Electron transfer, between metal ions outer sphere

Electron transfer between metal ions contained in complexes can occur in two different ways, depending on the nature of the metal complexes that are present. If the complexes are inert, electron transfer occurring faster than the substitution processes must occur without breaking the bond between the metal and ligand. Such electron transfers are said to take place by an outer sphere mechanism. Thus, each metal ion remains attached to its original ligands and the electron is transferred through the coordination spheres of the metal ions. 

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... 

In aqueous solution outer-sphere electron transfer between metal ions and alkyl hydroperoxides [reactions (95) and (96)] is expected to be favorable. In nonpolar solvents, electron transfer probably proceeds via the formation of inner-sphere, covalently bonded complexes. The overall reaction constitutes a catalytic decomposition of the hydroperoxide into alkoxy and alkylperoxy radicals ... 

In electron transfer between metal ions, a metal-ion catalyst normally reacts by nonassociative activation, in which the species do not form long-lived binuclear intermediates. The catalytic process often can be rationalized by reactivity patterns e.g., the Cu catalyses of the oxidation "of V(III) by Fe(III). This catalysis by Cu occurs by outer-sphere mechanisms as in ... 

Electron transfer between metal ions may occur either as inner-sphere (is) or an outer-sphere (os) reaction, The first case involves a ligand exchange and the... 

Like all redox reactions26,28,967,968 those of copper(II) may be divided into two types (a) outer sphere mechanisms involving electron (or proton) transfer between coordination shells that remain essentially intact and (b) inner sphere mechanisms in which the oxidizing and reducing species are connected by a bridging ligand, which is common to both metal ion coordination spheres."9... 

Derivation of the Marcus relation for outer-sphere electron-transfer reactions between metal ions in solution... 

For a series of related outer-sphere electron-transfer reactions between metal ions, the Marcus equation predicts a relation between the free energies of activation and of reaction, namely Equation (9.19) (Section 9.1.2.5). This equation is a quadratic, and so a plot of against (which is equivalent to a plot of log kobs against log ATobs) will not... 

To make it easier for an electron to move from one metal ion to another, it makes sense that they should be as close to each other as possible. Assuming, for the moment, that their two coordination spheres stay intact, the distance between two metal ions will be at a minimum when the two coordination spheres are in contact. An outer-sphere mechanism occurs when an electron is transferred among metal ions whose intact coordination spheres are in contact at their outer edges. 

Historically, the development of ET theory has been based on inorganic systems, in which the (metal-ion) redox centers are surrounded by coordinated ligands [52]. In those cases in which no new metal-ligand bonds are formed or bond breakage is observed, the interaction between the redox centers is weak (usually Hda < 200 cm-1), and such reactions are conventionally designated as outer-sphere (OS) electron transfer [52, 53]. 

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