Synthesis and crystal structure of novel highly nitrogen-containing compound of polyazidotriazole

2,5,2′-trichloro-1,1′-azo-1,3,4-triazole (1) was treated with sodium azide to afford a novel high nitrogen compound of polyazidotriazole involving a tetrazene (N-N=N-N) structure: 2,5,2′-triazido-1,1′-azo- 1,3,4-triazole (3). Under the same condition, 2,5,2′,5′-tetraazido- 1,1′-azo-1,3,4-triazole (b) was not accomplished, whereas its decomposed product 3,5-diazido-1,2,4-triazole (4) has been obtained in an acceptable yield. The crystal structures of 3 and 4 have been determined by X-ray diffraction analysis. The crystal measurement of 4 showed that the annular tautomerism phenomenon was due to the NH acidity and the intermolecular hydrogen bonds leading to a trimer with a 9-membered cycle.