Substitutional disorder in a hypervalent diorganotin(IV) dihalide

The structure of bromidochloridobis[2-(dimethylaminomethyl)phenyl]tin(IV), [SnBr0.65Cl1.35(C9H12N)2], contains two 2-(Me2NCH2)C6H4 units bonded to a Sn atom which lies on a twofold axis. The compound exhibits substitutional disorder of the halide atoms bonded to the Sn, with 1.35 occupancy for Cl and 0.65 for Br; it is isomorphous with the corresponding dichloride. The Sn atom is hexacoordinated with a (C,N)2SnX 2 (X = Cl/Br) distorted octahedral core as a result of the strong intramolecular N→Sn coordination trans to the Sn—X bonds (N1—Sn1—X1 = 165.8°). As a result of the intermolecular contacts, viz. H⋯X and H⋯benzene interactions, the molecules are arranged in a three-dimensional supramolecular manner in the crystal structure.

The structure of bromidochloridobis[2-(dimethylaminomethyl)phenyl]tin(IV), [SnBr 0.65 Cl 1.35 (C 9 H 12 N) 2 ], contains two 2-(Me 2 NCH 2 )C 6 H 4 units bonded to a Sn atom which lies on a twofold axis. The compound exhibits substitutional disorder of the halide atoms bonded to the Sn, with 1.35 occupancy for Cl and 0.65 for Br; it is isomorphous with the corresponding dichloride. The Sn atom is hexacoordinated with a (C,N) 2 SnX 2 (X = Cl/Br) distorted octahedral core as a result of the strong intramolecular N!Sn coordination trans to the Sn-X bonds (N1-Sn1-X1 = 165.8 ). As a result of the intermolecular contacts, viz. HÁ Á ÁX and HÁ Á Ábenzene interactions, the molecules are arranged in a three-dimensional supramolecular manner in the crystal structure.
Financial support from the National University Research Council (CEEX 63/2006) is greatly appreciated. We also thank the National Center for X-Ray Diffraction, Cluj-Napoca, for help with the solid-state structure determination.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: GD2029).  (Varga et al., 2001, 2005, 2006, 2007, Rotar et al. 2007, the title compound (I) was isolated. It contains two 2-(Me 2 NCH 2 )C 6 H 4 units bonded to a tin atom which lies on a twofold axis of the space group C2/c. The compound exhibits substitutional disorder of both halide atoms bonded to the Sn with chlorine being the major (1.35) and the bromine the minor (0.65) component.
The structure of [2-(Me 2 NCH 2 )C 6 H 4 ] 2 SnCl 2 was also determined (Varga et al., 2001) and is isomorphous with the title compound. Both have space group C2/c; the cell constants as well as the volume differ slightly (0.39% increase for the title compound) as the result of the presence of a different halide in the molecular unit.
The molecules of the compound feature a metal atom strongly coordinated by two nitrogen atoms of the pendant arms [Sn-N1 = 2.64 (1) Å; the Sn-N distance exceeds the sum of the covalent radii for the corresponding atoms, Σ cov (Sn,N) = 2.1 Å (Emsley, 1994)] trans to an Sn-halogen bond (N1-Sn1-X1 = 165.8°). This results in a (C,N) 2 SnX 2 (X = Cl/Br) core in the title compound with a trans-SnC 2 fragment, while the N and X atoms are cis positions (Fig. 1). The octahedral geometry around the Sn atom is distorted from the ideal geometry as a consequence of the small 'bite' of the pendant arm ligand [C1-Sn1-N1 = 71.4°] and the steric repulsion between the organic groups bonded to the Sn atoms. All these features are similar to the corresponding dichloride.
As a result of the intramolecular coordination of the nitrogen to the tin atom a five-membered SnC 3 N ring is formed. This ring is not planar but is folded along the Sn(1)···C methylene axis with the N atom out of the best plane defined by the residual SnC 3 , thus inducing planar chirality, with the phenyl ring as chiral plane and the nitrogen as pilot atom (IUPAC, 1979).
Indeed, the compound crystallizes as a racemate, i.e. a mixture of R N1 R N1 i and S N1 S N1 i [symmetry code: (i) 2 − x, y, 0.5 − z].

Refinement
All hydrogen atoms were placed in calculated positions using a riding model, with C-H = 0.93-0.97 Å and with U iso = 1.5U eq (C) for methyl H and U iso = 1.2U eq (C) for aryl H. The methyl groups were allowed to rotate but not to tip. The two halide atoms were refined as substitutional disorder between chlorine and bromine, with 1.35 occupancy for Cl and 0.65 occupancy for Br.