Crystal Packing of Low-Sensitivity and High-Energy Explosives

Abstract

Low-sensitivity and high-energy explosives (LSHEs) are highly desired for their comprehensive superiority of safety and energy. Crystal packing is crucial to both the safety and energy, and therefore becomes of interest in energetic crystal engineering. This work carries out systemic analyses on the crystal packing of 11 existing LSHEs with both energy and safety close or superior to TNT. As a result, we find that the LSHE crystals wholly feature π−π stacking with the aid of intermolecular hydrogen bonding. Each LSHE molecule is πbonded with a big conjugated structure composed of all nonhydrogen atoms in the entire molecule. Intramolecular hydrogen bonding exists in most LSHE molecules with strongly active hydrogen bond (HB) donors of amino and hydroxyl groups, and various strength. These big π-conjugated structures and intramolecular HBs lead to planar molecules with high stability, settling a base of π−π stacking in crystals. With the help of intermolecular HBs, the π−π stacking holding the LSHE crystals appears in four modes. Among them, the face-to-face stacking (always offset) gives rationally the smallest steric hindrance when interlayer slide occurs in crystal, which is the reason for very low impact sensitivity. This work suggests that the planar conjugated molecular structure and intermolecular hydrogen bonding supporting the π−π stacking are necessary to the crystal engineering of LSHEs.

1,2,4‐Oxadiazole‐Bridged Polynitropyrazole Energetic Materials with Enhanced Thermal Stability and Low Sensitivity

“…Most red dots located on the edges primarily denote the intermolecular hydrogen bonds interactions such as O−H⋅⋅⋅N and N−H⋅⋅⋅O, whereas those on the plate faces usually denote intermolecular π‐π interactions including C−N and C−O interactions . Recent research has demonstrated that plate‐shaped surface representing planar conjugated molecular structures contributes efficiently to π‐π stacking and lead to better stability . Compounds 3 a and 3 b are more platelike compared with 5 a and 5 b , which is in agreement with experimental thermal stability and sensitivity (Figure a and Figure a).…”

“…By definition, the red and blue on the Hirshfeld surfaces denotes the high and low close contact populations, respectively. Most red dots located on the edges primarily denote the intermolecular hydrogen bonds interactions such as O−H⋅⋅⋅N and N−H⋅⋅⋅O, whereas those on the plate faces usually denote intermolecular π‐π interactions including C−N and C−O interactions . Recent research has demonstrated that plate‐shaped surface representing planar conjugated molecular structures contributes efficiently to π‐π stacking and lead to better stability .…”

A high density pyrazolo-triazine explosive (PTX)

“…1,[6][7][8] The crystal lattice packing resulting from these features allows slipping between graphite-like layers in the explosive crystals, decreasing the likelihood of generating hotspots that inadvertently initiate the material to reactivity and ultimately detonation. 1,[6][7][8] The crystal lattice packing resulting from these features allows slipping between graphite-like layers in the explosive crystals, decreasing the likelihood of generating hotspots that inadvertently initiate the material to reactivity and ultimately detonation.…”

“…1c). [6][7][8][9] The explosive performance of PTX was calculated using the Cheetah thermochemical code. 1c as dashed lines between amino and nitro groups (H2-O6, 2.29Å).…”

Syntheses and Promising Properties of Dense Energetic 5,5′‐Dinitramino‐3,3′‐azo‐1,2,4‐oxadiazole and Its Salts

“…[1] Such a structure could lead to high density, good detonation performance and low sensitivity. [2] Furthermore, a single nitrogen-rich heterocyclic ring (such as tetrazole [3] , triazole [4] , pyrazole [5] and oxadiazole [6] ) with diverse energetic functional groups also is aromatic and has attracted considerable interest.…”