Stability constants of lithium complexes with 15-crown-5 and 18-crown-6 in a hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulphonyl]imide

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 log K(Li + L) and ΔНo(Li + L) at 25 °C are determined: 1.66 (0.03), ∼0 kJ/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”.

Graphical abstractThermodynamic data for lithium complexes formation with 15-crown-5 and 18-crown-6 in a hydrophobic room temperature ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulphonyl]imide ([BMIM][N(Tf)2]) are measured with NMR 7Li technique at 27–57 °C.Figure optionsDownload full-size imageDownload as PowerPoint slide