Accelerating the discovery of insensitive high-energy-density materials by a materials genome approach

Symmetric Refunctionalization of Diaminodinitropyrazine with Hydrazine and Aminotetrazole: Strategy for Enhancing Detonation Performance and Safety in Energetic Materials

Two novel nitrogen-rich green energetic compounds were synthesized for the first time from readily available and cost-effective pyrazine starting materials. All newly synthesized molecules were comprehensively characterized, including infrared spectroscopy, nuclear magnetic resonance, elemental analysis, mass spectrometry, and thermogravimetric analysis-differential scanning calorimetry. All compounds have additionally been validated by single-crystal X-ray diffraction analysis. The physicochemical properties of compounds 2, 4, and 5 were thoroughly investigated. Notably, all compounds exhibit remarkable performance, such as a high density (>1.84 g cm-3), excellent detonation properties (VOD > 8582 m s-1, and DP > 31.3 GPa), outstanding thermostability (>205 °C), and high insensitivity (IS > 35 J, and FS = 360 N). These attributes are quite comparable to those of secondary benchmark explosives such as TATB, RDX, LLM-105, and FOX-7. This tuned performance evidences that the incorporation of hydrazine, nitro, and aminotetrazole into the pyrazine framework fosters robust nonbonded interactions, ultimately enhancing thermal stability and reducing sensitivity. The findings of this study not only signify that compounds 2 and 5 have excellent detonation properties and stability but also prove that the strategy of replacing amino groups with hydrazine and aminotetrazole is a practical means of developing new insensitive energetic materials.

Fused Triazole-Tetrazine Assembled with Different Functional Moieties: Construction of Multipurpose Energetic Materials

Azido, amino, and azo functionalities were introduced into tetrazine backbones to access multifunctional energetic materials. AzNTT demonstrates effective initiation capability (MPC = 50 mg), whereas NTTA balances well between the energy and stability. Azo-functionalized BNTTD has a high density of 1.908 g cm-3, with performance comparable to that of the benchmark material HMX. This work underscores the scope of energetic functionalization and the outstanding comprehensive performance of polycyclic tetrazines.

High precision deep-learning model combined with high-throughput screening to discover fused [5,5] biheterocyclic energetic materials with excellent comprehensive properties

Finding novel energetic materials with good comprehensive performance has always been challenging because of the low efficiency in conventional trial and error experimental procedure. In this paper, we established a deep learning model with high prediction accuracy using embedded features in Directed Message Passing Neural Networks. The model combined with high-throughput screening was shown to facilitate rapid discovery of fused [5,5] biheterocyclic energetic materials with high energy and excellent thermal stability. Density Functional Theory (DFT) calculations proved that the performances of the targeting molecules are consistent with the predicted results from the deep learning model. Furthermore, 6,7-trinitro-3H-pyrrolo[1,2-b][1,2,4]triazo-5-amine with both good detonation properties and thermal stability was screened out, whose crystal structure and intermolecular interactions were also analyzed.

Exploring the Explosive Potential: Synthesis and Characterization of Ring-Fused Oxadiazolo[3,4-b]pyrazine 1-Oxide Polymorphs with Balanced Energetic Properties

A novel fused-ring compound, 5-azido-6-oxo-6,7-dihydro-[1,2,5]oxadiazolo[3,4-b]pyrazine 1-oxide (3a), was synthesized for the first time with simple two-step process and characterized using various spectroscopic techniques such NMR, IR, EA and HRMS. Two polymorphs (α-3a and β-3a) identified by SCXRD differ in crystal packing and noncovalent interactions, demonstrating high density, substantial heat of formation, and superior detonation properties with reduced mechanical sensitivity compared to TNT, TATB, and close to RDX, suggesting their potential as environmentally friendly high energy density materials.

Zwitterionic Energetic Materials: Synthesis, Structural Diversity and Energetic Properties

Zwitterionic compounds are an emergent class of energetic materials and have gained synthetic interest of many in the recent years. Due to their better packing efficiencies and strong inter/intramolecular electrostatic interactions, they often ensue superior energetic properties than their salt analogues. A systematic review from the perspective of design, synthesis, and physicochemical properties evaluation of the zwitterionic energetic materials is presented. Depending on the parent ring(s) used for the synthesis and the type of moieties bearing positive and negative charges, different classes of energetic materials, such as primary explosives, secondary explosives, heat resistant explosives, oxidizers, etc., may result. The properties of some of the energetic zwitterionic compounds are also compared with analogous energetic salts. This review will encourage readers to explore the possibility of designing new zwitterionic energetic materials.

