Comparison of Electronic and Physicochemical Properties between Imidazolium-Based and Pyridinium-Based Ionic Liquids.

To compare 1-butyl-3-methylimidazolium ([BMIM]+)- and 1-butyl-3-methylpyridinium ([BMPy]+)-based ionic liquids (ILs) and investigate the influence of intramolecular and intermolecular interactions on physicochemical properties, a systematic study was performed on the electronic structures and physicochemical properties of [BMIM]+ tetrafluoroborate ([BMIM][BF4]), [BMIM]+ hexafluorophosphate ([BMIM][PF6]), [BMIM]+ hydrogen sulfate ([BMIM][HSO4]), [BMIM]+ methylsulfate ([BMIM][MSO4]), [BMIM]+ ethylsulfate ([BMIM][ESO4]), [BMPy]+ tetrafluoroborate ([BMPy][BF4]), [BMPy]+ hexafluorophosphate ([BMPy][PF6]), [BMPy]+ hydrogen sulfate ([BMPy][HSO4]), [BMPy]+ methylsulfate ([BMPy][MSO4]), and [BMPy]+ ethylsulfate ([BMPy][ESO4]) using density functional theory and molecular dynamics simulation. The results reveal that aggregation behavior exists in [HSO4]-- and [ESO4]--based ILs, and the differences between their densities and self-diffusion coefficients are smaller when there is an aggregation effect in ILs. A dimer is formed by two strong hydrogen bonds between two [HSO4]- anions in [HSO4]-based ILs, and the existence of hydrogen bonds in ILs increases density and decreases the self-diffusion coefficient. The intermolecular interaction strength of [BMIM]+-based ILs is stronger than that of [BMPy]+-based ILs.