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.