Isomerism as a Design Tool: Tuning the Energy–Safety Balance of a Fused Pyrazolo-Triazine N-Oxide Energetic Material

Addressing the inherent trade-off between energy content and safety remains a long-standing priority in the field of energetic materials. In this work, we employed a straightforward isomer design strategy, synthesizing a structural isomer of 4-amino-7-methyl-5-nitro-7H-pyrazolo[3,4-d][1,2,3]triazine-2-oxide (MPTO), namely 4-methylamino-5-nitro-7H-pyrazolo[3,4-d][1,2,3]triazine-2-oxide (1). Despite involving only a subtle difference in the connectivity of substituents, compound 1 exhibits a dramatically distinct crystal packing mode compared to MPTO. This structural variation directly translates into a remarkable performance enhancement: compound 1 not only delivers superior detonation velocity (8193 m·s−1) and detonation pressure (25.6 GPa) relative to the parent compound, but also shows substantially reduced mechanical sensitivities (impact sensitivity > 20 J, friction sensitivity > 360 N), while maintaining favorable thermal stability (296 °C). This study not only provides a promising candidate energetic molecule with well-balanced overall performance, but also highlights, from a crystal engineering perspective, the significant potential of isomer design in fine-tuning the properties of fused-ring energetic materials.