1,1,2,2-tetrachlorodisilane (Cl2HSi-SiHCl2): molecular structure, conformation and torsional potential as determined by gas-phase electron diffraction, vibrational spectroscopic data and ab initio molecular orbital calculations

The molecular structure, conformational composition and torsional potential of 1,1,2,2-tetrachlorodisilane (TCDS), Cl2HSi-SiHCl2, were studied using g as phase electron diffraction (GED) data at 23 degrees C, together with ear lier recorded spectroscopic data and normal coordinate- and ab initio molec ular orbital calculations, The title compound exists in the gas phase at ro om temperature as a mixture of two conformers, anti, with a torsion angle p hi(HSiSiH) = 180 degrees, and gauche, with a torsion angle phi(HSiSiH) appr oximate to 60 degrees. The gauche conformer predominates, occupying approxi mately 80% of the gas composition at 23 degrees C. Some structural paramete r values obtained from the GED refinements, using results from the earlier spectroscopic work and ab initio molecular orbital calculations as constrai nts, are as follows (gauche conformer with estimated 2 sigma uncertainties) : bond lengths (r(g)): r(Si-Si) = 2.310(8) Angstrom, r[(Si-Cl)] = 2.039(2) Angstrom (average value), r(Si-H) = 1.511 Angstrom (assumed value). Bond an gles (angle alpha): angle[SiSiCl] = 108.9(4)degrees (average value), angle ClSiCl = 109.7(3)degrees, angle SiSiH = 111.5 degrees (assumed value). (C) 1999 Elsevier Science B.V. All rights reserved.