[N-N=N-N]-linked fused triazoles with π-π stacking and hydrogen bonds: Towards thermally stable, Insensitive, and highly energetic materials

It is the main task and challenge to reach a fine balance between high energy density and good molecular stability in energetic material research. In this study, two series of energetic compounds, 3-amino-7,7′-azo-[1,2,4] triazolo[4,3–b][1,2,4]triazole and 3,6-diamino-7,7′-azo-[1,2,4]triazolo[4,3–b][1,2,4] triazole featuring the N4 [N-N=N-N] linkage and fused triazoles, are presented. Their structures were determined by single crystal X-ray diffraction, elemental analysis, NMR, and IR spectroscopy. Their properties were studied in terms of density, thermal stability, detonation performance, and mechanical sensitivity. The N4 [N-N=N-N] linkages accord these compounds with high heat of formation, thus increasing the detonation performance. All fused triazoles exhibit planar structures, which result in low mechanical sensitivity. Through careful investigation of crystal data, strong π-π stacking and extensive hydrogen-bonding interactions were observed between molecules, which gives positive impact on mechanical sensitivity and thermal stability. The properties between different cations (or ions) were carefully studied. Quantum chemistry calculations were performed to investigate the potential relationship between structures and properties. Among them, compound 5 possesses high thermal stability (T_d: 275 °C), good detonation performance (D: 8677 m s⁻¹; P: 36.1 GPa), and excellent insensitivity (IS: 40 J; FS: 360 N), which makes it a balanced and promising energetic material.