Binding of molecular dioxygen to Co(II) complexes in aqueous solutions

The reaction of dioxygen addition to Co(II) complexes in aqueous solution and the possible further evolution of dioxygen adducts are taken into consideration. A short survey is given of the thermodynamic features shown by the reactions of the formation of superoxo and peroxo compounds corresponding to Co(II) complexes with simple and superstructured ligands. Two topics are then developed. In the first one, the connections between the structure of the ligand bonded to Co(II) and the type and the thermodynamic and kinetic stability of the dioxygen adducts formed are discussed. Open-chain and cyclic tetraazotate saturated amines with nitrogens connected by ethylenic or propylenic bridges different in number and in their order are discussed. In the second, the state of the art concerning the dioxygen adducts corresponding to Co(II) complexes with binucleating ligands is summarized. Attention is focused on the behaviour towards molecular oxygen shown, in aqueous solutions, by Co(II) complexes with saturated open-chain or cyclic amines containing 9 or 10 nitrogens connected by ethylenic chains over a large range of R (= C-L(0)/C-Co(0)) and pH values.