Hollow circular compound-based inclusion complexes of an ionic liquid

Abstract

Inclusion complex formation between hollow circular compounds, e.g. crown ethers, and an ionic liquid, 1-methyl-3-octylimidazolium tetrafluoroborate, in acetonitrile solvent is studied by means of conductivity measurements, IR spectra and NMR spectra. The results reveal the formation of 1 : 1 complexes between the crown ethers and ionic liquid molecules in acetonitrile. Crown ether complexes with electron-deficient imidazolium cations are formed by H-bond formation between the acidic protons of the imidazolium ring of the ionic liquid and the lone pair of electrons of the crown oxygen atom. In the case of dibenzo-18-crown-6, complexation is caused by H-bonding; however, π-stacking or charge-transfer interactions also appear to have minor contributions to the complex formation. Thus, hydrogen bonding is mainly responsible for the complexation, and ion–dipole interactions also may be responsible for complex formation between ionic liquid molecules and the crown ethers. The interactions in the complexation are analyzed and discussed.