The microscopic structure of 1-Methoxyethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EOMIMTFSI) during dilution with polar solvents

Abstract

Ether-functionalized ionic liquids (ILs) have attracted increasing attention in the fields of electrochemistry and energy; however, few fundamental studies of the microscopic properties of ether-functionalized ILs have been reported. In this work, the hydrogen bonding interactions between the ether-functionalized IL 1-methoxyethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EOMIMTFSI) and co-solvents, chloroform (CHCl3), acetonitrile (CH3CN) and dimethyl sulfoxide (DMSO), were investigated at the whole concentration range by Fourier transform infrared spectroscopy (FTIR), excess infrared spectroscopy, and quantum chemical calculations. The following conclusions were made: (1) during dilution with co-solvents, the hydrogen bonding interactions in the three systems were strengthened, and the strength of the hydrogen bonds decreased in the following order: EOMIMTFSI−DMSO > EOMIMTFSI−CHCl3 > EOMIMTFSI−CH3CN. (2) DMSO could disrupt the hydrogen bonding interactions between the cations and anions in EOMIMTFSI, and [EOMIM]+−DMSO complexes were observed in the excess infrared spectrums. CHCl3 and CH3CN were unable to disrupt the electrostatic interactions, and only ion cluster–co-solvent and ion pair–co-solvent complexes were observed. (3) The main interaction sites were different in the studied systems. In the systems of EOMIMTFSI−CHCl3 and EOMIMTFSI−DMSO, the main interaction sites between the co-solvent and cations were C2−H, whereas in the EOMIMTFSI−CH3CN system, the corresponding interaction site was C5−H.