Imidazolium-based ionic liquids having different anions (1-butyl-3-methylimidazolium [BMIM]X: X = Cl�, Br�, I�, and BF4-) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. IR spectra of these ionic liquids in CHx stretching region changed dramatically for different anions especially for C-H bonds in the imidazolium ring, and NMR chemical shifts of protons in the imidazolium ring also differ markedly for ILs having different anions. With increasing water concentration in the aqueous solution, both IR and proton NMR spectra of [BMIM]X (X = Cl�, Br�, I�) showed significant changes, while those for [BMIM]BF4 did not change appreciably. H-D isotopic exchange rates of C(2)-H in [BMIM]X/D2O mixtures exhibited an order: C(2)-H���Cl > C(2)-H���Br > C(2)-H���I, while the C(2)-H of [BMIM]BF4 was not deuterated at all. These experimental findings, supported by DFT calculations, lead to the microscopic bulk configurations in which the anions and the protons of the cations in the halide ionic liquids have specific, hydrogen-bond type of interaction, while the BF4- anion interacts less specifically by positioning itself more above the ring plane of the imidazolium cation.

Structure of ionic liquid/water mixtures investigated by IR and NMR spectroscopy

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.