Nitronickelate
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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(NO2)5] | trirubidium pentanitronickelate(II) | [1] | ||
| Cs3[Ni(NO2)5] | tricaesium pentanitronickelate(II) | dark red, formed from caesium nitrite and nickel nitrite in water | [2] | |
| K3[Ni(NO2)5]·KNO2 | potassium pentanitronickelate potassium nitrite | monoclinic, a = 7.240 Å, b = 10.946 Å, c = 7.120 Å, β = 98.086°; Z = 2; 4 nitro groups bonded to Ni by N, 1 by O (–ONO) | formed by heating monohydrate at 100 °C dark purple; hygroscopic | [2][3][4] |
| 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][4] |
| K2Ca[Ni(NO2)6] | potassium calcium hexanitronickelate | cubic, a = 10.31 Å, Z = 4 | buff | [5] |
| K2Sr[Ni(NO2)6] | potassium strontium hexanitronickelate | cubic, a = 10.5063 Å, Z = 4, density = 2.867 g/cm3 | brown yellow | [6] |
| K2Ba[Ni(NO2)6] | potassium barium hexanitronickelate | cubic Fm3 (and m3m), a = 10.7800 Å, Z = 4, density = 2.918 g/cm3 | brown yellow | [7] |
| K2Pb[Ni(NO2)6] | potassium lead hexanitronickelate | cubic Fm3, a = 10.577 Å, Z = 4, density = 3.480 g/cm3: No NO2 group disorder | buff colour | [8] |
| N(CH3)4[Ni(NO2)3] | tetramethylammonium nickel nitrite TMNIN | hexagonal perovskite P3m1, a = 9.103 Å, c = 7.082 Å, V = 508.2 Å3, Z = 2, density = 1.770 g/cm3; 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][9][10] |