Bis[1,2-bis(4-chlorophenyl)ethylene-1,2-dithiolato(1–)]nickel(II)

Bis[1,2-bis(4-chlorophenyl)ethylene-1,2-dithiolato(1−)]nickel(II) crystallizes as pairs of molecules related by an inversion center with close intermolecular C—H⋯S and C—H⋯Ni contacts.

The title compound, [Ni(S 2 C 2 (C 6 H 4 -p-Cl) 2 ) 2 ] or [Ni(C 14 H 8 Cl 2 S 2 ) 2 ], crystallizes in the triclinic space group P1 as pairs of molecules disposed about an inversion center at the bc face of the cell. Close intermolecular C-HÁ Á ÁS (2.884 Å ) and C-HÁ Á ÁNi (3.032 Å ) contacts that are less than the sum of the van der Waals radii appear to induce slight bowing of the molecular planes toward one another. The angles at which the four p-ClC 6 H 4 -rings join the NiS 2 C 2 chelate rings [39.37 (9)-53.41 (6) ] are similarly influenced by these intermolecular contacts. In the larger packing arrangement, sheets of molecules extend in the direction of the ac face diagonal.
Compounds of this type are electrochemically rich and typically support two successive ligand-based one-electron reductions that correspond to the transformations depicted as data reports Fig. 1. The redox-active molecular orbital has rather modest metal character and is best described as being delocalized among both dithiolene ligands, which individually may be regarded as radical monoanions but which collectively have their spins paired such that the chargeneutral state is diamagnetic. In structure (c), both dithiolene ligands are in a fully reduced ene-1,2-dithiolate dianionic state. The potentials at which these reductions occur are quite sensitive to the nature and placement of ring substituents. As part of an effort to more fully map the potential range in which the electron transfers in these complexes occur, we have undertaken the synthesis and characterization of aryl-substituted nickel(II) bis(dithiolene) complexes bearing electronwithdrawing groups. Although a known compound, the nickel(II) bis(dithiolene) variant with p-ClC 6 H 4 -substituents has not been the subject of an X-ray diffraction study, nor has a coordination compound of this ligand with any other metal. We briefly relate here the structural and crystal packing features of [((p-ClC 6 H 4 ) 2 C 2 S 2 ) 2 Ni].
The packing arrangement for bis[1,2-bis(4-chlorophenyl)ethylene-1,2-dithiolato(1À)]nickel(II) is such that molecules occur in centrosymmetric pairs around the inversion centers that occur at each bc face of the cell (Fig. 3). These pairwise associations juxtapose two molecules in a nearly parallel planar fashion but with an offset that places the phenyl groups of one ligand over the relatively open NiS 4 interior of its partner molecule. Relatively close intermolecular C-HÁ Á ÁS (2.884 Å ) and C-HÁ Á ÁNi (3.032 Å ) contacts are made (Fig. 4), two each that are related by the inversion symmetry. The C-HÁ Á ÁS and C-NÁ Á ÁNi close contacts are less than the sum of the hydrogen-sulfur and hydrogen-nickel van der Waals radii (Batsanov, 2001) and appear to be favorable interactions that induce a slight but discernible concave bowing of the mol-

Figure 3
Packing arrangement of molecules of bis[1,2-bis(4-chlorophenyl)ethylene-1,2-dithiolato(1À)]nickel(II) in the unit cell. Ellipsoids are shown at the 50% probability level, and all H atoms are omitted for clarity. Pairs of molecules are related by inversion across the center of symmetry at the center of the bc face.  ecules toward one another (Fig. 4). This curvature, defined as the angle between the seven-atom mean planes given by each NiS 2 C 2 chelate and the first carbon atom of each aryl ring, is 11.87 (5) . It is likely that the angled disposition of some of the aryl substituents with respect to the NiS 2 C 2 chelate have their origin in these intermolecular interactions. The larger packing arrangement is best described as translations of these centrosymmetric pairs along the a axis, the upshot of which is that extended molecular sheets are formed that are oriented in the direction of the ac face diagonal (Fig. 5).

Synthesis and crystallization
The title compound was prepared from 4,4 0 -dichlorobenzil, P 4 S 10 , and NiCl 2 Á6H 2 O according to the literature procedure (Schrauzer & Mayweg, 1965). Yield: 50%. Intense green column-shaped crystals were grown by the diffusion of tertbutyl methyl ether vapor into a solution of the title compound in 1,2-dichloroethane.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. One reflection affected by the beamstop was omitted from the final refinement.

Figure 4
Illustration of the C-HÁ Á ÁS and C-HÁ Á ÁNi contacts that occur between closest pairs of bis[1,2-bis(4-chlorophenyl)ethylene-1,2-dithiolato(1À)]nickel(II) molecules. Ellipsoids are presented at the 50% probability level. Symmetry operation: Àx, 1 À y, 1 À z. Special details Experimental. The diffraction data were obtained from sets 11 of frames, each of width 0.5° in ω or φ, collected with scan parameters determined by the "strategy" routine in APEX3. The scan time was 15 sec/frame. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. Hatoms attached to carbon were placed in calculated positions (C-H = 0.95 Å). All were included as riding contributions with isotropic displacement parameters 1.2 times those of the attached atoms.