N–CH ₂ –C-Bridged Dinitropyrazole and 1,2,4(5)-Oxadiazole: Design Strategy, Syntheses, and Properties of a Series of New Melt-Cast Explosives

Melt-cast explosives, as the predominant category of energetic materials used in military composite explosives, play an essential role in balancing high detonation energy with operational safety. Oxadiazole links and polynitropyrazole rings give rise to compounds with ideal energetic properties in carrier explosives. All of the synthesized compounds were fully characterized using nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and elemental analysis. The target compounds 5, 8, and 9 were unambiguously characterized by single-crystal X-ray diffraction. The melting points of 5 and 8 are 91.4 and 108.4 °C, respectively. These compounds displayed remarkable thermal stability (Td > 220 °C) while maintaining low sensitivity to both impact (IS > 40 J) and friction (FS > 360 N), suggesting favorable safety characteristics. Using the EXPLO5 version 6.05.04 program, we calculated their detonation performances. Among them, compound 8 displays the most promising overall energetic properties (detonation velocity (D) = 7953 m·s–1; detonation pressure (P) = 26.7 GPa). Comprehensive evaluation reveals that their properties significantly exceed those of the established melt-cast explosives. Our findings suggest that the N–CH2–C bridging strategy could be a promising platform for developing new melt-cast explosives.