Two Energetic Framework Materials Based on DNM-TNBI as Host Molecule: Effectively Coordinated by Different Cations

With the demand of develop outstanding-performance energetic materials, 1-(dinitromethyl)-4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (DNM-TNBI) emerged as a great contender (D: 9102 m ⋅ s-1; P: 37.6 GPa). However, the relatively poor thermal stability (Td: 142 °C) limits its practical application. In this study, DNM-TNBI as a host molecule to synthesize two new energetic open-framework materials by effectively coordinated with different cations. Their supramolecular structures were investigated and indicated that [DNM-TNBI2 -][2NH4 +] and [DNM-TNBI2 -][2K+] can be classified as a new energetic hydrogen-bonded ammonium framework (EHAF) and an energetic metal organic framework (EMOF). Meanwhile, their thermal stabilities are higher than that of DNM-TNBI and have satisfactory detonation performance ([DNM-TNBI2 -][2NH4 +], D: 8050 m ⋅ s-1, P: 26.4 GPa; [DNM-TNBI2 -][2K+], D: 8301 m ⋅ s-1, P: 30.8 GPa).

Intelligent Biomaterialomics: Molecular Design, Manufacturing, and Biomedical Applications

Materialomics integrates experiment, theory, and computation in a high-throughput manner, and has changed the paradigm for the research and development of new functional materials. Recently, with the rapid development of high-throughput characterization and machine-learning technologies, the establishment of biomaterialomics that tackles complex physiological behaviors has become accessible. Breakthroughs in the clinical translation of nanoparticle-based therapeutics and vaccines have been observed. Herein, recent advances in biomaterials, including polymers, lipid-like materials, and peptides/proteins, discovered through high-throughput screening or machine learning-assisted methods, are summarized. The molecular design of structure-diversified libraries; high-throughput characterization, screening, and preparation; and, their applications in drug delivery and clinical translation are discussed in detail. Furthermore, the prospects and main challenges in future biomaterialomics and high-throughput screening development are highlighted.

Detonation Performance of Insensitive Nitrogen-Rich Nitroenamine Energetic Materials Predicted from First-Principles Reactive Molecular Dynamics Simulations

Because of the excellent combination of high detonation and low sensitivity properties of the 1,1-diamino-2,2-dinitroethylene (FOX-7) energetic material (EM), it is useful to explore new energetic derivatives that start with the FOX-7 structure. However, most such derivatives are highly sensitive, making them unsuitable for EM applications. An exception is the new nitroenamine EM, 1,1-diamino-2-tetrazole-2-nitroethene (FOX-7-T) (synthesized by replacing a nitro group with a tetrazole ring), which exhibits good stability. Unfortunately, FOX-7-T shows an unexpected much lower detonation performance than FOX-7, despite its higher nitrogen content. To achieve an atomistic understanding of the insensitivity and detonation performance of FOX-7 and FOX-7-T, we carried out reactive molecular dynamics (RxMD) using the ReaxFF reactive force field and combined quantum mechanics MD (QM-MD). We found that the functional group plays a significant role in the initial decomposition reaction. For FOX-7, the initial decomposition involves only simple hydrogen transfer reactions at high temperature, whereas for FOX-7-T, the initial reaction begins at much lower temperature with a tetrazole ring breaking to form N2, followed by many subsequent reactions. Our first-principles-based simulations predicted that FOX-7-T has 34% lower CJ pressure, 15% lower detonation velocity, and 45% lower CJ temperature than FOX-7. This is partly because a larger portion of the FOX-7-T mass gets trapped into condensed phase carbon clusters at the CJ point, suppressing generation of gaseous CO2 and N2 final products, leading to reduced energy delivery. Our findings suggest that the oxygen balance is an important factor to be considered in the design of the next generation of high-nitrogen-containing EMs.

Highly Dense N-N-Bridged Dinitramino Bistriazole-Based 3D Metal-Organic Frameworks with Balanced Outstanding Energetic Performance

