68906 1.69095 1.6907 1.69075 1.69075 1.69075 1.68334 1.68014 1.67473 1.67094 1.66426 1.6581 1.64925 1.63948 1.62935 1.61797 1.60408 1.58415 1.56673 1.15341 1.52502 1.50877 1.50217

1.57141 1.64856 1.66895 1.67588 1.67924 1.68257 1.68421 1.68519 1.68584 1.6863 1.68665 1.68692 1.68714 1.68731 1.68746 1.68758 1.68769 1.68778 1.68786 1.68793 1.68799 1.68805 1.6881 1.68815 1.68818 1.68822 1.68826 1.68829 1.68832 1.68834 1.68837 1.68839

Appendices

203

2) Crystallographic data

(1) (2)

Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group

Unit cell dimensions

Volume (Å3), Z

Density (calc.) Mg/m3

Absorption coeff

F(000)

Crystal size (mm)

θ Range for data collect.

Index range

Reflections collected

Independent reflect.

Absorption correction

Data/restraints/param.

Goodness -of-fit on F2

Final R indices

[I>2σ(I)]

R indices (all data)

C36 H30 As Co N2 S2

688.59

100(2)K

0.71073Å

Tetragonal

P4 1

a = 9.8486(6) Å

b = 9.8486(6) Å

c = 31.672(2) Å

α = 90.00 deg

β = 90.00 deg

γ = 90.00 deg

3072.0(3)

1.489 Mg/m3

1.792 mm-1

1408

0.34 x 0.26 x 0.22

3.90 to 30.94 deg.

-13<=h<=14

-14<=k<=14

-38<=l<=45

33228

8491 [R(int) =0.0383]

Not corrected

8491/7/404

1.128

R1 = 0.0433,

wR2 = 0.0799

R1 = 0.0515

wR2 = 0.0827

C28 H46 Co N3 S2

547.73

100(2)K

0.71073Å

Monoclinic

P2 1/n

a = 13.2840(3) Å

b = 16.1915 (5) Å

c = 13.6370(4) Å

α = 90.00 deg

β = 98.972 deg

γ = 90.00 deg

2897.26(14)

1.256 Mg/m3

0.757 mm-1

1176

0.42 x 0.08 x 0.08

2.94 to 30.00 deg.

-18<=h<=18

-22<=k<=22

-19<=l<=19

65433

8447 [R(int) =0.0596]

Gaussian, face-indexed

8447/1/320

1.060

R1 = 0.0410,

wR2 = 0.0816

R1 = 0.0575,

wR2 = 0.0877

Appendices

204

(3) (4a) + (4b) Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range





Goodness-of-fit on F2

Final R indices

[I>2σ(I)]


C58 H105 Cr3 N3 Na O10 S3

1279.62

100(2)K

0.71073Å

Trigonal

R3c

a = 22.149(2) Å

b = 22.149(2) Å

c = 46.029(4) Å

α = 90.00 deg

β = 90.00 deg

γ = 120.00 deg

19556 (3), 12

1.304

0.649 mm-1

8220

0.20 x 0.10 x 0.06

1.84 to 23.50 deg.

-29<=h<=29

-29<=k<=29

-57<=l<=65

20785

6416 [R(int) =0.0785]

Not corrected

6387 / 150 / 495

1.071

R1 = 0.0631,

wR2 = 0.1221

R1 = 0.0982

wR2 = 0.1882

C101 H186 Cr6 N6 Na2 O20 S6

2354.90

100(2)K

0.71073Å

Trigonal

R3c

a = 22.1675(6) Å

b = 22.1675 (6) Å

c = 44.509(2) Å

α = 90.00 deg

β = 90.00 deg

γ = 120.00 deg

18941.4(11), 6

1.239

0.664mm-1

7536

0.22 x 0.11 x 0.11

2.84 to 28.50 deg.

-29<=h<=29

-29<=k<=29

-59<=l<=59

89330

10658 [R(int) =0.0596]


10658 /143 / 472

1.098

R1 = 0.0446,

wR2 = 0.0934

R1 = 0.0516,

wR2 = 0.0964

Appendices

205

(5) (5b)

Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C26 H20 N2 Ni S2

483.27

100(2)K

0.71073Å

Monoclinic

P2 (1)/n

a = 8.4938(3) Å

b = 24.0875(8) Å

c = 10.7572(4) Å

α = 90.00 deg

β = 102.09(1) deg

γ = 90.00 deg

2152.05(15), 4

1.492 mm-1

1.112

1000

0.33 x 0.17 x 0.06

4.18 to 31.03 deg.

