Equilibrium studies of reactions of 4-chloro-1,2-diaminobenzene, 1-methyl-1,2-diaminobenzene, 4-methoxy-1,2-diaminobenzene and 4,5-dimethyl-1,2-diaminobenzene with dinuclear cobalt(II) 1,4,7,13,16,19-hexaaza-10,22-dioxacyclotetracosane

Potentiometric equilibrium studies and UV-Vis spectrophotometric measuremen ts were carried out to determine the degree of binding of 4-chloro-1,2-diam inobenzene (ClDB), 4-methyl-1,2-diaminobenzene (MeDB), 4-methoxy-1,2-diamin obenzene (MeODB) and 4,5-dimethyl-1,2-diaminobenzene (diMeDB) with dicobalt (II)-OBISDIEN complexes (OBISDIEN is 1,4,7,13,16,19-hexaaza-10,22-dioxacycl otetracosane) in the absence and presence of dioxygen. Equilibrium constant s for all major complexes formed are reported, and the results are presente d in the form of distribution diagrams showing the concentrations of indivi dual complexes as a function of p[H]. The log of oxygenation constants are: 2.37, 3.49, 3.51 and 3.71 for ClDB, MeDB, MeODB and diMeDB, respectively, and they increase with the protonation constants of these substrates. (C) 1 999 Elsevier Science S.A. All rights reserved.