Hydrogen bonding in ionic liquids probed by linear and nonlinear vibrational spectroscopy

Abstract

Three imidazolium-based ionic liquids of the type [Cnmim][NTf2] with varying\nalkyl chain lengths (n = 1, 2 and 8) at the 1 position of the imidazolium ring\nwere studied applying IR, linear Raman, and multiplex CARS spectroscopy. The\nfocus has been on the CH-stretching region of the imidazolium ring, which is\nsupposed to carry information about a possible hydrogen bonding network in the\nionic liquid. The measurements are compared to calculations of the\ncorresponding anharmonic vibrational spectra for a cluster of [C2mim][NTf2]\nconsisting of four ion pairs. The results support the hypothesis of weak\nhydrogen bonding involving the C(4)-H and C(5)-H groups and somewhat stronger\nhydrogen bonds of the C(2)-H groups.\n