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.