A new co-crystallised tri-metallic nickel(II) complex:...

~ ) Pergamon PII : S0277-5387(97)00348-3

Polyhedron Vol. 17, No. 9, pp. 1571 1577, 1998 4") 1998 Published by Elsevier Science Ltd

All rights reserved. Printed in Great Britain 027~5387/98 $1900+0.00

A new co-crystallised tri-metallic nickel(ll) complex: bis(A,A-bis(ethylenediamine- N,N')bis(thiocyanato)-nickel(II))-A,A- tris ( e th ylenediamine-N,N') nick e l (II)-

hexafluorophosphate

Michael James,*t Hiroyuki Kawaguchi and Kazuyuki Tatsumi

Department of Chemistry, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan

(Received 23 June 1997; accepted 14 August 1997)

Abstract--The title compound, [A,A-Ni(en)2(NCS)2]2[A,A-Ni(en)3] [PF612 (1) (en = ethylenediamine) has been synthesised via a molecular rearrangement reaction of trans-Ni(en)2(NCS)2. 1 consists of [Ni(en)2(NCS)2]2 (la), [Ni(en)3] 2+ (lb) and [PF6]- (le) molecular units in a 2 : 1 : 2 ratio, such that both l a and lb crystallise in an ordered racemic sequence of A and A chiral units. Extensive intermolecular hydrogen bonding is observed between amine protons of the en chelate rings and the fluorine atoms of the [PF6]- counteranions, as well as between the amine protons and sulfur atoms of the NCS ligands. The en chelates display ring conformations of A22 for la and A~66 for lb. © 1998 Published by Elsevier Science Ltd. All rights reserved

Keywords: hydrogen bonding; amine protons; co-crystallisation.

The absolute configurations of optically active coordination compounds has been of long-standing inter- est to chemists. Since the structure and absolute configuration of the [Co(en)3] 3+ (en =ethylenediamine) cation were determined in 1955 by Saito et al. [1], numerous studies of structurally related compounds have been made. Where such compounds con- tain five-membered chelating ethylenediamine (en) rings, two possible enantiomeric configurations (A or A) and two possible ring conformations (6 and 2) may be formed. In the case of the tris-chelating pseudo- octahedral complex, [M(en)3] "÷, combination of these ring conformations and configurations leads to eight possible different isomers (A~66, A662, A622, A222, A866, A862, A622 or A222); while for bis-chelating molecules, cis-[M(en)2]Xz, there may be six different isomeric forms (A66, A62, A22, A66, A62 or A22) [2]. In the solid state both complexes usually occur as

* Author to whom correspondence should be addressed. t New Address: Neutron Scattering Group, ANSTO,

Lucas Heights Research Laboratories, PMB1, Menai N.S.W. 2234, Australia.

racemic mixtures, crystallising in centrosymmetric space groups that lead to an equal number of A and A metal centres.

As part of a continuing study into polymetallic complexes of linearly coupled paramagnetic metal ions, we have focused on the synthesis and structural characterisation of systems based on the trans- Ni(en)2X2 monomeric unit ; where X typically is a N- or O-donor ligand or a non-coordinated counteranion. More specifically, we have been invest- igating the reactivity of linear di-nitrogen bridging ligands such as pyrazine and 4,4'-bipyridine with trans-Ni(en)2(NCS)2. In the case of pyrazine, we observed that the bridging ligand was not sufficiently reactive under the conditions used to form a polymeric species. Rather, a molecular rearrangement reaction takes place whereby one monomer unit loses its thiocyanato ligands to another chelating en ligand and two other monomer units trans-/cis- isomerise. Tog- ether these three molecular units co-crystallise along with PF 6 counterions to form a complex salt. Here we present the synthesis and structural analysis of this new tri-nickel complex salt: [A,A-Ni(en)2 (NCS)2 ]2 [A ,A-Ni (en ) 3] (PF6)2.

1571

1572 M. James et al.

E X P E R I M E N T A L Table 1. Summary of crystallographic data for 1

Ni(NCS)E~/2H20, ethylenediamine, NH4PF6 and pyrazine were obtained from commercial sources and used as received. Methanol was of A.R. grade and was used without further purification.

