Unexpected Hydrogen Bond Dynamics in Imidazolium-Based Ionic Liquids

Employing first-principles molecular dynamics simulations, we characterize the structural and dynamical hydrogen bonding in the ionic liquid [C(2)C(1)im][SCN]. The geometric picture indicates a superior role for the most acidic hydrogen bond (at H2) as compared to the two other hydrogen atoms at the rear. Despite the structural picture, the hydrogen bond dynamics at H2 is found to decay faster than the according dynamics at the H4 and H5 proton. Neglecting the directionality provides a dynamics which reflects the geometrical analysis. Two movements are identified. First, a fast (<0.3 ps) hopping of the anion above and below the imidazolium ring and second translational motion of the anion away from the cation in-plane of the imidazolium ring (5-10 ps).