Study of imidazolium dicationic ionic liquids by Raman and FTIR spectroscopies: The effect of the nature of the anion

Abstract

In a previous paper, we investigated the comparison between monocationic and dicationic ionic liquids. In this study three new dicationic ionic liquids were synthesized, labeled: bis-methyl imidazolium methylidene iodide [M(CH2)IM2+][2I−], bis-methyl imidazolium methylidene hexafluorophosphate [M(CH2)IM2+][2PF6−], bis-methyl imidazolium methylidene bis (trifluoromethanesulfonyl) imide [M(CH2)IM2+][2NTf2−]. In order to study the effect of the nature of the anion on the vibrational behaviors, their structures were identified by H, C, P, F NMR, FTIR/ATR and FT-RAMAN spectroscopies.However, we observe very different vibrational modes between ionic liquids following the chosen anion. According to the type of anion, the interaction anion–cation is translated by different intensities for the same vibrational mode, by frequency shifts and by appearance of modes specific to the anion.