The structures of alkylimidazolium fluorohydrogenate molten salts studied by high-energy X-ray diffraction

Abstract The structures of a series of XF·2.3HF (X=1-methylimidazolium, 1-ethyl-3-methylimidazolium (EMI), 1-butyl-3-methylimidazolium, 1-hexyl-3-methyl-imidazolium (HMI)) room temperature molten salts have been investigated by the high-energy synchrotron X-ray diffraction technique. The correlation peaks appearing in the total correlation function are mainly ascribed to an intra-molecular correlation of alkylimidazolium cations. However, it is suggested that the peak near 3.6 A is ascribed not only to intra-molecular but also inter-molecular correlations of the cation. The contribution of the latter is also supported by the first sharp diffraction peak of the total structure factor found at almost the same position as that of a Bragg peak in the simulated X-ray diffraction pattern of solid EMIF·HF with a layered structure, corresponding to the layer separation.