Hexacyanoferrate(III)
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Ferricyanide is the name of the
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
CN)6">cyanide.html" ;"title="e(cyanide">CN)6sup>3−. It is also called hexacyanoferrate(III) and in rare, but systematic name">systematic nomenclature Chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC). IUPAC ...
, hexacyanidoferrate(III). The most common salt of this anion is potassium ferricyanide, a red crystalline material that is used as an oxidant in organic chemistry.


Properties

e(CN)6sup>3− consists of a Fe3+ center bound in
octahedral geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...
to six
cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...
ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
s. The complex has Oh
symmetry Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is Invariant (mathematics), invariant und ...
. The iron is
low spin Spin states when describing transition metal coordination complexes refers to the potential spin configurations of the central metal's d electrons. For several oxidation states, metals can adopt high-spin and low-spin configurations. The ambiguity ...
and easily reduced to the related
ferrocyanide Ferrocyanide is the anion 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 ...
ion e(CN)6sup>4−, which is a ferrous (Fe2+) derivative. This redox couple is reversible and entails no making or breaking of Fe–C bonds: : e(CN)6sup>3− + ee(CN)6sup>4− This
redox couple Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
is a standard in
electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between Electric potential, electrical potential difference and identifiable chemical change. These reactions involve Electron, electrons moving via an electronic ...
. Compared to main group
cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...
s like
potassium cyanide Potassium cyanide is a compound with the formula KCN. It is a colorless salt, similar in appearance to sugar, that is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include ...
, ferricyanides are much less toxic because of the strong bond between the cyanide ion (CN) and the Fe3+. They do react with mineral acids, however, to release highly toxic
hydrogen cyanide Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...
gas.


Uses

Treatment of ferricyanide with iron(II) salts affords the brilliant, long-lasting pigment
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue, Parisian and Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula . It consists of cations, where iron is in the oxidat ...
, the traditional color of
blueprints A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets introduced by Sir John Herschel in 1842. The process allowed rapid and accurate production of an unlimited number ...
.


See also

*
Potassium ferricyanide Potassium ferricyanide is the chemical compound with the formula K3 e(CN)6 This bright red salt contains the octahedral molecular geometry, octahedrally coordination compound, coordinated ferricyanide, e(CN)6− ion. It is soluble in wat ...
*
Ferrocyanide Ferrocyanide is the anion 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 ...


References

{{Cyanides Anions Iron complexes Cyanometallates Iron(III) compounds