N—H S and N—H O hydrogen bonding in tetra-n-butylammonium (imidazolidine-2- thione-2jS)dioxo-1jO-di-l-sulfido-1:2jS:S- copper(I)tungstate(VI)

# 2005 International Union of Crystallography Printed in Great Britain – all rights reserved In the title complex, (C16H36N)[WCuO2S2(C3H6N2S)], the W and Cu atoms have tetrahedral and trigonal-planar coordination, respectively. Two sulfide ligands bridge the two metal centres; tungsten is additionally coordinated by two terminal oxo ligands and copper by the exocyclic S atom of imidazolidine-2-thione. There is an intramolecular N—H S hydrogen bond in the anion, and anions are linked into chains by N—H O intermolecular hydrogen bonds. The more loosely held cation is disordered.

In the title complex, (C 16 H 36 N)[WCuO 2 S 2 (C 3 H 6 N 2 S)], the W and Cu atoms have tetrahedral and trigonal-planar coordination, respectively. Two sulfide ligands bridge the two metal centres; tungsten is additionally coordinated by two terminal oxo ligands and copper by the exocyclic S atom of imidazolidine-2-thione. There is an intramolecular N-HÁ Á ÁS hydrogen bond in the anion, and anions are linked into chains by N-HÁ Á ÁO intermolecular hydrogen bonds. The more loosely held cation is disordered.
The structure of the bimetallic anion is shown in Fig. 1 and selected geometric parameters are given in Table 1. The disordered cation is geometrically unexceptional. In the [O 2 WS 2 Cu(Imt)] À anion (Imt is imidazolidine-2-thione), the coordination environments of tungsten(VI) and copper(I) are slightly distorted tetrahedral and rather more strongly distorted trigonal planar, respectively. The angular deviations around the Cu atom may be attributed to steric effects and the constraints of the WS 2 Cu four-membered ring. Copper is coordinated by two bridging S and a terminal, monodentate Sdonating Imt ligand. The bridging angles at S are the smallest angles in the complex and are only slightly larger than the value required for regular edge-sharing tetrahedra (70.5 ; Summerville & Hoffman, 1976). Narrowing of the bridging angle is inevitably accompanied by a reduction in the WÁ Á ÁCu separation distance, which is not, however, considered as indicating a direct metal-metal bond. The Cu-S1 distance and Cu-S-C angle are typical of terminal monodentate Sdonating thiones attached to trigonal planar Cu(I) (Beheshti et al., 2004). In common with other thione complexes, a slight lengthening of the S-C distance occurs, relative to that of the C S bond length in the free Imt ligand, due to a reduction in the -bond character of the thione linkage accompanying metal-thione coordination. The Cu-S2 and Cu-S3 distances are in the range [2.168 (9)-2.340 (9) Å ] reported for (Et 4 N)[WO 2 S 2 Cu(Hmimt)], where Hmimt is the closely related ligand 1-methylimidazole-2(3H)-thione (Beheshti et al., 2004).
Although there are many crystallographically characterized examples of complexes in which Cu I is bonded across SÁ Á ÁS edges of [WS 4 ] 2À and [OWS 3 ] 2À tetrahedra, the title complex appears to be only the third case for [O 2 WS 2 ] 2À , the others being the closely related Cu(Hmimt) complex mentioned above (Beheshti et al., 2004) and a CuPPh 3 complex (Beheshti et al., 2001).
The striking feature of the structure of the anion is the orientation of the thione ligand; this brings one NH group of the heterocyclic ligand into a position close to one bridging sulfur atom of the WO 2 S 2 group, with the formation of an intramolecular N-HÁ Á ÁS hydrogen bond ( Fig.1 and Table 2). In addition to the intramolecular N-HÁ Á ÁS hydrogen bond, the second NH group of Imt forms an intermolecular hydrogen bond with an oxo ligand attached to tungsten in a neighbouring anion (Fig. 2 and Table 2). This hydrogen bond generates a chain of anions. Such hydrogen bonds have been found to play important roles in regulating the properties of metal-sulfur proteins as well as their model complexes (Houseman et al., 1992;Sun et al., 1993).
In the solid state, infrared spectroscopy may also be used to probe the mode of coordination of Imt and [WO 2 S 2 ] 2À ligands. Uncoordinated Imt exhibits N-H stretching and C S bands at 3200 and 510 cm À1 , respectively. The corresponding N-H and C S vibration bands were observed at 3308 and 500 cm À1 for the complex. The shifts of (N-H) (108 cm À1 upwards) and (C S) (10 cm À1 downwards) and the absence of a (S-H) band at 2500 cm À1 clearly indicate that the Imt ligand is coordinated only via the thione sulfur in the complex. The W O stretching frequencies of the [WO 2 S 2 ] 2À ligand in the complex (918 and 867 cm À1 ) are shifted to higher values than for the free [WO 2 S 2 ] 2À anion (850 and 795 cm À1 in the ammonium salt; McDonald et al., 1983); this indicates that the [WO 2 S 2 ] 2À ligand is coordinated through its sulfur atoms. The band at 437 cm À1 is assigned to the bridging W-S bonds.
Thus, the infrared spectroscopic results are consistent with the X-ray structural analysis.

