prussiate

Prussiate is a historical name used for salts containing the prussiate ion, most commonly the ferrocyanide anion [Fe(CN)6]4−. The term is often applied to salts such as potassium ferrocyanide and sodium ferrocyanide, but may also be encountered in reference to ferricyanide salts [Fe(CN)6]3− in specific contexts. In common usage, “prussiate” is associated with ferrocyanide compounds.

The ferrocyanide ion consists of an iron(II) center coordinated to six cyanide ligands in an octahedral arrangement. Ferrocyanide salts, including K4[Fe(CN)6] and Na4[Fe(CN)6], are typically white, crystalline solids that dissolve readily in water. Ferricyanide salts, such as K3[Fe(CN)6] and Na3[Fe(CN)6], are related compounds but are described separately as ferricyanides. Ferrocyanide is unusually stable to heat and light and is generally considered relatively low in toxicity under normal conditions.

Historically, ferrocyanide played a key role in the production of Prussian blue, a deep blue pigment formed by reaction of ferrocyanide with iron(III) salts. This connection to the pigment gives the term “prussiate” its name in some contexts. Today, ferrocyanide and ferricyanide salts have a range of uses beyond pigments, including applications as anticaking agents in salt, in electroplating and photography, and in various chemical processes. Regulatory status and approved uses vary by country.

Safety notes: ferrocyanide salts have low acute toxicity, but cyanide release can occur under strongly acidic conditions or with certain oxidizers. Standard chemical safety practices should be followed.