Precursor formation, outer-sphere processes

A general difficulty encountered in kinetic studies of outer-sphere electron-transfer processes concerns the separation of the precursor formation constant (K) and the electron-transfer rate constant (kKT) in the reactions outlined above. In the majority of cases, precursor formation is a diffusion controlled step, followed by rate-determining electron transfer. In the presence of an excess of Red, the rate expression is given by... 

Just as we did with outer-sphere reactions, we can dissect an inner sphere redox process into individual steps. Specifically, let us examine the reaction of (HjO) with Co "(NH3)5L. The first step is the formation of the precursor complex > >20.54-56... 

The rate-controlling step in reductive dissolution of oxides is surface chemical reaction control. The dissolution process involves a series of ligand-substitution and electron-transfer reactions. Two general mechanisms for electron transfer between metal ion complexes and organic compounds have been proposed (Stone, 1986) inner-sphere and outer-sphere. Both mechanisms involve the formation of a precursor complex, electron transfer with the complex, and subsequent breakdown of the successor complex (Stone, 1986). In the inner-sphere mechanism, the reductant... 

The reductant and oxidant [M(II) and N(III), respectively] first come together to form a precursor complex. In an outer-sphere reaction this involves a simple diffusional process in an inner-sphere reaction a substitutional step culminating in the formation of... 

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