Molecular and Crystal Features of Thermostable Energetic Materials: Guidelines for Architecture of “Bridged” Compounds

Abstract

Extensive density functional theory (DFT) calculation and data analysis on molecular and crystal level features of 60 reported energetic materials (EMs) allowed us to define key descriptors that are characteristics of these compounds' thermostability. We see these descriptors as reminiscent of "Lipinski's rule of 5", which revolutionized the design of new orally active pharmaceutical molecules. The proposed descriptors for thermostable EMs are of a type of molecular design, location and type of the weakest bond in the energetic molecule, as well as specific ranges of oxygen balance, crystal packing coefficient, Hirshfeld surface hydrogen bonding, and crystal lattice energy. On this basis, we designed three new thermostable EMs containing bridged, 3,5-dinitropyrazole moieties, HL3, HL7, and HL9, which were synthesized, characterized, and evaluated in small-scale field detonation experiments. The best overall performing compound HL7 exhibited an onset decomposition temperature of 341 °C and has a density of 1.865 g cm −3 , and the calculated velocity of detonation and maximum detonation pressure were 8517 m s −1 and 30.6 GPa, respectively. Considering HL7's impressive safety parameters [impact sensitivity (IS) = 22 J; friction sensitivity (FS) = 352; and electrostatic discharge sensitivity (ESD) = 1.05 J] and the results of small-scale field detonation experiments, the proposed guidelines should further promote the rational design of novel thermostable EMs, suitable for deep well drilling, space exploration, and other high-value defense and civil applications.

Novel All‐Nitrogen Molecular Crystals of Aromatic N10

“…Covalent bond energies were calculated by the integrated value of crystal orbital Hamilton population (COHP) at the band energy using the HASEM package. [ 40,41 ]…”

Heat‐Resistant Energetic Materials Deriving from Benzopyridotetraazapentalene: Halogen Bonding Effects on the Outcome of Crystal Structure, Thermal Stability and Sensitivity

“…Here, Kissinger and Ozawa‐Doyle's methods are conducted based on the first exothermic peak temperatures ( T p ) measured at different heating rates of 5, 10, 15, 20 °C min −1 . As shown in Figure 4(d)‐4(f), under the heating rate of 5 °C min −1 , the decomposition of compound 6‐a commenced at 334.13 °C, and reached the peak at 347.91 °C incredibly, which is superior to most of heat‐resistant explosives such as TNT ( T d : 295 °C) [9], HNS ( T d : 318 °C) [6], bis(2,4,6‐trinitrophenyl) ether (BTNPE) ( T d : 256 °C) [1] and bis(2,4,6‐trinitrophenyl) (BTNPTE) ( T d : 310 °C) [1], but slightly lower than that of BPTAP ( T d : 366 °C). Compound 6‐b started to decompose at 324.5 °C, and arrived at 330.53 °C as its peak, which also surpasses those of TNT and HNS.…”

“…Additionally, the correlation between N‐heterocyclic skeleton and thermal stability as well as energy density has not been thoroughly referred [3–5]. Over the past few years, a series of thermally‐stable heterocyclic organic explosives emerged in large numbers, such as 1,3,4‐oxadiazole bridged trinitrophenyl derivatives [6], fused triazolo‐tetrazine [7], furazano[3,4‐b]pyrazine [8], bridging nitropyrazole derivatives with 1,3,4‐oxadiazole [9], 1,2,4‐oxadiazole [10], 1,2,5‐oxadiazole [11], 5,6‐fused bicycles [12], combination of 1,2,4‐oxadiazole derivatives with 1,2,5‐oxadiazole [13], polyaminotriazole derivatives and energetic salts [14–16], fused heterocyclic derivatives [17], etc. Heat‐resistant energetic materials for practical application that express significant features and properties including but not limited to: (1) their thermal stability should not be lower than 300 °C; (2) low cost and facile synthetic methods; (3) a lack of hypertoxic procedure or chemicals being utilized in its synthesis; (4) adequate solubility in most of solvents or at least high‐polar solvents for crystal modification and nano‐energetic materials for MEMS or detonator devices.…”

Recent Advances in Synthesis and Properties of Nitrated-Pyrazoles Based Energetic Compounds

“…The properties of these compounds are showed in Table 14. Moreover, Li et al [124] synthesized the compound 106 with the procedure shown in Figure 34. This compound exhibited an excellent decomposition temperature (341 • C), high calculated detonation velocity of 8.52 km•s −1 , and detonation pressure of 30.6 GPa.…”

“…Afterwards, their group used a similar route to prepare bis(3,4-dinitro-1 H -pyrazol-1-yl)methane ( 89 ) and bis(3,5-dinitro-1 H -pyrazol-1-yl)methane ( 90 ) with high decomposition temperature and low sensitivities having capability as future energetic materials ( Table 13 ) [ 94 ]. Gozin et al [ 124 ] explored the possible influence factor of the thermostable property of explosives, and under the guidelines they proposed, they synthesized the compounds 91 and 92 with excellent thermal stability and moderate sensitivities shown in Figure 31 and Table 13 .…”