Theoretical study on cation–anion interaction and vibrational spectra of 1-allyl-3-methylimidazolium-based ionic liquids

In order to deepen the understanding of the cation–anion interaction in ionic liquids, the structures of cation, anions, and cation–anion ion-pairs of 1-allyl-3-methylimidazolium-based ionic liquids are optimized using density functional theory (DFT), and their most stable geometries are discussed. The structural parameters, hydrogen bonds and interaction energies of 1-allyl-3-methylimidazolium dicyanamide ([Amim]DCA), 1-allyl-3-methylimidazolium chloride ([Amim]Cl), 1-allyl-3-methylimidazolium formate ([Amim]FmO) and 1-allyl-3-methylimidazolium acetate ([Amim]AcO) ion pairs are studied. The vibrational frequencies of [Amim]DCA and [Amim]Cl have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes.

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► 1-allyl-3-methylimidazolium–based ionic liquids
► The hydrogen bonding interactions between the anions and the H atoms of CC–H group in ring and of –CH2– group in alkyl side chain.
► The rotation of allyl group can lead the low viscosity of Amim+–based ion pairs.
► The vibrational spectra of 1-allyl-3-methylimidazolium chloride and 1-allyl-3-methylimidazolium dicyanamide were reported.