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. The can be considered the double nitrites of nickel nitrite.

formula	name	structure	Remarks	references
Rb3[Ni(NO2)5]	trirubidium pentanitronickelate(II)			[1]
Cs3[Ni(NO2)5]	tricesium pentanitronickelate(II)		dark red, formed from cesium nitrite and nickel nitrite in water	[2]
K4[Ni(NO2)6]	potassium hexanitronickelate	4 nitro groups bonded to Ni by N, 2 by O (-ONO)	formed by heating monohydrate at 100 °C dark purple; hygroscopic	[2][3]
K4[Ni(NO2)6]•H2O	potassium hexanitronickelate monohydrate	hexagonal, a = 7.634 Å, c = 22.45 Å, Z = 3; nitro groups bonded to Ni via N; water not coordinated	formed from KNO2 and NiCl2 mix in water; orange brown; stable in vacuum	[2][3]
K2Ca[Ni(NO2)6]	potassium calcium hexanitronickelate	cubic, a = 10.31 Å, Z = 4	buff	[4]
K2Sr[Ni(NO2)6]	potassium strontium hexanitronickelate	cubic, a = 10.5063 Å, Z=4, density = 2.867	brown yellow	[5]
K2Ba[Ni(NO2)6]	potassium barium hexanitronickelate	cubic Fm3 (and m3m), a=10.7800 Å, Z = 4, density = 2.918	brown yellow	[6]
K2Pb[Ni(NO2)6]	potassium lead hexanitronickelate	cubic Fm3, a = 10.577 Å, Z = 4, density = 3.480: No NO2 group disorder	buff colour	[7]
N(CH3)4[Ni(NO2)3]	tetramethylammonium nickel nitrite TMNIN	hexagonal perovskite P3m1, a = 9.103 Å, c = 7.082 Å, V = 508.2 Å^3, Z = 2, density = 1.770; all nitros are bidentate, nickel either links to N or O of the NO2, forming a chain of nickel alternating with ONO	yellow brown; one-dimensional Heisenberg antiferromagnet; Haldane material; phase transitions at 409.1 and 428.4 K due to rotation of N(CH3)4	[2][8][9]

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. Goodgame, David M. L.; Hitchman, M. A. (April 1967). "Spectroscopic studies of some compounds with octahedral polynitrite anions". Inorganic Chemistry. 6 (4): 813–816. doi:10.1021/ic50050a034.
3. 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.
4. 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.
5. Takagi, S.; Joesten, M. D.; Lenhert, P. G. (15 August 1976). "Potassium strontium hexanitrocuprate(II) and potassium strontium hexanitronickelate(II)". Acta Crystallographica Section B. 32 (8): 2524–2526. doi:10.1107/S0567740876008121.
6. Takagi, S.; Joesten, M. D.; Lenhert, P. G. (15 July 1975). "Potassium barium hexanitronickelate(II)". Acta Crystallographica Section B. 31 (7): 1970–1972. doi:10.1107/S0567740875006590.
7. Takagi, S.; Joesten, M. D.; Lenhert, P. G. (15 July 1975). "Potassium lead hexanitronickelate(II)". Acta Crystallographica Section B. 31 (7): 1968–1970. doi:10.1107/S0567740875006589.
8. Chou, Liang-Kuei; Abboud, Khalil A.; Talham, Daniel R.; Kim, W. W.; Meisel, Mark W. (November 1994). "Structure- and Orientation-Dependent Magnetic Susceptibility of Tetramethylammonium Nickel Nitrite, (CH3)4N[Ni(NO2)3]: An S = 1 One-Dimensional Heisenberg Antiferromagnet". Chemistry of Materials. 6 (11): 2051–2055. doi:10.1021/cm00047a026.
9. Kong, Li-Hui; Fu, Da-Wei; Ye, Qiong; Ye, Heng-Yun; Zhang, Yi; Xiong, Ren-Gen (June 2014). "Iso-structural phase transition in tetramethylammonium nickel(II) nitrite [(CH3)4N][Ni(NO2)3]". Chinese Chemical Letters. 25 (6): 844–848. doi:10.1016/j.cclet.2014.05.028.