Energetic Cocrystallization as the Most Significant Crystal Engineering Way to Create New Energetic Materials

Crystal engineering is a highly efficient way to create new materials with the desired properties. Energetic cocrystallization has been thriving for ∼10 years since the appearance of a series of TNT-based energetic cocrystals (ECCs). ECCs serve as one important aspect of the crystal engineering of energetic materials (EMs). This article presents a brief overview of ECCs regarding the component, intermolecular interaction, packing structure, main properties, and preparation, as well as a theoretical treatment and some issues raised for future development. In most cases, the properties of an ECC are each moderated between those of the pure components, setting a basis for tuning properties by existing molecules, instead of synthesizing new molecules; meanwhile, there are also some exceptions, such as a higher density, higher detonation properties, or lower impact sensitivity in comparison with both of the pure components. These exceptions with mutated properties will expand EMs. Generally, the ECCs currently are staying at the primary stage, with much effort being required to solve some urgent issues, such as property evaluation, large-scale fabrication, and future applications. Still, energetic cocrystallization is a promising alternative to create new EMs with existing molecules; after all, it is a huge challenge to synthesize a satisfactory new energetic molecule.