ACIDITY CONSTANTS, DIOXYGEN AFFINITY, UV-VISIBLE, ESR, AND ELECTROCHEMICAL STUDIES OF SOME COBALT(II) (N-MONOSUBSTITUTED OR C-MONOSUBSTITUTED) TETRAAZAMACROCYCLES COMPLEXES - DEVELOPMENT OF AN ELECTROCHEMICAL DIOXYGEN GENERATOR

The use of Cobalt(II)-(N- or C-monosubstituted)-tetraazamacrocycle com plexes as potential dioxygen carriers is studied. The physicochemical properties (pK(a), half lifetime of the oxygenated complex, dioxygen a ffinity, redox potentials) depend on the macrocyclic cavity size and o n the nature and place of the substituent in the macrocycle. A whole r ange of macrocycles substituted by a pendent arm bearing a terminal am ine, o- or m-picolyl, or a terminal carboxylic function have been synt hesized. Their studies connected the physicochemical properties of the ir cobalt complexes with the ring size and the substituent. The K-O2 d etermination, ESR spectra, and electrochemical studies afford particul arly important insights into the nature of the dioxygen adduct that is obtained. In order to synthesize a ligand suitable for the developmen t of an industrial electrochemical dioxygen generator, we have underta ken to understand the influence of the pendent arm for substituted mac rocycles. Through UV-visible and electrochemical studies, it turns out that macrocycles substituted by functions bearing terminal carboxylic groups exhibit more efficient properties than their parent compounds bearing amine terminated substituents. The redox potential depends mor e on the size of the macrocycle than on the nature of the substituent, but this influence is reversed within the half lifetime. (C) 1996 Aca demic Press, Inc.