DaltonTransactions

Dynamic Article Links

Cite this: Dalton Trans., 2011, 40, 10038

www.rsc.org/dalton PAPER

Highly emissive dinuclear complexes [Au2{l-(PPh2)2C2B9H10}(C6F5)(PR3)]with different gold fragments coordinated to an anionic diphosphine†

Olga Crespo,*a Cesar Dıez-Gil,a M Concepcion Gimeno,*a Antonio Laguna,a Miguel Mongeb andIsaura Ospinoa

Received 11th May 2011, Accepted 22nd July 2011DOI: 10.1039/c1dt10890e

Reaction of the yellow-green emitters [Au{(PPh2)2C2B9H10}(PR3)] with [Au(C6F5)(tht)] affordsorange-red emissive gold complexes [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)] which contain differentneutral (PR3) and anionic (C6F5) auxiliary ligands and an anionic diphosphine. The resultingcomplexes are among the few reported in which an ortho-carborane diphosphine acts in a bridgingmode, and are unique in containing not a closo- (neutral), but a nido-carborane (anionic) cluster. DFTand TDDFT calculations led to the prediction of the origin of the two first singlet–triplet transitions,which is consistent with the experimental results. Although the blue emissive nido-diphosphine plays akey role in the transitions of the three-coordinate precursors and the final dinuclear complexes, it is theenvironment around the gold centre that controls the emission energy.

Introduction

Luminescent complexes are attractive since they show possible ap-plications in VOC detectors, as the presence of organic moleculesmay change the emission maxima, their intensity or even lead toluminescence quenching.1 Furthermore, complexes with a tripletexcited state may be used as phosphor dopants in the fabricationof OLEDs. As a consequence, phosphorescent complexes may betaken into account for such an application.2

We have lately focused our efforts on the study of luminescentgold complexes3 and the modulation of their emissive behaviorby selection of both the ligands and the geometry of the systems.We have also tried to understand, as much as possible, the sort oftransitions which lead to the emissive behaviour. Regarding goldcomplexes, the presence of emissions arising from metal-centredtransitions is favoured both by three coordination at the goldcentre and by the presence of aurophilic interactions.4 The ligandsmay also play an important role, as ligand centred transitionsand charge transfer transitions may be also responsible for theluminescence.

Part of our work has been focused on carborane chemistry.Not many studies have dealt with the analyses of the influence ofthese three factors: the ligand, coordination around the metal, andthe presence of aurophilic interactions in the emissive behavior of

aDepartamento de Quımica Inorganica, Instituto de Sıntesis Quımica yCatalisis Homogenea (ISQCH). Universidad de Zaragoza-CSIC, PedroCerbuna 12, 50009, Zaragoza, SpainbDepartamento de Quımica. Universidad de La Rioja, Grupo de SıntesisQuımica de La Rioja UA-CSIC Complejo CientıficoTecnologico, 26004,Logrono, Spain† CCDC reference number 785468. For crystallographic data in CIF orother electronic format see DOI: 10.1039/c1dt10890e

gold complexes. Our previous studies on carborane chemistry haveshown us that this sort of ligand may be suitable for such studies.

Despite the versatility of such ligands, few studies of lumines-cent properties have focused their efforts on carborane basedcompounds5,6 and, among them, studies in the solid state arescarcely represented. Carborane luminescent compounds may bedivided into two groups, based on the presence or absence ofmetallic atoms in the structure. In many cases, those which donot contain any metal5 are the result of the incorporation ofcarborane fragments in aromatic systems (even chiral). Someexamples are the carborane isomers themselves,3d,5a carboranylfunctionalized aryl ether derivatives,5c adducts of ortho-nido-undecaborate(-2)5b or polymeric materials.5d–5g Coordination com-pounds include organometallic gold complexes,3d ruthenium co-ordinated to functionalised para-carborane,6a metallacarboranesof different transition metals6b–6g and carborane monothiolateplatinum complexes.6h Some Ni, Pd and Pt examples6i with thenido-diphosphine [(PPh2)2C2B9H10]- and heterobimetallic trinu-clear clusters [Ag2MS4{(PPh2)2C2B10H10}] (M = Mo, W) whichcontain the closo-diphosphine [(PPh2)2C2B10H10] have also beendescribed.6j

Some of the compounds above mentioned show interest-ing behaviours, like the modification of the luminescenceby different solvents;5c,5k the influence of carboranes in in-duced aggregation emission;5h–5j,5l quenching of the emissive be-haviour of species by introducing carboranes,6g mechano6e,6f andelectroluminescence.6e,6f

During our studies we have found that the tetranuclear goldclusters [Au4{(PR2)2C2B9H10}2L2] (L = AsPh3, PR3) which containthe same diphosphine are red emitters. These emissions arisefrom the presence of aurophilic interactions.3c The nido-carboranediphosphines [(PR2)2C2B9H10]- (R = Ph, iPr) give weak blue

10038 | Dalton Trans., 2011, 40, 10038–10046 This journal is © The Royal Society of Chemistry 2011

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online / Journal Homepage / Table of Contents for this issue

emissions. Coordination to gold leads to the three-coordinated[Au{(PR2)2C2B9H10}(PR3)] complexes, increases the intensity ofthe emissions and shifts the emission maxima to the yellow-greenregion. A weak red emission is also observed depending on theR substituent. Diphosphine orbitals with contribution of goldorbitals, to a greater or lesser extent, seem to be involved in thetransitions responsible for both emissions.3b The lowest excitedstate of these three-coordinated complexes has been studied.3e

We have reported the synthesis and crystal struc-ture of [Au2{m-(PPh2)2C2B9H10}(C6F5)(PPh3)],7 starting from[Au{(PR2)2C2B9H10}(PPh3)]. The gold atoms display aurophilicinteractions. This compound exhibits interesting differences whencompared with other gold dinuclear derivatives in which thegold centres are bridged by a neutral diphosphine. Luminescentdinuclear gold species of stoichiometry [Au2X2{m-(R2P~PR2)}](R2P~PR2 = neutral diphosphine, X = anionic auxiliary ligandas halide, pentafluorophenyl, thiolate or acetylide) are extensivelyrepresented.8 The structures of these complexes are governed bythe diphosphine substituent (R), the alquilic or arylic nature of thechain, its length and also by the anionic auxiliary ligand. Thus, theorigin of the emissions may also be very different. In many casesintraligand (diphosphine) transitions (modified, to a greater orlesser extent, by the presence of gold) are thought to be responsiblefor the highest energy emissions. Inter or intramolecular aurophilicinteractions may lead to emissions at lower energies, and forthiolate and acetylide complexes charge transfer transitions fromthe auxiliary ligand (X) to the gold centre have been claimed to bethe origin of emissions over a wide energy range.

