Electron-transfer processes in macrobicyclic complexes

Relatively simple syntheses for the majority of macrobicyclic complexes, compared with conventional techniques for the preparation of macrocyclic compounds, have made such complexes attractive not only for research, but also for practical application as electron carriers, catalysts for electro- and photochemical processes, and some other purposes (e.g., protein redox titrants, biological electrochemical mediators, and ionophore and electrode modifiers). 

There have been numerous publications concerning electron transfer processes with the participation of macrobicyclic complexes. Moreover, cobalt(II) and cobalt(III) complexes have received the most attention, presumably due to their availability. Several papers deal with electrochemistry of chromium, ruthenium, rhodium, manganese, nickel, iron, and copper complexes. 

1 Redox properties of d-metal sarcophaginates and related compounds 

The redox potentials of macrobicyclic complexes vary over a wide range. They are much lower than those of metal aqua ions and are dependent on the central ion and on the nature of the cage. In this section, the dependence of the redox properties on the central ion is discussed. The redox potentials for several d-metal aqua ions and sarcophaginates are summarized in Table 32 and Fig. 42. Fig. 42 also shows ionization potentials Z n=i In and LFSEs [323]. 

A correlation between Em values and M-N distances in manganese, iron, ruthenium, and cobalt(III) sarcophaginates (Table 3, Section 3.1) is observed. 

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