Bis(tetra-n-butylammonium) tetrakis[chloro- (l3-sulfido)copper(I)]tungstate(VI): a second polymorph

# 2004 International Union of Crystallography Printed in Great Britain ± all rights reserved The title compound, (C16H36N)2[WS4(CuCl)4], has been obtained in a second polymorphic form. The anion, in which four of the six S S edges of the central WS4 tetrahedron are bridged by CuCl neutral molecular units to give a planar pentanuclear WCu4 framework, is disordered on a crystallographic fourfold rotation axis, requiring equal occupancy of two sets of four positions for the S atoms. Copper has distorted trigonal planar coordination, involving two 3-S atoms and a terminal Cl atom. The two independent cations lie on positions of symmetry 4.

The title compound, (C 16 H 36 N) 2 [WS 4 (CuCl) 4 ], has been obtained in a second polymorphic form. The anion, in which four of the six SÁ Á ÁS edges of the central WS 4 tetrahedron are bridged by CuCl neutral molecular units to give a planar pentanuclear WCu 4 framework, is disordered on a crystallographic fourfold rotation axis, requiring equal occupancy of two sets of four positions for the S atoms. Copper has distorted trigonal planar coordination, involving two " 3 -S atoms and a terminal Cl atom. The two independent cations lie on positions of symmetry 4.

Comment
We recently reported the structure of a second tetragonal polymorph of (N n Bu 4 ) 2 [MoS 4 (CuCl) 4 ] in space group P4/n (Brooks et al., 2004); the ®rst polymorph, in space group I4, had very similar cell parameters (Se Â cheresse et al., 1991). The title tungsten analogue, (I), was also prepared as a precursor for the synthesis of complexes with the WS 4 Cu 4 core and a range of terminal ligands (Hossaini Sadr et al., 2004) and it is found to be isostructural with the second polymorph of the molybdenum complex. There are no signi®cant differences between the two structures, and a full discussion was given in the previous report.
Se Â cheresse et al. (1991) reported that the compound was isostructural with the molybdenum analogue in its bodycentred tetragonal form, though only the cell parameters and space group are given and the Cambridge Structural Database entry (refcode SORLIU; Version 5.25; Allen, 2002) contains no atomic coordinates or other information indicating that the crystal structure has been fully determined. Two other salts of the same anion have been reported: in the tetraphenylphosphonium salt (Clegg et al., 1987), the anion forms dimers through pairs of chloro bridges between Cu atoms, and in the tetra-n-propylammonium salt (Se Â cheresse et al., 1991), further bridges are formed, linking the anions into a polymeric chain. A combination of terminal and bridging halogen atoms has been found in some other [MS 4 (CuX) n ] 2À complexes (Nicholson et al., 1983), and the interplay is clearly subtle.

Experimental
A mixture of (NH 4 ) 2 [WS 4 ] (0.35 g, 1.0 mmol), solid (NBu 4 )Br (0.65 g, 2.0 mmol) and CuCl (0.40 g, 4.0 mmol) in dry acetone (120 ml) was stirred vigorously in air at ambient temperature for 14 h. The resulting solution was ®ltered and the ®ltrate was concentrated to about 20 ml. The product was precipitated from the solution by addition of diethyl ether (4 Â 25 ml) and removal of the supernatant solution each time. The orange±red precipitate was washed with diethyl ether (3 Â 20 ml) and dried in vacuo. A saturated acetone solution of the complex was rendered slightly turbid by addition of npentane and air-stable orange crystals suitable for X-ray diffraction were collected after 48 h. The crystals were washed with diethyl ether several times. IR (KBr, cm À1 ): (WÐS) 441 (s).
The space group P4/n was determined unambiguously from the systematic absences and con®rmed by successful re®nement; there is pseudo-body-centring, re¯ections with h + k + l = 2n + 1 having an average intensity approximately half that for re¯ections with h + k + l = 2n. Atom W lies on a crystallographic fourfold rotation axis (4 or C 4 ), while the two N atoms lie at improper fourfold rotation sites (4 or S 4 ); thus, the asymmetric unit of the structure consists of one-quarter of the anion and two separate quarters of cations. The coordinates of the isostructural molybdenum complex were taken as starting parameters for re®nement. As in the previous structure, the S atoms are disordered equally over two independent sets of equivalent positions, generating eight positions around the central W atom; each anion contains two S atoms from one set (S) and two from the other (S H ). H atoms were placed geometrically (CÐH = 0.98±0.99 A Ê ) and re®ned with a riding model; U iso (H) values were constrained to be 1.2 (1.5 for methyl groups) times U eq of the carrier atom. The ®nal difference map contains one peak greater than 1 e A Ê À3 , which lies 0.88 A Ê from the W atom. The structure of the anion, with atom labels for the asymmetric unit and 50% probability displacement ellipsoids. Only one component of the disorder is shown for the S atoms.

Figure 2
The anion with both disorder components, viewed along the crystallographic fourfold rotation axis. The second disorder component is shown with dashed ellipsoids and bonds; four of the WÐS bonds are obscured by the four that are visible.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.