The compound [Au2{m-(PPh2)2C2B9H10}(C6F5)(PPh3)]corresponds to the general formula [Au2(nido-carborane-diphoshine)XL] with different neutral (L) and anionic (X)auxiliary ligands. This is only possible because of the presence of achelate bidentate anionic diphosphine. As far as we know, only twocomplexes with different auxiliary ligands have been reported.These are the compounds [Au2(dcpm)Br(C14H9)]9 [dcpm =bis(dicyclohexyl)phosphinomethane] and [Au2(dcpe)Br(CN)]10

[dcpe = bis(dicyclohexyl)phosphinoethane], in which both ofthe auxiliary ligands are anionic. Also the fact that a carboranediphosphine is acting as a bridging ligand is notable, since thesediphosphines show a preference towards the chelating mode.Examples of carborane diphosphines acting as bridging ligandsare scarcely represented. In addition, the complexes reported hereare the only examples of species which contain a nido-diphosphineas a bridging ligand.

Our renewed interest in [Au2{m-(PPh2)2C2B9H10}(C6F5)(PPh3)]was stimulated by the change in the luminescence observed duringsynthesis and because of its own emissive properties. During thereaction an astonishing change of the emissions from yellow-green(of the three-coordinated precursor [Au{(PPh2)2C2B9H10}(PPh3)])to red has been observed. At the same time, the geometry aroundthe gold centre changes from trigonal planar to linear. Thisobservation has prompted us to prepare a family of complexes[Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)] (PR3 = tertiary phosphine).The understanding of the origin of their emissive propertiesrepresents a challenge for a theoretical study. They combine thepresence of a nido-carborane diphosphine (which, based on ourstudies, can lead to luminescence) and aurophilic interactions(which are also known to be responsible for the emissions observedin many gold complexes).2 In order to elucidate the transitions

responsible for the luminescence, DFT and TDDFT theoreticalstudies have been carried out.

Results and discussion

Synthesis and characterization

Reaction of the three-coordinated compounds[Au{(PPh2)2C2B9H10}(PR3)] with [Au(C6F5)(tht)] in a 1 : 1molar ratio affords dinuclear complexes of stoichiometry [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)] which display intense orange orred emissions. Thus, a change in the luminescence from yellowor green, in the three-coordinated precursors, to orange or redoccurs upon the formation of the dinuclear complexes (Scheme 1).

Scheme 1 Synthesis of 1–4. The photographs below the equationcorrespond to the emission, under UV light of pellets made from complex1 (right) and the corresponding starting product (left) and silica. Thestarting products emit in the yellow-green region, whereas the complexes1–4 display emissions in the orange-red region.

The I.R. spectra of 1–4 show the bands corresponding to theu(BH) vibration at about 2600 cm-1 and those corresponding tothe presence of the pentafluorophenyl groups bonded to the goldatom at about 950 cm-1.

In their 1H NMR spectra the aromatic hydrogen atoms appear inthe 6–8 ppm region, the bridging hydrogen atom of the carboranecluster at about -2 ppm and a broad resonance, between 1 and3 ppm, is assigned to the BH hydrogen atoms. In addition tothese signals, compounds 2–4 display a resonance in the 2–3ppm region, which arises from the hydrogen atoms of the methylgroups. The 31P{1H} NMR spectra for these complexes consist ofan AMX system (Table 1). The AX part corresponds to one of thephosphorus atoms of the diphosphine and the phosphorus atomof the monophosphine and the M part to the other phosphorusatom of the diphosphine (Fig. 1). A small coupling constant JAM

is observed. The resonances of the diphosphine atoms appearbetween 53.5 and 54.6 ppm, in the three-coordinated precursorsthey are equivalent and appear at about 60 ppm. As expected, the

Table 1 31P{1H} NMR data for complexes [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)]

PR3 (Compound) 31P{1H}, d/J (Hz)

PPh3 (1) dX = 39.1 dA = 54.0 dM = 49.8; JAX = 306.7 JAM = 56.6PPh2Me (2) dX = 24.4 dA = 54.3 dM = 49.6; JAX = 411.1 JAM = 64.8PPh2(p-tol) (3) dX = 38.7 dA = 54.9 dM = 52.4; JAX = 409.5 JAM = 74.5P(p-tol)3 (4) dX = 37.7 dA = 53.6 dM = 50.0; JAX = 308.7 JAM = 56.6

This journal is © The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 10038–10046 | 10039

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

Table 2 Bond distances (A) and angles (◦) for complexes [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)]

PR3 Au ◊ ◊ ◊ Au Au–Pa Au–Pb P–Au–P C–Au–P

PPh2Me (2) 2.9286(6) 2.3074(17) 2.2961(17) 160.12(6) 169.65(17)2.3221(16)

PPh37 (1) 2.9885(8) 2.312(2) 2.300(2) 164.69(7) 166.66(2)

2.326(2)

a Monophosphine. b Diphosphine

Fig. 1 Labelling of the phosphorus atoms correspondingto the observed 31P{1H} NMR AMX system in complexes[Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)] (1–4).

chemical shift of the PPh2Me phosphorus atom appears at higherfield, compared with that observed for the arylic phosphines. The19F NMR spectra display three signals corresponding to the ortho,meta, and para fluorine nuclei in the pentafluorophenyl ring.

The structure of compound 2 has been determined by X-ray diffraction studies (Fig. 2). Bond distances and anglesfor 2 and the previously described 17 are in the same range(Table 2). The gold ◊ ◊ ◊ gold intramolecular distances indicate thepresence of aurophilic interactions. These distances are shorterthan those found in [Au2(dcpm)Br(C14H9)]9 (3.175 A), whereas in

Fig. 2 Perspective view of the X-ray structure of complex 2 showingthe atom labelling scheme. Hydrogen atoms have been omitted for clarity.Ellipsoids represent 50% probability levels.

