One of the important features affecting the properties of ionic liquids (ILs) is ion pair formation.[1,2] Thus we studied the cation-anion and cation-solvent interactions in protic ionc liquids of type [Et3NH][Anion] dissolved in solvents of different polarity by means of far infrared vibrational (FIR) spectroscopy, density functional theory (DFT) calculations and molecular dynamics simulations (MD).[3,4] The dissociation of contact ion pairs (CIPs) and the resulting formation of solvent-separated ion pairs (SIPs) could be observed and analyzed as a function of solvent concentration, solvent polarity and temperature. In apolar environments the CIPs dominate for all solvent concentrations and temperatures. At high concentrations of polar solvents SIPs are favored over CIPs. In these PIL/solvent mixtures CIPs are reformed with increasing temperature either due to entropic reasons or due to decreasing polarity of the solvent. Overall, this approach provides equilibrium constants, free energies, enthalpies and entropies for ion pair formation in trialkylammonium containing protic ionic liquids. Hofmeister effects for ion pair formation can be also reported. These results have important implications for solvation chemistry and the reactivity of ionic liquids.[3,4][1] Y. Marcus, G. Hefter, Chem. Rev. 20  06 , 106, 4585.[2] Y. Jiang, H. Nadonly, S. K�shammer, S. Weibels, W. Schr�er, H. Weing�rtner, Faraday Discuss. 20  12 , 154, 391.[3] P. Stange, K. Fumino, R. Ludwig, Angew. Chem. 2013  , 125, 3064; Angew. Chem. Int. Ed. 2013 , 52, 2990.[4] K. Fumino, P. Stange, V. Fossog, R. Hempelmann, R. Ludwig, Angew. Chem. 2013  , 12667; Angew. Chem. Int. Ed. 2013  , 52, 12439.

Ion pairing in protic ionic liquids: The effects of solvent polarity, solvent concentration, and temperature

248th National Meeting (2014)

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