Preparation of A,A-[Ni(en)2(NCS)2]2-A,A-[Ni(en)3] (PF6)2

trans-Ni(en)2(NCS)2 was prepared from Ni (NCS)21/2H20 and ethylenediamine in the manner reported by Brown and Lingafelter [3]. The absolute configuration of this compound was confirmed as trans- by X-ray diffraction of a single crystal. To an aqueous solution of trans-Ni(en)2(NCS)2 (1 mmol, 30 ml) and NH4PF6 (2 mmol) was added a methanolic solution of pyrazine (1 mmol, 10 ml) with rapid stirring. No immediate precipitate resulted. Upon reducing the vol- ume to ~ 20 ml on a hotplate and allowing the solution to stand in air for 3 weeks pale purple crystals of (1) suitable for X-ray diffraction were formed, along with a number of dark purple crystals of [Ni(en)2(#N.S- NCS)]2[PF6]2 (2). The physical and structural characterisation of 2 is reported elsewhere [4].

Crystal structure determination

Measurements were made on Rigaku AFC7R diffractometer at ambient temperature using mon- ochromated Mo-K, radiation (2 = 0.71069 A). A pale purple single crystal of 1 was placed at the end of a glass fibre. Cell constants were obtained by least- squares analysis of 25 strong reflections in the range 22.04 ° < 20 < 24.90 °. Details of crystal data, data col- lection and structure refinement are summarised in Table 1. The intensity data were corrected for Lorentz and polarisation effects and an empirical absorption correction based on azimuthal scans of several reflections was also applied. The structure of I was solved by direct methods and developed by alternating cycles of difference Fourier syntheses and full matrix least- squares refinements. The positions of the non-hydrogen atoms were determined unequivocally. The non- hydrogen atoms were refined anisotropically, while the hydrogen atoms were placed at calculated positions for the final refinement and their thermal par- ameters refined isotropically. Neutral atom scattering factors were taken from Ref. 5 and anomalous dis- persion corrections were taken from Ref. 6. Crys- tallographic calculations were carried out with a teXsan crystallographic software package of Molec- ular Structure corporation (1985 & 1992).

RESULTS AND DISCUSSION

Molecular and crystal structure

The compound [A,A-Ni(en)2(NCS)2MA,A- Ni(en)3](PF6)2 (1) crystallises in the monoclinic space

Chemical formula Ni3CIsH56N lsS4P2FI2 Formula weight 1119.026 Crystal system Monoclinic Space group CJc (No. 15) a (A) 24.715(3) b (A) 12.806(2) c (A) 17.328(2) ct (°) 90 fl (°) 124.532(6) ), (~') 90 V (A 3) 4518(1) Z 4 p (Mo-K~) (cm -~) 22.02 Crystal size (mm) 0.30 × 0.10 × 0.10 Dc~zc (gcm 3) 1.645 Radiation (A) 0.71069 20m,x (°) 50.0 Reflections collected 3143 Reflections used 1738 (I > 3a(/)) Variables 260 (A/o-)max 0.01 /0max/Pmin (e ~k -3) 0.58/-0.38 R" 0.049 Rw h 0.056 GOF' 1.60

° R = ~ l l F o l - tFclll~lFol. hR, = [Zw(leol- IFcl)~trwlFol2] ':2. <GOF = [~(IFol- [Fd)2/~2(N~n.s--gp . . . . . )]1/2

group C2/c (No. 15) with a=24 .715(3 ) /~, b = 12.806(2) A, c = 17.328(2) A, fl = 124.532(6) °, V = 4518(1) /~3 and Z = 4. The arrangement of the three distinct molecules cis-[Ni(en)2(NCS)2] ( la) , [Ni(en)3]2+(lb) and the counteranion [PF6]- (lc) in the asymmetric unit of I is shown in Fig. 1. Selected bond lengths are given in Table 2 and selected bond angles in Table 3. The bis-chetate molecule (la) is centred at a general (x,y,z) 8-fold crystallographic site ; while the tris-chelate molecule (lb) and the coun-

