Abstract
Thermodynamic data for lithium complexes formation with 15-crown-5 (15C5, L) and 18-crown-6 (18C6, L) in a hydrophobic room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulphonyl]imide ([BMIM][N(Tf)2]) are measured with NMR 7Li technique at 27–57°C. For 15C5 and 18C6 only LiL+ complexes are found. The stability of lithium complexes in RTIL is estimated to be in the range between water and acetonitrile. The following values for logK(Li+L) and ΔНo(Li+L) at 25°C are determined: 1.66 (0.03), ∼0kJ/mol for 15C5 and 2.0 (0.1), −17.0 (0.5)kJ/mol for 18C6, respectively. Unlike the situation with molecular solvents the lithium complex with 15C5 in [BMIM][N(Tf)2] is entropy stabilized. The polarity of [BMIM][N(Tf)2] fits well the existing empirical solvent polarity scale for molecular solvents characterizing the polarity of this RTIL as rather normal instead of “superpolar”.
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