An SCF-MS-Xα study of the bonding and nuclear quadrupole coupling in 1 : 1 complexes of amines with diatomic halogens and interhalogens

Abstract

SCF-MS-Xα calculations of the electronic structure of the 1 : 1 complexes of pyridine with I₂, IBr and ICl, and of the 1 : 1 trimethylamine–I₂ complex have been carried out to investigate the bonding and nuclear quadrupole coupling in these molecules. Good agreement (to within 10% in most cases) is obtained between the calculated and observed halogen nuclear quadrupole coupling constants for these molecules. The agreement in the case of the nitrogen quadrupole coupling parameters is not as good, but the calculations do support some of the previously reported conclusions concerning the changes in the nitrogen orbital populations which occur upon complex formation. The results essentially support previous conclusions, based on Townes and Dailey analyses of the experimental quadrupole coupling data, concerning the extent of charge transfer and the distribution of the transferred charge in these molecules. They are, however, at variance with some of the results obtained from chemical shifts in the photoelectron spectra. The electric dipole moments of the molecules have also been calculated. These are ca. 30% higher than the highest reported experimental values, but show the expected trends from one compound to another.