Photochemistry of the adduct between [Co(CN)₅H₂O]^2- and the polyammonium macrocyclic receptor [32]ane-N₈: evidence for the supramolecular structure

The photochemistry of aqueous solutions of [Co(CN)₅H₂O]^2- in the presence of the polyammonium macrocyclic receptor [32]ane-N₈H₈⁸⁺ was studied. The quantum yield for cyanide release in free [Co(CN)₅H₂O]^2- (Φ=0.003 at 313 nm, pH 1.5) is reduced approximately threefold in the presence of the protonated macrocycle, which provides evidence for the formation of a supramolecular structure. Further evidence for the supramolecular structure is obtained from the thermal anation of [Co(CN)₅H₂O]^-2 with Br^- (40 °C, pH 1.0), the rate of which is increased in the presence of [32]ane-N₈H₈⁸⁺, suggesting that the ligand water is not involved in hydrogen bonds with the macrocycle. These results are interpreted in terms of possible supramolecular structures.