Cupric fluoride, CuF₂

Evaporation or precipitation with alcohol of a solution of cupric oxide or carbonate in excess of hydrofluoric acid yields the Cupric fluoride, CuF₂, in the form of dihydrate. It crystallizes in small, blue needles, slightly soluble in cold water, and converted by heat into the anhydrous salt. The interaction of gaseous hydrogen fluoride and cupric oxide also produces the anhydrous form as a white solid. It is soluble in mineral acids, is reduced by hydrogen, and is converted into cupric oxide by heating in air. Hot water transforms it into a pale green, slightly soluble basic fluoride, Cu(OH)₂,CuF₂, a substance also produced by interaction of solutions of cupric sulphate and potassium fluoride. An acid salt, CuF₂,5HF,5H₂O, has also been described.