First Alliance of Pyrazole and Furoxan Leading to High-Performance Energetic Materials

Nitrogen heterocyclic scaffolds retain
their leading position as
valuable building blocks in material science, particularly for the
design of small-molecule energetic materials. However, the search
for more balanced combinations of directly linked heterocyclic cores
is far from being exhausted and aims to reach ideally balanced high-energy
substances. Herein, we present the synthetic route to novel pyrazole-furoxan
framework enriched with nitro groups and demonstrate a promising set
of properties, viz., good thermal stability, acceptable mechanical
sensitivity, and high detonation performance. In-depth crystal analysis
showed that the isomers having lower-impact sensitivity values in
both types of regioisomeric pairs are those with the exocyclic furoxan
oxygen atom being closer to the pyrazole ring. Owing to the favorable
combination of high crystal densities (1.83–1.93 g cm–3), positive oxygen balance to CO (up to +13.9%), and high enthalpies
of formation (322–435 kJ mol–1), the synthesized
compounds show high calculated detonation velocities (8.4–9.1
km s–1) and excellent metal accelerating abilities.
The incorporation of the 3-nitrofuroxan moiety increases the thermal
stability (by ca. 20 °C) and decreases the mechanical sensitivity
of target hybrid materials in both types of regioisomeric pairs. Simultaneously,
the detonation performance of 3-nitrofuroxans is almost identical
to that of 4-nitrofuroxans, highlighting the potential of the regioisomeric
tunability in the future design of energetic materials.