Bis(tetrabutylammonium) bis(3,4,5-trioxocyclopent-1-ene-1,2-dithiolato-κ2 S,S′)cadmate(II) 0.25-hydrate

The title compound, (C16H36N)2[Cd(C5O3S2)2]·0.25H2O, contains two disordered tetrabutylammonium cations, a complex [Cd(C5O3S2)2]2− anion and a 0.25-hydrate water. The anion is composed of a bidentate coordinated 3,4,5-trioxocyclopent-1-ene-1,2-dithiolate (dtcroc) group forming a distorted tetrahedral configuration around the CdII ion. The dihedral angle between the least-squares planes of the ten-atom sulfur-substituted croconate groups in the anion is 84.10 (8)°. The crystal packing is stabilized by weak C—H⋯O and C—H⋯S cation–anion hydrogen-bond interactions. In each of the two cations one butyl group is disordered over two positions in the ratios 0.589 (11):0.411 (11) and 0.796 (12):0.204 (12).

They have also proven useful as precursors for the preparation ofnovel molecular conductors, non-linear optical materials and magnetic charge-transfer salts. Accordingly, we have interests in investigating the solid chemistry based on the 3,4,5-trioxo-cyclopent-1 ene-ene-1, 2-dithiolate ion (C 5 O 3 S 2 2-), also abbreviated as dtcroc (alternative name sulfur-substituted croconate). The coordination behavior of the dtcroc dianion (C 5 O 3 S 2 2-) towards d 8 transition metal ions, such as Pt 2+ (Deplano,et al. 2005) and Ni 2+ (Deplano,et al. 2006), have been investigated and all show a planar configuration. We present here the synthesis and characterization of a new Cd(II) coordination compound of dtcroc, which shows a distorted tetrahedral coordination conformation.
Deviations of oxygen atoms, sulfur atoms and the cyclic five-membered ring in C 5 O 3 S 2 2are less than 0.09 Å, indicating a planar molecular geometry for both ligands. The C≐O bonds in the title compound, vary by 1.209 (5)-1.224 (5)Å and show typical Csp 2 double bond character, while the C≐S bonds are in the range of 1.683 (4)-1.699 (4) Å, which are intermediate between the lengths of typical single C-S and double C≐S bonds. The difference among C-C distances within the ligands are in the range of 1.402 (5)-1.505 (6) Å, establishing a π-electron localized C 2v molecular symmetry which compares well with similar structure croconate anions (Dunitz, et al., 2001;Castro, et al., 2002;Maji, et al.2004).
The tetrabutlyammionium cations are disordered in the title crystal and a few solvent water molecules were cocrystalized to stabilize the structure. The [Cd(C 5 O 3 S 2 ) 2 ] 2units form stacks along [1 0 0], surrounded by tetrabutylamonium cations (Fig.2). Crystal packing is stabilized by weak C-H···O, C-H···S cation-anion hydrogen bond interactions (Table 1).

Experimental
To a solution containing K 2 dtcroc (0. sup-2 (0.40 g, 0.95 mmol) in ethanol (5 mL). Solid product was collected by suction filtration, washed with water and dried in air. Red block crystals were obtained by recrystallization from acetone.

Refinement
All H atoms were geometrically fixed and allowed to ride on their attached atoms, which O-H = 0.85Å with U iso (H)= 1.5U eq (O) and C-H = 0.96-0.97Å with U iso (H)= 1.2-1.5U eq (C). Butyl groups are disordered in title structure. Some butyl groups were refined as a rigid body, which C-C bond are fixed to 1.54Å and the distances between alternate C atom are fixed to 2.54 Å. Terminal ethyl group C13-C14 is refined to a rigid model around the bond C11-C12 with ethyl group C13'-C14' in the ratio 0.59:0.41 and C41-C42 is refined to a rigid model around the bond C39-C40 with ethyl group C41'-C42' in the ratio 0.80:0.20. Fig. 1. Coordination configuration of the title compound with thermal ellipsoids at 30% probability levels. Hydrogen atoms have been omiitted for clarity. Dashed lines indicate disordered butyl groups. Bis(tetrabutylammonium) bis(3,4,5-trioxocyclopent-1-ene-1,2-dithiolatoκ 2 S,S')cadmate(II) 0.25-hydrate

Figures
Crystal data (C 16