Raman and ab initio study of the conformational isomerism in the 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

Abstract

The calculated and experimental Raman spectra of the (EMI+)TFSI− ionic liquid, where EMI+ is the 1-ethyl-3-methylimidazolium cation and TFSI− the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI+ and TFSI− conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non-planar (np) EMI+ conformers are identified using the reference (EMI+)Br− salt. The anion conformer of C2 symmetry is confirmed to be more stable than the cis (C1) one by 4.5± 0.2 kJ mol−1. At room temperature, the population of trans (C2) anions and np cations is 75± 2% and 87± 4%, respectively.