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A. Domínguez-Vidal, N. Kaun, M.J. Ayora-Cañada, B. Lendl:
"Probing intermolecular interactions in water/ionic liquid mixtures by THz spectrosc";
Vortrag: International Conference on Advanced Vibrational Spectroscopy, ICAVS 4, Corfu; 10.06.2007 - 15.06.2007.

The study of water dissolved in room-temperature ionic liquids (ILs), which are versatile solvents with a variety of research and industrial applications, is a recent topic of interest. Far infrared spectroscopy is a valuable tool for gaining insight into the processes of the liquid state on a molecular scale. In this study FIR spectra of water dissolved in three ILs at different concentrations have been recorded to gain more information about the origin of the spectral features of water in the FIR spectral region. Two widely used hydrophilic ionic liquids, (1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate) and a hydrophobic one (1-butyl-3-methylimdazolium hexafluorophosphate) were studied. FIR spectra of the pure ionic liquids and their mixtures with water at different concentrations were recorded. Multivariate curve resolution analysis has been employed to retrieve the pure spectra and concentration profile of the different species.
Shifts of the librational water bands are found to be related to the strength of the interaction between the water molecules and the anions. Thus less hindered rotation of single water molecules was observed for the hydrophobic ionic liquid. Multivariate curve resolution was used to investigate the presence of different species upon increasing water concentration. Formation of water dimers in the hydrophobic ionic liquid was only detected in hydrophilic ionic liquids as a small contribution at 202 cm-1. The major contribution in the studied spectral region (centered at 148 cm-1) corresponds to water molecules that do not bond each other via H-bonding. It is therefore assigned to a hindered translation arising from the stretching of the hydrogen bond between BF4- anions and water molecules. This spectral contribution cannot be unambiguously detected in PF6-based ionic liquids, which indicates an extremely weak interaction between water molecules and this anion.

http://publik.tuwien.ac.at/files/pub-tch_7520.pdf

Projektleitung Bernhard Lendl:
Verstehen von Ionischen Flüssigkeiten als neue Lösungsmittel für die Grüne Chemie