hexacyanide

Hexacyanide refers to compounds containing the hexacyano ligand, [Fe(CN)6]. The most common and stable form is the hexacyanoferrate(III) ion, [Fe(CN)6]3-, also known as ferricyanide. This ion has an iron atom in the +3 oxidation state coordinated to six cyanide ligands. The related hexacyanoferrate(II) ion, [Fe(CN)6]4-, also known as ferrocyanide, features iron in the +2 oxidation state. These hexacyanide complexes are often referred to as cyanidoferrates.

Ferricyanide salts, such as potassium ferricyanide (K3[Fe(CN)6]), are typically bright red or orange crystalline solids. Ferrocyanide salts, like potassium ferrocyanide (K4[Fe(CN)6]), are usually pale yellow. Both ferricyanide and ferrocyanide ions are generally considered to have low toxicity due to the strong bonding between the iron and cyanide ions, which prevents the release of free cyanide.

These compounds have various applications. Potassium ferricyanide is used in blueprinting, as an oxidizing agent in photography and organic synthesis, and as a laboratory reagent for detecting ferrous ions. Potassium ferrocyanide is used as an anti-caking agent in salt, in pigment production (Prussian blue), and in tempering steel. The characteristic colors of these complexes and their redox chemistry make them useful in analytical chemistry.