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 + (CH 3 OH) n and X - (CH 3 OH) k, and salt clusters: Li + (Li + X - ) s (CH 3 OH) m and X - (Li + X - ) p (CH 3 OH) r, were observed in the mass spectra. The number of methanol molecules around Li +, especially in Li + (Li + X - ) s (CH 3 OH) m clusters, increased when changing the anions from Cl - to I -, which suggested that there was a complementary relation between a Li + −CH 3 OH interaction and a Li + −X - interaction. In the case of X - = I -, the Li + −CH 3 OH 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.