On the nature of the interaction in donor-acceptor van der Waals complexes:: BH3•••CO, BF3•••CO, BH3•••NH3 and BF3•••NH3

Ab initio calculations at the MP2/6-31G** level have been carried out to analyze the nature of the interaction in BH3 ... CO, BF3 ... CO, BH3 ... NH3 and BF3 ... NH3 van der Waals complexes. There is a good correlation between charge transfer, as measured by a method based on the expansion of the MOs of a complex system in terms of the MOs of its fragments, and the corresponding bond lengths. Additional consideration of the energy gaps between the frontier orbitals involved in the charge transfer allows for rationalization of the strength of the donor-acceptor bonds. (C) 1998 Elsevier Science B.V.