Cucurbit[6]uril-based multifunctional supramolecular assemblies: synthesis, removal of Ba(ii) and fluorescence sensing of Fe(iii)

A novel cucurbit[6]uril-based (Q[6]) supramolecular assembly {(NH4)(2)Q[6](HDTNB)(2)2H(2)O} (1) with a three-dimensional (3D) framework structure was successfully constructed via outer-surface interactions between Q[6] and a flexible aromatic compound, 5,5-dithiobis-(2-nitrobenzoic acid) (H2DTNB), as a structure-directing agent. It is interesting to find that assembly 1 can selectively capture Ba(ii) cations among the common alkaline-earth metal ions of Mg(ii), Ca(ii), Sr(ii) and Ba(ii), resulting in the formation of an isomorphic 3D assembly {Ba(H2O)(2)Q[6]}(HDTNB)(2) (2). Furthermore, both assemblies 1 and 2 exhibit the selective sensing of Fe(iii) ions through fluorescence quenching, which has rarely been reported for Q[n]-based supramolecular assemblies.