Synthesis and Properties of 3,6-Dinitropyrazolo[4,3-c]-pyrazole (DNPP) Derivatives

A series of novel fused-ring pyrazolo[4,3-c]pyrazole derivatives featuring N-dinitromethyl and N-fluorodinitromethyl energetic groups (compounds 3–7) were synthesized using a nine-step reaction. All these compounds were characterized using multinuclear nuclear magnetic resonance (NMR) spectroscopy, infra-red (IR) spectroscopy, and elemental analysis. X-ray diffraction analysis was performed, and the single-crystal structures of compounds 3, 4, 6, and 7 were obtained. For these newly prepared energetic materials, the thermal stability was determined using differential scanning calorimetry (DSC), while the sensitivities were evaluated using BAM drop hammer and friction test. The calculated heat of formation values and the measured densities were used to determine the detonation parameters, including detonation velocity and pressure, using the EXPLO5 program. Of all the prepared compounds, dipotassium 1,4-bis(dinitromethyl)-3,6-dinitro-1,4-dihydropyrazolo[4,3-c]pyrazole (3) was crystallized as a three-dimensional energetic metal-organic framework (MOF) and showed outstanding detonation performances, which even outperformed the traditional primary explosive lead azide. Compound 7 exhibited a high crystal density of 1.939 g cm⁻³, the high decomposition temperature of 213 °C and desirable impact and friction sensitivities (IS: 12 J; FS: 240 N). These combined properties and performances make these novel fused-ring energetic compounds suitable candidates for high-performance energetic materials.