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.