Nickel Fluoride, NiF₂

When anhydrous Nickelous Fluoride or Nickel Fluoride, NiF₂ is heated with an excess of ammonium fluoride to the point of fusion, nickel ammonium fluoride is produced, of formula NiF₂.2NH₄F. This is a yellow, amorphous powder, soluble in water. When heated in a current of an inert gas it yields amorphous nickelous fluoride, the ammonium fluoride being volatilised. The nickel fluoride is yellow, and almost insoluble in water. When heated to 1200-1300° C. in hydrogen fluoride it is converted into green prisms, which are almost insoluble in water, quite insoluble in ether and in alcohol, and of density 4.63. When heated in air, nickelous fluoride yields the oxide; with sulphur, the sulphide; whilst hydrogen reduces it to metallic nickel. When heated with potassium hydrogen fluoride, a double salt, nickel potassium fluoride, NiF₂.KF, is obtained in green plates of density 3.27.

The trihydrate, NiF₂.3H₂O, is obtained as bluish green crystals by dissolving either the anhydrous salt in water, or nickelous hydroxide or carbonate in aqueous hydrogen fluoride and concentrating. Boiling water decomposes it with the formation of a pale green oxyfluoride, insoluble in water.

A dihydrate, NiF₂.2H₂O, has also been described as a green crystalline salt soluble in water.

A crystalline acid salt, NiF₂.5HF.6H₂O, and an ammonia derivative, 5NiF₂. 6NH₃.8H₂O, have been described. Other derivatives and double salts are known.