The Thermodynamics of Mixed Solvent Cluster Ions: K⁺(CH₃OH)_n(H₂O)_m

Abstract

One of the motivations for research on cluster ions is the parallel that the growth of cluster ions has with phenomena such as nucleation^1,2 and solvation.^3,4 For instance, the thermodynamics involved in the clustering of molecules about ions have been related to single ion heats of solvation.^5,6 Most studies of clustering have been concerned with the sequential attachment of one particular species to an ion, as evident in a recent compilation⁷ of thermodynamic data on clusters ions. Few studies of competitive clustering by two different solvent species to yield mixed solvent cluster ions have been performed. In such systems, clustering may be enhanced or hindered by solvent-solvent interactions. Furthermore, the environment, as for example the natural atmosphere,⁸ is such that mixed cluster ions are prevalent and data for single component systems is inadequate. The purpose of this study is to expand the data base for binary solvent systems and to explore relationships with condensed phase binary solutions. Specifically, we have chosen to investigate the competitive clustering of water and methanol onto the potassium ion K⁺.