Nitronickelate

The nitronickelates are a class of chemical compounds containing a nickel atom complexed by nitro groups, -NO₂. Nickel can be in a +2 or +3 oxidation state. There can be five (pentanitronickelates), or six, (hexanitronickelates) nitro groups per nickel atom.

formula	name	Ni Ox	structure	Remarks	references
Rb3[Ni(NO2)5]	trirubidium pentanitronickelate(II)	2			[1]
K4[Ni(NO2)6]	potassium hexanitronickelate			formed by heating monohydrate dark purple	[2]
K4[Ni(NO2)6]•H2O	potassium hexanitronickelate monohydrate			formed from KNO2 and NiCl2 mix in water; orange brown	[2]
K2Ca[Ni(NO2)6]	potassium calcium hexanitronickelate		cubic a=10.31 Z=4	buff	[3]
K2Sr[Ni(NO2)6]	potassium strontium hexanitronickelate		cubic a=10.5063 Z=4 density=2.867	brown yellow	[4]
K2Ba[Ni(NO2)6]	potassium barium hexanitronickelate		cubic Fm3 (and m3m) a=10.7800 Z=4 density=2.918	brown yellow	[5]
K2Pb[Ni(NO2)6]	potassium lead hexanitronickelate		cubic Fm3 a=10.577 Z=4 density=3.480: No NO2 group disorder	buff colour;	[6]

References

1. Hathaway, B. J.; Slade, R. C. (1966). "The properties of trirubidium pentanitronickelate(II)". Journal of the Chemical Society A: Inorganic, Physical, Theoretical: 1485. doi:10.1039/J19660001485.
2. Green, RW; Bell, B (1973). "Complex nickel nitrites. I. Complexes of N-substituted Propane-1,3-diamines". Australian Journal of Chemistry 26 (8): 1663. doi:10.1071/CH9731663.
3. Hathaway, B. J.; Slade, R. C. (1968). "The influence of cations on the properties of the hexanitrometallate anions in the K₂M^IIM^II(NO₂)₆ type of complex of the nickel(II) and copper(II) ions". Journal of the Chemical Society A: Inorganic, Physical, Theoretical: 85. doi:10.1039/J19680000085.
4. Takagi, S.; Joesten, M. D.; Lenhert, P. G. (15 August 1976). "Potassium strontium hexanitrocuprate(II) and potassium strontium hexanitronickelate(II)". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry 32 (8): 2524–2526. doi:10.1107/S0567740876008121.
5. Takagi, S.; Joesten, M. D.; Lenhert, P. G. (15 July 1975). "Potassium barium hexanitronickelate(II)". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry 31 (7): 1970–1972. doi:10.1107/S0567740875006590.
6. Takagi, S.; Joesten, M. D.; Lenhert, P. G. (15 July 1975). "Potassium lead hexanitronickelate(II)". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry 31 (7): 1968–1970. doi:10.1107/S0567740875006589.