DFT and vibrational spectroscopy study of 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid

KAUSTEKLIS, JONAS; ALEKSA, VALDEMARAS; IRAMAIN, MAXIMILIANO A.; BRANDÁN, SILVIA ANTONIA

JOURNAL OF MOLECULAR STRUCTURE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019 vol. 1175 p. 663 - 676

0022-2860

Structural and vibrational characterizations for the 1-butyl-3-methylimidazolium trifluoromethanesulfonateionic liquid ([BMIM][OTF]) were performed combining the experimental Ramanspectrum with density functional theory (DFT) calculations based in the hybrid B3LYP/6-311þþG** levelof theory. Structurally, the trifluoromethanesulfonate anion, [OTF] is linked to 1-butyl-3-methylimidazolium cation, [BMIM] by a bidentate coordination by means of two different SeOe?Hhydrogen bonds. The [OTF] anion plays a very important role in the structure and stability of [BMIM][OTF], as observed by the strong increase in the dipole moment value when the anion is added to cation.Intramolecular H and halogen bonds evidence the high stability of ionic liquid, as supported by NBO andAIM calculations. Very good correlations were observed between the predicted infrared and Ramanspectra with the corresponding experimental ones. The different Mulliken charges observed on the Oatoms of Oe?H bonds support the asymmetric bidentate coordination of [OTF] anion with the [BMIM]cation. The [OTF] anion increase the reactivity of [BMIM][OTF], as compared with [BMIM][NO3]. Inaddition, the [OTF] anion reduces drastically the electrophilicity and nucleophilicity indexes of cationevidencing the strong influence of anion on the properties of cation. The vibrational analyses haverevealed a very important shifting of one of the two antisymmetric modes of [BMIM][OTF] towards lowerwavenumbers due probably to an asymmetric of S]O/H bond interaction which is no observed in theanion. The complete vibrational assignments were performed for ionic liquid, cation and anion and theharmonic scaled force constants were reported at the same level of theory