Nitronickelate Explained

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

formula	name	structure	Remarks	references
Rb3[Ni(NO<sub>2</sub>)<sub>5</sub>]	trirubidium pentanitronickelate(II)			^[1]
Cs3[Ni(NO<sub>2</sub>)<sub>5</sub>]	tricesium pentanitronickelate(II)		dark red, formed from cesium nitrite and nickel nitrite in water	^[2]
K3[Ni(NO<sub>2</sub>)<sub>5</sub>]·KNO2	potassium pentanitronickelate potassium nitrite	monoclinic, a = 7.240 Å, b = 10.946 Å, c = 7.120 Å, β = 98.086º; Z = 2; 4 nitro groups bonded to Ni by N, 1 by O (–ONO)	formed by heating monohydrate at 100 °C dark purple; hygroscopic	^[3]
K4[Ni(NO<sub>2</sub>)<sub>6</sub>]·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	^[4]
K2Ca[Ni(NO<sub>2</sub>)<sub>6</sub>]	potassium calcium hexanitronickelate	cubic, a = 10.31 Å, Z = 4	buff	^[5]
K2Sr[Ni(NO<sub>2</sub>)<sub>6</sub>]	potassium strontium hexanitronickelate	cubic, a = 10.5063 Å, Z = 4, density = 2.867 g/cm^3	brown yellow	^[6]
K2Ba[Ni(NO<sub>2</sub>)<sub>6</sub>]	potassium barium hexanitronickelate	cubic Fm3 (and m3m), a = 10.7800 Å, Z = 4, density = 2.918 g/cm^3	brown yellow	^[7]
K2Pb[Ni(NO<sub>2</sub>)<sub>6</sub>]	potassium lead hexanitronickelate	cubic Fm3, a = 10.577 Å, Z = 4, density = 3.480 g/cm^3: No NO2 group disorder	buff colour	^[8]
N(CH3)4[Ni(NO<sub>2</sub>)<sub>3</sub>]	tetramethylammonium nickel nitrite TMNIN	hexagonal perovskite Pm1, a = 9.103 Å, c = 7.082 Å, V = 508.2 Å^3, Z = 2, density = 1.770 g/cm^3; 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	^[9] ^[10]

Notes and References

1. Hathaway. B. J.. Slade. R. C.. The properties of trirubidium pentanitronickelate(II). Journal of the Chemical Society A: Inorganic, Physical, Theoretical. 1966. 1485. 10.1039/J19660001485.
2. Goodgame. David M. L.. Hitchman. M. A.. Spectroscopic studies of some compounds with octahedral polynitrite anions. Inorganic Chemistry. April 1967. 6. 4. 813–816. 10.1021/ic50050a034.
3. Green. RW. Bell. B. Complex nickel nitrites. I. Complexes of N-substituted Propane-1,3-diamines. Australian Journal of Chemistry. 1973. 26. 8. 1663. 10.1071/CH9731663.
4. Grey . Ian E. . Hitchman . Michael A. . Rowbottom . Graham L. . Scarlett . Nicola V. Y. . Wilson . Jenny . 1994-01-01 . Crystal and molecular structure and spectra of K4[Ni(NO2)6]·H2O and K3[Ni(NO2)4(O2N)] ]. Journal of the Chemical Society, Dalton Transactions . en . 4 . 595–601 . 10.1039/DT9940000595 . 1364-5447.
5. Hathaway. B. J.. Slade. R. C.. 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. 1968. 85. 10.1039/J19680000085.
6. Takagi. S.. Joesten. M. D.. Lenhert. P. G.. Potassium strontium hexanitrocuprate(II) and potassium strontium hexanitronickelate(II). Acta Crystallographica Section B. 15 August 1976. 32. 8. 2524–2526. 10.1107/S0567740876008121. 1976AcCrB..32.2524T .
7. Takagi. S.. Joesten. M. D.. Lenhert. P. G.. Potassium barium hexanitronickelate(II). Acta Crystallographica Section B. 15 July 1975. 31. 7. 1970–1972. 10.1107/S0567740875006590. 1975AcCrB..31.1970T .
8. Takagi. S.. Joesten. M. D.. Lenhert. P. G.. Potassium lead hexanitronickelate(II). Acta Crystallographica Section B. 15 July 1975. 31. 7. 1968–1970. 10.1107/S0567740875006589. 1975AcCrB..31.1968T .
9. Chou. Liang-Kuei. Abboud. Khalil A.. Talham. Daniel R.. Kim. W. W.. Meisel. Mark W.. 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. November 1994. 6. 11. 2051–2055. 10.1021/cm00047a026.
10. Kong. Li-Hui. Fu. Da-Wei. Ye. Qiong. Ye. Heng-Yun. Zhang. Yi. Xiong. Ren-Gen. Iso-structural phase transition in tetramethylammonium nickel(II) nitrite [(CH₃)4_N][Ni(NO₂)₃]. Chinese Chemical Letters. June 2014. 25. 6. 844–848. 10.1016/j.cclet.2014.05.028.