Observation of isolated ionic liquid cations and water molecules in an inert solvent

Abstract

1-Octyl-3-methyl imidazolium halides ([OMIM]I and [OMIM]Cl) were loaded on top of CCl₄, and an in situ inclusion process was monitored from the CCl₄ phase as time elapses by infrared absorption spectroscopy. Absorption from the bands corresponding to the C(2)–H and C(4,5)–H stretch modes in the imidazolium cation was reduced significantly compared to the bulk IL spectra. This indicates that (1) the [OMIM] cation exists in CCl₄ as a monomer, dissociated from the anion and other cations, and (2) hydrogen bonding between the anion and the cation increases the dipole strength of the CH moieties in the imidazolium ring. [OMIM]I was found to transfer into the CCl₄ phase much faster than [OMIM]Cl, and this instigated us to compare the transfer of aqueous solutions of ionic liquids, 1-butyl-3-methyl imidazolium halides ([BMIM]I and [BMIM]Cl) into the CCl₄ matrix. Not only [BMIM]I but also water molecules transferred faster compared to those in the [BMIM]Cl aqueous solution. Water molecules in CCl₄ were shown to form clusters in [BMIM]I; presumably, I⁻ anions work as nucleation centers of water clusters.