Molecular-Shape-Dominated Crystal Packing Features of Energetic Materials

Abstract

Molecular shape is observed to greatly determine the properties of energetic materials (EMs); that is, the spherical molecules generally have high energy while the planar molecules have low sensitivity in common. Nevertheless, how the molecular shapes along with their packing modes affect the crystal packing features, such as crystal density and packing coefficient (PC), that are crucial factors describing the energy and sensitivity properties of EMs, is still unclear. Herein, this issue was addressed via a statistical analysis of more than 103 available energetic crystals. Despite crystal density having an overall increasing trend with PC, high crystal density and high PC are dominated by spherical and planar molecules, respectively. Intra- and intermolecular hydrogen bonds are important factors that affect molecular shapes and packing features of EMs, respectively. Hopefully, the results reported here can deepen the understanding of the structure–property relationship to rationally design novel EMs with outstanding properties. Moreover, the present study provides a route to quantitatively identify the molecular shapes and packing modes based on simple structural parameters, which can be further applied to the detailed identification and analysis of energetic crystals with specific packing modes.