Potassium hexafluoronickelate(IV)

Potassium hexafluoronickelate(IV) is an inorganic compound with the chemical formula K
₂NiF
₆. It can be produced through the reaction of potassium fluoride, nickel dichloride, and fluorine.

It reacts violently with water, releasing oxygen. It dissolves in anhydrous hydrogen fluoride to produce a light-red solution. Potassium hexafluoronickelate(IV) decomposes at 350 °C, forming potassium hexafluoronickelate(III), nickel(II) fluoride, and fluorine:

${\displaystyle {\rm {\ 3K_{2}NiF_{6}{\xrightarrow {\Delta }}2K_{3}NiF_{6}+NiF_{2}+F_{2}}}}$

Potassium hexafluoronickelate is a strong oxidant. It can turn chlorine pentafluoride and bromine pentafluoride into ClF⁺
₆ and BrF⁺
₆, respectively:

${\displaystyle {\rm {\ K_{2}NiF_{6}+5AsF_{5}+XF_{5}{\xrightarrow {aHF}}XF_{6}AsF_{6}+Ni(AsF_{6})_{2}+2KAsF_{6}}}}$

( X = Cl or Br , -60 °C , aHF = anhydrous hydrogen fluoride).

Potassium hexafluoronickelate decomposes at high temperatures to release fluorine gas; like terbium(IV) fluoride, the emitted fluorine is primarily monatomic rather than the typical diatomic.

It adopts the structure seen for K₂PtCl₆ and Mg₂FeH₆.