Tetraethylammonium [1-methylimidazole-2(3H)-thione]copper(I)-di-[mu]-sulfido-dioxotungstate(VI)

# 2004 International Union of Crystallography Printed in Great Britain ± all rights reserved In the title complex, tetrethylammonium [1-methylimidazole-2(3H)-thione-2 S]dioxo-1 O-di-sul®do-1:2 S:S-copper(I)tungstate(VI), (C8H20N)[WCuO2S2(Hmimt)], where Hmimt is 1-methylimidazole-2(3H)-thione (C4H6N2S), the W and Cu atoms have tetrahedral and trigonal planar coordination, respectively. Two sul®de ligands bridge the two metal centres; tungsten is additionally coordinated by two terminal oxo ligands and copper by the exocyclic S atom of Hmimt. The bridged W Cu distance is 2.670 (3) AÊ . Anions are linked into chains by NÐH O hydrogen bonds between Hmimt and oxo ligands.


Comment
Monovalent coinage metals are typical soft acids and their chemistry is largely based upon coordination by soft bases, such as sulfur donor ligands. Among the sulfur-containing ligands, heterocyclic thiones are of particular interest. Complexes of these ligands with transition metals are of interest in bioinorganic chemistry, because of the search for simple model compounds for metal proteins (Raper, 1996;Akrivos, 2001). In view of this, Cu I (Dai et al., 2004;Aslanidis et al., 2004;Cox et al., 1999), Ag I (Isab et al., 2002;Casas et al., 1996) and Au I (Ahmad, 2004;Isab & Hussain, 1985, 1986 complexes with thiones have been widely studied in recent years. We report here the synthesis and characterization of a copper(I) complex with Hmimt [1-methylimidazole-2(3H)thione] and [WO 2 S 2 ] 2À as a sulfur-donor ligands. The anion of the title compound, (I), is only the second example of copper coordination by the [WO 2 S 2 ] 2À metalloligand to be veri®ed by X-ray crystallography (Beheshti et al., 2001) and only the third example for any metal, the other being a palladium complex (Long et al., 1999).
A view of the structure is shown in Fig. 1 Atkinson et al., 1985). The bending at the thione S atom introduces an asymmetry in the anion which is also apparent in the dimensions of the WS 2 CuS core. In particular, the S3ÐCuÐS1 angle on the same side of the anion as the Hmimt ligand is signi®cantly greater than the other two bond angles at the Cu atom. This deviation from ideal trigonal±planar angles of 120 is attributed to steric effects and the bonding requirements of the Hmimt ligand.
The C2ÐC3 bond length in the Hmimt ligand is clearly consistent with a localized double bond and the thione C S bond is weakened and lengthened on coordination relative to that of the uncoordinated Hmimt molecule (1.676 A Ê ; Raper et al., 1983), due to a reduction in the %-bond character of the thione linkage accompanying metal±thione coordination. The 1 H NMR signals of Hmimt are shifted down®eld from those for the uncoordinated molecule, indicating that the ligand remains attached to Cu in solution in dimethyl sulfoxide. The 13 C NMR signals, compared with their positions in the spectrum of the uncomplexed ligand, support the coordination through S, leading to a weakening of the C S bond and some partial double bond character for CÐN (Popovic et al., 2000;Bierbach et al., 1998).
Tungsten has only slightly distorted tetrahedral coordination. The double sul®de bridges generate a short WÁ Á ÁCu distance of 2.670 (3) A Ê , which is not interpreted as a signi®cant direct metal±metal bond.
The NH group of Hmimt forms a hydrogen bond with an oxo ligand attached to tungsten in a neighbouring anion, with an NÁ Á ÁO distance of 2.70 (3) A Ê and an NÐHÁ Á ÁO angle of 177 . Repetition of this hydrogen bond by a screw axis generates a chain of anions along the b axis (Fig. 2). The tautomeric form of Hmimt is also con®rmed by characteristic bands in the FTÐIR spectrum, with an NÐH but no SÐH stretching vibration, and by the presence of a 1 H NMR signal for H bonded to N. There are no other signi®cant interactions among the components apart from normal coulombic and van der Waals forces; the packing is shown in Fig. 3.
The FT±IR spectrum of the complex exhibits strong features at 902 and 837 cm À1 characteristic of the symmetric and asymmetric stretching vibrations of the W O bonds in the coordinated [WO 2 S 2 ] 2À anion, respectively. The band at 437 cm À1 is assigned to the bridging WÐS bonds.

Experimental
(NH 4 ) 2 [WO 2 S 2 ] (0.316 g, 1.0 mmol) was dissolved in dimethylformamide (5 ml) and solid (Et 4 N)Br (0.441 g, 2.1 mmol) was added. The mixture was stirred at room temperature for 5 min. CuCl (0.1 g, 1.01 mmol) was added and the mixture was stirred for another 5 min and then ®ltered. 2-Propanol (10 ml) and diethyl ether (20 ml) were added to the ®ltrate. After stirring for 5 min, the precipitate was collected by ®ltration. It was washed with 2-propanol (3 ml) and diethyl ether (5 ml) and dried in vacuo to give a hygroscopic orange powder of (Et 4 N)[O 2 WS 2 CuCl] (yield 59%). (Et 4 N) 2 [O 2 WS 2 CuCl] (0.128 g, 0.2 mmol) was dissolved in acetonitrile (5 ml). Hmimt (0.049 g, 0.43 mmol) was added and the mixture was stirred at room temperature for 30 min and then ®ltered. Dry diethyl ether was added to the ®ltrate until a cloudiness persisted throughout the solution. Upon leaving the solution to stand in a sealed¯ask at 278 K overnight, pale-orange crystals of (Et 4   The molecular structure, with atom labels and 50% probability ellipsoids for non-H atoms.

Figure 2
The chain of anions generated by NÐHÁ Á ÁO hydrogen bonding (shown as dashed lines).
Crystal data (C 8  H atoms were positioned geometrically and re®ned with a riding model, and with U iso values constrained to be 1.2 (1.5 for methyl groups) times U eq of the carrier atom. Large and highly anisotropic displacement ellipsoids for the atoms of the cation indicate probable disorder, but no simple disorder model could be resolved; re®nement was assisted by restraints on geometry and displacement parameters, and the overall precision of the structure is relatively low as a result. The cation and anion are both achiral, but the compound crystallizes in a non-centrosymmetric space group; the re®ned Flack (1983) parameter of 0.35 (5) indicates partial inversion twinning of the structure. The maximum and minimum ®nal difference electron density features both lie almost 1 A Ê from the W atom.