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

Abstract

• Energetic molecule 3 features with a nearly coplanar asymmetric backbone. • The thermal stability of 3 ranks the highest among fully C -nitrated bicyclic azoles. • Compound 5 exhibits an enhanced decomposition temperature of 354 °C. • A synthetically simple approach for improving molecular thermostability. 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-1 H -pyrazol-5-yl)-3-nitro-1 H -1,2,4-triazole ( 3 ) and 1,2-bis(3-(3,4-dinitro-1 H -pyrazol-5-yl)-1 H -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 ( T d = 354 °C), which is superior to that of HNS ( T d = 318 °C), and approaches that of TATB ( T d = 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.