1,1,2-tri-tert-butyldisilane, Bu(t)2HSiSiH2Bu(t):: vibrational spectra and molecular structure in the gas phase by electron diffraction and ab initio calculations

The molecular structure of 1,1,2-tri-tert-butyldisilane, (Bu2HSiSiH2But)-H-t, has been determined in the gas phase by electron diffraction (GED) and ab initio molecular-orbital calculations. Vibrational spectra are consistent with a vapour consisting of one conformer, identified by the structural study as a syn arrangement in which each of the butyl groups eclipses an Si-H bond. Important structural parameters (r(a)) for the conformer are: Si-Si 236.3(8), Si-C (mean) 191.1(3), C-C 154.5(1), C-H 112.4(1) pm, Si(1)-Si(2)-C(21) 116.0(8), Si(2)-Si(1)-C(11) 111.2(10), Si(2)-Si(1)-C(12) 108.7(9), C(11)-Si(1)-C(12) 121.1(11) and C(21)-Si(2)-Si(1)-H(13) -6.2(11)degrees, where C(11), C(12) and C(21) are the central carbon atoms of the three >$($) over bar tert</>-butyl groups. These experimental observations are supported by theoretical predictions obtained at the D95*/MP2 level, which also identify two higher-energy conformers.