Dichloridobis(pyridine-2-thiolato-κ2 N,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 SnIV 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 SnIV 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).

The title compound, [SnCl 2 (C 5 H 4 NS) 2 ], is the product of reaction of 2,2 0 -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 P1, 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][3299][3300][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-HÁ Á ÁCl hydrogen bonds, whereas in the crystal of the triclinic polymorph, molecules form chains along the a axis by attractive SÁ Á ÁS interactions. The crystal studied was a pseudomerohedral twin; the refined BASF value is 0.221 (1).
The molecule of I possesses overall intrinsic C 2 symmetry. In contrast to the triclinic polymorph (the space group P1, the molecule occupies a common position), this symmetry is realised in the crystal of the monoclinic polymorph (the space group C2/c, the molecule occupies a special position on the twofold axis). The tin atom adopts a distorted octahedral geometry, with the two bidentate 2-pyridinethiolato ligands forming two planar four-membered chelate rings (Fig. 2). The two Sn-Cl, two Sn-N and two Sn-S bonds are in cis-, cis-and trans-configurations, respectively. Generally, the molecular structure of the monoclinic polymorph of I is very close to that of the triclinic polymorph.
Apparently, the formation of the two polymorphs of I is determined by the different systems of intermolecular nonvalent interactions. In the crystal of the monoclinic polymorph, the molecules are bound into the ribbons along the c axis by the weak intermolecular C3-H3···Cl1 i hydrogen bonds (Fig. 3, Table 1), whereas, in the crystal of the triclinic polymorph, the molecules form the chains along the a axis by the weak attractive intermolecular S···S (3.544 (3)Å) interactions (Fig. 4). Symmetry code: (i) -x+1, -y+1, -z.

Experimental
A solution of SnCl 4 (0.13 g, 0.5 mmol) in CH 2 Cl 2 (25 ml) was added to a solution of 2,2′-dipyridyl disulfide (0.11 g, 0.5 mmol) in CH 2 Cl 2 (25 ml) with stirring at room temperature. After 1 h, the powder of complex (C 5 H 4 NS) 2 SnCl 6 was separated by filtration. The filtrate was concentrated in vacuo. The solid was re-crystallized from CH 3 CN to give I as
The hydrogen atoms were placed in calculated positions with C-H = 0.95Å and refined in the riding model with fixed isotropic displacement parameters U iso (H) = 1.2U eq (C).

Figure 1
Reaction of 2,2′-dipyridyl disulfide with tin tetrachloride.  The H-bonded ribbons along the c axis in the monoclinic polymorph of I. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.81 e Å −3 Δρ min = −0.53 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > σ(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.  (10) Geometric parameters (Å, º)