Design and Synthesis of a Series of CL-20 Cocrystals: Six-Membered Symmetrical N-Heterocyclic Compounds as Effective Coformers

Cocrystallization of energetic compounds has recently been considered as an effective method to adjust the properties through the selection of coformers, particularly to improve the detonation properties and reduce the mechanical sensitivity of CL-20. In this research, a reliable and promising design strategy to synthesize CL-20-based cocrystals was presented, where (i) the coformer should show local structural similarity to CL-20, i.e., five- or six-membered symmetric heterocycles, and (ii) the molecular structure of the coformer should contain electron-donating groups. In order to verify the adaptability of this design strategy, pyrazine, 2,6-dimethoxy-3,5-dinitropyrazine, and 2,5-dimethylpyrazine were selected as the templates of six-membered symmetrical N-heterocyclic compounds for cocrystallization with CL-20. Fortunately, on the basis of the results of the experiments and the crystal analysis, three compounds were successfully cocrystallized with CL-20. Moreover, two cocrystals with the same components and different stoichiometric ratios were formed by pyrazine and CL-20. In addition, the properties of the designed cocrystals, including thermal stability, detonation properties, and sensitivities, were also studied in detail. Cocrystallization of CL-20 with the aforementioned coformers demonstrates the appropriateness of six-membered symmetrical N-heterocyclic compounds as coformers. In light of this finding, the safety and detonation properties of CL-20 can be modulated by employing suitable six-membered N-heterocyclic compounds as coformers.