Enforced Planar FOX-7-like Molecules: A Strategy for Thermally Stable and Insensitive π‑Conjugated Energetic Materials

Exploring
new energetic derivatives of 1,1-diamino-2,2-dinitroethylene
(FOX-7) is still a key aspect in the field of energetic materials.
However, so far most of the attention has been focused on modification
of FOX-7 via different reaction strategies. Now we report the design
of three new FOX-7-like compounds (3–5) where one nitro group in FOX-7 is replaced by a nitrogen-rich heterocyclic
ring. Each of them is characterized by single-crystal X-ray crystallography.
Electronic structures are studied through computational methods in
comparison with FOX-7. In addition, the chemical reactivity of 3 was also investigated. Its hydroxylammonium (7), hydrazinium (8), and ammonium (9) salts
were prepared, and the nitrate product (10) was also
isolated. Compound 10 has a C–N bond length of
1.577 Å that is one of the longest values found for the C–NO2 bond. It was found that the incorporation of a tetrazole
or triazole ring into the backbone of a conjugated nitroenamine does
lead to a planar structure, which not only enhances the thermal stability
but also improves the sensitivity of the product.