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Selective Separation of Hexachloroplatinate(IV) Dianions Based on Exo-Binding with Cucurbit[6]uril.

Since anions are vital for many chemical, biological and environmental processes, their recognition and separation continue to attract attention from chemists, materials scientists and engineers. Employing exo-binding of artificial macrocycles to recognize selectively anions remains a challenge in supramolecular chemistry. Herein, we report the instantaneous co-crystallization and concomitant co-precipitation between hexachloroplatinate dianions and cucurbit[6]uril, a phenomenon which relies on the selective recognition of these dianions through the noncovalent bonding interactions on the outer surface of cucurbit[6]uril. The selective hexachloroplatinate dianion recognition is driven by the weak [Pt-Cl···H-C] hydrogen bonding and [Pt-Cl···C=O] ion-dipole interactions. The synthetic protocol is highly selective. It is not observed in combinations between cucurbit[6]uril and other Pt- and Pd- or Rh-based chloride anions. We have also demonstrated that cucurbit[6]uril is able to separate selectively hexachloroplatinate dianions from mixtures of hexachloroplatinate, tetrachloropalladate, and hexachlororhodate anions. This highly selective and fast co-crystallization process, in principle, could be exploited to recover platinum from the spent vehicular three-way catalytic converters and other platinum-bearing metal waste.