Potentiometric equilibrium studies were carried out to determine the degree of binding of phosphite and phosphate ions with various protonated forms of OBISDIEN, 1,4,7,13,16,19-hexaaza-10,22-dioxacyclotetracosane, with its cobalt 1:1 and 2:1 M:L complexes and with the protonated chelates. The dioxygen affinity of the mu-phosphitodicobalt(II)-OBISDIEN complex was determined. Kinetic studies at pH 8 and pH 9 were carried out at 60, 70, and 80-degrees-C to measure the rate of degradation of the OBISDIEN-dicobalt-dioxygen-mu-phosphito complex. The phosphate ion produced was identified through P-31 NMR and by an O-18-tracer experiment.