Direct insight into the formation driving force, sensitivity and detonation performance of the observed CL-20-based energetic cocrystals

Abstract

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is the most powerful commercially available explosive. This paper discusses the molecular structures and intermolecular interactions of pure ε-CL-20 and three CL-20-based energetic–energetic cocrystals, CL-20/2,4-dinitro-2,4-diazapentane (DNDAP), CL-20/2,5-dinitrotoluene (DNT) and CL-20/1-methyl-3,5-dinitro-1,2,4-triazole (MDNT). The underlying mechanisms of their dramatic and divergent sensitivity and detonation performance were revealed as well. We find that CL-20/DNDAP and CL-20/DNT cocrystals arrange in layered motifs, while CL-20/MDNT features irregular but compact packing. Overall, the non-covalent interactions govern the structures of the cocrystals. Regarding sensitivity, in the case of CL-20/DNDAP and CL-20/DNT, the high impact sensitivity of CL-20 is reduced, making the two cocrystals viable explosives. Conversely, CL-20/MDNT uniquely exhibits higher impact sensitivity compared with pure CL-20, which may be caused by weak intermolecular interactions and molecular transformation of CL-20 from stable ε-form to α-form. Furthermore, CL-20/MDNT possesses the greatest detonation performance due to its excellent density and high heat of formation, followed by CL-20/DNDAP and CL-20/DNT. These results confirm that a layered packing pattern and weak hydrogen bonding are among the key factors for insensitive cocrystal explosives. Meanwhile, cocrystals of CL-20 with multi-nitrogen energetic compounds have the potential to be promising high-performance energetic materials.