High-Energy and Insensitive Tetrazole-Substituted 2,5-Dinitroiminooctahydroimidazo[4,5-d]imidazole: Synthesis, Characterization, and Energetic Properties

Herein, we present the synthesis and characterization of three novel energetic compounds based on 2,5-dinitroiminooctahydroimidazo[4,5-d]imidazole (DNII). The tetrazole groups were linked to DNII through an ethylene bridge (3), a methylene bridge (5), or direct connection (6). These compounds were fully characterized and their detonation properties were well determined by quantum chemical calculations. Among them, compound 5 exhibited two crystal forms (U-5 and T-5) in methanol and water. Compared to U-5, T-5 increased in density, formation enthalpy, detonation velocity, and pressure by 0.04 g/cm3 (2.3%), 0.22 kJ/g (8.1%), 0.34 km/s (4.2%), and 2.6 GPa (10.8%), respectively, owing to the tighter packing model. More importantly, with the gradual shortening of the linkages between imidazole and tetrazole, the performance of these compounds was gradually improved. Moreover, compound 6 showed the best detonation properties (D = 9.08 km/s, P = 33.1 GPa), which was better than TNT and close to HMX, while its sensitivity toward external forces (impact sensitivity (IS) = 40 J, friction sensitivity (FS) = 360 N) was much lower, making it safer. This work aims to prepare high-energy, low-sensitivity materials and hope to be helpful for the development of future energetic materials.