Study on the interaction properties of ionic liquid mixtures with a common anion: A combination of spectral and theoretical study

Ionic liquid mixtures have garnered significant attention due to their promising applications. Despite this interest, there remains a limited understanding of these mixtures, particularly regarding their microstructure. A comprehensive understanding of their microstructural characteristics and properties is essential for harnessing the full potential of ionic liquid mixtures. In this work, the structural properties and interactions were investigated within mixtures of two specific ionic liquids: 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4C1im][NTf2]) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4C1pyrr][NTf2]). Employing a combination of experimental and theoretical methods, the following conclusions were obtained: (1) The cis- and trans-configurations of [NTf2]− coexist in pure ionic liquids and their mixtures; (2) The primary interaction site of [C4C1im]+ and [C4C1pyrr]+ are C2 − H and H on the methylene group attached to the N atom, respectively. It mainly interacts with O atoms in [NTf2]− anions through hydrogen bond interactions; (3) The introduction of [C4C1pyrr][NTf2] weakens the hydrogen bonding interactions within the ionic liquid mixtures.