An ab Initio Study of M+(CH3OH)n Clusters (M = K, Rb, Cs). Competition between Interior and Surface Structures

Abstract

Clusters consisting of a variable number of methanol molecules and K+, Rb+, or Cs+ ions were subjected to ab initio and DFT calculations. Various minima corresponding to interior or surface structures were thus located on the corresponding potential surfaces. In interior structures, methanol molecules interact in a direct manner with the ion but scarcely among themselves; in surface structures, however, the methanol molecules coordinated to the ion also establish hydrogen bonds among them. The O···M+ distance (M = K, Rb, Cs) increases and the strength of the ion−methanol interaction decreases with increasing cluster size. The calculations predict changes in intramolecular geometry that vary very little with cluster size in the interior structures; on the other hand, the presence of hydrogen bonds in the surface clusters results in a significantly lengthened O−H distance, the effect increasing with increase in cluster size. Beyond five methanol molecules, all clusters exhibit hydrogen-bonded structures. In...