Cobalt Thiocyanate, Co(CNS)₂

Cobalt Thiocyanate, Co(CNS)₂.xH₂O, was obtained by Meitzendorff as a result of dissolving cobalt carbonate in hydrogen thiocyanate, and, describing it as a yellowish brown crystalline mass, attributed to it the formula 2Co(CNS)₂.H₂O. Rosenheim and Cohen prepared the tri-hydrate, Co(CNS)₂.3H₂O, in an analogous manner as violet crystals, appearing red by transmitted light, and belonging to the rhombic system. On solution in water they yield a blue colour which becomes pink on dilution. In alcohol a deep blue colour is obtained.

Grossmann and Htinseler prepared the tetrahydrate, Co(CNS)₂.4H₂O, by double decomposition of solutions of cobalt sulphate and barium thiocyanate. The solution is at first red, but becomes blue on concentration, and after remaining in vacuo for some time, deposits beautiful wine-red rhombic crystals. These are unstable in air, becoming browtt and opaque upon prolonged exposure.

The following double salts have been prepared:

Potassium cobalto-thiocyanate, K₂Co(CNS)₄.4H₂O;
Sodium cobalto-thiocyanate, Na₂Co(CNS)₄.8H₂O;
Ammonium cobalto-thiocyanate, (NH₄)₂Co(CNS)₄.4H₂O;
Barium cobalto-thiocyanate, BaCo(CNS)₄.8H₂O;
Silver cobalto-thiocyanate (dark blue), AgCo(CNS)₃.2H₂O;
Caesium cobalto-thiocyanate (blue), Cs₂Co(CNS)₄.2H₂O; and
Caesium silver cobalto-thiocyanate, Cs₂Ag₂Co(CNS)₆.2H₂O (pink).

The close similarity between the constitution of the cobalti-nitrites and cobalti-cyanides naturally leads one to inquire whether or not the radicles (NO₂) and (CN) are interchangeable. To a certain extent this appears to be the case, for the following salts have been prepared:

Na₆Co₄(CN)₁₀NO₂.11H₂O, K₄Co₂(CN)₉NO₂.3H₂O, and Ag₅Co₂(CN)₁₀.NO₂.6H₂O.