Hydrated Cobaltous Fluoride, CoF₂

Hydrated Cobaltous Fluoride, CoF₂.2H₂O, is easily prepared as rose-red crystals by evaporation of a solution of the oxide or carbonate in aqueous hydrogen fluoride. Boiling water decomposes the salt, yielding an insoluble oxy-fluoride of light red colour.

A crystal ine hydrated acid salt, CoF₂. 6H₂O.5HF, isomorphous with the corresponding nickel salt, has been described. The double salts, CoF₂.KF.H₂O and CoF₂.NaF.H₂O, have been prepared. By warming on the water-bath a solution of ammonium fluoride with cobalt oxide or hydroxide, the double ammonium cobalt fluoride, CoF₂.2NH₄F.2H₂O, is obtained, isomorphous with the corresponding nickel, zinc, and copper salts of general formula RF₂.2NH₄F.2H₂O, where R stands for a divalent metal.