[Zurück]

M. López Pastor, B. Lendl, M.J. Ayora-Cañada, A. Ríos, M. Valcárcel:
"Evidence for the presence of different water clusters in ionic liquids deduced from the mid-IR spectra of ionic liquids-water mixtures";
Poster: Euroanalysis XIII, Salamanca; 05.09.2004 - 10.09.2004.

Ionic liquids (ILs) are attracting increased attention as environmental friendly solvents. Compared to organic solvents they are non-volatile and easily recoverable, which makes them very interesting for organic synthesis, catalytic reactions and analytical separations. The presence of water in ILs may affect many of their solvent properties like polarity, viscosity and conductivity. Changed rates and yields have been reported for chemical reactions in dry ionic liquids compared with ionic liquids mixed with water. Nevertheless few works are reported that investigate the interactions of water with ILs, which would be necessary to explain these different behaviours.
In this work we report on an infrared spectroscopic study of 3 ILs (emimBF4, bmimBF4 and bmimPF6) mixed with water in concentrations ranging from ( - %). The spectra were analyzed in the OH stretching region (3800-3200 cm-1) by Two dimensional correlation spectroscopy and Multivariate curve resolution - Alternating least squares. Both chemometric analyses give evidence that at low concentrations water molecules exist mainly in symmetric 1:2 type H-bonded complexes. The corresponding infrared spectra reveal 2 sharp and well-resolved bands assigned to the symmetric and asymmetric OH stretching vibration. In bmimPF6, the most hydrophobic IL, only this molecular state is observed, but in emimBF4 and bmimBF4 a second water complex can be identified additionally at higher concentrations, which can be associated to 1:1 type H-bonded complexes. In these complexes one O-H bond of the water molecule can interact with other water molecules forming small water clusters. No evidence was found that bigger water clusters are formed in these ILs at the used water concentrations