Crystal Packing of Impact-Sensitive High-Energy Explosives

Molecular and crystal designs are crucial to the engineering of high-energy explosives, which are a class of substantial materials usually with high costs and high risks. Understanding their structures, properties, and performances, and the relationships among them is the basis for the design. As a continuation of a systemic analysis of the crystal packing of low-sensitivity and high-energy explosives (LSHEs) ( Cryst. Growth Des. 2014, 14, 4703-4713), we present in this work another analysis of 10 existing impact-sensitive high-energy explosives (SHEs), which possess both velocities of detonation and impact sensitivity close to or higher than those of RDX. We find that SHE molecules are usually less stable than LSHE ones, due to the deficiencies of big p-conjugated molecular structures, and adequate and strong intramolecular hydrogen bonds (HBs) even though H atoms are contained. The intermolecular HBs cannot be formed sometimes in H-contained SHE crystals, and the noncovalent O center dot center dot center dot O interactions dominate the connection of SHE molecules to build a three-dimensional network and hold crystals, generally, with the strength above intermolecular HBs. The absence of single-atom-layered stacking in SHE crystals makes the intermolecular sliding difficult or even unallowed when against impact, which leads to inefficiency of energy buffering and ease of molecular decay, hot spot formation, and final combustion or detonation. In contrast to LSHEs, SHEs are disadvantageous on dual structural levels causing their high sensitivity: molecules with low stability and crystals without HB-aided single-atom-layered stacking. It re-verifies that the intermolecular HB-aided pp stacking is necessary for crystal engineering of LSHEs, which are highly desired currently.