trans-Di-μ-iodido-bis[(3H-1,2-benzodithiole-3-thione)iodidomercury(II)]

The complete molecule of the dinuclear title compound, [Hg2I4(C7H4S3)2], is generated by crystallographic inversion symmetry. The complex has a dimeric structure in which each HgII ion adopts a tetrahedral geometry and is coordinated by two bridging I atoms, one terminal iodide ion and one thiocarbonyl S atom (C=S) of the ligand. The square plane formed by the Hg and I atoms and their symmetry counterparts makes a dihedral angle of 89.66 (3)° with the DDT plane. There is no classical hydrogen bonding, but weak S⋯S interactions of 3.4452 (7) and 3.6859 (7) Å maintain the cohesion of the crystal structure.

The complete molecule of the dinuclear title compound, [Hg 2 I 4 (C 7 H 4 S 3 ) 2 ], is generated by crystallographic inversion symmetry. The complex has a dimeric structure in which each Hg II ion adopts a tetrahedral geometry and is coordinated by two bridging I atoms, one terminal iodide ion and one thiocarbonyl S atom (C S) of the ligand. The square plane formed by the Hg and I atoms and their symmetry counterparts makes a dihedral angle of 89.66 (3) with the DDT plane. There is no classical hydrogen bonding, but weak SÁ Á ÁS interactions of 3.4452 (7) and 3.6859 (7) Å maintain the cohesion of the crystal structure.
Technical support (X-ray measurements at SCDRX) from Université Henry Poincaré, Nancy 1 is gratefully acknowledged.  Sulfur-rich organic donor-acceptor compounds or radical salts are widely used as bricks in the crystal architecture of molecular materials. The S···S interaction or contact in this compounds is one of the most important contributors to their unique electronic properties (Klinsberg et al., 1962, Cassoux et al., 1991. It has been understood that intermolecular S···S interactions are providing the pass way of the electrons in the molecular conductor. Up to now great efforts have been made to design the molecular packing and to strengthen the S···S contacts by modifying the structure of the organic molecule itself, by changing the size of the conter ion and even the co-crystallized solvent molecules (Pullen et al., 1999;Schlueter et al., 1996). In this context a series of polymeric complexes have been reported with (Ag+) metal Dai, Kudora-Sowa et al., 1997) and a tetra-nuclear cluster CuI4 . In this paper an organic-inorganic hybrid compound is reported with the formula: [Hg 2 I 4 (DTT) 2 ](1),DTT=C 7 H 4 S 3 , 4,5-benzo-1,2-dithiole-3-thione.
The complex [Hg 2 (C 14 H 8 S 6 )I 4 ] is found to be a halogen-bridged dimer related by an inversion centre. An ORTEP view of the complex together with the atomic labeling scheme is given in Fig.1. The mercury atom is four-coordinated with significant distortion from tetrahedral. Two of these bonds are formed by two asymmetric iodide bridges, while the remaining two bonds are formed by a terminal iodide ion and thiocarbonyl sulfur atom of the ligand. The square-like plane formed by mercury and iodide atoms with their symmetry counterparts makes 89.66 (3)° dihedral angle with DDT plane.
The selected bond lengths and angles for the complex are listed in table (1) in which the data of the dimeric unit are comparable to those reported in the literature for related chloride bridged dimeric Hg(II) complexes (Brodersen et al., 1987;Dean, 1978).
Coordination modes of the C 7 H 4 S 3 ligand have been classified into four types (Dai, Kudora-Sowa et al., 1997). They are monodentate coordination by the thiocarbonyl group (type I), bridge formation by the sulfur of the thiocarbonyl group (type II), bidentate coordination by both thiocarbonyl group and thioether group (type III) and tridentate coordination by the thiocarbonyl sulfur (acting as a bridge) and the thioether sulfur (type IV).
Although the coordination of the ligand in type I has been found in complex: [Cu 4 I 4 (C 5 H 4 S 5 ) 4 ]∞ and{[Ag(C 5 H 4 S 5 ) 3 ]ClO 4 CH 3 CN} 2 (Dai, Kudora-Sowa et al., 1997;, other coordination types co-exist in these complexes. [Hg 2 (C 7 H 4 S 3 ) 2 I 4 ] is the complex found in the coordination of the ligands only in type I. The S(2)-C(1)distance of 1.703 (2)Å in this compound is longer than that for the free ligand 1.645Å .
This longer S(2)-C(1) distance attributes to the strong coordination of the thiocarbonyl sulfur to soft mercury(II) ion that weakens the S(2)-C(1) bond.
supplementary materials sup-2 The absence of intermolecular hydrogen bonding shows that the molecules are retained to each other by Van der Walls interaction only. The second type of bonds arises from an S(2)-I(1) and S(3)-I(1) interaction with two different bond lengths, 3.4452 (7)Å and 3.6859 (7) Å respectively (Fig.2). These bonds maintain the cohesion of the crystalline structure.

Experimental
The reagent C 7 H 4 S 3 was prepared using a literature method (Klinsberg et al., 1962) and characterized. The solvent was dried and distilled by a standard method before use. All other chemicals were obtained from commercial sources and used without further purification. Infrared spectra were measured as KBr disc on a Nicolet 205 F T-IR spectrometer.
A solution of HgI 2 (2.5 m mol, 1,130 g) in acetone (15 ml) was added to a solution of C 7 H 4 S 3 (2.5 m mol, 0,460 g) in acetone at room temperature under argon atmosphere. An orange precipitate was formed immediately and the mixture was stirred for 50 min. The precipitate was filtered, washed with petroleum ether (yield: 60%). Orange crystals for x-ray measurement were obtained by recrystaling the solid in THF. IR (KBr, cm -1 ):n(C=C) 1447 ms, n(C=S) 991,3vs, n(Hg-S) 256,5 ms, n(Hg-I) 167,8vs.

Refinement
H atoms were positioned geometrically and refined in the riding-model approximation, with C-H = 0.93 Å and with U iso (H) = 1.2 U eq (C)

trans-Di-µ-iodido-bis[(3H-1,2-benzodithiole-3-thione)iodidomercury(II)]
Crystal data [Hg 2 I 4  ω scans h = −12→12 Absorption correction: analytical (Clark et al., 1995) k = −13→13 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 > σ(F 2 ) is used only for calculating Rfactors(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.