The Molecular Structure of Hexamethyldigermane Determined by Gas-Phase Electron Diffraction with Theoretical Calculations for (CH3)(3)M-M(CH3)(3) Where M = C, Si, and Ge

Abstract

Gas-phase electron diffraction (GED) data together with results from ab initio molecular orbital calculations (HF and MP2/6-311+G(d,p)) have been used to determine the structure of hexamethyldigermane ((CH3)3Ge−Ge(CH3)3). The equilibrium symmetry is D3d, but the molecule has a very low-frequency, large-amplitude, torsional mode (CGeGeC) that lowers the thermal average symmetry. The effect of this large-amplitude mode on the interatomic distances was described by a dynamic model which consisted of a set of pseudoconformers spaced at even intervals. The amount of each pseudoconformer was obtained from the ab initio calculations (HF/6-311+G(d,p)). The results for the principal distances (ra) and angles (h1) obtained from the combined GED/ab initio (with estimated 1σ uncertainties) are r(Ge−Ge) = 2.417(2) Å, r(Ge−C) = 1.956(1) Å, r(C−H) = 1.097(5) Å, GeGeC = 110.5(2)°, and GeCH = 108.8(6)°. Theoretical calculations were performed for the related molecules ((CH3)3Si−Si(CH3)3 and (CH3)3C−C(CH3)3).