Complexes of mixed silicon halides with 4-picoline

The reaction products of an addition reaction of five different silicon tet rahalides with the aromatic nitrogen base 4-methylpyridine are presented. T he following five structures are isomorphous: (I) tetrachlorobis(4-methylpy ridine)silicon, C12H14Cl4N2Si, (II) bromotrichlorobis(4-methylpyridine)sili con, C12H14BrCl3N2Si, (III) dibromodichlorobis(4-methylpyridine)silicon, C1 2H14Br2Cl2N2Si, (IV) tribromochlorobis(4-methylpyridine)silicon, C12H14Br3C lN2Si, and (V) tetrabromobis(4-methylpyridine)silicon, C12H14Br4N2Si. The m olecules of (I) and (V), with D-2h symmetry, have crystallographic C-2h sym metry, while the molecules of (II), (III) and (IV) have a lower molecular s ymmetry, but as a result of the disorder of the halogen ligands, they appea r to be of the same crystallographic symmetry. The environment around the S i atom can be described as a slightly distorted octahedron with the methylp yridine ligands occupying axial positions and the four halogen ligands in t he equatorial plane. In spite of the different substitution pattern of the silicon centre, there are only insignificant differences between these five structures.