Due to the inherent conflict between energy and safety, the construction of energetic materials or energetic metal-organic frameworks (E-MOFs) with balanced thermal stability, sensitivity, and high detonation performance is challenging for chemists worldwide. In this regard, in recent times self-assembly of energetic ligands (high nitrogen- and oxygen-containing small molecules) with alkali metals were probed as a promising strategy to build high-energy materials with excellent density, insensitivity, stability, and detonation performance. Herein, based on the nitrogen-rich N,N'-([4,4'-bi(1,2,4-triazole)]-3,3'-dial)dinitramide (H2BDNBT) energetic ligand, two new environmentally benign E-MOFs including potassium [K2BDNBT]n (K-MOF) and sodium [Na2BDNBT]n (Na-MOF) have been introduced and characterized by NMR, IR, TGA-DSC, ICP-MS, PXRD, elemental analyses, and SCXRD. Interestingly, Na-MOF and K-MOF demonstrate solvent-free 3D dense frameworks having crystal densities of 2.16 and 2.14 g cm-3, respectively. Both the E-MOFs show high detonation velocity (VOD) of 8557-9724 m/s, detonation pressure (DP) of 30.41-36.97 GPa, positive heat of formation of 122.52-242.25 kJ mol-1, and insensitivity to mechanical stimuli such as impact and friction (IS = 30-40 J, FS > 360 N). Among them, Na-MOF has a detonation velocity (9724 m/s) superior to that of conventional explosives. Additionally, both the E-MOFs are highly heat-resistant, having higher decomposition (319 °C for K-MOF and 293 °C for Na-MOF) than the traditional explosives RDX (210 °C), HMX (279 °C), and CL-20 (221 °C). This stability is ascribed to the extensive structure and strong covalent interactions between BDNBT2- and K(I)/Na(I) ions. To the best of our knowledge, for the first time, we report dinitramino-based E-MOFs as highly stable secondary explosives, and Na-MOF may serve as a promising next-generation high-energy-density material for the replacement of presently used secondary thermally stable energetic materials such as RDX, HNS, HMX, and CL-20.

Obtaining superior high-density fused-ring energetic materials via the introduction of carbonyl, o-NH2-NO2 and nitroamino groups

Two carbonyl and o-NH2-NO2-containing energetic materials and their analogues were effectively designed, synthesized and fully characterized with multinuclear NMR, IR and elemental analyses. Their structures were also further confirmed via X-ray diffraction. Among them, compound 7 exhibits good potential for application as a secondary explosive with extremely high density (2.04 g cm-3), good sensitivity (IS > 40 J, FS > 360 N), and excellent calculated detonation performance (Dv = 8943 m s-1, P = 35.0 GPa). Furthermore, a detailed comparative study based on X-ray diffraction, Hirshfeld surfaces and 2D fingerprint plots among compounds 4, 7 and 9 has demonstrated that the density and detonation performance could be effectively improved via introducing a carbonyl group into fused-ring compounds. More importantly, the sensitivity of the resulting energetic materials did not deteriorate. Obviously, this strategy via introducing carbonyl, o-NH2-NO2 and nitroamino groups into fused-ring energetic compounds will help in the design of next-generation high-energy and insensitive fused-ring energetic materials.

Exploring a Fused Triazole-Tetrazine Binary CN Material for a Promising Initiating Substance

The pursuit of binary carbon-nitrogen (CN) materials with high density and good thermal stability presents a significant challenge due to the inherent trade-off between high-energy storage and low bond dissociation energy. In this study, we designed and synthesized (S)-1,2-bis(3-azido-1H-1,2,4-triazol-1-yl)diazene (BAzTD) and 2,9-diazidobis([1,2,4]-triazolo)[1,5-d:5',1'-f][1,2,3,4]tetrazine (DAzTT) through a straightforward reaction. Remarkably, DAzTT demonstrated a high density of 1.816 g·cm-3 (at 298 K) and a considerable thermal decomposition temperature of 216.86 °C. These properties outperform those of previously reported binary heterocyclic CN compounds and polyazido heterocyclic compounds. The quantum-chemical methods further substantiated the integral role of aromaticity as the driving force behind this difference. Additionally, the initiation capability of DAzTT was evaluated by a notably low minimum primary charge (MPC = 40 mg), surpassing conventional organic primary explosives, such as commercial 2-diazo-4,6-dinitrophenol (DDNP, MPC = 70 mg). The exceptional priming ability highlights the potential as an environmentally friendly replacement for toxic lead azide. DAzTT sets a new standard for binary CN compounds and provides a valuable precursor for high-nitrogen carbon nitride materials.

