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.