1 I I teranions (lc) occupy 4-fold sites at (5,y,~), (0,y,~) and 11 (~, ~, 0) respectively, leading to a ratio of 2 : 1 : 2 in the unit cell. Numerous uni-metallic [7-19] complex salts containing the optically active [Ni(en)2X:] or [Ni(en3)] 2÷ structural units have been studied ; as have a number ofdi-nickel salts containing one or the other of these structural units [20-23]. To our knowledge, there has only been one other report of a co-crystallised salt containing both of these elements, notably [Ni(en)2(benzoyl-hydrazine)][Ni(en)3]I4" H20 [24].

The Ni(en)2(NCS)2 structural motif (la)

The structure of l a is in itself noteworthy. As an isolated molecule Ni(en)2(NCS)2 has only been detected in the solid state as a trans-isomer ; although, two different structural modifications have been reported [3,25]. To our knowledge, this is the first

A new co-cr' rstallised tri-metallic Ni(II) complex 1573

F 6 ~ F6*

F4 ~ F5*

C8".

C9" ' ~ C 9 N47. Ng*a_x~ ~ 9

N 7 ~ C 7 i ~ N~ N8 ~ ) S I

1.

q. c5

C 3 ~ ~ 3 F3 ~ F I

Fig. 1. An ORTEP drawing of the asymmetric unit of [Ni(en)2(NCS)2]2[Ni(en)31(PF6)2 (1). Hydrogen atoms have been omitted for clarity. All atoms are represented by the thermal ellipsoids at 50% probability.

Table 2. Selected bond lengths (A) for la, lb and le

la cis-[Ni(en)2(NCS)2 ] Ni(1)--N(I) 2.083(6) N(I)--C(1) 1.142(8) C(I)--S(1) 1.656(17) Ni(1)--N(2) 2.070(6) N(2)--C(2) 1.153(9) C(2)--S(2) 1.635(8) Ni(1)--N(3) 2.126(5) N(3)--C(3) 1.45(1) C(3)--C(4) 1.29(1) N(4)--C(4) 1.42(1) Ni(1)--N(4) 2.094(7) Ni(I)--N(5) 2.090(7) N(5)--C(5) 1.46(1) C(6)--C(5) 1.47(1) N(6)--C(6) 1.44(1) Ni(1)--N(6) 2.123(6)

lb [Ni(en)3] 2+ Ni(2)--N(7) 2.135(6) N(7)--C(7) 1.43(1) C(7)--C(8) 1.43(1) N(8)--C(8) 1.43(1) Ni(2)--N(8) 2.133(6) Ni(2)--N(9) 2.117(6) N(9)--C(9) 1.44(1) C(9)--C(9) 1.37(2)

lc [PFd- P--F(average) 1.528(7)

1574 M. James et al.

Table 3. Selected bond angles ( ) for la, lb and lc

la cis-[Ni(en)2(NCS)2] N(1)--Ni(I)--N(2) 9 2 . 2 ( 2 ) N(I)--Ni(1)--N(3) 174.6(3) N(I)--Ni(I)--N(5) 9 0 . 4 ( 3 ) N(1)--Ni(I)--N(6) 88.9(2) N(2)--Ni(1)--N(4) 8 8 . 8 ( 3 ) N(2)--Ni(I)--N(5) 92.1(3) N(3)--Ni(I)--N(4) 8 1 . 9 ( 2 ) N(3)--Ni(I)--N(5) 94.9(2) N(4)--Ni(I)--N(5) 1 7 6 . 6 ( 2 ) N(4)--Ni(1)--N(6) 96.2(3) Ni(1)--N(1)--C(I) 1 7 1 . 1 ( 6 ) N(1)--C(I)--S(I) 179.3(7) N(2)--C(2)--S(2) 1 7 9 . 6 ( 8 ) Ni(1)--N(3)--C(3) 107.0(5) C(3)--C(4)--N(4) 1 2 1 . 3 ( 9 ) C(4)--N(4)--Ni(1) 108.7(6) N(5)--C(5)--C(6) 1 1 2 . 4 ( 7 ) C(5)--C(6)--N(6) 112.0(8)

