Structural and electronic properties of alkyl-trifluoroborate based ionic liquids: A theoretical study

In this study, ionic liquids formed between 1-ethyl-3-methylimidazolium cation ([emim]+) and alkyl-trifluoroborate ([RBF3]−, R = n-CmH2m+1 (m = 1–5)) anions have been investigated theoretically. The interactions between the cation and anions have also been calculated at the MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) level of theory. The calculated interaction energies were found to decrease in magnitude with the increase of side-chain length in anions. The results of energy decomposition analysis (EDA) show that the interaction of these anions with [emim]+ cation is electrostatic in the nature and the side chain length in the anions has an important effect on the contribution of ΔEelect term. The H-bonds in the most stable ion pairs occur between fluorine atoms of anion and hydrogen atoms of methyl, ethyl groups and the hydrogen atom on the imidazolium ring (C2H). These H-bonds were also considered by quantum theory of atoms in molecules (QTAIM).