1,1,2-Tri-tert-butyldisilane, But2HSiSiH2But: vibrational spectra and molecular structure in the gas phase by electron diffraction and ab initio calculations

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The molecular structure of 1,1,2-tri-tert-butyldisilane, But2HSiSiH2But, 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 (ra) 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)°, where C(11), C(12) and C(21) are the central carbon atoms of the three tert-butyl groups. These experimental observations are supported by theoretical predictions obtained at the D95*/MP2 level, which also identify two higher-energy conformers.