ferrocyanid

Ferrocyanide, also called hexacyanoferrate(II), is the anion [Fe(CN)6]4-. The iron center is in the +2 oxidation state and is coordinated by six cyanide ligands in an octahedral arrangement. The ion forms salts with alkali metals such as potassium and sodium, for example potassium ferrocyanide (K4[Fe(CN)6]) and sodium ferrocyanide (Na4[Fe(CN)6]). These salts are typically white crystalline solids that dissolve readily in water.

In aqueous solution the ferrocyanide ion is relatively stable under neutral to mildly basic conditions. It is less stable in strongly acidic or highly oxidizing environments, where cyanide can be released from the complex under adverse conditions.

Ferrocyanide salts have several practical applications. They can react with ferric ions to form Prussian blue, Fe4[Fe(CN)6]3, a historic blue pigment used in painting and printing. In industry and food production, ferrocyanide salts are used as anti-caking agents in salt and as stabilizers in various processes; the cyanide ligands are tightly bound to iron, making them relatively inert under normal use.

Safety: Ferrocyanide salts are considered to have low acute toxicity because the cyanide groups are strongly bound to iron. Release of cyanide, if any, requires strongly acidic conditions or high temperatures. Regulatory guidelines limit exposure in food-grade applications, and handling in industrial settings follows standard chemical-safety practices.