Hydrogen Bonding in CHON-Containing Energetic Crystals: A Review

Hydrogen bonding (HB) universally exists in CHON-containing energetic materials (EMs) and significantly influences their structures, properties, and performances. As time proceeds, some new types of EMs such as energetic cocrystals (ECCs) and energetic ionic salts (EISs) are thriving currently and richening insight into the HB of EMs, and these are reviewed in this article as well. The intramolecular HB mostly exists in stable molecules while seldom in less stable molecules; weak and abundant HBs dominate intermolecular interactions and consolidate crystal packing. For ECCs with neutral heterogeneous molecules, intermolecular HBs serve as one of the strategies for crystal design. In comparison, the HBs in EISs are greatly strengthened as their polarity significantly increases with ionization. A strong intramolecular HB usually enhances molecular stability with large pi-bonds and packing coefficients and facilitates reversible H transfer, which is advantageous for low mechanical sensitivity. The intermolecular HB-aided pi-pi stacking that favors low mechanical sensitivity is observed in all three kinds of EMs, including traditional EMs with neutral homogeneous molecules, ECCs with neutral heterogeneous molecules, and EISs. However, a strong intermolecular HB in an EM causes a ready intermolecular H transfer, thereby worsening thermal stability. Thus, the influence of HBs on the stability of EMs can go both ways, and there should be a balance when new HB-containing EMs are designed.