Fluoronickelate Explained

The fluoronickelates are a class of chemical compounds containing an anion with nickel at its core, surrounded by fluoride ions which act as ligands. This makes it a fluoroanion. The nickel atom can be in a range of oxidation states from +2, +3 to +4. The hexafluoronickelate(IV)²⁻ ion NiF₆²⁻ contains nickel in the maximal +4 state, and is in octahedral coordination by the fluoride atoms. It forms a commercially available salt Potassium hexafluoronickelate(IV) K₂NiF₆. Solid double salts can also contain tetrafluoronickelate NiF₄ eg K₂NiF₄.

formula	name	Ni Ox	structure	Remarks	references
(NH4)2NiF4	ammonium tetrafluoronickelate	2		Fuse NiCl2 with NH4F, light green color	^[1] ^[2]
(NH4)2NiF4·2H2O	ammonium tetrafluoronickelate dihydrate	2		Formed from Ni(OH)2 and NH4F in water	^[3]
K2NiF4	potassium tetrafluoronickelate	2
Rb2NiF4	rubidium tetrafluoronickelate	2
Ba2NiF6	barium nickel fluoride	2		yellow square plates cas=18115-49-6	^[4]
Pb2NiF6	lead(II)nickel(II) fluoride	2		cas=27037-78-1
Li3NiF6		3	Pna2 C^92v a=9.60 Å b=8.37 Å c=4.09 Å Z=4 density=3.27 / 3.24	formed at 500° 70 bar F2	^[5] ^[6]
Na3NiF6	sodium hexafluoronickelate	3		violet cas=22707-99-9
K3NiF6	potassium hexafluoronickelate	3		violet cas=14881-07-3
KCs2NiF6	dicesium potassium hexafluoronickelate	3		lilac colour cas=53479-35-9
Li2NiF6	lithium hexafluoronickelate	4	hexagonal a=8.321 Å c=4.598 Å V=275.7 Å^3 Z=3	pink sol 0.5 g/100 g HF at 0°	^[7]
(O2)2NiF6	dioxygenyl hexafluoronickelate			possibly existing, decompose 10°	^[8] ^[9]
(NO2)2NiF6	dinitronium hexafluoronickelate	4		ΔH=-471 kJ/mol, ΔH^0f=-1120
Na2NiF6	sodium hexafluoronickelate	4	cubic; or tetragonal	purple red	^[10]
K2NiF6	potassium hexafluoronickelate	4	K2PtCl6 structure	red cas=17218-47-2
CaNiF6	calcium hexafluoronickelate	4		ΔH=-363 kJ/mol, ΔH^0f=-1951 kJ/mol sold as a fluorine source	^[11]
Rb2NiF6	rubidium hexafluoronickelate	4	K2PtCl6 structure	red cas=17218-48-3
Cs2NiF6	Cesium hexafluoronickelate	4	K2PtCl6 structure	red cas=17218-49-4
SrNiF6	strontium hexafluoronickelate	4		red cas=66456-12-0
BaNiF6	barium hexafluoronickelate	4	K2PtCl6 structure	red cas=66456-13-1
(NF4)2NiF6	bis-tetrafluoroammonium hexafluoronickelate	4	tetragonal K2PtCl6 structure	red cas=63105-40-8
(ClF2O)NiF6	bis [difluorooxychlorine (V)] hexafluoronickelate (IV)	4		deep purple, stable to 60 °C	^[12] ^[13]

Notes and References

1. Chaudhuri. Mihir K.. Ghosh. Soumitra K.. Hiese. Zavei. Synthesis of tetrafluoronickelate(II) and tetrafluorozincate(II) complexes from aqueous media: a novel route to fluorometalates. Journal of the Chemical Society, Dalton Transactions. 1984. 8. 1763. 10.1039/DT9840001763.
2. Handbook of inorganic substances 2017
3. Web site: Mellor. J. W.. Nickel. A COMPREHENSIVE TREATISE ON INORGANIC AND THEORETICAL CHEMISTRY VOLUME XV Ni Ru, Rh Pd, Os, Ir. 31 May 2016. 404. May 1936.
4. Book: Macintyre. Jane E.. Dictionary of Inorganic Compounds. CRC Press. 9780412301209. 3222. 25 April 2016. en. 1992-07-23.
5. Whalen. J.M.. Lucier. G.M.. Chacón. L.. Bartlett. N.. The room temperature conversion of nickel difluoride to hexafluoronickelate(IV) salts of alkali cations. Journal of Fluorine Chemistry. March 1998. 88. 2. 107–110. 10.1016/S0022-1139(98)00105-5.
6. Grannec. J.. Lozano. L.. Sobre. P.. Portier. J.. Hagenmuller. P.. Sur un nouvel hexafluorure de nickel trivalent de formule Li3NiF6.. Journal of Fluorine Chemistry. September 1975. fr. 6. 3. 267–274. 10.1016/S0022-1139(00)83005-5.
7. Web site: Chacon. Lisa Carine. The Synthesis, Characterization and Reactivity of High Oxidation State Nickel Fluorides. University of California. 27 April 2016. Berkeley California. December 1997.
8. Bougon. Roland A.. Christe. Karl O.. Wilson. William W.. Dioxygenyl salts containing doubly charged mononuclear counterions. Journal of Fluorine Chemistry. November 1985. 30. 2. 237–239. 10.1016/S0022-1139(00)80892-1.
9. Marx. Rupert. Seppelt. Konrad. Structure investigations on oxygen fluorides. Dalton Trans.. 2015. 44. 45. 19659–19662. 10.1039/C5DT02247A. 26351980.
10. Book: Macintyre. Jane E.. Dictionary of Inorganic Compounds. CRC Press. 9780412301209. 3223. 25 April 2016. en. 1992-07-23.
11. Vorobyov. A.F.. Solovyov. S.N.. Minasian. K.A.. Dupal. A.Ja.. Sokolov. V.B.. Spirin. S.N.. Thermochemistry of certain hexafluorometalates and tetrafluoroborates. Journal of Fluorine Chemistry. September 1991. 54. 1–3. 333. 10.1016/S0022-1139(00)83842-7.
12. Foulds. G.A.. 1. Nickel. Coordination Chemistry Reviews. February 1990. 98. 2. 10.1016/0010-8545(90)80069-6.
13. Wilson. William W.. Christe. Karl O.. Synthesis and characterization of bis[difluorooxychlorine(V)] hexafluoronickelate(IV), (ClF2O)2NiF6. Inorganic Chemistry. September 1984. 23. 20. 3261–3262. 10.1021/ic00188a048.