Review of the Intermolecular Interactions in Energetic Molecular Cocrystals

Energetic cocrystallization is thriving now and presents a promising perspective to create new energetic materials (EMs). In comparison with the single-component EMs, the creation of energetic cocrystals exhibits a greater significance of crystal engineering, whose central scientific issue is intermolecular interaction. This article reviews the current progress in studying the intermolecular interactions of energetic molecular cocrystals (EMCCs), as well as the molecular stacking and the thermodynamics for EMCC formation. The intermolecular interactions include hydrogen bonding (HB), π interactions, and halogen bonding. The strength of these interactions is found to be generally weak, similar to that of single-component energetic molecular crystals. By means of cocrystallization, the molecular stacking can be improved to be prone to layered stacking, facilitating low impact sensitivity. This could be feasible for alleviating the energy–safety contradiction of EMs. The driving force of the EMCC formation is thought to be the increase in entropy, because the EMCCs are in nature the products of an increase in randomness, with a small variation of intermolecular interactions in comparison with original pure components. Finally, the dependence of the properties of EMCCs on the compositions and molecular structures of original pure components is proposed to attract increasing attention, as it is a base for creating new EMs with tunable compositions, structures, and properties by way of crystal engineering.