-12<=h<=12

-34<=k<=34

-15<=l<=15

74726

6861 [R(int) =0.03851]


6861 / 0 / 288

1.073

R1 = 0.0275

wR2 = 0.0693

R1 = 0.0308

wR2 = 0.0710

C36 H30 Co N2 Ni S2

672.38

100(2)K

0.71073Å

Monoclinic

C2 / c

a = 16.3388(6) Å

b = 10.2331(4) Å

c = 18.2833(6) Å

α = 90.00 deg

β = 110.28(1) deg

γ = 90.00 deg

2863.41(18), 4

1.558 mm-1

1.411

1388

0.24 x 0.10 x 0.10

3.03 to 31.52 deg.

-24<=h<=24

-15<=k<=15

-26<=l<=26

37260

4760 [R(int) =0.0633]


4760 / 0 / 192

1.055

R1 = 0.0257,

wR2 = 0.0637

R1 = 0.0361

wR2 = 0.0668

Appendices

206

(6) (6b)

Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C26 H20 Co N2 S2

483.49

100(2)K

0.71073Å

Monoclinic

P2 (1)/n

a = 8.4252(3) Å

b = 24.2702(9) Å

c = 10.7163(4) Å

α = 90.00 deg

β = 101.48(1) deg

γ = 90.00 deg

2147.44(14), 4

1.495 mm-1

1.010

996

0.22 x 0.04 x 0.03

3.82 to 30.96 deg.

-11<=h<=12

-35<=k<=35

-15<=l<=15

34574

6805 [R(int) =0.0746]


6805/0/288

1.074

R1 = 0.0486,

wR2 = 0.0883

R1 = 0.0720

wR2 = 0.0961

C36 H30 Co2 N2 S2* 0.5

CH3CN

693.13

100(2)K

0.71073Å

Monoclinic

P2 (1)/c

a = 10.1342(5) Å

b = 17.186(2) Å

c = 17.838(2) Å

α = 90.00 deg

β = 91.67(2) deg

γ = 90.00 deg

3105.5(5), 4

1.483 mm-1

1.234

1428

0.20 x 0.20 x 0.15

4.57 to 31.00 deg.

-14<=h<=14

-24<=k<=24

-25<=l<=25

82019

9798 [R(int) =0.0633]


9798 / 3 / 398

1.194

R1 = 0.0841,

wR2 = 0.2363

R1 = 0.0922

wR2 = 0.2406

Appendices

207

(7)

Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C26 H20 N2 S2 Zn

489.93

100(2)K

0.71073Å

Monoclinic

P2 1/c

a = 26.5572(6) Å

b = 7.0143(1) Å

c = 26.6855(4) Å

α = 90.00 (1) deg

β = 118.65(1) deg

γ = 90.00 (1) deg

4362.4(2), 8

1.492 mm-1

1.334

2016

0.15 x 0.08 x 0.07

3.16 to 31.56 deg.

-39<=h<=39

-10<=k<=10

-39<=l<=39

125768

14548 [R(int) =0.0641]

Not corrected

14548 / 0 / 559

1.065

R1 = 0.0365,

wR2 = 0.0718

R1 = 0.0483

wR2 = 0.0762

Appendices

208

(8) (9) Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C58 H96 Cr N S6

1051.72

100(2)K

0.71073Å

Monoclinic

P2 (1)/c

a = 14.4072(8) Å

b = 21.579(2) Å

c = 20.1333(12) Å

α = 90.00 deg

β = 90.703(5) deg

γ = 90.00 deg

6258.8(8), 4

1.116 mm-1

0.417

2284

0.14 x 0.12 x 0.05

3.40 to 24.00 deg.

-16<=h<=16

-24<=k<=24

-22<=l<=23

38236

9790 [R(int) =0.10015]

Not corrected

9790 / 0 / 617

1.059

R1 = 0.0685

wR2 = 0.1358

R1 = 0.1212

wR2 = 0.1605

C56 H66 As Cr N2 O S4

1038.27

100(2)K

0.71073Å

Monoclinic

P2 (1)/n

a = 10.0423(6) Å

b = 19.7433(12) Å

c = 26.800(2) Å

α = 90.00 deg

β = 96.93(1) deg

γ = 90.00 deg

5274.8(6), 4

1.307 mm-1

1.038

2180

0.10 x 0.10 x 0.04

4.02 to 25.00 deg.

-11<=h<=11

-23<=k<=23

-28<=l<=31

45009

9203 [R(int) =0.0953]


9203 / 6 / 613

1.202

R1 = 0.09982,

wR2 = 0.2040

R1 = 0.1240

wR2 = 0.2149

Appendices

209

(10) Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C42 H60 Cr N3 O6

712.90

100(2)K

0.71073Å

Monoclinic

C2 / c

a = 22.1182(9) Å

b = 19.1114(9) Å

c = 10.0921(3) Å

α = 90.00 deg

β = 95.184(5) deg

γ = 90.00 deg

4248.6 (3), 4

1.115

0.310 mm-1

1536

0.10 x 0.07 x 0.02

4.05 to 25.00 deg.

