Electron transfer reaction mechanisms are often classified into inner and outer sphere categories in both homogeneous chemical redox reactions that occur in the solution phase and in heterogeneous reactions in electrochemistry that take place across an electrode-solution interface. In a chemical redox reaction, the homogeneous outer sphere class mechanism * Fe(CN) (aq) + Fe(CN) (aq) ---- * Fe(CN) 4- 6 (aq) + Fe(CN) (aq), (25) which is the homogeneous analogue of the electrochemical one of interest in this study, while in the inner class, ligands involving bridging to a common metal centre may be involved.