Cooperativity of hydrogen bonds in the nitroamide crystal: a prototypical case study of low-sensitivity and high-energy explosives

Abstract

Currently, crystal engineering has attracted much attention as a promising strategy to balance the energy and sensitivity of explosives, such as energetic–energetic co-crystals. A deep understanding of the intermolecular interactions in explosive crystals from a microscopic point of view is meaningful for the development of low-sensitivity and high-energy (LSHE) explosives. Herein, the cooperativity of hydrogen bonds (HBs) in the nitramide (NA) crystal was quantitatively investigated with the aid of computational methods as a prototypical study of LSHE crystals. Two types of HB interactions were identified via both geometry and electron density analysis, and the electrostatic interactions dominantly contribute to the HB formation. The cooperativities of the single HB type and induced by other intermolecular interactions were quantified in various structural models, including linear clusters and layer fragments. The deconstruction of the NA crystal shows that the interaction energy for crystal stabilization was reduced by about 21% in comparison with that of the dimer as a result of an overall anti-cooperativity of the HB interactions, which is energetically unfavored for the formation of explosive crystals due to the weakening of the intermolecular interactions. This prototypical study is aimed to establish a theoretical strategy for further exploration of intermolecular interaction cooperativities in practical LSHE explosives, and is envisioned to open a new perspective to improve the knowledge of the crystal structure-sensitivity relationship.