lb [Ni(en)3] 2+ N(7)--Ni(2)--N(7) 1 7 0 . 7 ( 3 ) N(7)--Ni(2) N(8) 91.8(2) N(7)--Ni(2)--N(9) 9 3 . 2 ( 2 ) N(7)--Ni(2)--N(9) 93.8(2) N(8)--Ni(2)--N(9) 1 7 1 . 8 ( 2 ) N(8)--Ni(2)--N(9) 91.9(2) Ni(2)--N(7)--C(7) 1 0 7 . 5 ( 5 ) N(7)--C(7)--C(8) 114.7(8) C(8)--N(8)--Ni(2) 1 0 8 . 2 ( 5 ) Ni(2)--N(9)--C(9) [08.1(4)

lc [PF6] F--P--F(range) 85.8(5) and 178.3(8)-

93.6(5) 178.7(3)

N(I)--Ni(I)--N(4) 92.8(3) N(2)--Ni(I)--N(3) 88.4(2) N(2)--Ni(I)--N(6) 174.8(3) N(3)--Ni(1)--N(6) 90.9(2) N(5)--Ni(I)--N(6) 82.8(3) Ni(1)--N(2)--C(2) 164.9(7) N(3)--C(3)--C(4) 119.5(8) Ni(1)--N(5)--C(5) 108.1(6) C(6)--N(6)--Ni(1) 107.8(5)

N(7)--Ni(2)--N(8) 81.9(2) N(8)--Ni(2)--N(8) 94.7(3) N(9)--Ni(2)--N(9) 81.8(3) C(7)--C(8)--N(8) 114.8(7) N(9)--C(9)--C(9) 116.3(7)

report of an optically active Ni(ll) centre containing bis-chelating en rings as well as two monodentate N- donor thiocyanato ligands in a c/s-arrangement. Monomeric molecular structures of the type Ni(en)2(NCS)X have been reported where X = CI-, Br or NO3 [18]; while dimeric structures [Ni(en)2(#N.s-NCS)]zX2 have been characterised for X = I - o r C I O 4 [19]. As a part of our own study, the dimeric species [Ni(en)2(#N,s-NCS)]2[PF6]2 (2) has also been isolated [4]. Recently, the 1-dimensional polymeric Ni(II) complex {catena-(#~,s-NCS)[Ni- (en)2]} (PF6) has been reported [26]. Polymeric structures with bridging nitrito groups have also been noted for {catena-(#-NO2)[Ni(en)2]}X where X = B F 4 [27], ClOg [28], and 13 and PF6 [29].

The N i I - - N bond lengths of the thiocyanato ligands of la (2.083(6) ~, ( N i l - N 1 ) and 2.070(6) A ( N i l - N 2 ) ) are significantly shorter than that found in the case of the trans-isomer (2.15/~) [3], and slightly longer than that reported for cis-Ni(en)2(NCS)Cl (2.01/~) [18]. The N 1 - - N i l - - N 2 bond angle between the NCS ligands is 92.2(2) °, while the average bond angle between the Ni l - -N(en) bonds and the N i l - -N(NCS) bonds are 90.2(3) ° and 174.8(3)'. The average N - - N i l - - N bond angle within the en rings of 82.4(3) ° is characteristic of deviations away from regular octahedral geometry that have been observed for other chelating systems [7-13,20,21 ]. Ni 1--N(en) bond lengths are typical of those found in other uni- metallic Ni(en)2(X)2 complexes; although in la, a clear trans effect is observed relative to the thiocyanato ligands (Table 2). This feature has also been observed by Poraj-Kosic in the case of the compounds Ni(en)2(NCS)CI and Ni(en)2(NCS)(NO3) [18]. The

bond lengths (Table 2) and bond angles (Table 3) of the en and NCS ligands of la are characteristic of those found in other coordination complexes.

