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In light of the low yields and complex reaction routes of some well-known 5,5-fused and 5,6-fused bicyclic compounds, a series of 5,7-fused bicyclic imidazole-diazepine compounds were developed with high yields by only two efficient steps. Significantly, the seven-membered heterocyclic ring has a stable energetic skeleton with multiple modifiable sites. However, the 5,7-fused bicyclic energetic compounds were rarely reported in the area of energetic materials. Three neutral compounds 1, 2 and 4 were synthesized in this work. To improve the detonation performances of the 5,7-fused neutral compounds, corresponding perchlorate 1a and 2a were further developed. The physicochemical and energetic performances of all newly developed compounds were experimentally determined. All newly prepared energetic compounds exhibit high decomposition temperatures (Td: 243.8–336 °C) and low mechanical sensitivities (IS: >15 J, FS: >280 N). Among them, the velocities performances of 1a (Dv = 7651 m/s) and 4 (Dv = 7600 m/s) are comparable to that of typical heat-resistant energetic material HNS (Dv = 7612 m/s). Meanwhile, the high decomposition temperature and low mechanical sensitivities (Td = 336 °C; IS = 32 J; FS > 353 N) of 4 are superior to that of HNS (Td = 318 °C; IS = 5 J; FS = 250 N). Hence, the 5,7-fused bicyclic compounds with high thermostability, low sensitivities and adjustable detonation performance have a clear tendency to open up a new space for the development of heat-resistant energetic materials.

Abstracts: In this study, a series of energetic compounds based on C–C linked 1,2,3-triazole and 1,2,4-triazole were synthesized and characterized, i.e., 5-(5-nitro-2H-1,2,3-triazole-4-yl)-4H-1,2,4-triazole-3,4-diamine (compound 1), N-(3-amino-5-(5-nitro-2H-1,2,3-triazole-4-yl)-4H-1,2,4-triazole-4-yl) nitramide (compound 4), and their energetic salts (compounds 2, 3, 5, and 6). The structures of compounds 1, 2, and 4 were determined by X-ray diffraction. All the new compounds feature acceptable thermal stability (Tdec ​= ​185–266 ​°C), with thermal decomposition temperature higher than that of RDX (Tdec ​= ​204 ​°C) except for compound 6 (Tdec ​= ​185 ​°C). Moreover, the detonation velocities of compounds 5 and 6 are 9200 ​m·s−1 and 9024 ​m·s−1, respectively, which are higher than that of RDX (D ​= ​8795 ​m·s−1). Furthermore, the new compounds show low mechanical sensitivity (IS ​= ​20 ​J, FS ​= ​240 ​N) compared to RDX (IS ​= ​7.4 ​J, FS ​= ​120 ​N). These results will help to accelerate the development of new high-energy density materials.

In this study, a new series of 3-amino-4-(5-amino-1,3,4-oxadiazole-yl) furoxan derivatives including neutral compounds and energetic salts were synthesized. Their physicochemical properties such as sensitivity, thermal behavior, and energetic properties were investigated during the study. Additionally, to explain their structure-property relationship, quantum chemical calculations were conducted, including Hirshfeld surface analysis, noncovalent interaction analysis, and electrostatic potential surface analysis. The crystal structures of compounds 2, 3a, and 3b were confirmed by using single-crystal X-ray diffraction. All of these new compounds showed satisfactory detonation performance, with detonation velocities ranging from 8430 ​m ​s−1 to 9258 ​m ​s−1 and detonation pressures of 30.1–37.5 ​GPa. These results were comparable to those of the commonly used secondary explosive RDX (8795 ​m ​s−1 and 34.9 ​GPa, respectively), making these new compounds potential secondary explosives.