From the LiI-(CH3CN)1–10 small clusters to the solvation process in acetonitrile solutions of lithium iodide

Abstract

The small LiI-(CH3CN)1–10 clusters and acetonitrile solutions of lithium iodide have been investigated by performing extensive Molecular Dynamics simulations at different conditions. The formulation of the involved force field represents in a proper way both energetics and structure of the systems. The smallest LiI–CH3CN aggregate has been also characterized from a static point of view, by considering different approaches of LiI to CH3CN and the comparison between static and dynamics results has proved that the binding energies can be satisfactorily estimated from Molecular Dynamics simulations by extrapolating to 0K the values of the mean potential energy obtained at different temperatures. For several structures, namely the LiI-(CH3CN)4–8,10 aggregates, more than one isomer has been detected.The acetonitrile solutions of lithium iodide have been studied in the 0.030moldm−3–0.887moldm−3 concentration range, by adding 1, 5, 10, 20 and 27 molecules of LiI to an ensemble of 675 molecules of solvent. Each solution has been investigated at temperatures ranging from 250K to 350K. It has been observed that the addition of the LiI salt to acetonitrile results in a volumetric contraction that originates changes in the structure of the solvent. Moreover, it has been observed that, except for solutions containing only one LiI molecule, the salt molecules tend to dissociate, thus allowing the formation of well-defined solvation shells around the ions. All these findings are representatives of a coupled dynamics of solute and solvent molecules controlling simultaneously the formation of the solvation shells and the salt dissociation.