FECn

FeCN refers to ferrocyanide and ferricyanide, coordination complexes with the formula [Fe(CN)6]4− and [Fe(CN)6]3−. In aqueous solutions, these salts are highly soluble and widely used in chemistry and electrochemistry. The ferrocyanide and ferricyanide ions are related by a one-electron redox couple and are often employed as standard redox mediators and analytical reagents.

Structure and properties: Both species feature an octahedral arrangement where an iron center is coordinated by six cyanide ligands, each bound through carbon to iron. In ferrocyanide, iron is in the +2 oxidation state (FeII) and the complex is diamagnetic (low-spin d6). In ferricyanide, iron is in the +3 state (FeIII) and the complex is paramagnetic with a low-spin configuration. Ferrocyanide salts, such as potassium ferrocyanide, are typically pale or colorless, while ferricyanide salts, such as potassium ferricyanide, are characteristically deep blue.

Redox chemistry: The ferri/ferrocyanide couple, [Fe(CN)6]3−/[Fe(CN)6]4−, is a reversible one-electron redox system with a standard potential around +0.36 V vs SHE under standard conditions, though the exact potential depends on pH and ionic strength. This redox pair is highly stable and is a common standard in electrochemical experiments and biosensor design.

Applications: Ferro-/ferricyanide compounds are used as redox mediators in electrochemistry, calibration standards, and in various enzymatic and analytical assays. They also appear in discussions of Prussian blue chemistry, due to the interaction of ferricyanide with iron-oxide networks.

Safety: Although relatively low in acute toxicity compared with free cyanide salts, ferrocyanide and ferricyanide are cyanide-containing compounds and should be handled with appropriate laboratory safety precautions. Avoid strong acids and handle solutions with standard cyanide safety practices.