Preparation of Ferrous Ferricyanide

WE have synthesized ferrous ferricyanide, Fe3+2 (FeIII (CN)6)2 by vacuum pyrolysis of Prussian blue (ferric ferrocyanide, Fe4+3 (FeII (CN)6)3)—see refs. 1 and 2. This completes the preparation of the curious quartet of iron–iron cyanides. The cation in each case is high spin ferrous (2+) or ferric (3+) iron, and the cyanide-surrounded anion is low spin ferrous (II) or ferric (III) iron. These compounds precipitate from solution when soluble salts are mixed; ferric chloride and potassium ferrocyanide, for example, yield Prussian blue (ferric ferrocyanide).