High performance and heat-resistant pyrazole-1,2,4-triazole energetic materials: Tuning the thermal stability by asymmetric framework and azo-bistriazole bridge

Driven by ever-increasing application of thermal stable explosives in the deep mining and aerospace industries in recent years, the search for heat-resistant energetic materials with remarkable thermostability and high-energy level has attracted great attention. In this work, two advanced pyrazole-1,2,4-triazole-based heat-resistant explosives 5-(3,4-dinitro-1H-pyrazol-5-yl)-3-nitro-1H-1,2,4-triazole (3) and 1,2-bis(3-(3,4-dinitro-1H-pyrazol-5-yl)-1H-1,2,4-triazol-5-yl)diazene (5) were obtained using straightforward two-step synthetic routes. With a high crystal density of 1.873 g cm−3, compound 3 features with an excellent thermal decomposition temperature of 336 °C, which ranges the highest among fully C-nitrated bicyclic azoles. In comparison to 3, tetracyclic compound 5 exhibits enhanced thermostability (Td = 354 °C), which is superior to that of HNS (Td = 318 °C), and approaches that of TATB (Td = 350 °C). Furthermore, the energetic properties (e.g., detonation velocity: 8568 and 8404 m s−1, respectively) of 3 and 5 remarkably surpass those of HNS (7612 m s−1) and TATB (8179 m s−1), thereby highlighting 3 and 5 as promising candidates for advanced heat-resistant explosives. Our described molecular design, incorporating asymmetric structural motifs with azo-bis(1,2,4-triazole) bridge, will provide a synthetically simple approach for improving thermostability of energetic materials.