Nickel(II) fluoride
Nickel(II) fluoride is the chemical compound with the formula NiF2. Unlike many fluorides, NiF2 is stable in air. NiF2 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 is one of the few materials that can be used to store fluorine because it forms this coating. It is also used as a catalyst for the synthesis of chlorine pentafluoride.
NiF2 is prepared by treatment of anhydrous nickel(II) chloride with fluorine at 350 °C:
The corresponding reaction of cobalt(II) chloride results in oxidation of the cobalt, whereas nickel remains in the +2 oxidation state 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. Nickel(II) fluoride is also produced when fluorine reacts with nickel metal.
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