Structure and interaction properties of MBIL [Bmim][FeCl4] and methanol: A combined FTIR and simulation study

Ionic liquids (ILs) arc a kind of novel solvents of which some are green with many possible applications, e.g., as efficient catalyst. Structures and properties of ILs arc determined by coulomb and van der Waals interactions and also by hydrogen-bonding between cations and anions. Particularly, metal-based ionic liquids (MBILs) exhibit excellent catalytic properties in the lignin conversions due to their superiority in paramagnetism, Lewis acidity, and electrochemistry. Nevertheless, the structural properties of MBILs are scarcely understood. Therefore, the hydrogen-bonding interactions between [Bmim][FeCl4] and methanol at different concentration were studied in this work by using excess infrared spectroscopy, density functional theory (DFT) and molecular dynamics (MD) simulations. The results showed that hydrogen-bonding interactions between cations and anions of [Bmim][FeCl4] were gradually weakened with increasing the concentration of methanol. However, cations and anions tended to bind together because of the original stable hydrogen-bonding network when the mole fraction of methanol was <0.2. The MD simulations verified that [Bmim][FeCl4] could be dissociated into individual ions when the molar ratio of methanol to [Bmim][FeCl4] exceeded 2 for the reason that methanol simultaneously interacted with cations and anions of [Bmim][FeCl4]. Due to the electron-donating group (-CD3), which made positive contributions to the stability of the O-D center dot center dot center dot Cl hydrogen bond, methanol had priority to interacting with [FeCl4](-) anions. It was found that [Bmim][FeCl4] ion clusters, [Bmim][FeCl4]-methanol complex, and the free ions were the primary aggregation forms in the mixed systems. We hope that the findings obtained from this work can give an in-depth understanding of the hydrogen-bonding interactions between MBILs and methanol, which can take advantage of MBILs as a functional medium. (C) 2020 Published by Elsevier B.V.