-24<=h<=26

-22<=k<=22

-10<=l<=12

13998

3727 [R(int) =0.1032]

Not corrected

3727 / 0 / 222

1.058

R1 = 0.0578,

wR2 = 0.1020

R1 = 0.1112

wR2 = 0.1252

Appendices

210

(11) (12) Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C46 H73 Mo N3 O S3

876.19

100(2)K

0.71073Å

Monoclinic

P2 1 / n

a = 13.8156(7) Å

b = 20.8414(9) Å

c = 16.5381(8) Å

α = 90.00 deg

β = 92.154(4) deg

γ = 90.00 deg

4758.6 (4), 4

1.223

0.442 mm-1

1872

0.18 x 0.11 x 0.06

2.95 to 26.00 deg.

-17<=h<=17

-25<=k<=25

-20<=l<=20

58033

9327 [R(int) =0.0846]

Gaussian

9327/ 21 / 529

1.155

R1 = 0.0546,

wR2 = 0.1115

R1 = 0.0686

wR2 = 0.1177

C42 H60 Mo S6

853.20

100(2)K

0.71073Å

Monoclinic

P2 1 / n

a = 13.3491(6) Å

b = 18.5592(8) Å

c = 19.3158(6) Å

α = 90.00 deg

β = 99.663(5) deg

γ = 90.00 deg

4717.6 (19), 4

1.201

0.569 mm-1

1800

0.10 x 0.09 x 0.02

2.99 to 30.98 deg.

-19<=h<=19

-26<=k<=26

-27<=l<=27

111338

14979 [R(int) =0.0617]

Not corrected

14979 / 31 / 489

1.027

R1 = 0.0389,

wR2 = 0.0756

R1 = 0.0648

wR2 = 0.0855

Appendices

211

(12b) (13) Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C60 H99 Mo N2 S6

1136.71

100(2)K

0.71073Å

Monoclinic

P2 1 / c

a = 14.5012(6) Å

b = 21.7374(9) Å

c = 20.2212(4) Å

α = 90.00 deg

β = 90.563(5) deg

γ = 90.00 deg

6373.8 (5), 4

1.185

0.438 mm-1

2444

0.24 x 0.07 x 0.06

3.30 to 27.50 deg.

-18<=h<=18

-28<=k<=28

-26<=l<=26

83077

14617 [R(int) =0.0752]


14617 / 1 / 627

1.111

R1 = 0.0546,

wR2 = 0.1004

R1 = 0.0762

wR2 = 0.1074

C42 H60 S6 W

961.64

100(2)K

0.71073Å

Monoclinic

P2 1 / n

a = 10.7227(5) Å

b = 18.7101(6) Å

c = 23.7213(6) Å

α = 90.00 deg

β = 94.045(1) deg

γ = 90.00 deg

4747.18 (17), 4

1.346

2.725 mm-1

1972

0.28 x 0.17 x 0.04

2.98 to 26.35 deg.

-13<=h<=13

-23<=k<=23

-29<=l<=29

90719

4997 [R(int) =0.0491]


4997 / 34 / 292

1.133

R1 = 0.0340,

wR2 = 0.0774

R1 = 0.0358

wR2 = 0.0786

Appendices

212

(13b) Empirical formula

Formula weight

Temperature

Wavelength (MoKα)

Crystal system

Space group


Volume (Å3), Z


Absorption coeff

F(000)

Crystal size (mm)


Index range






Final R indices

[I>2σ(I)]


C58 H96 N S6 W *0.19 CH2Cl2

1199.49

100(2)K

0.71073Å

Monoclinic

P2 1 / c

a = 14.5159(8) Å

b = 21.949(2) Å

c = 20.174(2) Å

α = 90.00 deg

β = 91.68(1) deg

γ = 90.00 deg

6424.9 (9), 4

1.240

2.042 mm-1

2516

0.10 x 0.05 x 0.02

2.96 to 22.50 deg.

-15<=h<=15

-21<=k<=23

-21<=l<=19

28186

8319 [R(int) = 0.0698]


8319 / 13 / 617

1.089

R1 = 0.0510,

wR2 = 0.0881

R1 = 0.0860,

wR2 = 0.0995

Appendices

213

3) Curriculum Vitae

Personal

Name: Ms. Kapre, Ruta

Date of Birth:

20.12.1977

Place of Birth:

Medha, Maharashtra, India

Nationality:

Indian

Education

1994-1997 Sangamner college, Pune University, India (Bachlor of science)

1997-1999 Department of Chemistry, Pune University, India (Master of Science, with Prof. Dr. R. S. Kusurkar).

Apr1999-Dec 2000 National Chemical Lab (CSIR), Pune, India Project assistant

Feb 2001-July 2002 Ruhr University Bochum, Germany (Project assistant with Prof. M. Driess)

Aug 2002-July 2005 Max-Planck-Institute for Bioinorganic Chemistry, Muelheim an der Ruhr, Germany (Phd with Prof. Dr. K. Wieghardt).

Experimental Study on Transition Metal Complexes ...

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