Regulating the Thermal Stability and Energy of Fused-Ring Energetic Materials by Hydrazo Bridging and Hydrogen-Bonding Networks

In this work, a combined strategy of bridging two tetrazolo[1,5-b]pyridazine rings and introducing intramolecular hydrogen bonds (N-H···O) with a hydrazo group was developed to construct a new high-energy and heat-resistant energetic compound named 6,6′-hydrazo-bis(8-amino-7-nitrotetrazolo[1,5-b]pyridazine) (1). Its dehydrogenated derivative 6,6′-azo-bis(8-amino-7-nitrotetrazolo[1,5-b]pyridazine) (2), which had fewer intramolecular hydrogen bonds (N-H···O), was also synthesized for comparison. Compounds 1 and 2 were characterized by high-resolution mass spectrometry, nuclear magnetic resonance, single-crystal X-ray diffraction, infrared spectroscopy, and elemental analysis. Their properties, such as densities (ρ: 1.87 g·cm^-3 for 1, 1.77 g·cm^-3 for 2), heat of formation values (ΔH_f: 1079 kJ·mol^-1 for 1, 1235 kJ·mol^-1 for 2), detonation velocities (D_v: 9064 m·s^-1 for 1, 8429 m·s^-1 for 2), detonation pressures (P: 35.2 GPa for 1, 27.8 GPa for 2), decomposition temperatures (T_d: 292 °C for 1, 260 °C for 2), impact sensitivities (IS: 16 J for 1, 4 J for 2), and friction sensitivities (FS: >360 N for 1, 160 N for 2), were tested. These results suggest that compound 1 is a promising high-energy and thermally stable energetic material.