Ferrocyanide is the name of the anion CN)₆">cyanide.html" ;"title="e(cyanide">CN)₆sup>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. e(CN)₆sup>4− is a diamagnetic species, featuring low-spin iron(II) center in an octahedral ligand environment. Although many salts of

cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of a ...

are highly toxic, ferro- and ferricyanides are less toxic because they tend not to release free cyanide. It is of commercial interest as a precursor to the pigment

Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...

and, as its potassium salt, an

anticaking agent An anticaking agent is an additive placed in powdered or granulated materials, such as table salt or confectioneries, to prevent the formation of lumps (caking) and for easing packaging, transport, flowability, and consumption. Caking mechanisms d ...

Reactions

Treatment of ferrocyanide with ferric-containing salts gives the intensely coloured pigment

(sometimes called ferric ferrocyanide and ferrous ferricyanide). Ferrocyanide reversibly oxidized by one electron, giving ferricyanide: : e(CN)₆sup>4− ⇌ e(CN)₆sup>3− + e⁻ This conversion can be followed spectroscopically at 420 nm, 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

pigments. Sodium ferrocyanide is a common anti-caking agent. Specialized applications involves their use as precipitating agents for production of citric acid and wine.

Research

Ferrocyanide and its oxidized product ferricyanide cannot freely pass through the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

. For this reason ferrocyanide has been used as a probe of extracellular electron acceptor in the study of redox reactions in

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

. Ferricyanide is consumed in the process, thus any increase in ferrocyanide can be attributed to secretions of reductants or transplasma membrane electron transport activity. Nickel ferrocyanide (Ni₂Fe(CN)₆) is also used as catalyst in

electro-oxidation Electro-oxidation (EO), also known as anodic oxidation or electrochemical oxidation, is a technique used for wastewater treatment, mainly for industrial effluents, and is a type of advanced oxidation process (AOP). The most general layout comprises ...

( anodic oxidation) of urea. Aspirational applications range from hydrogen production for cleaner energy with lower CO₂ emission to

wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...

. Ferrocyanide is also studied as an electrolyte in flow batteries.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

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, Fe4 e(CN)6 File:Ag4Fe(CN)6.jpg, Ag4Fe(CN)6 File:Nickel(II) ferrocyanide.jpg, Ni4

e(CN)6 E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plura ...

File:Potassium ferrocyanide.jpg, K4 e(CN)6

References