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

[Display omitted] •Synthesis of dicationic ionic liquids [M(CH2)IM2+][2I−][M(CH2)IM2+][2PF6−][M(CH2)IM2+][2NTf2−].•FTIR/ATR and FT-RAMAN spectroscopy study of the previous dicationic ionic liquids.•Comparison between our liquids, effect of the nature of the anion.•There are more active modes in FT-RAMAN than in FTIR/ATR spectroscopy.•Each sample particularise with its own vibrational mode. 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.