Molecular interactions and macroscopic effects in binary mixtures of an imidazolium ionic liquid with water, methanol, and ethanol

Intermolecular interactions in mixtures of room-temperature ionic liquids (RTILs) and co-solvents define the properties of the solution. In this work, we study the mixing behavior in the binary systems [EMIM][EtSO4]/water, [EMIM][EtSO4]/methanol and [EMIM][EtSO4]/ethanol, which is governed by a change in the balance of molecular interactions present in neat [EMIM][EtSO4]. The mixing behavior and interactions are investigated at molecular level by means of Raman spectroscopy, and at macroscopic level utilizing excess data taken from the literature. The discussion of the results aims at a distinct interpretation of the spectroscopic data and at identifying the relationships between molecular phenomena and macroscopic behavior. The Raman spectra of the binary systems indicate that the balance of intermolecular interactions in the neat RTIL is dominantly distorted by solute–solvent interactions involving hydrogen atoms (IIHAs). In concert with former studies, the spectroscopic and macroscopic data suggest, that the IIHA include a combination of conventional (red-shifting) and unconventional (blue-shifting) hydrogen bonds. With increasing co-solvent concentration, the interionic bonds become successively weaker and eventually ion-co-solvent interactions even replace those between the RTIL counter ions leading to ion pair dissociation.

► Raman spectroscopy reveals interaction changes between RTIL and polar solvents.
► Interactions include conventional and unconventional hydrogen bonds.
► Addition of solvent leads to replacement of electrostatic interionic interactions.
► Spectroscopy shows strong correlations with volumetric and thermodynamic properties.