Complementary Relation between Ion−Counterion and Ion−Solvent Interaction in Lithium Halide−Methanol Solutions

Mass spectrometric study on the cluster structure of methanol solutions containing lithium halides (LiX = LiCl, LiBr, and LiI) is reported. Solvated ions: Li+(CH3OH)n and X-(CH3OH)k, and salt clusters: Li+(Li+X-)s(CH3OH)m and X-(Li+X-)p(CH3OH)r, were observed in the mass spectra. The number of methanol molecules around Li+, especially in Li+(Li+X-)s(CH3OH)m clusters, increased when changing the anions from Cl- to I-, which suggested that there was a complementary relation between a Li+−CH3OH interaction and a Li+−X- interaction. In the case of X- = I-, the Li+−CH3OH interaction was enhanced in comparing with the case of X- = Cl-, because a Li+−I- interaction is weaker than a Li+−Cl- interaction. This observed complementary relation is a kind of intrinsic property of a liquid phase. Furthermore, mass distribution of the solvated ions and the salt clusters had correlations with physicochemical properties such as solvation energies and molar conductivities.