THE VIBRATIONAL-SPECTRA OF THE BORON HALIDES AND THEIR MOLECULAR-COMPLEXES .4. AB-INITIO PREDICTIONS OF THE STRUCTURES AND VIBRATIONAL-SPECTRA OF THE COMPLEXES OF BORON-TRIFLUORIDE WITH DIMETHYL ETHER AND DIMETHYL SULFIDE

The optimized structures and vibrational spectra of the 1:1 complexes of boron trifluoride with dimethyl ether and dimethyl sulphide have be en determined by means of a series of ab initio calculations using the GAUSSIAN-90 computer program at the Hartree-Fock level with the 6-31G * basis set. The results have been rationalized on the basis of the i nteractions of the Lewis acid (BF3) with a hard ((CH3)(2)O) and a soft ((CH3)(2)S) base. The magnitudes of the wavenumber shifts, both for t he acid and the base fragments, are far larger for the complex with th e hard than with the soft base. The computed results have been used as aids in the interpretation of the infrared spectra of BF3 co-condense d with (CH3)(2)O and with (CH3)(2)S in cryogenic matrices, to be repor ted in a forthcoming publication.