Transition metal redox couples

Tables I and II contain electrochemical kinetic and related thermodynamic parameters for several transition-metal redox couples gathered at the mercury-aqueous interface. These systems were selected since the kinetics can be measured accurately under experimental conditions where the diffuse-layer potentials, , are small and/or could be estimated with confi-...

Molecular Motions Driven by Transition Metal Redox Couples Ion Translocation and Assembling-Disassembling of Dinuclear Double-Strand Helicates... 

MOLECULAR MOTIONS DRIVEN BY TRANSITION METAL REDOX COUPLES... 

In the context of the present discussion, it is worth noting that virtually all the experimental systems that exhibit such "anomalous temperature-dependent transfer coefficients are multistep inner-sphere processes, such as proton and oxygen reduction in aqueous media [84]. It is therefore extremely difficult to extract the theoretically relevant "true transfer coefficient for the electron-transfer step, ocet [eqn. (6)], from the observed value [eqn. (2)] besides a knowledge of the reaction mechanism, this requires information on the potential-dependent work terms for the precursor and successor state [eqn. (7b)]. Therefore the observed behavior may be accountable partly in terms of work terms that have large potential-dependent entropic components. Examinations of temperature-dependent transfer coefficients for one-electron outer-sphere reactions are unfortunately quite limited. However, most systems examined (transition-metal redox couples [2c], some post-transition metal reductions [85], and nitrobenzene reduction in non-aqueous media [86]) yield essentially temperature-independent transfer coefficients, and hence potential-independent AS orr values, within the uncertainty of the double-layer corrections. 

Several transition metal phosphate systems are found to catalyze mild oxidations of organic molecules. Catalytic activity is due to transition metal redox couples see Oxidation Catalysis by Transition Metal Complexes and Oxide Catalysts in Solid-state Chemistry), but the phosphate groups are important in determining the underlying and surface structures. 

Electrochemical rate constants and activation parameters for inorganic electrochemical reactions span wide ranges e.g., standard rate constants vary from ca. 10 to > 10 cm s. For transition-metal redox couples, values of AH vary - from 0 to 80 kJ mol". As for homogeneous redox processes, it is highly desirable to elucidate the underlying reasons that are responsible for the observed rate parameters. In the following sections, the theory of electrochemical electron-transfer kinetics is outlined, followed by a discussion of some pertinent experimental results. 

Sahami S, Weaver MJ (1981) Entropic and enthalpic contributions to the solvent dependence of the thermodynamics of transition-metal redox couples Part I. Couples containing aromatic ligands. J Electroanal Chem 122 155-170... 

Hupp IT, Weaver Ml (1984) Solvent, ligand, and ionic charge effects on reaction entropies for simple transition-metal redox couples. Inorg Chem 23 3639-3644... 

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