Structure, Reaction Enthalpies, Entropies, and Free Energies of Cation−Molecule Complexes. A Theoretical Study by Means of the ab Initio Complete Basis Set CBS-Q Method

Ab initio molecular orbital calculations at the CBS-Q level of theory have been performed for 72 complexes in order to determine the effects of molecular structure on gas-phase basicity toward H +, Li +, and Mg 2+ . It is shown that basicities toward metal cations Li + and Mg 2+ differ considerably from the corresponding gas-phase basicities toward H + . Calculated interaction energies vary as H + ≫ Mg 2+ > Li + . The relative basicities of the bases studied depend characteristically on type of cation and coordination site.