Ferrocyanide is the anion Fe(4−. Salts of this coordination complex give yellow solutions. It is usually available as the salt potassium ferrocyanide, which has the formula K4Fe(CN)6. Fe(CN)64− is a diamagnetic species, featuring low-spin iron(II) center in an octahedral ligand environment. Although many salts of cyanide are highly toxic, ferro- and are less toxic because they tend not to release free cyanide.
Reactions
Treatment of ferrocyanide with ferric-containing salts gives the intensely coloured pigment Prussian blue[ (sometimes called ferric ferrocyanide and ferrous ferricyanide).
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Ferrocyanide can be reversibly oxidized by one electron, giving ferricyanide:
- Fe(CN)64− ⇌ Fe(CN)63− + e−
This conversion can be followed spectroscopically at 420 nanometer, since ferrocyanide has negligible absorption at this wavelength while ferricyanide has an extinction coefficient of 1040 M−1 cm−1.
Applications
The dominant use of ferrocyanides is as precursors to the Prussian blue pigments. Sodium ferrocyanide is a common anti-caking agent. Specialized applications involves their use as precipitating agents for production of citric acid and wine.[
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Research
Ferrocyanide and its oxidized product ferricyanide cannot freely pass through the plasma membrane. For this reason ferrocyanide has been used as a probe of extracellular electron acceptor in the study of in cells. Ferricyanide is consumed in the process, thus any increase in ferrocyanide can be attributed to secretions of or transplasma membrane electron transport activity.
Nickel ferrocyanide (Ni2Fe(CN)6) is also used as catalyst in electro-oxidation (anodic oxidation) of urea.
Ferrocyanide is also studied as an electrolyte in flow battery.[Developing Organic Flow Batteries for Energy Storage (arpa-e.gov) http://arpa-e.energy.gov/sites/default/files/documents/files/HarvardFlowBattery_OPEN2012_ExternalProjectImpactSheet_FINAL.pdf]
Nomenclature
According to the recommendations of IUPAC, ferrocyanide should be called "hexacyanidoferrate(II)". Cyanides as a chemical class were named because they were discovered in ferrocyanide. Ferrocyanide in turn was named in Latin to mean "blue substance with iron." The dye Prussian blue had been first made in the early 18th century. The word "cyanide" used in the name is from κύανος kyanos, Greek for "(dark) blue."
Gallery
File:Pigment Berliner Blau.JPG|[Prussian3]]
File:Ag4Fe(CN)6.jpg|Ag4Fe(CN)6
File:Nickel(II) ferrocyanide.jpg|Ni4Fe(CN)62
File:Potassium hexacyanidoferrate(II).jpg|K4Fe(CN)6
See also
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Ferricyanide
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Perls' Prussian blue - a histology stain
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Potassium ferrocyanide
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Sodium ferrocyanide
