A cesium-133 nuclear magnetic resonance study of the cesium cation сomplexation by macrocyclic polyethers in hydrophobic RITLs

Thermodynamic data for cesium complexes formation with 18-crown-6 (18C6, L) in five hydrophobic room temperature ionic liquids (RTIL): trioctylmethylammonium salicylate ([TOMA][Sal]), tetrahexylammonium dihexylsulfosuccinate ([THA][DHSS]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([BMIM][N(Tf)2]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([HMIM][N(Tf)2]) as well as with 12-crown-4 (12C4, L) and 15-crown-5 (15C5, L) in [BMIM][N(Tf)2] are measured with NMR 133Сs technique at 27–50 °C. Only [Cs(18C6)]+ complexes are found for [TOMA][Sal], [THA][DHSS], [BMIM][PF6], while in [BMIM][N(Tf)2] and [HMIM][N(Tf)2] both [Cs(18C6)]+ and [Cs(18C6)2]+ species are formed. For 12C4 and 15C5 only [CsL]+ species are registered in [BMIM][N(Tf)2]. For [BMIM][N(Tf)2] the log K1 values are steadily increasing: 12C4 < 15C5 < 18C6. А comparative study of [Cs(18C6)]+ stability in RTILs is estimated to be in the range between water and acetonitrile with constants increasing in the order [THA][DHSS] < [TOMA][Sal] < [BMIM][PF6] < [BMIM][N(Tf)2] < [HMIM][N(Tf)2]. It is demonstrated that unlike hydrophilic RTIL the entropy change with an exception of [BMIM][PF6], promotes complex formation while the corresponding enthalpy change is either positive or gives rather small contribution to the complex stability.

Thermodynamic data for cesium complexes formation with 18-crown-6 in five hydrophobic room temperature ionic liquids (RTIL): trioctylmethylammonium salicylate ([TOMA][Sal]), tetrahexylammonium dihexylsulfosuccinate ([THA][DHSS]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([BMIM][N(Tf)2]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([HMIM][N(Tf)2]) as well as with 12-crown-4 and 15-crown-5 in [BMIM][N(Tf)2] are measured with NMR 133Сs technique at 27–50 °C.Figure optionsDownload as PowerPoint slide