Construction of High Energy Nanoscale Lead Azide Composite with Improved Flame Sensibility from Intercalated Hydroxide

It is of great significance to develop efficient methods for preparing high-content modified nanoscale lead azide (LA) composites used in microinitiating devices. In this work, a structurally controllable salicylate-intercalated lead hydroxide with a nanoscale mesoporous structure is designed. Using it as a precursor, carbon-based lead azide (LA/C) and salicylate-based lead azide (LA/SA) are fabricated by the gas-solid azidation of the framework (GAF) method within 3 h, greatly reducing the preparation time of nano-LA composites. The characterizations of the composites demonstrate that the Pb in the precursors is transformed into nanoscale LA attached to the salicylate radical or its carbonized skeleton. Due to the unique embedded nanostructures and excellent electrical and thermal conductivity of salicylate-derived carbon materials, LA/C exhibits excellent electrostatic safety (E50 = 0.25 J) and flame sensitivity (H50 = 28 cm). The adjustable organic-inorganic ratio of intercalated hydroxides allows the LA content in LA/C to reach as high as 92.5%, enabling 6.50 mg of LA/C to successfully detonate secondary explosive CL-20 in a microinitiating device, demonstrating an amazing detonation ability superior to other reported LA complexes. The research provides a new perspective for the development of nanoscale LA composites with high LA content and appropriate sensitivity.

Controlling the Energetic Properties of N-Methylene-C-Linked 4-Hydroxy-3,5-dinitropyrazole- and Tetrazole-Based Compounds via a Selective Mono- and Dicationic Salt Formation Strategy

In the quest to synthesize high-performing insensitive high-energy density materials (HEDMs), the main challenge is establishing an equilibrium between energy and stability. For this purpose, we explored 4-hydroxy-3,5-dinitropyrazole- and tetrazole-based energetic scaffolds connected via a N-methylene-C bridge. The hydroxy functionality between nitro groups on the pyrazole ring promotes physical stability via inter- and intramolecular hydrogen bonding and contributes to oxygen balance, supporting better energetic performance. Due to two acidic sites (OH and NH) with different reactivities, a series of monocationic and dicationic salts were synthesized, and their overall performance was compared. All compounds synthesized in this study have high physical stability with impact sensitivity >40 J and friction sensitivity >360 N. Monocationic salts were generally found to have better thermal stability with respect to their corresponding dicationic energetic salts, which showed better energetic performance. The salt formation strategy effectively improved the thermal stability of 2 (Td = 168 °C), where most energetic salts have decomposition temperatures higher than 220 °C. All of the compounds were characterized through IR, multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), and elemental analysis. The structure-property relationship was studied using Hirshfeld surface analysis, noncovalent interaction (NCI) analysis, and electrostatic potential studies.

Polynitro-functionalized 4-phenyl-1H-pyrazoles as heat-resistant explosives

A new class of heat-resistant explosives was synthesized by coupling N-methyl-3,5-dinitropyrazole with polynitrobenzene moieties through carbon-carbon bonds. Simple Pd(0)-based Suzuki cross-coupling reactions between N-methyl-4-bromo-3,5-dinitropyrazole and 4-chloro/3-hydroxy-phenylboronic acid followed by nitration, amination and oxidation lead to the formation of C-C connected penta-nitro energetic derivatives 6 and 10. Various other energetic derivatives, such as amino (5), azido (7), nitramino (8) and energetic salts (11-14), were also explored to fine-tune their properties. All the compounds were thoroughly characterized using IR, NMR [1H, 13C{1H}], differential scanning calorimetry (DSC), elemental analysis, and HRMS studies. Compounds 5, 10 and 13 were further characterized through 15N NMR, and the crystal structures of 6 and 14 were confirmed through single-crystal X-ray diffraction studies. The physicochemical and energetic properties of all the energetic compounds were explored. Most of the synthesized compounds demonstrated high thermal stability (decomposition temperature Tdec > 250 °C), among which compounds 5 and 6 showed excellent thermal stability, having decomposition temperatures above 300 °C. The excellent thermal stability, acceptable sensitivity and good energetic properties of compounds 5, 6, 10 and 13 make them promising heat-resistant explosives. Furthermore, these compounds were found to be more thermally stable than the known N-methyl-3,5-dinitropyrazole-based and C-N coupled 3,4,5-trinitrobenzene-azole-based energetic compounds.

Triazole-induced planarization of a twisted tetrazole-based molecule towards energetic materials with improved thermostability and insensitivity

Pursuing the structural planarization of energetic materials is an efficient method for achieving improved performance. Although many planar energetic molecules have been prepared so far, the innovation of advanced planar explosives still relies on the scientific intuition, experience and trial-and-error of researchers. Now, a triazole-induced planarization strategy is proposed based on the regulation of aromaticity, charge distribution, and hydrogen bonds. The incorporation of a triazole ring into the non-planar molecule 5-amino-1-nitriminotetrazole (VII) results in a planar energetic material named N-[5-amino-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-3-yl]nitramide (3). Compared with VII (T_d = 85 °C; IS < 0.25 J; FS < 5 N), 3 shows remarkably improved thermal stability (T_d = 145 °C) and reduced sensitivities (IS = 20 J; FS > 360 N). The variation of thermal stability and mechanical sensitivity from VII to 3 reflects the effectiveness and superiority of the planarization strategy. Benefiting from the properties of 3, its energetic salt 5 exhibits excellent overall performance (D_v = 9342 m s^-1; P = 31.6 GPa; T_d = 201 °C; IS = 20 J; FS = 360 N), which is comparable to that of HMX. Moreover, the triazole-induced planarization strategy may serve as a guide for exploring advanced energetic materials.

