Cobalt(II) cyanide is the inorganic compound with the formula Co(CN)2. It is coordination polymer that has attracted intermittent attention over many years in the area of inorganic synthesis and homogeneous catalysis.
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Cobalt(II) cyanide has been used as a precursor to dicobalt octacarbonyl.[1]
The trihydrate salt is obtained as a reddish-brown precipitate by adding two equivalents of potassium cyanide to a cobalt salt solution:[2]
CoCl2(H2O)6 + 2 KCN → Co(CN)2 + 2 KCl + 6 H2OWith excess cyanide, the red brown dicyanide dissolves to give pentacyanocobaltate.[3]
Solid cobalt(II) cyanide is a coordination polymer consisting of cobalt ions linked by cyanide units in a cubic arrangement, each such cobalt atom having octahedral geometry, and an additional cobalt atom in half of the cubic cavities.[4] That is, the structure is actually Co[Co(CN)<sub>3</sub>]2 in a zeolite-like structure. It forms hydrates and other inclusion complexes by having substances diffuse into the cavities that do not contain the cobalt atoms.[4]