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

Abstract

The molecular structure, conformational composition and torsional potential of 1,1,2,2-tetrachlorodisilane (TCDS), Cl2HSi–SiHCl2, were studied using gas phase electron diffraction (GED) data at 23°C, together with earlier recorded spectroscopic data and normal coordinate- and ab initio molecular orbital calculations. The title compound exists in the gas phase at room temperature as a mixture of two conformers, anti, with a torsion angle φ(HSiSiH)=180°, and gauche, with a torsion angle φ(HSiSiH)≈60°. The gauche conformer predominates, occupying approximately 80% of the gas composition at 23°C. Some structural parameter values obtained from the GED refinements, using results from the earlier spectroscopic work and ab initio molecular orbital calculations as constraints, are as follows (gauche conformer with estimated 2σ uncertainties): bond lengths (rg): r(Si–Si)=2.310(8)Å, r〈(Si–Cl)〉=2.039(2)Å (average value), r(Si–H)=1.511Å (assumed value). Bond angles (∠α): ∠〈SiSiCl〉=108.9(4)° (average value), ∠ClSiCl=109.7(3)°, ∠SiSiH=111.5° (assumed value).