[Au2(dcpe)Br(CN)]10 the gold ◊ ◊ ◊ gold distance of 3.462 A is on theborderline of Au ◊ ◊ ◊ Au aurophilic distances.

No intermolecular metallic interactions are present in 2. Theshortest distance between gold atoms belonging to differentmolecules is about 8 A. Weak C–H ◊ ◊ ◊ F interactions have beenfound (Table 3), some of them are intramolecular interactions.Intermolecular hydrogen bonds C(62)–H(62) ◊ ◊ ◊ F(3) lead to theformation of chains (Fig. 3). They involve one phenylic hydrogenatom of the PPh2Me monophosphine and one fluoride atom ofthe pentafluorophenyl ring.

Fig. 3 Formation of chains in 2 through intermolecular hydrogen bonds.

Photophysical studies

Diffuse reflectance UV spectra

The diffuse reflectance UV spectra for complexes 1–4 displaysimilar patterns consisting of one band in the 200–250 nm regionand more intense bands at about 310 nm. For complexes 3 and4 the band at 310 nm displays a shoulder with a maximum atabout 380 nm (Fig. 4). High energy bands at l = 300 nm have beenattributed to transitions which involve orbitals of the diphosphinearyl substituents. The lower energy bands could be attributedboth to aurophilic interactions or charge transfer processes whichimplicate the gold centre orbitals.

Table 3 Hydrogen bonds for 2 [A and ◦]

D–H . . . A d(D–H) d(H . . . A) d(D . . . A) <(DHA)

C(16)–H(16) . . . F(5) 0.93 2.50 3.203(8) 132.8C(71)–H(71A) . . . F(1) 0.96 2.73 3.644(9) 159.8C(100)–H(10A) . . . F(5) 0.97 2.57 3.294(11) 131.9C(62)–H(62) . . . F(3)#1 0.93 2.61 3.421(8) 146.3

Symmetry transformations used to generate equivalent atoms: #1 -x +3/2, y -1/2, -z +1/2

10040 | Dalton Trans., 2011, 40, 10038–10046 This journal is © The Royal Society of Chemistry 2011

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

Table 4 Emission (excitation)a maxima (in nm) and lifetime values for complexes [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)]

Compound/PR3 1/PPh3 2/PPh2Me 3/PPh2(p-tol)c 4/P(p-tol)3

Solid state 298 Klex 375; 475 sh 375; 420 sh 330; 450 360; 450lem 660 (6)b 660 (5)b 660 (5)b 660 (5)b

Solid state 77 Klex 375; 450 365; 410 350; 425 330; 440lem 515; 675 640 660 630Frozen solutionlex 310; 340, 425 370; 430sh 330; 375,435sh 375; 425lem 540; 670 475, 625 550; 650 530; 650Solution 298 Klex 335 330 315; 340lem 485 485 450

a When two emissions are observed the emission on the right corresponds to the excitation on the right, when three excitation values are given the one onthe left corresponds to the emission at high energy. b t/ms; c The solutions decompose at room temperature during the measurement.

Fig. 4 Diffuse reflectance UV spectrum for 4.

Luminescence

The complexes are emissive both in solution and in the solid stateat room temperature and 77 K (Fig. 5). Table 4 shows the emissionand excitation maxima under different conditions, as well as thelifetime values in the solid state at room temperature. The emissionand excitation spectra for all of them display similar features. Inthe solid state one band at about 660 nm is observed, both at roomtemperature and at 77 K. Excitation spectra display two bands ora broad band and a shoulder. The maximum of one of the bandsappears between 330–375 nm, that of the other band (or shoulder)between 420 and 475 nm. The Stokes shift and lifetime values, inthe microsecond range, indicate a phosphorescent nature of theemissions.

Fig. 5 Powder of complexes 1, 2, 3 (right to left) top and 4 (bottom) underwhite light (left) or UV light (right).

The dichloromethane solutions (5 ¥ 10-5 M) only display oneemission (maxima between 450 and 485 nm) whose correspondingexcitation maxima range from 315 to 340 nm. In frozen solutionstwo emissions are observed (Fig. 6). One of them resembles thatin the solid state, the other the one present in solution at room

Fig. 6 The two emission bands observed for 1 in frozen dichloromethanesolution upon excitation at 340 nm (dotted line) or 430 nm (straight line),respectively.

temperature. The emission at lower energy is always the mostintense. In some cases (as for complex 2) it is possible to observeboth emissions upon exciting at energies lower than 400 nm, andthe relative intensity of each band is modified with the excitationemission energy. Upon excitation at higher energies the intensityof the band at 475 nm increases. Upon exciting at lower energiesthe increment is observed for the band at 625 nm.

The band at high energy resembles that observed in the three-coordinated complexes [Au{(PR¢2)2C2B9H10}(PR3)] (R¢ = Ph, iPr;PR3 = tertiary phosphine) which has been attributed to intraligand(IL) transitions modified by the presence of gold. The low energyemissions resemble the weak emissions observed in this regionfor the mentioned three-coordinated complexes, which have beenattributed to metal-to-ligand charge transfer processes. Theselow energy emissions also resemble the intense red emissionsobserved for the tetranuclear clusters [Au4{(PPh2)2C2B9H10}2L2](L = tertiary phosphine or arsine), which have been proposed tooriginate from metal-centred transitions, involving the gold clusteratoms.

It is worth mentioning the different emissive behaviour of 1–4compared to the two dinuclear complexes presented above, whichcontain two different gold fragments bridged by a diphosphine.In spite of the presence of aurophilic interactions, complex[Au2(dcpm)Br(C14H9)],9 displays a structured emission in the blueregion in dichloromethane solution and in the solid state (bothat room temperature and 77 K), assigned to the anthracenemoiety, whereas no emissive behaviour has been reported for[Au2(dcpe)Br(CN)].10

This journal is © The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 10038–10046 | 10041

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

Fig. 7 The most important molecular orbitals involved in the theoretical electronic transitions for model system [Au2{m-(PPh2)2C2B9H10}(C6F5)(PPh3)](1).

