Abstract
To begin with, some definitions: ‘mixed valency’ is one of several names, such as ‘mixed oxidation state’ or ‘non-integral oxidation state’, used to describe inorganic or metal-organic compounds in which an element is present in more than one level of oxidation. Since the conventional definition of ‘oxidation state’ implies that we can define the number of valence shell electrons associated with each atom in a compound we shall exclude compounds in which covalency or electron delocalization between the constituent atoms is so great that we cannot judge, even approximately, how many valence shell electrons should be assigned to each kind of atom. Thus Fe3O4 comes within our compass but Cu3Si does not. Without any doubt in Fe3O4. the most loosely bound electrons are mainly localized on the Fe atoms. The choice then is to say that each Fe has 5.33 d-electrons on average, or that one Fe per formula unit has 6 while two others have__5. The same argument applies to Prussian Blue, Fe4 /Fe(CN)6_/314H2O, or the Creutz-Taube ion (NH3)5Ru (pyrazine) Ru (NH3) 5 5+ .
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