The interactions between polar solvents (methanol, acetonitrile, dimethylsulfoxide) and the ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide

In practical applications, ionic liquids (ILs) are usually used in mixtures with polar solvents to reduce the cost of neat ILs and to manipulate their physicochemical properties. To apply such mixtures in a targeted manner, it is necessary to know the influence of the solvents on the properties of the ILs. In this work, the microscopic structure and hydrogen bonding interactions between 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIMFSI) and three polar solvents (methanol, acetonitrile, and dimethylsulfoxide) are investigated by employing spectroscopic techniques and quantum chemical calculations. For neat EMIMFSI, hydrogen bonds are a secondary factor to decide the microscopic structure, which is significantly different to most other imidazolium-based ILs. Particular attention is given to the imidazolium ring C2-H group in the neat IL and its mixtures with the three solvents. Our results show that CH3CN cannot break the strong electrostatic interactions in the [EMIM](+)-[FSI](-) ion pair. In contrast, CH3OH and DMSO can break them to form [EMIM](+)-solvent complexes. Due to the fact that DMSO can form stronger hydrogen bonds with EMIMFSI, more [EMIM](+)-solvent complexes can be found in the EMIMFSI-DMSO mixtures. The results indicate that solvents can influence the microscopic structure of the ILs and thereby change the properties in a targeted fashion. (C) 2019 Elsevier B.V. All rights reserved.