Cobaltous Fluoride, CoF₂

Cobaltous Fluoride, CoF₂, may be obtained in the anhydrous condition as follows: on heating to fusion the chloride with excess of ammonium fluoride, the double fluoride, CoF₂.2NH₄F, is obtained; on further heating to redness in an atmosphere of an inert gas, the ammonium fluoride is volatilised, leaving amorphous cobalt fluoride which may be rendered crystalline by heating in gaseous hydrogen fluoride. Prepared in this manner the salt is formed in rose-coloured prisms, slightly soluble in water, and of density 4.43.

It fuses when heated in gaseous hydrogen fluoride to 1200-1300° C. to a ruby-red mass, and sublimes with difficulty at 1400° C. When heated with potassium hydrogen fluoride, KHF₂, a double salt, CoF₂.KF, is obtained in garnet-red crystalline plates of density 3.22.