Aggregation of ions in methanol–water solutions of sodium halides

Molecular-dynamics simulations have been performed for NaCl and NaI solutions in methanol–water mixtures to investigate an association of ions. Molecules of water and methanol have been represented by flexible models. Iodide ion was considered as charged Lennard-Jones sphere, whereas interactions of sodium and chloride ions were described by either the sum of Coulomb and Lennard-Jones potential or the potentials derived from ab initio calculations. Analysis of aggregation has been based on radial distribution functions, association constants, geometry and lifetime of the ion clusters. Computed association constants are in good agreement with experimental data. Clustering of either unlike or like ions occurs in all simulated systems and the ratio of free ions to aggregated ions is independent of the solvent composition.