Isomeric engineering of pyrazine- and pyrazine-1,4-dioxide-bridged nitrogen-rich heterocycles for balanced energetics.

Isomerism has emerged as a powerful molecular design strategy for controlling the physicochemical properties of functional molecules; however, its potential in energetic materials remains largely underexplored beyond a limited number of heterocyclic systems. Now we have established pyrazine- and pyrazine-1,4-dioxide-bridged isomeric engineering as a general strategy for simultaneously tuning energetic performance, thermal stability, and mechanical safety. A series of pyrazine-bridged 1,3,4-oxadiazole and 1,2,4-oxadiazole regioisomers together with pyrazine- and pyrazine-1,4-dioxide-bridged tetrazole and tetrazol-1-ol derivatives, including their hydroxylammonium salts, were synthesized and systematically investigated. Comparative analysis of these closely related isomers reveals that both heterocyclic connectivity and bridge identity profoundly influence crystal packing, density (1.73-1.86 g cm-3), decomposition temperature (176-265 °C), positive heats of formation (371 to 690 kJ mol-1), and calculated detonation velocities (7859-8538 m s-1), while maintaining low mechanical sensitivities (IS ≥ 15 J; FS ≥ 360 N). These findings establish pyrazine- and pyrazine-1,4-dioxide-bridged isomeric engineering as a versatile molecular design strategy beyond conventional substituent modification, providing new structure-property relationships for developing next-generation energetic materials with an improved balance of performance, thermal stability, and safety.