Virial partitioning of BH₃ and BF₃ and their Lewis adducts

Abstract

The virial partitioning method is applied to the systems BH₃, BF₃ and their Lewis adducts BH₃H^-, BH₃F^-, BF₃H^- and BH₃CO. This is a spatial partitioning of a molecule which divides the system into atomic-like fragments and its properties into a sum of fragment contributions, in a manner determined by the topographical properties of the charge distribution. The virial theorem is obeyed separately within the domain of each fragment and as a consequence each fragment acts as an isolated entity, responding only to the net changes in the external forces exerted on it.

The virial theorem is used to relate the kinetic energy of binding of each fragment in BH₃ and BF₃ to the changes in their potential and total energies. The energies of formation of the Lewis adducts BH₃-H^-, BH₃-F^-, BF₃-H^- and BH₃-CO are partitioned into fragment contributions in an analysis of the relative abilities of BH₃ and BF₃ to act as electron acceptors. The change in energy of each fragment is related to the change in the distribution of charge within the fragment. It is concluded that the relative abilities of BH₃ and BF₃ to act as Lewis acids is determined not so much by the net charge and energy of the (B) fragment, as by the properties of the terminal (H) and (F) fragments.

The wavefunctions employed in this work are SCF single-determinantal functions constructed from large basis sets which include polarizing functions.