Nickel(II) fluoride is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula NiF₂. It is an ionic compound of

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

and

fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactiv ...

and forms yellowish to green tetragonal crystals. Unlike many fluorides, NiF₂ is stable in air. Nickel(II) fluoride is also produced when nickel metal is exposed to fluorine. In fact, NiF₂ comprises the passivating surface that forms on nickel alloys (e.g.

monel Monel is a group of alloys of nickel (from 52 to 67%) and copper, with small amounts of iron, manganese, carbon, and silicon. Monel is not a cupronickel alloy because it has less than 60% copper. Stronger than pure nickel, Monel alloys are res ...

) in the presence of

hydrogen fluoride Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock ...

or elemental

. For this reason, nickel and its alloys are suitable materials for storage and transport these fluorine and related fluorinating agents. NiF₂ is also used as a catalyst for the synthesis of

chlorine pentafluoride Chlorine pentafluoride is an interhalogen compound with formula ClF5. This colourless gas is a strong oxidant that was once a candidate oxidizer for rockets. The molecule adopts a square pyramidal structure with C4v symmetry, as confirmed by ...

Preparation and structure

NiF₂ is prepared by treatment of anhydrous

nickel(II) chloride Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for c ...

with

at 350 °C: :NiCl₂ + F₂ → NiF₂ + Cl₂ The corresponding reaction of

cobalt(II) chloride Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula . The compound forms several hydrates ·''n'', for ''n'' = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed.M. T. Saug ...

results in

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

of the

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

, whereas nickel remains in the +2

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

after fluorination because its +3 oxidation state is less stable. Chloride is more easily oxidized than nickel(II). This is a typical halogen displacement reaction, where a halogen plus a less active halide makes the less active halogen and the more active halide. Like some other metal difluorides, NiF₂ crystallizes in the

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visib ...

structure, which features octahedral Ni centers and planar fluorides.

Reactions

A melt of NiF₂ and KF reacts to give successively potassium trifluoronickelate and

potassium tetrafluoronickelate Potassium tetrafluoronickelate is the inorganic compound with the formula K2NiF4. It features octahedral (high spin) Ni centers with Ni-F bond lengths of 2.006 Å. This green solid is a salt of tetrafluoronickelate. It is prepared by melting a mixt ...

: :NiF₂ + KF → K iF₃ :K iF₃+ KF → K₂ iF₄ The structure of this material is closely related to some superconducting oxide materials. Nickel(II) fluoride reacts with strong bases to give nickel(II) hydroxide: :NiF₂ + 2 NaOH → Ni(OH)₂ + 2 NaF

References

External links

IARC Monograph "Nickel and Nickel compounds"

{{fluorine compounds Nickel compounds Fluorides Metal halides