Crown-ether enclosure generated by ionic liquid components—synthesis, crystal structure and Raman spectra of compounds of imidazolium based salts and 18-crown-6

Abstract

Bis(1,3-dimethylimidazolium methylsulfate) [18-crown-6] (1), ([DMIm]2[CH3SO4]2[18-crown-6], bis(1-butyl-3-methylimidazolium methylsulfate) [18-crown-6] (2), ([BMIm]2[CH3SO4]2[18-crown-6]), bis(1-ethyl-3-methylimidazolium methanesulfonate) [18-crown-6] (3), ([EMIm]2 [CH3SO3]2[18-crown-6]) and bis(1-ethyl-3-methylimidazolium trifluoromethanesulfonate) [18-crown-6] (4), ([EMIm]2[CF3SO3]2[18-crown-6]) were prepared and characterized by single-crystal X-ray diffraction, NMR and Raman spectroscopy. Coulomb interactions between the ionic (liquid) components as well as hydrogen bonding are important. No significant close contacts are observed between the ionic components and the 18-crown-6 molecules. Crystal structures of all compounds consist of alternated layers of crown-ether molecules and respective ionic units compounds. Within the layers of the ionic components (compounds 1, 3 and 4), two cations are linked to each other by C–H⋯π interactions between one methyl carbon and the imidazolium ring of another cation.