Nickel(II) fluoride has the tetragonal rutile structure with only slightly tetragonally
compressed NiF6 octahedra; the Ni-F distances being 2.01 and 1.98 ?. Above the
melting point it sublimes as a linear gaseous molecule. The anhydrous fluoride is rather
unreactive towards concentrated acids; it is only slightly soluble in anhydrous hydrogen
fluoride and is not attacked by electronegative elements such as chlorine, sulphur and phosphorus.
The pale green tetrahydrate is slightly soluble in water; when heated, several intermediate hydrates are formed prior to N1F2.
Nickel fluoride?comprises the passivating surface that forms on nickel alloys, e.g. monel, which is why such materials are good to store or transport hydrogen fluoride or elemental fluorine.
Nickel fluoride tetrahydrate [13940-83-5], NiF2.4H2O, and its anhydrous counterpart, nickel fluoride [10028-18-9], NiF2 , are the only known stable binary compounds of nickel and fluorine. The former is a greenish light yellow crystal or powder prepared by the addition of nickel carbonate to 30-50% aqueous HF solution. The nickel fluoride formed first goes into solution and then precipitates out as the tetrahydrate as the concentration of Nickel fluoride increases and that of HF decreases. When the addition of nickel is complete, the solution and the precipitates are dried at 75-100°C until all the water is expelled. The tetrahydrate has high solubility in aqueous HF, eg, 13.3 wt % in 30% HF. It is slightly soluble in water and insoluble in alcohol and ether.
Anhydrous Nickel fluoride, a light yellow colored powder, is prepared by the action of anhydrous HF on anhydrous NiCl2 , or nickel fluoride tetrahydrate at 300°C. It is also prepared by heating a mixture of NH4.HF2 and NiF2.4H2O. The other methods include the fluorination of metal salts using excess SF4 or using ClF3 at elevated temperatures, or the reaction of NiCO3 and anhydrous HF at 250°C.
Flammability and Explosibility
Non flammable
NTP 10th Report on
Carcinogens. Reacts violently with
potassium. Chronic exposure may cause
mottling of teeth, changes in bones.
Mutation data reported. When heated to
decomposition it emits toxic fumes of F-.
See also FLUORIDES and NICKEL
COMPOUNDS.