In our case the presence of aurophilic interactions could beresponsible for the low energy emissions, although charge transferprocesses may not be excluded. In order to elucidate this pointand the influence of the gold environment in the emission energywe have carried out theoretical studies.

Theoretical studies

As commented before, luminescence lifetimes in the microsecondsrange suggest that the emissions probably originate from anexcited state of triplet parentage and, consequently, are tentativelyassigned to phosphorescence. Phosphorescent emissions originatefrom triplet states owing to the heavy atom effect of gold.2a–2c

DFT and TDDFT calculations were performed to interpret theoptical properties of the complexes described above. The electronicstructures of complexes 1 and 2 were obtained through single-point DFT calculations on model systems built up from theX-ray structures, in order to gain a deeper insight into thenature of the frontier molecular orbitals of the compounds whichcould be involved in the electronic transitions responsible for thephosphorescent emissions.

Therefore, we could check the contribution of each part of themolecule to the active molecular orbitals. Figures 7 and 8 show that

the HOMO to HOMO-5 orbitals are mainly located on the ligands(phenylphosphines and nido-carborane). The HOMO-1 is slightlydifferent, having a large contribution from both metal centres. Itcan be observed that the HOMO-1 of each model system displaysa 5dz

2 s* character, typical of d10 metal complexes with aurophilicinteractions. Moreover, in the HOMO orbitals of both models theelectronic delocalization derived from the hydride atom on theopen face of the nido-carborane is evident. The strong influenceof the orbitals belonging to the open face atoms in the emissionscould probably be due to the electronic delocalization. The emptyLUMO to LUMO+5 orbitals are predominantly located on themetal and the phenylphosphine ligands. The LUMO shows aninteresting feature, which is its localization, mainly between thetwo gold atoms showing a 6p s character, typical of d10 metalcomplexes with metal ◊ ◊ ◊ metal interactions.

Overall, the frontier orbital analysis shows that the ligandsand Au(I) ◊ ◊ ◊ Au(I) aurophilic contacts may have some influencein the phosphorescent properties of the reported complexes.The TDDFT method was employed to analyze the first twosinglet–triplet transitions. These lowest spin-forbidden transitionsare compared with the experimental excitation wavelengths re-sponsible for the two first singlet to triplet emissions foundexperimentally.

Fig. 8 The most important molecular orbitals involved in the theoretical electronic transitions for model system[Au2{m-(PPh2)2C2B9H10}(C6F5)(PPh2Me)] (2).

10042 | Dalton Trans., 2011, 40, 10038–10046 This journal is © The Royal Society of Chemistry 2011

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

Table 5 TDDFT data for the two first singlet to triplet transitions for complexes [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)]; PR3 = PPh3 (1); PPh2Me (2)

Compound PPh3 (1) HOMO(259); LUMO(260) PPh2Me (2) HOMO(243); LUMO(244)

Excitation lT lEx Transition lT lEx TransitionTriplet 1 371.2 475 259 → 260 431.3 420 243 → 244Triplet 2 347.6 375 259 → 261 394.9 375 243 → 246

lT = Theoretical excitation wavelength in nm, lEx = Experimental excitation wavelength in nm.

The TDDFT calculations analysis shows that the orbitalsinvolved in the two first theoretical singlet–triplet transitions forcompound 1 are: triplet 1: HOMO(259a) to LUMO(260a); triplet2: HOMO(259a) to LUMO+1(261a); whereas for compound 2they are: triplet 1: HOMO(243a) to LUMO(244a); triplet 2:HOMO(243a) to LUMO+2(246a) (Table 5). Studies of analogouscompounds containing intramolecular Au ◊ ◊ ◊ Au contacts andbridging-diphosphine ligands often show that both give riseto unique electronic spectroscopic features, in which intenseemissions from yellow-green to orange-red are phosphorescentin nature. This is also supportive of an assignment of the emissivestates as derived from states of a triplet character.2e,6d,11 Thesinglet–triplet transition at low-energy (first theoretical singlet totriplet transitions) could be associated with the experimental low-energy emission at 600 nm. The singlet to triplet transition athighest energy (second theoretical singlet to triplet transitions)may probably be associated with the emission at 500 nm in viewof the experimental and theoretical results shown in Table 5.

One of the most important parameters in the structures of 1and 2 is the presence of Au ◊ ◊ ◊ Au contacts of 2.9885(8) A and2.9286(6) A, respectively. Thus, we might expect that the originwould involve a triplet state of metal-centred character due to thepresence of the strong metal ◊ ◊ ◊ metal interactions.2 Nevertheless,the theoretical studies discussed above exclude an emissive statederived from a metal-centred origin and the emission energiesresemble those found in gold(I) three-coordinated complexespreviously described. These data indicate a ligand character inthe origin of the emission.

The low-energy emission probably originates from a ligand nido-carborane (L) to interacting Au(I) centres (MM) charge transfertransition (LMMCT) for the two theoretical model systems.A LMMCT origin has been suggested for emissions found indifferent complexes in the solid state.12 Such an origin is likely forthe present complexes, since there is evidence of intramoleculargold ◊ ◊ ◊ gold interactions.

We propose the assignment of the high-energy emission asderived from a ligand nido-carborane (L) to the group metal–ligand AuPPh3 (ML¢) charge transfer transition (LML¢CT) forcomplex 1 [HOMO(259a) to LUMO+1(261a)]. For complex 2,the assignment of the high-energy emission is proposed to havea ligand nido-carborane (L) to ligand phenylphosphine PPh2Me(L¢) charge transfer transition (LL¢CT) origin, taking into accountthe shape of the orbitals involved in both high energy singletto triplet transitions [HOMO(243a) to LUMO+2(246a)]. Thedifferent electronic character of both monophosphines could beassociated with the different origin of the emissions. Thus, thegreater donating character of PPh2Me, compared with PPh3,would be consistent with the assignment of the singlet to tripletLL¢CT transition for complex 2. An assignment of an excited

state of triplet ligand-to-metal–ligand charge transfer (LML¢CT)character for complex 1 could be explained on the basis thatthe AuPPh3 group would render the gold(I) centre more electrondeficient, lowering the metal acceptor-orbital energy.

