Nitrosylazide

Nitrosylazide is a highly labile nitrogen oxide with chemical formula N4O. 
Synthesis.
Nitrosylazide can be synthesized via the following reaction of sodium azide and nitrosyl chloride at low temperatures:
Properties.
Below −50 °C, nitrosylazide exists as a pale yellow solid. Above this temperature, it decomposes into nitrous oxide (N2O) and molecular nitrogen (N2):
Characterization of the compound with IR and Raman spectroscopy show absorption bands that agree well with calculated values for a "trans"-structure. Quantum chemical calculations show a "cis"-form higher in energy by 4.2 kJ·mol−1 and an aromatic ring form that is more stable by 205 kJ·mol−1. However, the cyclization to the ring form would have to surpass the 205 kJ·mol−1 activation energy barrier require to bend the azide group, which might explain why nitrosyl azide is stable enough to be isolated at low temperature.