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

TLDR: In this paper, the authors 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 conformational isomerism as a function of temperature.

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. Fast cooling quenches a metastable glassy phase composed of mainly C2 anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C1 anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.