The different emissive behaviour found for the different states(solid or solution) of the samples represents an interesting pointand its explication from a physical point of view is a challengethat may not be explained by theoretical studies. Nevertheless,these data are useful in order to make a proposal. As the lowestenergy triplet involves the gold ◊ ◊ ◊ gold interaction a possibleexplanation for the different emissive behaviour is the modificationof the gold ◊ ◊ ◊ gold distance with the aggregation state. Anotherpossible explanation for the experimental observations could bethe quenching of the lowest energy triplet, depending on themeasurement conditions. It is not frequent to observe emissionsfrom two triplet excited states, but such an origin has beenproposed in order to explain the emissive behavior of some goldcomplexes.13

Conclusions

Intense yellow-green luminescent three-coordinated complexes[Au{(PPh2)2C2B9H10}(PR3)] react with [Au(C6F5)(tht)] to affordintense orange-red emissive dinuclear species. This dramaticchange in the luminescence behavior is produced on going frommononuclear complexes, with a trigonal planar environment forthe gold centre, to dinuclear compounds with linear geometry forthe gold centres and aurophilic interactions.

Complexes of formula [Au2{m-(PPh2)2C2B9H10}(C6F5)(PR3)]display different emissive behaviour in the solid state from that insolution. In the solid state one band at about 660 nm is observed,both at room temperature and at 77 K. Dichloromethane solutions(5 ¥ 10-5 M) display only one emission at about 520 nm and frozensolutions show two bands.

TDDFT calculations for [Au{(PPh2)2C2B9H10}(PPh3)] (1) and[Au{(PPh2)2C2B9H10}(PPh2Me) (2) indicate that the highest en-ergy emissions at lEx = 340–370 nm, correspond to the calculatedsecond triplet transitions. They can be assigned as spin forbiddenLML¢CT and LL¢CT transitions for 1 and 2, respectively. Thelowest energy emissions at lEx = 400–406 nm correspond to thefirst triplet transitions. They can be assigned as spin forbiddenLMMCT transitions. The prediction of the two first singlet–triplettransitions using TDDFT calculations is consistent with thoseobtained in the experimental results.

The results indicate that Au(I) ◊ ◊ ◊ Au(I) interactions clearlyinfluence the luminescent properties of these complexes. Althoughthe nido-diphosphine plays a key role in the transitions of boththe three-coordinate precursors and the dinuclear complexes, thecoordination towards the gold centre is the factor that controls the

This journal is © The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 10038–10046 | 10043

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

emission energy. Thus, modification of the geometry of the goldatom from three-coordinate to linear (which allows the presenceof aurophilic attraction) may tune the emission energy, despite thepresence in both cases of the nido-carborane-diphosphine ligand,which displays weak blue emissions.

Experimental

Instrumentation

Infrared spectra were recorded in the range 4000–200 cm-1 on aPerkin–Elmer 883 spectrophotometer using Nujol mulls betweenpolyethylene sheets. C and H analyses were carried out with aPerkin-Elmer 2400 microanalyzer. NMR spectra were recordedon a Bruker ARX-400 MHz spectrometer in CDCl3. Chemicalshifts are cited relative to SiMe4 (1H, external), CFCl3 (19F,external) and 85% H3PO4 (31P, external). Diffuse reflectance UVspectra were recorded on a EVOLUTION 600 spectrophotometerequipped with a Praying Mantis integrating sphere. The solidsamples were mixed with silica to obtain an homogeneous powder.Intensities are represented in Kubelka–Munk units. Steady-statephotoluminescence spectra were recorded with a Jobin-YvonHoriba Fluorolog FL-3-11 spectrometer using band pathways of3 nm for both excitation and emission. Phosphorescence lifetimeswere recorded with an IBH 5000 F coaxial nanosecond flashlamp.The lifetime data were fitted using the Jobin-Yvon IBH softwareDAS6 v6.1.

Computational details for DFT and TDDFT calculations

The molecular coordinates used in the theoretical studies of 1and 2 were obtained from the X-ray diffraction data. In boththe ground-state calculations and the subsequent calculationsof the electronic excitation spectra, the B3-LYP functional14 asimplemented in Gaussian 0315 was used. The excitation energieswere obtained at the density functional level by using TimeDependent Density Functional Theory (TDDFT), which is aDFT generalization of the Hartree–Fock linear response (HF-LR) or random-phase approximation (RPA) method.16 The twofirst singlet–triplet transitions were calculated within the TDDFTformalism as implemented in Gaussian. The TDDFT calculationsdo not evaluate the spin–orbit coupling, and the values areaveraged. In all calculations, the Karlsruhe split-valence-qualitybasis sets augmented with polarization functions were used(SVP).17 The Stuttgart effective core potential was used for Au.18

Starting materials

The starting materials [Au{(PPh2)2C2B9H10}(PR3)]19 and[Au(C6F5)(tht)]20 were prepared according to publishedprocedures.

Synthesis of [Au2{l-(PPh2)2C2B9H10}(C6F5)(PR3)] [(PR3) =PPh2Me (2), PPh2(p-tol) (3), P(p-tol)3 (4)]

In a similar procedure to that described for 1,7 to a solution of[Au{(PPh2)2C2B9H10}(PR3)] (0.1 mmol: (PR3) = PPh2Me, 89.8 mg,PPh2(p-tol), 134.9 mg, P(p-tol)3, 137.7 mg) in dichloromethane(ca. 20 mL) [Au(C6F5)(tht)] (0.1 mmol, 45.2 mg) was added. Thesolution was stirred for 30 min. and concentrated (ca. 5 mL).

