title: Controlling the subtle energy balance in protic ionic liquids: dispersion forces compete with hydrogen bonds.
abstract: The properties of ionic liquids are determined by the energy-balance between Coulomb-interaction, hydrogen-bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen-bonding to dispersion-dominated interaction between cation and anion in the PIL [(C6 H13 )3 NH][CF3 SO3 ]. The characteristic vibrational features for both ion-pair species can be detected and assigned in the far-infrared spectra. Our approach gives direct access to the relative strength of hydrogen-bonding and dispersion forces in a Coulomb-dominated system. Dispersion-corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3 kJ mol(-1) per additional methylene group in the alkyl chains of the ammonium cation.
authors: Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, Dr.-Lorenz-Weg 1, 18059, Rostock (Germany).
authors: Koichi
authors: K
authors: Fumino
authors: Verlaine
authors: V
authors: Fossog
authors: Peter
authors: P
authors: Stange
authors: Dietmar
authors: D
authors: Paschek
authors: Rolf
authors: R
authors: Hempelmann
authors: Ralf
authors: R
authors: Ludwig
keywords: DFT calculations; FIR spectroscopy; dispersion forces; hydrogen bonding; ionic liquids