Proton NMR Studies of Room Temperature Molten Salts

Mixtures of 1-(1-butyl)pyridinium chloride or 1-methyl-3-ethylimidazolium chloride with aluminum chloride are liquid at room temperature. The chemical shifts of protons on the cations of the melts are highly dependent on the proportions of aluminum chloride and organic chloride salt. The largest effect is in the basic melts, where there is an excess of organic chloride over aluminum chloride. The chemical shift behavior may be explained by assuming that the anions in the melt affect the chemical shift of the cation hydrogens and that the anions and cations interact in the fast exchange regime on the NMR time scale. The model implies that the melts are relatively organized in the liquid state, especially basic compositions. The addition of LiCl or nonelectrolyte solvents to binary aluminum chloride-imidazolium or -pyridinium chloride mixtures also affects chemical shifts of the cation protons. (Author)