Self-Assembled Cationic Cages for Anion Recognition in Aqueous Solution

Two types of supramolecular cages were synthesized in high yields via a self-assembled dynamic organic reaction: tricationic cages, <b>PT</b>³⁺/<b>MT</b>³⁺, and hexacationic cages, <b>PH</b>⁶⁺/<b>MH</b>⁶⁺. The formar imine cages are only stable in their <i>in situ</i> self-assembly solutions and showed limited anion recognition. In contrast, the latter hydrazone cages are kinetically inert and isolable as solid-state compounds via counterion exchange. The hexacationic cages exhibited significantly enhanced anion binding properties. For example, both <b>PH</b>⁶⁺ and <b>MH</b>⁶⁺ with chloride counterions can recognize Br^–, NO₃^– and SO₄^2– in aqueous media, where these anions are considered highly hydrated.