The ring pucker of the chelate rings in 1 can be quantified by the dihedral angle (09) between the planes defined, for example, by N 3 - - C 3 - - C 4 and C3- -C4- -N4. The values of o9 for the N3- -N4 and N5--N6 rings were found to be 14(1) ° and 48(1) ° respectively; the former being substantially smaller than usually found (~50 °) in tri-chelating en complexes [9,11] This atypical ring pucker of the N3- -N4 chelate may be a consequence of the strong hydrogen bonds that form between amine protons and acceptor sites on the counteranions (see below).

The [Ni(en)3] 2+ structural motif(lb)

While the [Ni(en)3] 2+ (lb) moiety displays C3 pseudo-symmetry typical of tris-chelating molecular units, it is noteworthy that the true site symmetry in this crystal is C> The average N i2 - -N bond length of 2.128(7) A in lb is characteristic of those found in other uni-metallic [Ni(en)3] 2+ complex salts [7-13]. N - - N i 2 - - N bond angles within the en chelate rings of 81.9(3) ° (N7--Ni2- -N8) and 81.7(4) ° (N9--Ni2--N9*) also show the usual deviations away from regular octahedral geometry that have been observed in other systems [7-13]. The average values for N - - N i 2 - - N bond angles between adjacent chelate rings are 92.9(3) ~' and 171.5(3) ° ; being consistent with the above compounds. In general, the other bond lengths and bond angles within the chelate rings of lb are consonant with those observed in other

A new co-crystallised tri-metallic Ni(II) complex

[Ni(en)3] 2+ complex salts [7-13]. Dihedra l angles (~o) of 4 3 ( l y and 38(1) ° for the N 7 - - N 8 and N 9 - - N 9 * chelates indicate modera te ring pucker.

Hydrogen bondin9

Extensive hydrogen bond ing is observed in 1 between the amine pro tons and Lewis base (acceptor) sites. Table 4 conta ins selected intra- and intermolecular hydrogen bond ing distances and angles. Figure 2 shows intermolecular hydrogen bond ing (dashed lines) and part ial packing of the uni t cell, projected along the b-axis between - 0 . 2 8 ~< y ~< 0.28. Both chiral elements l a and l b show strong intermolecular hydrogen bonding, part icularly between amine d o n o r pro tons and the fluorine a toms of l c ; forming a 3-dimensional ne twork within the crystal. In the case of la , the majori ty of s t rong hydrogen bonds occur between amine protons tha t are parallel to the pseudo-C3 axis. The converse is true in the case of lb, where s t rong hydrogen bonds are formed a lmost exclusively by amine pro tons tha t present oblique angles to the pseudo-C3 axis of the molecule. Weaker in termolecular hydrogen bonds are also observed between amine p ro tons and Lewis base sites at S a toms of the th iocyana to ligands and N a toms of other en groups.

In termolecular hydrogen bond ing is a feature com- monly observed in compounds conta in ing chelat ing en rings. In the case of bis-chelating molecules, s t rong

1575

Fig. 2. Partial packing of the unit cell of I projected along the b-axis between -0.28 ~< y ~< 0.28.

in termolecular bonds have been observed between amine p ro tons and coord ina ted NO2 ligands [18], and C102 coun te ran ions [28]. While no t specifically men- t ioned by the au thors Monfo r t et al. in the case of

Table 4. Selected intermolecular hydrogen bonds (distances (A) and angles (')) for 1

D- -H -. • A" D. •. A H. • - A D - - H . . - A Symmetry h Direction'

