Determination of the gas-phase molecular structure of tris(trimethylsilyl)(trichlorosilyl) methane by electron diffraction

Abstract

The molecular structure of tris(trimethylsilyl)(trichlorosilyl)methane in the gas phase has been determined by electron diffraction. The mean inner SiC distance ( r a) is 190.9 (8) pm, with the difference between Me 3SiC and Cl 3SiC distances fixed at 2.3 pm. The outer SiCH 3 bonds are 187.8 (6) pm long, and r(SiCl) is 203.3 (6) pm. The SiCSi angles are close to tetrahedral, being 108.1 (6) ° between the Me 3Si groups and 110.9(6)° between Me 3Si and Cl 3Si groups. Effects of steric crowding are seen mainly in the angles at the silicon atoms, with C(Me)SiC(Me) 107.0 (11)° and ClSiC 114.6 (11)°. All the SiX 3 groups are twisted by about 23° from the fully eclipsed configuration, in which the central C(SiX 3) 4 skeleton approximates to T d symmetry, reducing this to approximate T symmetry. This twisting minimises long-range interactions between the silyl groups.