Ferricyanide
Ferricyanide is the anion 3−. It is also called hexacyanoferrate and in rare, but systematic nomenclature, hexacyanidoferrate. The most common salt of this anion is potassium ferricyanide, a red crystalline material that is used as an oxidant in organic chemistry.Properties
3− consists of a Fe3+ center bound in octahedral geometry to six cyanide ligands. The complex has Oh symmetry. The iron is low spin and easily reduced to the related ferrocyanide ion 4−, which is a ferrous derivative. This redox couple is reversible and entails no making or breaking of Fe–C bonds:
This redox couple is a standard in electrochemistry.
Compared to normal cyanides like potassium cyanide, ferricyanides are much less toxic because of the tight hold of the CN− to the Fe3+. They do react with mineral acids, however, to release highly toxic hydrogen cyanide gas.Uses
Treatment of ferricyanide with iron salts affords the brilliant, long-lasting pigment Prussian blue, the traditional color of blueprints.
