Host-aided intermolecular proton transfer in the inclusion complexes of imidazole ⊂ p-sulfonatocalix[4]arene

ABSTRACT Structural analysis of two multi-component complexes comprising p-sulfonatocalix[4]arene penta-anion as the host molecule and 1-methylimidazolium or 1-butylimidazolium monocation as the guest species, aquated gadolinium(III) ion along with tetraphenylphosphonium cation, is reported. An interesting process during the formation of these inclusion complexes was seen, in which a proton transfer from p-sulfonatocalix[4]arene to the neutral guest molecules took place via acid-base reaction. 1H NMR experiment confirms the formation of the host–guest complexes and the proton transfer between the calixarene and imidazolium species in solution. Careful analysis aided by CrystalExplorer, the dominant intermolecular interactions that contribute to the stabilisation of the host–guest complex formation were readily identified. Bilayer arrangement prevails in the extended structure for both complexes regardless of the type of guest species. Graphical Abstract