Mixed-valence complex

Mixed valence complexes contain an element which is present in more than one oxidation state. Well-known mixed valence compounds include the Creutz–Taube complex, Prussian blue, and molybdenum blue. Many solids are mixed-valency including indium chalcogenides. 
Robin–Day classification.
Mixed-valence compounds are subdivided into three groups, according to the Robin–Day classification:
Creutz–Taube ion.
The Creutz–Taube complex is a robust, readily analyzed, mixed-valence complex consisting of otherwise equivalent Ru(II) and Ru(III) centers bridged by the pyrazine. This complex serves as a model for the bridged intermediate invoked in inner-sphere electron transfer.
Mixed valence organic compounds.
Organic mixed valence compounds are also known. Mixed valency in fact seems to be required for organic compounds to exhibit electrical conductivity.