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Outer Sphere Electron-Transfer - Mechanism

Electron transfer from the reductant to the oxidant, with the coordination shells or spheres of each staying intact. (One reactant becomes involved with outer sphere or second coordination sphere of the other reactant)

Such reactions are observed in electron-transfer reactions of substitutionally inert complexes

Elementary Steps in the Outer Sphere Mechanism

Formation of a precursor (cage) complex


Chemical activation of the precursor, electron transfer and relaxation of the successor complex


Dissociation to the separated products


kobs = KAkel

Step 1. Formation of the Precursor Complex

This step is always considered to be fast, the rate is generally determined by kel.

Step 2. Chemical Activation and Electron Transfer

Important factors are: