Determination of the molecular structures of bis(methylsilyl) sulphide and bis(dimethylsilyl) sulphide in the gas phase by electron diffraction, supported by molecular mechanics calculations

Abstract

The molecular structures of S(SiH₂Me)₂and S(SiHMe₂)₂ in the gas phase have been determined by electron diffraction. In S(SiH₂Me)₂the Si–S bonds are twisted by –86(2) and 31 (2)° away from the positions in which they are anti with respect to the further S–Si bonds, and there is therefore an gauche CSi ⋯ SiC configuration when the molecule is viewed along the Si ⋯ Si axis. Other parameters (r_a) include r(Si–S) 214.1 (1), r(Si–C) 186.9(2) pm, SSiC 112.8(7) and SiSSi 97.9(5)°. Molecular mechanics calculations for S(SiHMe₂)₂were used to estimate the differences between the lengths of the four Si–C bonds, the two Si–S bond lengths, and the SSiC and CSiC angles. These differences were used as constraints in the refinements of the structure using electron diffraction data, and gave the following mean values: r(Si–S) 214.6(1), r(Si–C) 186.5(1) pm, SSiC 109.1(11) and CSiC 106.6(16)°. The angle SiSSi refined to 100.8(20)°. The SiHMe₂ groups were twisted by 148(2) and –87(4)° about the Si–S bonds away from the position in which the Si–H bonds eclipse the further Si–S bonds.