Synthesis, NMR, FT-IR, FT-Raman spectra and thermal studies of Choline bis(trifluoromethylsulfonyl)imide ionic liquid combined with DFT calculations

Abstract

In an environmentally friendly manner, the reaction of choline chloride ([CHOL+][(Cl−]) with lithium bis(trifluoromethanesulfonyl)imide ([Li+][(CF3SO2)2N−]) in water leads to the formation of the ionic liquid(IL)choline bis(trifluoromethanesulfonyl)imide ([CHOL+][(CF3SO2)2N−]).The ionic liquid IL have been characterized by using1H, 13C and, 19F-NMR, FT-IR and FT-Raman spectroscopies. The experimental spectra have been combined with B3LYP/6–311++G** calculations to obtain complete assignments of vibrational spectra of IL and its cation by using the scaled mechanical quantum force field (SQMFF) methodology and the Molvib program. Here, we reported the 102 vibration modes of IL and the 36 of cation together with the scaled force constants for both species. The predicted structure shows the formation of the S-O···H interaction in agreement with experiments. Very good correlations evidence the comparisons among the experimental and theoretical NMR, FT-IR and FT-Raman spectra. The existence of the strong S-O···H interaction and other weak H bonds interactions are supported by NBO and AIM calculations. The analyses of gap values suggest a higher reactivity of IL in gas phase and a higher stability in aqueous solution. The comparison of this IL with [C8DABCO+][(CF3SO2)2N−] reveal that the [C8DABCO+] cation increases the reactivity of latter IL in solution. Besides a detailed characterization of its thermal (TGA/DSC) is presented. Investigation of the thermal properties demonstrated that the investigated IL can be classified as an ionic liquid, as the melting temperature is near room temperature. A glass transition and a cold crystallization were revealed at -75 and -26 °C.