An electron diffraction, ab initio and vibrational spectroscopic study of 1,2-di- tert-butyldisilane

Abstract

The molecular structure of 1,2-di- tert-butyldisilane has been accurately determined by gas-phase electron diffraction (GED) and ab initio calculations. These techniques show that the large majority of molecules at room temperature have the anti conformation with overall symmetry C 2, and vibrational spectra confirm this conclusion. Infrared spectra of the gas and liquid phases, and Raman spectra of the liquid and solid phases, have been recorded for (CH 3) 3CSiH 2SiH 2C(CH 3) 3 and (CH 3) 3CSiD 2SiD 2C(CH 3) 3. The most striking feature of this structure ( r a) is a relatively large deviation of the SiSiC angle from the parent tetrahedral angle 109.5° (113.7(3)°, GED; 114.4°, SCF 6-31 G∗ as calculated for the anti form). That the SiSi bond length does not show any substantial deviation from its usual value (234.8(3) pm, GED; 236.8 pm, SCF 6-31 G∗ computed for the anti form) is also substantiated by the value of the SiSi valence force constant (169 N m −1) given by normal coordinate analysis. The t-butyl groups are tilted so that the SiC bonds (GED ( SCF 6-31 G∗ ): 190.1(1) (191.9) pm) do not coincide with the local C 3 axes of the C(CH 3) 3 groups in which the CC bond length is 154.1(1) (GED); 154.0 ( SCF 6-31 G∗ ) pm. The conformations along all the single bonds are more or less staggered.