Dichloridobis(pyridine-2-thiol­ato-κ²N,S)tin(IV): a new polymorph

The title compound, [SnCl₂(C₅H₄NS)₂], is the product of reaction of 2,2′-dipyridyl disulfide with tin tetra­chloride. The Sn^IV atom adopts a distorted octa­hedral geometry, with the two bidentate pyridine-2-thiol­ate ligands forming two planar four-membered chelate rings. The two Sn—Cl, two Sn—N and two Sn—S bonds are in cis, cis and trans configurations, respectively. The crystal grown from acetonitrile represents a new monoclinic polymorph in space group C2/c with the mol­ecule having twofold rotational symmetry, the Sn^IV atom lying on the twofold axis. The mol­ecular structure of the monoclinic polymorph is very close to that of the triclinic polymorph studied previously in space group P-1, the mol­ecule occupying a general position [Masaki & Matsunami (1976). Bull. Chem. Soc. Jpn, 49, 3274–3279; Masaki et al. (1978). Bull. Chem. Soc. Jpn, 51, 3298–3301]. Apparently, the formation of the two polymorphs is determined by the different systems of inter­molecular inter­actions. In the crystal of the monoclinic polymorph, mol­ecules are bound into ribbons along the c axis by C—H...Cl hydrogen bonds, whereas in the crystal of the triclinic polymorph, mol­ecules form chains along the a axis by attractive S...S inter­actions. The crystal studied was a pseudo-merohedral twin; the refined BASF value is 0.221 (1).