Crystal Engineering for Creating Low Sensitivity and Highly Energetic Materials

Energy and safety are the two most important concerns of energetic materials (EMs), while they usually contradict each other: the high energy typically goes together with low safety. Low sensitivity and highly energetic materials (LSHEMs) balance well the energy and safety and thus are highly desired for extensive applications. Nevertheless, on the whole, the energy safety contradiction, the energy and component limits, and insufficient knowledge about the relationships among components, structures, and properties and performances of EMs have made the development of LSHEMs, or even the entire group of EMs, evolve slowly. This Perspective focuses upon the current progress in the clarifications of the energy safety contradiction and the crystal packing impact sensitivity relationship of EMs. Also, we propose strategies for creating new LSHEMs or desensitized EMs through crystal engineering, covering traditional EMs composed of neutral single-component molecules, energetic cocrystals, and energetic ionic salts. Two levels of intrinsic structures, molecule and crystal, are accounted for in constructing LSHEMs: at the molecular level, it is proposed to store much chemical energy in bonds while avoiding any bond formation in an energetic molecule that is too weak to intrinsically balance the energy and safety; at the level of crystal, it is suggested that intermolecular interactions be enhanced to increase packing compactness and energy density and to strengthen the anisotropy of the intermolecular interactions to facilitate ready shear slide and low mechanical sensitivity; and overall, a big pi-bonded energetic molecule with an oxygen balance close to zero and a hydrogen bond-aided face-to-face pi-pi molecular stacking is preferred as a LSHEM. Hopefully, this Perspective will set a root for establishing a systematic theory for creating LSHEMs.