DFT study of structures and hydrogen bonds of imidazolium based halogen-free boron containing dicationic ionic liquids

Abstract

Halogen containing IL based lubricants are sensitive to the moistures and produce acidic corrosive products. So, there is a growing need towards the development and study of the halogen-free boron based ILs (hf-BILs).In this research, we used the Density Functional Theory (DFT) at the M06-2X/6-31G(d,p)level to study the interactions between 1,3-bis[3-methylimidazolium-yl] pentane dication ([C5(mim)2]2+) and bis(oxalato) borate [BOB]− and bis(malonato) borate [BMLB]− anions (halogen-free Boron based anions). The structures changes in the ion complexes have discussed. The interactions of a dication and anions in the ion pairs (IPs) and ion triplets (ITs) have characterized in terms of changes of vibrational frequencies, NBO charge distribution, reduced density gradient (RDG) analysis, and the stabilization energy E(2) values. The interaction energies, thermodynamic parameters and electronic properties of the isolated ions and their complexes were calculated. Electrostatic potential surface (ESP) studies have also been employed to understand the active sites of isolated ions, IPs and ITs. The results demonstrated that intermolecular hydrogen bonding and electrostatic interactions have a significant role in the stabilizing of the ion pairs and dicationic ionic liquids (DILs). The favorable sites for the cation–anion systems have been determined. The results of this research can shed light on the nature of bonding and interactions between ions to help the design of the new task-specific DILs with a lower impact on the environment.