Thermodynamic and ESR study on the reaction of dicobalt(II) diporphyrin complex with dioxygen

The reaction of dioxygen with a dicobalt di( meso - tetraphenylporphyrin) l inked by a diamido - aliphatic chain in N, N - dimethylformamide solution w as studied. Thermodynamic values under standard state (298K, 100kPa O-2) ar e: P-1/2 = 6.8kPa, n = 1.84, DeltaG(0) = - 12.3kJ . mol-(1), DeltaH(0) = - 172.09kJ . mol(-1), DeltaS(0) = - 536.21 J . mol(-1).K-1. Thermodynamic dat a show that each of the two cobalt( II) porphyrin rings has strong cooperat ive effect of oxygen binding with another. The reaction of dioxygen with th e complex was also studied by ESR spectroscopy. The results show that bondi ng way of dioxygen complex is of the superoxo Co - O-2(-) type.