The cyanonickelates are a class of chemical compound containing anions consisting of

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

atoms, and

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 ...

groups. The most important of these are the tetracyanonickelates containing four cyanide groups per nickel. The tetracyanonickelates contain the i(CN)₄sup>2− anion. This can exist in solution or in solid salts. The ion has cyanide groups arranged in a square around the central nickel ion. The symmetry of the ion is D_4''h''. The distance from the nickel atom to the carbon is 1.87 Å, and the carbon-nitrogen distance is 1.16 Å. In their crystals, the tetracyanonickelate(II) anions are often arranged in a columnar structure (e.g. in K₂ i(CN)₄ref name="vanner"> ICSD number 24099.). Tetracyanonickelate(II) can be oxidised electrochemically in solution to yield tetracyanonickelate(III) i(CN)₄sup>−. i(CN)₄sup>− is unstable and Ni(III) oxidises the cyanide to

cyanate The cyanate ion is an anion with the chemical formula . It is a resonance of three forms: (61%) ↔ (30%) ↔ (4%). Cyanate is the derived anion of isocyanic acid, H−N=C=O, and its lesser tautomer cyanic acid (a.k.a. cyanol), H−O−C� ...

OCN⁻. Tetracyanonickelate(III) can add two more cyanide groups to form hexacyanonickelate(III). In combination with alkyldiamines, and other metal ions, tetracyanonickelate ions can form cage structure that can accommodate organic molecules. This is a Hofmann-diam-type clathrate. If the cation is a very strong reducing agent, such as Yb²⁺, i(CN)₄sup>2− can be reduced to i₂(CN)₆sup>4− where nickel atom is in the +1 oxidation state.

References

{{cyanides Nickel complexes Cyanometallates