Noncovalent Modification of 4,4′-Azo-1,2,4-triazole Backbone via Cocrystallization with Polynitroazoles

The investigation of high-nitrogen compounds has been significant for the evolution of energetic materials. Azo-bis-1,2,4-triazole (aTRz) can be an excellent energetic backbone, owing to its characteristics: high heat of formation, high nitrogen content, and plane structure. Nevertheless, aTRz-based energetic compounds have been rarely synthesized using the covalent modification method, owning to the decomposition of aTRz under harsh reaction conditions. Cocrystallization has been widely used as a mild and efficient method for modulating the properties of energetic compounds. In this study, electrostatic potential (ESP) maps were used for theoretical guidance, and four aTRz-based energetic cocrystals have been obtained via cocrystallization. The single-crystal structures of these cocrystals indicated that the N···H–N hydrogen bonds between the side nitrogen atoms of aTRz and the amino groups of the nitro azole compounds were the driving force for the assembly of multimers with aTRz and polynitroazole compounds. Consequently, the formation of cocrystals via the self-assembly of these multimers was driven by other weak hydrogen bonds and van der Waals forces. The detonation performance of aTRz-based cocrystals was increased by appropriately selecting the coformers. Particularly, when 4-amino-3,5-dinitro-pyrazole (ADNP) was used as coformer, resultant cocrystal 3 was a potential high-energy density material that exhibited high density, high detonation velocity (8329 m s–1) and detonation pressure (28.6 GPa). Thus, in this study, cocrystallization has been demonstrated to be an effective method for the noncovalent modification of aTRz-based energetic materials.