Analysis of the valence electronic structures of some tin(IV) compounds

Abstract

An analysis of the charge distributions in a number of Sn^IV compounds, calculated by a modified CNDO method, is presented. The series includes tin halides and their anions, and a series of halogen-substituted methylstannanes. Overall, the results accord well with chemical intuition and, with few exceptions, fit into a pattern with clear-cut trends. Stannane and the methylstannanes are highly ‘covalent’ compounds, whilst the tetrahalides are much more ‘ionic’. Gradations occur along both series. Replacement of halogen atoms by methyl groups reduces the polarity of the tin–halogen bond because methyl groups act in this context as sources of electrons, largely via the π type orbitals. The involvement of 5d orbitals is small in stannane and the methylstannanes, larger in the tetrahalides and largest in the hexahalide anions. This involvement is also more marked with increasing atomic weight of the bonded halogen.