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Controlling the Subtle Energy Balance in Protic Ionic Liquids: Dispersion Forces Compete with Hydrogen Bonds
Author(s) -
Fumino Koichi,
Fossog Verlaine,
Stange Peter,
Paschek Dietmar,
Hempelmann Rolf,
Ludwig Ralf
Publication year - 2015
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201411509
Subject(s) - london dispersion force , dispersion (optics) , hydrogen bond , chemistry , trifluoromethanesulfonate , ion , ionic bonding , density functional theory , ionic liquid , ammonium , chemical physics , infrared spectroscopy , interaction energy , computational chemistry , inorganic chemistry , molecule , van der waals force , organic chemistry , physics , catalysis , quantum mechanics
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 [(C 6 H 13 ) 3 NH][CF 3 SO 3 ]. 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.