Experimental
(NH 4 ) 2 [WO 2 S 2 ] (0.316 g, 1.0 mmol) was dissolved in acetone (40 ml) and solid (n-Bu 4 N)Br (0.676 g, 2.1 mmol) was added. The mixture was stirred at room temperature for 5 min. CuCl (0.099 g, 1 mmol) was added and the mixture was stirred for 1 h. Imt (0.112 g, 1.1 mmol) was added and the mixture was stirred at room temperature for 4 h and then filtered. The filtrate was evaporated under vacuum. The oily residue was dissolved in dichloromethane (25 ml) and the solution filtered to remove any insoluble material. The filtrate was evaporated to dryness under vacuum. The residue was washed with distilled water (2 Â 2 ml), 2-propanol (2 Â 2 ml) and diethyl ether (2 Â 5 ml) and dried in vacuo to give a pale-brown powder. The yield at this stage was 0.43 g (46%). Crystals were obtained by diffusing diethyl ether into a saturated solution in acetone. On leaving the solution to stand in a refrigerator overnight, air-stable orange crystals were deposited, which are soluble in common organic solvents. 1 H NMR (DMSO-d 6 , 300 K): 8.38 (s, N-H), 3.68 (s, CH 2 ); 13 C NMR (DMSO-d 6 , 300 K): 180.23 (C1), 45.41 (C2 and C3) (using the atom numbering of Fig. 1). In the 1 H NMR spectrum of the complex, the ligand signals are shifted down-field from their positions in the spectrum of the free ligand (N-H,7.94 and CH 2 3.505 p.p.m.), but in the 13 C NMR spectrum of the complex, the C S signal is shifted upfield from its position in the spectrum of the free ligand (183.35 p.p.m.), due to the reduction of the C S bond order upon coordination and a shift of electron density producing partial double bond character in the C-N bond. These observations indicate that, in DMSO-d 6 , the ligand remains coordinated to the metal.
Crystal data (C 16   A section of the packing, viewed along the a axis. Hydrogen bonds are shown as dashed lines, and other H atoms have been omitted, together with minor disorder components.
The cation is disordered. Most C atoms could be resolved into two components with sensible connectivities. Separate occupancy factors were refined for the components of each n-butyl group, giving values of 0.747 (9), 0.660 (12), 0.690 (9) and 0.817 (10) for the major sites; similarity restraints were applied to the displacement parameters and bond lengths. The remaining C atoms may also be disordered, to a smaller extent, but this could not be resolved. H atoms bonded to N were located in a difference map and refined with a restrained N-H distance of 0.87 (2) Å , and with U iso (H) = 1.2U eq (N). Other H atoms were positioned geometrically and refined with a riding model, with C-H = 0.95-0.99 Å , and with U iso (H) = 1.2 (1.5 for methyl groups) times U eq (C).