Thermal decomposition of potassium hexanitronickelate(II) hydrate

The thermal decomposition of the complex K4[Ni(NO2)6]·H2O has been investigated over the temperature range 25–600 °C by a combination of infrared spectroscopy, powder X-ray diffraction, FAB-mass spectrometry and elemental analysis. The first stage of reaction is loss of water and isomerisation of one of the coordinated nitro groups to form the complex K4[Ni(NO2)4(ONO)]·NO2. At temperatures around 200 °C the remaining nitro groups within the complex isomerise to the chelating nitrite form and this process acts as a precursor to the loss of NO2 gas at temperatures above 270 °C. The product, which is stable up to 600 °C, is the complex K4[Ni(ONO)4]·NO2, where the nickel atom is formally in the +1 oxidation state.