N3- -H1- . -F2 3.32(1) 2.82 112.9 N3- -H2- - .F3 3.01(1) 2.15 148.5 N3--H1 .--SI 3.72(1) 2.84 153.7 N 4 ~ H 7 - • - F4 3.20(2) 2.43 136.1 N4--HT. - • F6 3.22(1) 2.44 138.5 N5--H9-- . F1 3.32(1) 2.44 152.0 N5--H9 . . • F3 3.29(1) 2.39 155.3 N 5 - - H I 0 . . . F 4 3.13(1) 2.24 157.4 N6--H 15 • - • F6 3.21(1) 2.67 119.7 N6--H16. . . $2 3.66(1) 2.78 153.7 N7--HI7 . • . F2 3.18(1) 2.24 172.6 N7- -HI7 . - .N7 3.14(1) 2.93 93.5 N8--H23 -.. F5 3.51(1) 2.67 161.3 NS--H23- • . N9 3.10(1) 2.88 94.5 NS--H24. . • $2 3.66(1) 2.94 153.7 N9--H25- . . $2 3.49(1) 2.60 155.2 N9--H26. . - F5 3.29(1) 2.41 152.0 N9--H26-- .N8 3.10(1) 2.87 95.0

ob pa ob pa pa pa pa ob ob pa ob ob ob ob pa pa ob ob

"D, hydrogen donor ; A, hydrogen acceptor. ~' Numbers refer to the following equivalent positions relative to the reference molecule at x,

v , z : ( l ) x , v , z ; ( 2 ) x , - y , z + ~ ; ( 3 ) I i i. l l ~ - x + ~ , y + ~ , - z + ~ , (4) - x + l , y , - z + ~ (5) x+~,y-~,z . ' Direction of N - - H bond relative to the pseudo-C3 axis of the Ni centre : pa = parallel;

ob = oblique.

1576

A~.~.

M. James et al.

q 9

SI

C4

C8 C8

""X'~ - K

A888

Fig. 3. Isomeric mirror image forms of (a) A22 and A66 for la and ; (b) A666 and A222 for lb. Hydrogen atoms have been omitted for clarity.

{catena-(llN,s-NCS)[Ni(en)2]}(PF6) [26], it seems likely that hydrogen bonding interactions should also play a significant role in stabilising this compound. Strong intermolecular hydrogen bonding has also been observed in many tris-chelating molecules between amine protons and oxygen atoms of nitrate [7]; sulfate [9]; acetate [1 I] and tartrate [12] counterions.

Absolute configurations of la and lb

Both molecular species l a and lh form chiral enti- ties; however, due to the constraints of crystal symmetry presented by the centrosymmetric C2/c space group, both A and A forms are present in equal quan- tities and ordered in the unit cell. The A22 and A66 forms of la are displayed in Fig. 3(a) ; while the A666

A new co-crystallised tri-metallic Ni(II) complex

and A22~. forms of lb are given in Fig. 3(b). The 7. following discussion will relate to the A configuration only, keeping in mind that for racemic systems, these 8. arguments hold equally true for their respective mirror 9. images having the A configuration. 10.

Much debate has centred around which chemical effects cause any of the four isomers (A666, A662, 11. A622, A222) to be the most stable. Factors that have been considered include anion size [20], hydrogen 12. bonding [30] and crystal packing forces [11]. Gollogly et al. [31] argued that entropy effects would cause 13. the A662 isomer to have the lowest free energy, and

14. structural characterisation of compounds containing 15. very few hydrogen bonds has lent weight to this pro- posal [13,32]. It has been observed that the most corn- 16. mon configuration is A66~, presumably because it is the one most easily stabilised by hydrogen bonds. 17. Cramer and Huneke [13] proposed that this isomer should have the second lowest energy ; while the rarely

18. observed A222 configuration which also has a strong tendency to from hydrogen bonds should be the iso- 19. mer with the highest energy. As was observed for Ib, Cramer and Huneke [13] found that in the case of the 20. A655 configuration, the strongest or greatest number of hydrogen bonds were formed to amine protons that had oblique angles to the pseudo-C3 axis. The 21. converse was observed for 2 rings; where a majority or the strongest bonds were formed with amine pro- 22. tons that were parallel to the pseudo-C 3 axis.

The conformations of his-chelating en rings have 23. received less attention; however, the absolute configuration of A)A for la is again consistent with a majority of strong hydrogen bonds being formed 24. between counteranions and "parallel" amine protons.

REFERENCES

25.

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26.