Table 6 X-ray data for complex 2

Formula C46H45Au2B9Cl2F5P3

Mr 1347.85HabitCrystal size (mm) 0.10 ¥ 0.09 ¥ 0.05Crystal system MonoclinicSpace group P21/nCell constants:a (A) / b (A) c (A) 14.013(3)/14.090(3)/25.494(5)b (◦) 101.88(3)V (A3) 4925.7(17)Z 4Dx (Mg m-3) 1.818m/mm-1 6.029F(000) 2592T/◦C -173(2)2qmax 50No. of refl.: Measured/independent 68116/8652Transmissions 0.7465, 0.5756Rint 0.0670Parameters/Restraints 609/26wR(F 2, all Refl.) 0.0785R(I , >2s(I)) 0.0409S 1.151max. Dr (e A-3) 1.450

Addition of n-hexane (ca. 10 mL) affords yellow solids. Thecomplexes were recrystallized from dichloromethane/hot ethanol.(2) Yield 83%. Analytical data, Found: C, 42.45; H, 3.40. Calcd. forC45H43Au2B9F5P3: C, 42.80; H, 3.45. 1H NMR d : -2.12 (m, br, 1H,BHB); 0–3 (m, br, 9H, BH); 2.05 (d, 3H, CH3, JPH 7.7 Hz); 7–7.6(m, br, 30H, Ph). 19F NMR d : -160.8 (m, 2F, m-F); -157.2 (t, 1F, p-F; J(FF) = 21.0 Hz); -113.8 (m, 2F, o-F). (3) Yield 74%. Analyticaldata, Found: C, 46.20; H, 3.75. Calcd. for C51H47Au2B9F5P3: C,45.75; H, 3.55. 1H NMR d : -2.12 (m, br, 1H, BHB); 0–3 (m, br,9H, BH); 2.37 (s, br, 3H, CH3); 7–7.6 (m, br, 34H, Ph+ C6H4).19F NMR d : -161.4 (m, 2F, m-F); -158.5 (t, 1F, p-F; J(FF) = 21.0Hz); -113.7 (m, 2F, o-F). (4) Yield 82%. Analytical data, Found:C, 46.20; H, 3.50. Calcd. for C53H51Au2B9F5P3: C, 46.55; H, 3.75.1H NMR d : -2.12 (m, br, 1H, BHB); 0–3 (m, br, 9H, BH); 2.38 (s,br, 9H, CH3); 7–7.6 (m, br, 32H, Ph+ C6H4). 19F NMR d : -160.9(m, 2F, m-F); -158.8 (t, 1F, p-F; J(FF) = 24.0 Hz); -113.6 (m, 2F,o-F).

Crystallography

A crystal of 2 was mounted in inert oil on a glass fiber andtransferred to the cold gas stream of an Xcalibur Oxford Diffrac-tion diffractometer equipped with a low-temperature attachment.Data were collected using monochromated Mo-Ka radiation (l =0.71073 A). Scan type w. Absorption correction based on multiplescans were applied with the program SADABS.21 The structure wasrefined on F 2 using the program SHELXL-97.22 All non-hydrogenatoms were refined anisotropically. Hydrogen atoms were includedusing a riding model. Further details of the data collection andrefinement are given in Table 6.

Acknowledgements

We thank the Ministerio de Ciencia e Innovacion D.G.I.(CTQ2010-20500-C02-01) and the Supercomputing Centre of

10044 | Dalton Trans., 2011, 40, 10038–10046 This journal is © The Royal Society of Chemistry 2011

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

Galicia (CESGA-CSIC) for providing access to the FINIS TER-RAE System.

Notes and references

1 (a) A. Laguna, T. Lasanta, J. M. Lopez-de-Luzuriaga, M. Monge,P. Naumov and M. E. Olmos, J. Am. Chem. Soc., 2010, 132, 156–457; (b) E. J. Fernandez, J. M. Lopez-de-Luzuriaga, M. Monge, M. E.Olmos, R. C. Puelles, A. Laguna, A. A. Mohamed and J. P. FacklerJr., Inorg. Chem., 2008, 47, 8069–8076; (c) A. Luquin, C. Flosua, E.Vergara, J. Estella, E. Cerrada, C. Bariain, I. R. Matias, J. Garrido andM. Laguna, Gold Bull., 2007, 40, 225–233; (d) S. Casado, C. Elosua,C. Bariain, A. Carretero, I. R. Matias, A. Fernandez, A. Luquin, J.Garrido and M. Laguna, Optical Engineering, 2006, 45, 044401.1–044401.7; (e) D. B. Leznoff and J. Lefebvre, Gold Bull., 2005, 38, 47–54;(f) J. Lefebvre, J. Batchelor and D. B. Leznoff, J. Am. Chem. Soc., 2004,126, 16117–16125; (g) E. J. Fernandez, J. M. Lopez de Luzuriaga, M.Monge, M. E. Olmos, J. Perez, A. Laguna, A. A. Mohamed and J. P.Fackler Jr., J. Am. Chem. Soc., 2003, 125, 2022–2023; (h) J. C. Vickery,M. M. Olmstead, E. Y. Fung and A. L. Balch, Angew. Chem., Int. Ed.Engl., 1997, 36, 1179–1181; (i) M. A. Mansour, W. B. Connick, R. J.Lachicotte, H. J. Gysling and R. Eisenberg, J. Am. Chem. Soc., 1998,120, 1329–1330; (j) E. Y. Fun, M. M. Olmstead, J. C. Wickery and A.L. Balch, Coord. Chem. Rev., 1998, 171, 151–159.

2 (a) C. H. Chen and J. Shi, Coord. Chem. Rev., 1998, 171, 161–174;(b) R. C. Evans, P. Douglas and C. J. Wiscom, Coord. Chem. Rev.,2006, 250, 2093–2126; (c) M. A. Baldo, M. E. Thompson and S.R. Forrest, Pure Appl. Chem., 1999, 71, 2095–2106; (d) H. Yersin,Highly Efficient OLEDs with phosphorescent Materials, Wiley-VCH,Weinheim, Germany, 2008; (e) H. Yersin, Top. Curr. Chem., 2004, 241,1–26; (f) G. Schwarz, S. Reineke, T. C. Rosenow, K. Walter and K. Leo,Adv. Funct. Mater., 2009, 19, 1319–1333; (g) Ma, X. Zhou, J. Shen,H.-Y. Chao and C.-M. Che, Appl. Phys. Lett., 1999, 74, 1361–1363;(h) Y. Ma, C.-M. Che, H.-Y. Chao, X. Zhou, W.-H. Chan and J. Shen,Adv. Mater., 1999, 11, 852–857.

