Effect of Counteranions on the Conformational Equilibrium of 1-Butyl-3-methylimidazolium-Based Ionic Liquids

Abstract EN

We have investigated the nonspherical anion effect on the trans-trans (TT) and gauche-trans (GT) equilibrium in pure 1-butyl-3-methylimidazolium ([bmim]+)-based room temperature ionic liquids (RTILs) by the Raman spectroscopy.

The intensity ratio of the [bmim]+ cation in [bmim]+-based RTILs having nonspherical anions changes with nature of the anions.

However, the enthalpy change of the [bmim]+ cation is approximately −1.0 kJ/mol for all [bmim]+-based RTILs used in this study and is independent of the anionic species.

The present results indicate that the conformational stability of the [bmim]+ cation in [bmim]+-based RTILs including nonspherical anions is driven by the entropic contribution associated with the orientation and configuration of the [bmim]+ cation with respect to the counteranion.