Synthesis, thermal properties, vibrational spectra and computational studies of Trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ionic liquid

In this work, Aliquat 336 ([Aliquat(+)]) based ionic liquids containing the fluorinated anion bis(trifluoromethylsulfonyl)imide [NTf2-] was successfully prepared by the anionic exchange replacement of the chloride anion. The reaction of lithium bis(trifluoromethylsulfonyl)imide with N-Methyl-N,N,N-trioctylammonium chloride ([N-1,N-8,N-8,N-8][Cl] in water lead to the corresponding IL, namely ([Aliquat(+)][NTf2-]). The obtained ionic liquid was characterized by using infrared and Raman spectra and its structure was confirmed by H-1 NMR, C-13 NMR, and F-19-NMR. The thermal properties were investigated by two complementary thermal analysis techniques: TGA and DTA. A hexadentate coordination mode between cation-anion was predicted by atoms in molecules (AIM) studies for the [Aliquat(+)][NTf2-] IL by using B3LYP/6-31G* calculations where three O atoms of the anion in Cis conformation are linked to six H atoms of cation by S-O center dot center dot center dot H interactions. Changes in the bond orders of S and O atoms of the cation supported such observations. The predicted cation-anion distances were in the range 2.30-2.60 angstrom. The harmonic force fields of cation and anion were calculated and the complete assignments were performed for both species while the most important bands observed in the infrared and Raman spectra of the IL were assigned. In addition, the scaled force constants of cation and anion of the IL were also reported. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this study, an ionic liquid based on Aliquat(+) with the fluorinated anion NTf2- was successfully prepared through anionic exchange. The structure of the obtained ionic liquid was characterized using various spectroscopic techniques, and its thermal properties were investigated. Theoretical calculations predicted a hexadentate coordination mode between the cation and anion in the IL.