Structure and gas phase stability of complexes L...M, where M = Li+, Na+ and Mg2+, and L = H2O, H2S, SiH2, NH3 and their methyl derivatives

Ab initio molecular orbital calculations at the G2 level of theory have been performed in order to determine the structure and gas phase energies of complexes formed by the Lewis bases NH3, H2O, H2S, SiH2 and their methyl derivatives with the cations Li+, Na+ and Mg2+. Calculated interaction energies vary as Mg2+ > > Li+ > Na+. The relative basicities of the bases studied depend on both the substituent and the character of cation. The gas-phase interaction energies computed by the G2, G2(MP2) and G1 methods were comparable in accuracy. The binding energies computed by these three methods reach the targeted "chemical" accuracy. (C) 1998 Elsevier Science B.V.