Electron exchange reaction of bis(terpyridine)cobalt(3+/2+) re-examined by NMR

The rate of the electron transfer self-exchange reaction between bis(terpyridine)cobalt(III) and bis(terpyridine)cobalt(II) has been reexamined by proton NMR. The rate constant of 4x10(2) M(-1) s(-1) at 50 degrees C is dependent on the identity of the anion. Average activation parameters of 32 kJ mol(-1) and -96 J K-1 mol(-1) are in agreement with previous measurements by other techniques. There is no evidence for either spin restrictions or non-adiabtaticity in this and related cobalt(III)/(II) electron exchange reactions. An alternative explanation is offered for the anomalously negative volumes of activation reported elsewhere.