4229The results presented here provide not only a synthetic method of a new type of chromium(II1) porphyrin complex but also an insight into the axial coordination mode of Cr(II1)-substituted cytochrome P450 if it is prepared.Acknowledgment. Redox Asymmetry and Metal-Metal Coupling in Pyrazine-Bridged Ruthenium Dimers Sir:Elucidation of the nature and extent of electronic coupling in mixed-valenck dimers continues to present a challenging theoretical and experimental problem.'-' The pyrazine-bridged diruthenium decaammine species [ R~( N H~)~l~p y z~+ (the Creutz-Taube ion4) presents a particularly intriguing case since it does not appear to fall squarely into either the predominantly valence-localized Robin and Day class I1 category or the fully delocalized class I11 category.s-6Brown, D. M., Ed. 'Mixed-Valence Compounds"; D. Reidel: Dordrecht, Holland, 1980.

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