Zinc Fluoride, ZnF₂

The anhydrous salt is produced as an amorphous white powder by the direct union of fluorine and zinc, or by dehydrating the tetrahydrate ZnF₂.4H₂O at 100° C. Since it vaporises at 700° C. in an atmosphere of hydrogen fluoride and condenses in colourless needles, it can be prepared crystalline by the action of hydrogen fluoride at a red heat on zinc, zinc chloride, zinc oxide, or the tetrahydrate ZnF₂.4H₂O. It crystallises in either the monoclinic or triclinic system, is insoluble in alcohol and more easily soluble in acids or ammonia. It probably dissolves in aqueous hydrofluoric acid to the acid salt ZnF₂.2HF. It dissolves sparingly in water. It melts at about 734° C., and at high temperatures hydrogen sulphide converts it into the sulphide, steam or oxygen converts it into the oxide, and hydrogen reduces it to metal.

Its density at 15° C. is 4.84, and it combines with phenylhydrazine.

The tetrahydrate, ZnF₂.4H₂O, is precipitated by potassium fluoride from solutions of zinc salts, and has been prepared by dissolving zinc oxide in hydrofluoric acid. The rhombic crystals dissolve in acids but are only sparingly soluble in water, and their density is 2.535 at 12° C., or 2.567 at 10° C.

The following double fluorides have been described: NaF.ZnF₂, KF.ZnF₂, 2KF.ZnF₂, 2NH₄F.ZnF₂, ZnF₂.AlF₃.7H₂O, ZnF₂.2CeF₄.7H₂O, ZnF₂.SiF₄.6H₂O, ZnF₂.TiF₄.6H₂O, ZnF₂.ZrF₄.6H₂O, and 2ZnF₂.ZrF₄.12H₂O.