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Cobalt(II) cyanide
Chemical compound From Wikipedia, the free encyclopedia
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Cobalt(II) cyanide is the inorganic compound with the empirical formula Co(CN)2 and structural formula Co3[Co(CN)5]2. It is a coordination polymer that has attracted intermittent attention over many years in the areas of inorganic synthesis and homogeneous catalysis.[2] The anhydrous and octahydrate forms are both blue solids insoluble in water.
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Preparation and structure
The octahydrate is prepared by the reaction between tetraethylammonium pentacyanocobaltate and cobalt(II) chloride:[3]
- 2 (Et4N)3[Co(CN)5] + 3 Co(H2O)6Cl2 → [Co(H2O)6]3[Co(CN)5]2 · 2H2O↓ + 6 Et4N+ + 6 Cl−
Heating of the octahydrate at 100 °C produces the anhydrous form.[3] The anhydrous form can also be prepared from the reaction of cobalt(II) bromide and potassium cyanide or sodium cyanide in liquid ammonia, then heating the resulting ammoniate to 210 °C in ethyl benzoate.[4]
The structural formula Co3[Co(CN)5]2 shows that cobalt(II) cyanide consists of Co2+ and [Co(CN)5]3– (pentacyanocobaltate) ions,[3] the latter of which also has cobalt in its +2 oxidation state.
Oxygenation and redox
A red trihydrated has also been reported,[5] but this was later shown to be the oxygenated derivative containing the ion [Co(CN)5(O2)]3–.[6][7][8]
The oxygenated derivative is obtained as a reddish-brown precipitate by adding two equivalents of potassium cyanide to a solution of cobalt(II) salts in air.[9] With excess cyanide, the red-brown solid dissolves to give pentacyanocobaltate, which oxidizes in the presence of oxygen to hexacyanocobaltate(III).[2][8]
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Uses
Cobalt(II) cyanide has been used as a precursor to dicobalt octacarbonyl.[10]
References
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