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:
(i) Solvent reorganisation
(ii) Electronic structure
(iii) M-L reorganisation small