Supramolecular coordination assemblies of a symmetrical octamethyl-substituted cucurbituril with alkali metal ions based on the outer-surface interactions of cucurbit[n]urils

Abstract

Interactions of alkali cations (A⁺ = Na⁺, K⁺, Rb⁺, Cs⁺) with a symmetrical octamethyl-substituted cucurbituril (OMeQ[6]) have been investigated in the presence of different structure-directing agents. Single-crystal X-ray diffraction analysis has revealed that the interaction results in the formation of coordination complexes of OMeQ[6] with K⁺ and Cs⁺ cations in OMeQ[6]–ACl–HCl systems, whereas no complexes were obtained from systems containing Na⁺ and Rb⁺ in the presence of polychloride cadmium anions such as [Cd₂Cl₈]⁴⁻, [CdCl₄]²⁻, or [Cd₂Cl₇]³⁻ as structure-directing agents; in the presence of p-hydroxybenzoic acid (Hyb) as a structure-directing agent, the interaction results in the formation of coordination complexes of OMeQ[6] with Na⁺ and Cs⁺ cations in OMeQ[6]–ACl–H₂O systems. More importantly, in the presence of these different structure-directing agents, OMeQ[6] or OMeQ[6]/A⁺ complexes can form different supramolecular assemblies based on the outer surface interaction of Q[n].