3 (a) O. Crespo, M. C. Gimeno and A. Laguna, J. Organomet. Chem.,2009, 694, 1588–1598; (b) O. Crespo, M. C. Gimeno, P. G. Jones, A.Laguna, J. M. Lopez-de-Luzuriaga, M. Monge, J. L. Perez and M.A. Ramon, Inorg. Chem., 2003, 42, 2061–2068; (c) M. J. Calhorda,O. Crespo, M. C. Gimeno, P. G. Jones, A. Laguna, J. M. Lopez-de-Luzuriaga, J. L. Perez, M. A. Ramon and L. F. Veiros, Inorg. Chem.,2000, 39, 4280–4285; (d) O. Crespo, M. C. Gimeno, A. Laguna, I.Ospino, G. Aullon and J. M. Oliva, Dalton Trans., 2009, 3807–3813;(e) R. Czerwieniec, T. Hofbeck, O. Crespo, A. Laguna, M. C. Gimenoand H. Yersin, Inorg. Chem., 2010, 49, 3764–3767; (f) Q. M. Wang, Y.A. Lee, O. Crespo, J. Deaton, C. Tang, H. J. Gysling, M. C. Gimeno, C.Larraz, M. D. Villacampa, A. Laguna and R. Eisengerg, J. Am. Chem.Soc., 2004, 126, 9488–9499; (g) O. Crespo, M. C. Gimeno, A. Laguna,C. Larraz and M. D. Villacampa, Chem.–Eur. J., 2007, 13, 235–246;(h) O. Crespo, M. C. Gimeno, A. Laguna, M. Kulcsar and C. Silvestru,Inorg. Chem., 2009, 48, 4134–4142; (i) O. Crespo, M. C. Gimeno, A.Laguna and C. Larraz, Z. Naturforsch, 2009, 64B, 1525–1534.

4 (a) J. M. Forward, J. P. Fackler Jr., Z. Assefa, in OptoelectronicProperties of Inorganic Compounds, M. Roundhill, J. P. Fackler Jr.ed.; Plenum Press, New York, 1999, 195–230; (b) A. Vogler and H.Kunkely, Coord. Chem. Rev., 2001, 219–221, 489–507; (c) J. M. Lopez-de-Luzuriaga, in Modern Supramolecular Gold Chemistry, A. Laguna,Ed., Wiley-VCH, Weinheim, 2008, 347–401; (d) V. W.-W. Yam and K.K.-W. Lo, Chem. Soc. Rev., 1999, 28, 323–334; (e) V. W. W. Yam, C.L. Chan, C. K. Li and K. M. C. Wong, Chem. Soc. Rev., 2008, 37,1806–1813.

5 (a) H. Kunkely and A. Vogler, Inorg. Chim. Acta, 2004, 357, 4607–4609;(b) V. V. Volkov, E. A. Il’inchik, O. P. Yur’eva and O. V. Volkov, J. Appl.Spectrosc., 2000, 67, 864; (c) F. Lerouge, C. Vinas, F. Teixidor, R. Nunez,A. Abreu, E. Xochitiotzi, R. Santillan and N. Farfan, Dalton Trans.,2007, 1898–1903; (d) K. Kenta and C. Yoshiki, Polym. J., 2010, 42, 363–367; (e) K. Kokado, Y. Tokoro and Y. Chujo, Macromolecules, 2009, 42,9238–9242; (f) K. Kenta, T. Yuichiro and C. Yoshiki, Macromolecules,2009, 42, 2925–2930; (g) K. Kokado, M. Tominaga and Y. Chujo,Macromol. Rapid Commun., 2010, 31, 1389–1394; (h) K. Kokado andY. Chujo, J. Org. Chem., 2011, 76, 316–319; (i) K. Kokado, A. Nagaiand Y. Chujo, Tetrahedron Lett., 2011, 52, 293–296; (j) K. Kokadoand Y. Chujo, Dalton Trans., 2011, 40, 1919–1923; (k) J. J. Peterson,A. R. Davis, M. Were, E. B. Coughlin and K. R. Carter, ACS Appl.

Mater. Interfaces, 2011, 3, 1796–1799; (l) K. Kokado, A. K. Nagai andY. Chujo, Macromolecules, 2010, 43, 6463–6468; (m) V. B. Nazarov, V.G. Avakyan, V. Y. Rudyak, M. V. Alfimov and T. G: Vershinnikova, J.Lumin., 2011, 131, 1932–1938; (n) V. V: Shelkovnikov, Z. M. Ivanova,N. A. Orlova, V. V. Volkov, M. K. Drozdova, K. G. Myakishev and A.I. Plekhanov, Opt. Spectrosc., 2004, 96, 824–833; (o) R. Luguya, F. R.Fronczek, K. M. Smih and M. G. H. Vicente, Appl. Radiat. Isot., 2004,61, 1117–1123; (p) J. J. Peterson, M. Werre, Y. C. Simon, E. B. Coughlinand K. R. Carter, Macromolecules, 2009, 42, 8594–8598.

6 (a) M. Ghiotti, P. F. H. Schwab, M. T. Indelli, C. Chiorboli and F.Scandola, Inorg. Chem., 2006, 45, 4331–4333; (b) M. F. Hawthorne, J.L. Zink, J. M. Skelton, M. J. Bayer, C. Liu, E. Livshits, R. Baer and D.Neuhauser, Science, 2004, 303, 1849; (c) M. J. Fisher, P. A. Jelliss, L. M.Phifer and N. P. Rath, Inorg. Chim. Acta, 2005, 358, 1531–1544; (d) P. A.Jelliss, Comments Inorg. Chem., 2008, 29, 1–25; (e) C. H. Shin, Y. Han,M. H. Lee and Y. Do, J. Organomet. Chem., 2009, 649, 1623–1631; (f) E.Hong, H. Jang, Y. Kim, S. C. Jeoung and Y. Do, Adv. Mater., 2001, 13,1094–1096; (g) J. Juarez-Perez, C: Vinas, F. Teixidor, R. Santillan, N.Farfan, A. Abreu, R. Yepez and R. Nunez, Macromolecules, 2010, 43,150–159; (h) J. A. Weinstein, M. T. Tierney, E. S. Davies, K. Base, A.A. Robeiro and M. W. Grinstaff, Inorg. Chem., 2006, 45, 4544–4555;(i) D. Zhang, J. Dou, D. Li and D. Wang, Inorg. Chim. Acta, 2006, 359,4243–4249; (j) J. Dou, D. Zhang, Y. Zhu, D. Li and D. Wang, Inorg.Chim. Acta, 2007, 360, 3387–3393.

