Concentration Dependence of Ion Pairing in Imidazolium-Based Ionic Liquid Solutions

Infrared vibrational spectroscopy was used to probe concentration-dependent ion pair dissociation of imidazolium-based ionic liquids with three different halide anions (I⁻, Br⁻, and Cl⁻) in deuterated chloroform. Dissociation of the ion pairs at low concentrations of ionic liquids was found to be the easiest for ionic liquid with Cl⁻ anion, the most electronegative anion among the three investigated. This anomalous trend of ion pair dissociation was explained in terms of varying interaction strength between the solvent (CDCl₃) and the anions investigated.