Theoretical Investigation on 1-Ethyl-3-Methylimidazolium Fluoride: A Density Functional Theory Study

The 1-ethyl-3-methylimidazolium fluoride is an ionic liquid that has multiple functions. The intramolecular interactions between the imidazole ring cation and the fluoride anion were not sufficiently understood. This work utilized quantum chemical analysis to determine its structures and intramolecular bonds, especially concerning intramolecular hydrogen bonds. The geometric characteristics were determined, and NBO analysis was performed using a three-parameter hybrid functional (B3LYP) with 6-31++G (d) basis set of the EMIM+ monomer. The intramolecular interactions between anions and cations of EMIMF were also studied using the geometries, bond orders, and topological analysis of the electron density concerning the density functional theory (DFT). We found that F− and EMIM+ formed an ionic bond inside the imidazole ring, F atoms form hydrogen bonds with nearby hydrogen outside the imidazole ring. Notably, the bond between H6 and F20 was the strongest. NBO analysis revealed that the most stable hydrogen bond was consisted by the donor C3 atom with a lone pair and acceptor H6-F20. The generated hydrogen bond weakened the strength of C–H stretching vibration. The topological parameters, bond order analysis, and electron density at BCPs provided a explanation for the strength of hydrogen bonds.