Comparative Studies of Synthesis, Performance, and Applications of Recently Developed CL-20 Based Co-crystals

Owing to promising characteristics including a high heat of formation (100 kcal·mol^-1), high density (2.04 g·cm^-3), and powerful explosive nature (14-20% more potent than 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)), the hollow cage-type molecular structure of polycyclic nitramine 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW/CL-20) has recently attained significant attention from scientists. Its high sensitivity toward mechanical stimuli raises safety concerns. The safety-power contradiction of high-energy explosives can be alleviated to a certain extent via a co-crystallization method. It is possible to modify the properties of energetic materials such as melting and decomposition point, density, detonation properties (detonation velocity and detonation pressure), and mechanical sensitivities (friction and impact) by forming a new chemical composition from the new/existing molecules through noncovalent interactions (π-π stacking, hydrogen bonds, and van der Waals forces). Energetic co-crystals have been developed by various approaches such as solvent evaporation, solvent/nonsolvent, grinding, slurry, resonant acoustic mixing, etc. This Review highlights an interesting overview of HNIW/CL-20 based energetic co-crystals, including their synthetic methods, intermolecular interactions, and physicochemical and energetic properties. Moreover, their applications, existing problems, and challenges for future work on CL-20-based co-crystals are also discussed.