1. Saito, Y., Nakatsu, K., Shiro, M. and Kuroya, 27. H., Acta Crvst., 1955, 8, 729.

2. Inor 9. Chem., 1970, 9, 1. 3. Brown, B. W. and Lingafelter, E. C., Acta Cryst., 28.

1963, 16, 753. 4. James, M., Kawaguchi, H. and Tatsumi, K., Acta 29.

Crystallogr. C, 1997 (In preparation). 5. Cromer, D. T. and Waber, J. T., International 30.

Tables for X-ray Crystallography, Vol. IV. ed. T. Hahn. Kynoch, Birmingham, England, 1974, 31. Table 2.2A.

6. Ibers, J. A. and Hamilton, W. C., Acta Crystal- 32. loyr., 1964, 17, 781.

Korp, J. D., Bernal, I., Palmer, R. A. and Robin- son, J. C., Acta Crystallogr., 1980, B36, 560. Mazhar-Ul-Haque, Caughlan, C. N. and Emer- son, K., Inorg. Chem., 1970, 9, 2421. Cramer, R. E., lnorg. Chem., 1972, 11, 1019. Raston, C. L., White, A. H. and Willis, A. C., Aust. J. Chem., 1978, 31, 415. Cramer, R. E., van Doorne W. and Huneke, J. T., Inorg. Chem., 1976, 15, 529. Mizuta, T., Yoneda, H. and Kushi, Y., Inorg. Chim. Acta, 1987, 132, 11. Cramer, R. E. and Huneke, J. T., Inorg. Chem., 1978, 17, 365. Yu. I. Smolin, J. Chem. Soc., D., 1969, 395. Singh, R. and Gautam, R. K., J. Indian Chem. Soc., 1987, 64, 631, Begum, N. S., Poojary, M. D. and Manohar, H., J. Chem. Soc., Dalton Trans., 1988, 1303. Tomlinson, A. A. G., Bonamico, M., Dessy, G., Fares, V. and Scaramuzza, L., J. Chem. Soc., Dalton Trans., 1976, 1671. Poraj-Kosic, M. A., Acta Crystallogr., 1966, 21, A149. Svelasvili, A. E., Acta Crystallogr., 1966, 21, A153. du Preez, J. G. H., Rohwer, H. E., Brecht, B. J. and Caira, M. R., J. Chem. Soc., Dalton Trans., 1984, 975. Chulmin Keum, Chonhan Kim, Chulsung Kim, Hyontae Kwak, Moonhee Kwon and Hae Namgung, Bull. Korean Chem. Soc., 1992, 13, 695. Cernak, J., Potocnak, I. and Dunaj-Jurco, M., Z. Kristallogr., 1994, 209, 757. Sisoeva, T. F., Arge, V. M., Trunov, V. K., Dyat- lova, N. M. and Ya. Fridman, A., Zh. Strukt. Khim., 1986, 27, 108. Shelvashvili, A. E., Vardosanidze, T. O., Sobolev, A. N., Beshkenadze, I. A. and Sokol, V. I., Soob. Akad. Navak. Gruz. SSR, 1983, 110, 49. Podberezskaya, N. V., Shakhshneider, T. P., Virovets, A. V. and Stabnikov, P. A., Zh. Struk. Khim., 1991, 32, 96-5. Monfort, M., Bastos, C., Diaz, C. and Ribas, J., Inor 9. Chim. Acta, 1994, 218, 185. Drew, M. G., Goodgame, D. M. L., Hitchman, M. A. and Rodgers, D., Chem. Commun., 1965, 477. Llewellyn, F. J. and Waters, J. M., J. Chem. Soc., 1962, 3845. Meyer, A., Gleizes, A., Girerd, J.-J., Verdaguer, M. and Kahn, O., Inor 9. Chem., 1982, 21, 1729. Raymond, K. N., Corfield, P. W. R. and Ibers, J. A., Inor 9. Chem., 1968, 7, 842. Gollogly, J. R., Hawkins, C. J. and Beattie, J. K., Inor9. Chem., 1971, 10, 317. Raymond, K. N., Corfield, P. W. R. and Ibers, J. A., Inor9. Chem., 1968, 7, 1362.

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