Syntheses, Structures, and Properties of a Series of Metal Ion-Containing Dialkylimidazolium Ionic Liquids

Abstract A series of metal ion-containing ionic liquids Bmim2MCl4 (M = Sn, Cu, Ni, Mn, Fe, Co, Zn, and Pt; Bmim = 1-butyl-3-methylimidazolium) and Bmim2ZrCl6 were synthesized and their single-crystal structures were determined by X-ray crystallographic analysis. The crystal structures showed the existence of an interaction between chlorometalate anions and imidazolium cations via C–H···Cl hydrogen bonding as well as an interaction between the cations through C–H···π hydrogen bonding and/or π···π stack interaction. The melting points of the metal salts were found to correlate with the number of halide ions coordinated to each metal ion and the overall symmetry of the chlorometalate anions. Ionic conductivity measured in super-cooled states of the synthesized salts unambiguously confirmed that these salts behaved as ionic liquids. The synthesized salts have a high thermal stability as evaluated by TGA and negligible vapor pressure before decomposition.