Steric and electronic effects on Si–Ge bond lengths: An experimental and theoretical structural study of Me2Ge(SiCl3)2 and Me3GeSiCl3

The molecular structures of dimethylbis(trichlorosilyl)germane [Me 2 Ge(SiCl 3 ) 2 ] and trimethyl(trichlorosilyl)germane (Me 3 GeSiCl 3 ) have been determined in the gas phase. Me 3 GeSiCl 3 was found ab initio to possess C 3 v symmetry, with a low-lying torsional motion of the SiCl 3 group relative to the GeMe 3 group. The gas electron diffraction data were modelled with C 3 symmetry, although little deviation from C 3 v symmetry was observed. Me 2 Ge(SiCl 3 ) 2 ( C 2 v symmetry) was also found to have a very low-lying vibrational frequency relating to the rotation of the SiCl 3 groups. This led to the gas electron diffraction data being modelled in C 2 symmetry, with the observed combined deviation of the SiCl 3 groups being 14° from the eclipsed structure calculated ab initio. The Ge–C bond lengths were unaffected by the addition of an extra SiCl 3 group to the central germanium atom, but the Ge–Si bond lengths were observed to increase by over 1 pm.