Metal cluster multiple redox states

The electrochemical behavior of heterometallic clusters has been reviewed clsewbcre."" The interest in examining clusters stems from their potential to act as "electron sinks " in principle, an aggregate of several metal atoms may be capable of multiple redox state changes. The incorporation of heterometals provides the opportunity to tune the electrochemical response, effects which should be maximized in very mixed"-metal clusters. Few very mixed -metal clusters have been subjected to detailed electrochemical studies the majority of reports deal with cyclic voltammetry only. Table XII contains a summary of electrochemical investigations of "very mixed"-metal clusters. 

Supramolecular assemblies of metal complexes are of considerable interest because of their versatile chemistry that can be adapted to produce materials with applications in several areas such as separation, electron transfer, catalysis, magnetic devices, and optical devices. Transition metal complexes with the ability to shuttle between multiple redox states are playing a pivotal role in developing such materials. Moreover, some of these complexes are important in understanding the complex clusters in biological macromolecules. 

The conversion of hydroperoxide/peroxide to superoxide is a one-electron redox reaction and requires the presence of transition metals having accessible multiple oxidation states as in biological iron or manganese clusters (e.g., Fe(II, III, IV) clusters of monooxygenase or the Mn(II, HI, IV) clusters of photosystems). Ti is usually not reduced at ambient temperatures. The various possibilities that could facilitate the transformation of hydroperoxo/peroxo to superoxo species are as follows ... 

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