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Pushing the Limits of Oxygen Balance in 1,3,4-oxadiazoles.


Gem-trinitromethyl groups were introduced into a 1,3,4-oxadiazole ring to give the first example of a bifunctionalized single five-membered ring with six nitro groups. 2,5-Bis(trinitromethyl)-1,3,4-oxadiazole (12) has a high calculated crystal density of 2.007 g cm-3 at 150 K and a very high positive oxygen balance (39.12%) which make it a strong candidate as a high energy dense oxidizer. The dihy-droxylammonium and dihydrazinium salts of bis(trinitromethyl)-1,3,4-oxadiazole (5 and 6) exhibit excel-lent detonation properties (5, vD = 9266 m s-1, P = 38.9 GPa; 6, vD = 8900 m s-1, P = 36.3 GPa) and ac-ceptable impact sensitivities (5 20 J, 6 19 J), which are superior to those of RDX (7.4 J) and HMX (7.4 J). Such attractive features support the application potential of the gem-polynitromethyl group in the design of advanced energetic materials. Surprisingly, 2,5-bis(trinitromethyl)-1,3,4-oxadiazole (12) is more thermally stable and less sensitive than its bis(dinitromethyl) analogue, 8. The compounds were fully characterized by using IR and multinuclear NMR spectroscopy, elemental analysis, and differential scan-ning calorimetry (DSC). The structures of the energetic salts (3•H2O, 5 and 13) and neutral compounds (8 and 12) were confirmed by single-crystal X-ray diffraction.