Bis[4-(dimethylamino)pyridinium] tribromidochloridodimethylstannate(IV)

The SnIV atom in the title salt, (C7H11N2)2[SnBr3(CH3)2Cl], lies on a center of inversion in a tetragonally compressed octahedron; two independent Br atoms share the same site as two independent chlorine atoms so that the anion effectively has one Cl and three Br atoms. The occupancies of the Br atoms are 0.721 (1) and 0.779 (1), and those of the Cl atoms are 0.279 (1) and 0.221 (1). The crystal structure involves N—H⋯halogen hydrogen bonds.

The Sn IV atom in the title salt, (C 7 H 11 N 2 ) 2 [SnBr 3 (CH 3 ) 2 Cl], lies on a center of inversion in a tetragonally compressed octahedron; two independent Br atoms share the same site as two independent chlorine atoms so that the anion effectively has one Cl and three Br atoms. The occupancies of the Br atoms are 0.721 (1) and 0.779 (1), and those of the Cl atoms are 0.279 (1) and 0.221 (1). The crystal structure involves N-HÁ Á Áhalogen hydrogen bonds.

S1. Comment
We have been investigating the reaction of organotin compounds with 4-dimethylpyridinium hydrobromide perbromide.
In the previous study, this compound was reacted with dimethyltin dichloride to afford bis(4-dimethylpyridinium) dibromidodichloridodimethylstannate (Lo & Ng, 2008), whose. The halogens are in the expected 2:2 molar ratio. The bromine atoms are disordered with respect to the chlorine atoms. In the present study, the organotin reactant, chlorodimethyltin dimethyldithiocarbamate contains only one chlorine atom. The resulting stannate (Scheme I, Fig. 1) is the expected tribromidochloridodimethylstannate; the two salts are isostructural. N1-H1···X hydrogen bonds (X is a disordered mixture of Cl and Br; symmetry code: x, y, z) link the anions and cations, Fig 1, Table 2.

S3. Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 to 0.98 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2 to 1.5U eq (C). The ammonium H atom was similarly treated (N-H 0.88 Å).
The two indepedent chlorine atoms are disordered with respect to the bromine atoms, so that each halogen site is occupied by both a chlorine and a bromine. Restraints were applied so that at each site; the atoms were restrained to have the same anisotropic temperature factors. Without occupancy restraints, occupancies of the chlorine atoms refined to nearly 0.5 and the total number of bromine atoms to approximately 1.5. The sum of the occupancies were then restrained to these values and, in the final refinement, occupancies refined to Br1 0.721 (1)  Thermal ellipsoid plot (Barbour, 2001) plot of [C 7 H 11 N 2 ] 2 [SnBr 3 Cl 2 (CH 3 ) 2 ] at the 70% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius. The Sn atom lies on a center-of-inversion such that the two independent Br atoms are disordered with respect to the two independent Cl atoms. Symmetry code: i = 1 -x, 1 -y, 1 -z. Dashed lines denote hydrogen bonds.