The study of A(CH3OH)(1-6) (A = Li+, Na+) in the gas phase based on ab initio calculations, analysis of the solvation process

A theoretical study of complexes formed by clusters consisting of up to six methanol molecules and Li+ or Na+ ions was performed with the HF, MP2, and DFT/B3LYP methods using the 6-31G* basis set. Several stationary points fo r each cluster were thus located and were characterized as minima from the frequency calculations. The intermolecular interaction energies of the clus ter minima, corrected for the basis set superposition error, were obtained. Additional properties, such as the enthalpy and Gibbs free energy changes, and the solvent-solvent interaction energy, were also calculated. From the results, it follows that both Li+ and Na+ ions form similar complexes in t he clusters with up to four methanol molecules; in the Li+ complexes, howev er, the first coordination shell saturates with four molecules and leads to conformations differing from those of the Naf complexes. All the propertie s studied change in a systematic manner upon addition of a further methanol molecule; this trend, however, is broken by the Na+ complexes with five an d six methanol molecules owing to the formation of hydrogen bonds between m ethanol molecules. Li+-containing complexes exhibit no sign of hydrogen bon ding between the molecules of the first coordination shell. Overall, the th eoretical results are acceptably consistent with their experimental counter parts and allow one to identify some features of the clustering process. (C ) 2000 Elsevier Science B.V. All rights reserved.