Hierarchical study of mono- and multicharged imidazolium encapsulation in p-sulfonatocalix[4]arene molecular capsules

Four ternary multi-component crystal structures comprising water-soluble p-sulfonatocalix[4]arene anion as the cavitand in the presence of different types of positively charged guest molecules comprising 1-butylimidazolium, 3,3 '-(1,4-phenylenebis(methylene))bis(1-methylimidazolium), 3,3 ',3 ''-(benzene-1,3,5-triyltris(methylene))tris(1-methylimidazolium), or 3,3 ',3 '',3 '''-(benzene-1,2,4,5-tetrayltetrakis(methylene))tetrakis(1-methylimidazolium) and aquated lanthanide(iii) ions (Gd(iii) or Ce(iii)) are reported. Careful crystallographic analysis shows that all positively charged imidazole rings are encapsulated by p-sulfonatocalix[4]arene for 1-butylimidazolium and 3,3 '-(1,4-phenylenebis(methylene))bis(1-methylimidazolium), however, partial encapsulation was observed for 3,3 ',3 ''-(benzene-1,3,5-triyltris(methylene))tris(1-methylimidazolium) and 3,3 ',3 '',3 '''-(benzene-1,2,4,5-tetrayltetrakis(methylene))tetrakis(1-methylimidazolium). The formation of a molecular capsule prevails in all structures regardless of the type of guest species. Supermolecules in three of the complexes self-assemble into a bilayer arrangement in the extended structure, whilst those involving p-sulfonatocalix[4]arene and 1-butylimidazolium form hydrated channels through alternative packing.