Structure and gas phase stability of complexes L-M, where M=Li+, Na+, Mg2+ and L is formaldehyde, formic acid, formate anion, formamide and their sila derivatives

Ab initio SCF and DFT methods were used to characterize the gas-phase complexes of selected carbonyl and silacarbonyl bases with Li+, Na+ and Mg2+. Geometries were optimized at the Hartree-Fock ab initio and Becke 3LYP DFT levels with the 6-31G* basis set. Frequency computations were performed at the RHF/6-31G* level of theory. Interaction energies of the cation-coordinated systems also were determined with the MP2/6-31G* method. The effect of extension of basis set (to the 6-31+G* basis) on the computed properties of anion-metal cation complexes was investigated. Calculated energies of formation vary as Mg2+ > Li+ > Na+. The Becke 3LYP DFT binding energies were comparable with those obtained at the correlated MP2 level and are in good agreement with available experimental data.