Comparative study of interactions between thiophene\\pyridine\\benzene\\heptane and 1-butyl-3-methylimidazolium trifluoromethanesulfonate by density functional theory

Abstract

Density functional theory has been employed to investigate the interactions between thiophene, pyridine, benzene, heptane and 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]). The GGA/PW91 functionals and DNP basis set were used to optimize their geometries. The interactions between [BMIM][OTf] and thiophene, pyridine, benzene, and heptane have been ascribed to the formation of hydrogen bonds by NBO and AIM methods. The most stable gas-phase structure of [BMIM][OTf] ion pair indicates that hydrogen bonding interactions between the oxygen atoms on [OTf] anions and the C2-hydrogen on the imidazolium ring play a dominating role in the formation of the ion pair. Additional interactions are observed between [OTf] anion and the hydrogen atoms on the adjacent alkyl side chains of [BMIM] cation. The [OTf] anion tends to be located near a ring C2-proton, suggesting that the adsorption of thiophene, pyridine, benzene, and heptane on [BMIM][OTf] did not change the dominant interactions of [BMIM]–[OTf] pair. The predicted geometries, interaction energies and frontier orbitals implied the preferential adsorption of thiophene and pyridine on the [BMIM][OTf].