Spectra and structure of gallium compounds: Part VII . Microwave, infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

Abstract

The infrared (100–3500 cm −1) and Raman (25–3200 cm −1) spectra of the solid phases of (CH 3) 3NGa(CH 3) 3 and (CH 3) 3 15NGa(CH 3) 3 have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm −1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH 3) 3NGa(CH 3) 3. The spectra have been interpreted on the basis of C 3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A −1) has a value intermediate between those of (CH 3) 3NGaH 3 and H 3NGa(CH 3 3). The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C 3 or C 3v site. A rhombohedral space group such as R3 m( C 5 3v) is consistent with these observations.