7 O. Crespo, M. C. Gimeno, A. Laguna and M. D. Villacampa, ActaCrystallogr., Sect. C: Cryst. Struct. Commun., 1998, 54, 203–205.

8 (a) M. C. Gimeno, A. Laguna, in Comprehensive Coordination Chem-istry II., ed. J. A. McCleverty andT. J. Meyer, Elsevier, New York,2003, vol. 5, p 911–1145; (b) M. C. Gimeno, in Modern SupramolecularGold Chemistry, ed, A. Laguna, WILEY-VCH, Weinheim, 2008; ch.1, p 1–63; (c) O. Crespo, in Modern Supramolecular Gold Chemistry,ed, A. Laguna, WILEY-VCH, Weinheim, 2008; ch. 2, p 65–129; (d) E.J. Fernandez, A. Laguna and M. E. Olmos, Coord. Chem. Rev., 2008,252, 1630–1667; (e) V. Pawlowski, H. Kunkely and A. Vogler, Inorg.Chim. Acta, 2004, 357, 1309–1312; (f) M. Bardajı, M. T. de la Cruz, P.G. Jones, A. Laguna, J. Martınez and M. D. Villacampa, Inorg. Chim.Acta, 2005, 358, 1365–1372; (g) A. Pintado-Alba, H. de la Riva, M.Nieuwhuyzen, D. Bautista, P. R. Taithby, H. A. Sparkes, S. J. Teat,J. M. Lopez-de-Luzuriaga and M. C. Lagunas, Dalton Trans., 2004,3459–3467; (h) E. R. T. Tiekink and J.-G. Kang, Coord. Chem. Rev.,2009, 253, 1627–1648; (i) H. Xiao, Y.-X. Weng, W.-T. Wong, T. C. W.Mak and C.-M. Che, Dalton Trans., 1997, 221–226; (j) M. Bardajı, P.G. Jones, A. Laguna, M. D. Villacamapa and N. Villaverde, DaltonTrans., 2003, 4529–4536; (k) V. W.-W Yam, S. W.-K. Choi and K.-K.Cheung, Organometallics, 1996, 15, 1734–1739; (l) I. O. Koshevoy, A.J. Karttunen, S. P. Tunik, M. Haukka, S. I. Selivanov, A. S. Melnikov,P. Yu. Serdobintsev, M. A. Khodorkovskiy and T. A. Pakkanen, Inorg.Chem., 2008, 47, 9478–9488; (m) I. O. Koshevoy, L. Koskinen, M.Haukka, S. P. Tunik, P. Yu. Serdobintsev, A. S. Melnikov and T. A.Pakkanen, Angew. Chem., Int. Ed., 2008, 47, 3942–3945.

9 W. P. Schaefer, T. M. McClesey and H. B. Gray, Acta Crystallogr. C,1992, 48, 1379–1399.

10 V. W.-W. Yam, K.-L. Cheung, S.-K. Yip and N. Zhu, Photochem.Photobiol. Sci., 2005, 4, 149–153.

11 (a) V. W.-W. Yam, C. K. Li and C. L. Chan, Angew. Chem., Int. Ed., 1998,37, 2857–2859; (b) H. Kunkely and A. Vogler, Inorg. Chem. Commun.,2006, 9, 866–868.

12 (a) V. W.-W. Yam, C. L. Chan, C. K. Li and K. M. C. Wong, Coord.Chem. Rev., 2001, 173, 216–217; (b) Q.-J. Pan and H.-X. Zhang,Chem. Phys. Lett., 2004, 394, 155–160; (c) Q.-J. Pan and H.-X. Zhang,Organometallics, 2004, 23, 5198–5209; (d) Q.-J. Pan, H.-X. Zhang, H-GFu and H-T Yu, Eur. J. Inorg. Chem., 2006, 1050–1059.

13 (a) Y.-A. Lee, J. E. McGarrah, R. J. Lachicotte and R. Eisenberg, J. Am.Chem. Soc., 2002, 124, 10662–10663; (b) B. Weissbart, D. V. Toronto,A. L. Balch and D. S. Tinti, Inorg. Chem., 1996, 35, 2490–2496.

14 R. G. Parr, W. Yang. Oxford University Press, Oxford, 1989.15 Gaussian03 Revision C.02: M. J. Frisch, G. W. Trucks, H. B. Schlegel,

G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr.,R. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.

This journal is © The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 10038–10046 | 10045

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online

Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G.Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A.Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, P. M. Challacombe,P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, J. A.Pople, Gaussian, Inc., Wallingford, CT, 2008.

16 (a) R. Stratmann, G. Scuseria and M. Frisch, J. Chem. Phys., 1998,109, 8218–8224; (b) A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652;(c) C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785–789.

17 (a) A. Schafer, H. Horn and R. Ahlrichs, J. Chem. Phys., 1992, 97,2571–2577; (b) T. H. Dunning Jr., J. Chem. Phys., 1994, 100, 5829–5835.

18 D. Andrae, U. Hausserman, M. Dolg, H. Stoll and H. Preuss, Theor.Chim. Acta, 1990, 77, 123–141.

19 O. Crespo, M. C. Gimeno, P. G. Jones and A. Laguna, Inorg. Chem.,1996, 35, 1361–1366.

20 R. Uson, A. Laguna and M. Laguna, Inorg. Synth., 1989, 26, 85–91.21 Bruker SADABS (version 2.03), Bruker AXS, Inc. Madison, WI, 2000.22 G. M. Sheldrick, SHELXL-97, A program for Crystal Structure

Refinement, University of Gottingen, 1977.

10046 | Dalton Trans., 2011, 40, 10038–10046 This journal is © The Royal Society of Chemistry 2011

Publ

ishe

d on

09

Sept

embe

r 20

11. D

ownl

oade

d by

Chr

istia

n A

lbre

chts

Uni

vers

itat z

u K

iel o

n 26

/10/

2014

13:

24:1

5.

View Article Online