Polarization and charge-transfer effects in Lewis acid-base complexes

An interaction energy decomposition method has been used to investigate bonding interactions in a series of Lewis acid-base complexes. It was found that the bonding interaction of these donor-acceptor complexes can be divided into two main groups. The first involves weakly interacting complexes, which have characteristic interaction energies of 3-9 kcal/mol and monomer separations of 2.5-3.1 Å. The second group consists of strongly bonding complexes, which have bonding energies of greater than 20 kcal/mol with short interaction distances (1.6-2.0 Å) between the donor and acceptor molecule. The bonding interactions of group I complexes are primarily electrostatic in nature, whereas charge polarization and charge transfer between the two interacting monomers dominate the interaction in group II complexes. A good linear relationship is observed between the charge-transfer energy and the amount of charge-transfer from the donor to the acceptor species. Interestingly, the total bonding energy also correlates linearly with the polarization energy and charge-transfer energy. Thus, a correlation between the total binding energy and charge transfer may also be observed.