Theoretical Studies of Physical, Chemical, and Vibrational Properties of Various Imidazolium-Based Ionic Liquids

Abstract

In the present paper, inter-ionic reactions involving two cations and four anions were used to model the formation of neutral ion pairs. Moreover, density functional theory technique has been used to describe the physical, chemical, and vibrational properties of the ionic liquids, containing imidazolium-based cations and different anions at functional B3LYP with a def2-SVP basis set. The chemical parameters have been investigated for different ionic liquids along with frontier orbitals “highest occupied molecular orbital” and “lowest unoccupied molecular orbital” studies. All the optimized structures of the ionic liquids did not produce imaginary frequency (i.e., imaginary frequency is zero), which validates that the structures are energetically stable. The density functional theory method provides the stability sequence for ionic liquids: [BMIM][PF6] > [EMIM][PF6] > [BMIM][TFSI] > [EMIM][TFSI] > [EMIM][Cl] > [BMIM][Cl] > [EMIM][Br] > [BMIM][Br]. Herein, [BMIM][PF6] ionic liquid has highest energy gap (4.833 eV) that means that [BMIM][PF6] is the most stable.