Cobalt(II) cyanate

Cobalt(II) cyanate is the hypothetical inorganic compound with the formula Co(OCN)2.

The simple cobalt(II) cyanate has not been proven to be made. However, the tetraisocyanatocobalt(II) ion (Co(NCO)42-) is known and its blue color and is used as a qualitative test for cobalt(II) ions.

History
Cobalt(II) cyanate was claimed to have been produced in 1952 by carefully heating pyridine cobalt(II) cyanate under vacuum. This has not been proven.

In contrast, the tetraisocyanatocobalt(II) ion (Co(NCO)42-) has been identified by X-ray crystallography and is widely known. After being first produced in 1871, it has been used as a qualitative test for cobalt(II).

Other cyanate complexes of cobalt have been discovered, such as tetrakis(pyridine)cobalt(II) cyanate.

Tetracyanatocobaltate(II)
Multiple compounds of the related tetracyanatocobaltate(II) has been structurally elucidated, such as [Co(C5H5)2]2[Co(NCO)4]. All of these complexes have an intense blue color.

Potassium tetraisocyanatocobaltate(II) has been produced by the reaction of potassium cyanate and cobalt(II) nitrate:
 * 4 KOCN + Co(NO3)2 → K2[Co(NCO)4] + 2 KNO3

Tetracyanatocobaltate(II) salts with other counterions, such as cobaltcenium [Co(C5H5)]+ and EMIM are known.

Other adducts
Cobalt(II) cyanate complexes have been produced by the addition of potassium cyanate to a soluble cobalt salt, such as cobalt(II) chloride, followed by the addition of the complexing agent, such as pyridine, bipyridine, quinoline, and 2,6-dimethylpyrazine.

Structure
Although the simple cyanate is unknown, the structure of the tetracyanatocobaltate(II) ion has been elucidated. The [Co(NCO)4]2- ion consists of a nitrogen-bonded tetrahederal central cobalt atom. The cobalt-nitrogen bond length is about 1.96 Å.