Intermolecular interactions, ion solvation, and association in mixtures of 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate and γ‐butyrolactone: insights from Raman spectroscopy

Abstract

By means of Raman spectroscopy coupled with density functional theory (DFT) calculations and perturbation correlation moving window two-dimensional correlation spectroscopy intermolecular interactions were assessed in mixtures of ionic liquid (IL) 1-nbutyl-3-methylimidazolium hexafluorophosphate (BmimPF 6 ) with polar aprotic solvent γ-butyrolactone (γ-BL) over the entire range of compositions. The symmetrical P-F stretching vibration of the IL anion was found to be insensitive to the changes in mixture concentration in contrast to the C¼O stretching vibration of the γ-BL and the imidazolium ring C-H stretching vibrations of the IL cation. Each of these vibrational profiles was decomposed in various spectral contributions, and their number was rationalized by the results of quantum-chemical calculations and/or previous controversial published data. Progressive redshift of the ring C-H stretching wavenumbers was referred to pronounced solvation of the cation at the imidazolium ring site accompanied with H-bond formation. This was especially pronounced at IL mole fraction less than 0.18. Complicated variations in the intensities of the individual contributions of the C¼O profile were treated as a manifestation of the changing with concentration pattern of the intermolecular interactions. The self-association of γ-BL molecules and distinct cation solvation as dominant intermolecular interactions at low IL content are replaced with weaker cation solvation and ion association at high concentrations of IL. Possible representative molecular structures were proposed on the basis of DFT calculations.

Probing structural patterns of ion association and solvation in mixtures of imidazolium ionic liquids with acetonitrile by means of relative1H and13C NMR chemical shifts

“…accordance with the relative hydrogen bond strength suggested from the NMR spectra discussed above 20. Moreover, the bandshape of the low-frequency part of this profile is substantially different between BmimTfO and BmimTFSI on one side and BmimBF 4 and BmimPF 6 on the other side.…”

“…Dashed black lines are guides to the eye. Band assignments are taken from the literature 20,88. The relative chemical shift variations in 1 H-NMR spectra of mixtures of BmimBF 4 , BmimPF 6 , BmimTfO, BmimTFSI with AN referenced to the chemical shift of terminal methyl group of cation's butyl chain as a function of IL mole fraction x IL are shown inFigure 4.…”

Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations

“…3,[27][28][29][30] Regarding the use of molecular simulations in explaining various spectroscopic observations one has to keep in mind that the vast majority of such experimental information reports the local molecular environment around specific sites of IL cations, e.g., 1 H NMR signals, CH vibrational bands, etc. [22][23][31][32][33][34] The importance of studying the influence of the anions on the microscopic structure around a reference cation is evident in this context.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part X

“…used Raman scattering to study intermolecular interactions, ion solvation, and association in mixtures of 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate and γ‐butyrolactone. In analysing the spectra possible representative molecular structures were proposed on the basis of DFT calculations . Pecinkova and co‐workers used joint analysis of Raman and UV absorption data to distinguish co‐existing unimolecular and bimolecular structural forms.…”

“…In analysing the spectra possible representative molecular structures were proposed on the basis of DFT calculations. [143] Pecinkova and co-workers used joint analysis of Raman and UV absorption data to distinguish co-existing unimolecular and bimolecular structural forms. They applied their techniques to the case study of RNA oligonucleotides, which can form imperfect intermolecular duplexes or intramolecular hairpin structures, [144] Sassi et al used FT-IR, Raman and Brillouin spectroscopy to study lipid phase behavior of hydrated as well as dried multilamellar L-α-phosphatidylcholine assemblies, in order to compare limitations and potentials of the different techniques.…”