Conformational evolution of TFSI⁻ in protic and aprotic ionic liquids

Abstract

Abstract We here report on the conformational evolution of the bis(trifluoromethanesulfonyl)imide anion (TFSI − ) in protic and aprotic TFSI − ‐based ionic liquids as a function of temperature. The investigation is performed by Raman spectroscopy in the spectral ranges 240‐380 cm −1 and 715‐765 cm −1 , where the interference from bands due to the cations is negligible. The contribution from each TFSI − conformation, i.e. the cisoid ( C 1 ) and the transoid ( C 2 ), is quantified in order to estimate the enthalpy of conformational change, Δ H , which is found to be in the range 3.4–7.3 kJ/mol in the liquid state. Conformational information is for the first time determined from the 740 cm −1 band, which previously mainly has been used as an indicator of ion‐ion interactions. The similarity in Δ H values obtained from the two spectral ranges demonstrates the validity of using also the 740 cm −1 band for the quantification of the TFSI conformational evolution. Copyright © 2010 John Wiley & Sons, Ltd.