The structure of bis(dimethylamino)silane in the gas phase, determined by electron diffraction

Abstract

We have studied the molecular structure of bis(dimethylamino)silane in the gas phase by electron diffraction. The molecule has no symmetry, the two dimethylamino groups having different CNC angles and conformations. Both nitrogens are non-planar, with the methyl groups displaced away from the other nitrogen in one case, towards it in the other case. The major structural parameters are r(SiN) 170.8 pm (both assumed equal), r(CN) 146.0 pm (all four assumed equal), and NSiN angle 112°. The asymmetry does not produce observable effects in the vibrational spectra, probably because the effects of coupling between dimethylamino groups are larger than any frequency differences due to the inequivalence. The vibrational spectra of the annealed solid are very similar to the i.r. spectrum of the gas, showing that no specific intermolecular association occurs on crystallisation.