Raman spectra and vibrational properties of FOX-7 under pressure and temperature: First-principles calculations

FOX-7 (1,1-diamino-2,2-dinitroethene) as one of the widely studied insensitive high explosives exists five polymorphs (α, β, γ, α', ε) whose crystal structures have been determined by XRD (X-rays Diffraction) and which are investigated by a density functional theory (DFT) approach in this work. The calculation results show that the GGA PBE-D2 method can reproduce the experimental crystal structure of FOX-7 polymorphs better. The calculated Raman spectra of FOX-7 polymorphs were compared in detail and fully with the experimental Raman spectra data and it was found that the calculated Raman spectra frequencies have an overall red-shift in middle band (800-1700 cm^-1), and that the maximum deviation does not exceed 4 % (The maximum point is the mode of CC in plane bending). The high-temperature phase transform path (α → β → γ) and the high-pressure phase transform path (α → α'→ε) can be well represented in the computational Raman spectra. In addition, crystal structure of ε-FOX-7 was performed up to 70 GPa to probe Raman spectra and vibrational properties. The results showed that the NH₂ Raman shift is jittering with pressure (not smooth compared to other vibrational modes) and NH₂ anti-symmetry-stretching appears red-shifted. The vibration of hydrogen mixes in all of other vibrational modes. This work shows that the dispersion-corrected GGA PBE method can reproduce the experimental structure, vibrational properties and Raman spectra very well.

Toward High-Energy and Low-Sensitivity Energetic Materials Based on a Fused [5,5,5,6]-Tetracyclic Backbone

A route for fused [5,5,5,6]-tetracyclic energetic compounds based on the facile cyclization reaction has been explored. Fused [5,5,5,6]-tetracyclic compound 4 shows a high measured density (1.924 g cm^-3), a low sensitivity (IS = 10 J, and FS = 144 N), and an excellent detonation velocity (9241 m s^-1), which are much better than those of RDX. The results indicate that compound 4 is a potential candidate as a secondary explosive and provide new insight into the construction of fused polycyclic heterocycles.

The design and synthesis of new advanced energetic materials based on pyrazole-triazole backbones

A series of derivatives of the nitropyrazole-triazole backbone were designed through units' screening of 219 N-heterocycle compounds and were synthesized. Among them, the thermal stability of DNPAT (T_dec = 314 °C) is close to that of traditional heat-resistant explosive HNS (318 °C) while the detonation performance and sensitivity (D = 8889 m s^-1; IS = 18 J) are better than those of HNS (D = 7612 m s^-1; IS = 5 J) and traditional high-energy explosive RDX (D = 8795 m s^-1; IS = 7.4 J), which is rarely reported in heat-resistant explosives. Moreover, compounds 4 and 6 show excellent performances (IS > 15 J, D > 9090 m s^-1, P > 37.0 GPa), illustrating that compounds 4 and 6 may be used as secondary explosives. All these results enrich prospects for the development of energetic materials.

Insensitive High-Energy Density Materials Based on Azazole-Rich Rings: 1,2,4-Triazole N-Oxide Derivatives Containing Isomerized Nitro and Amino Groups

It is an arduous and meaningful challenge to design and develop new energetic materials with lower sensitivity and higher energy. How to skillfully combine the characteristics of low sensitivity and high energy is the key problem in designing new insensitive high-energy materials. Taking a triazole ring as a framework, a strategy of N-oxide derivatives containing isomerized nitro and amino groups was proposed to answer this question. Based on this strategy, some 1,2,4-triazole N-oxide derivatives (NATNOs) were designed and explored. The electronic structure calculation showed that the stable existence of these triazole derivatives was due to the intramolecular hydrogen bond and other interactions. The impact sensitivity and the dissociation enthalpy of trigger bonds directly indicated that some compounds could exist stably. The crystal densities of all NATNOs were larger than 1.80 g/cm³, which met the requirement of high-energetic materials for crystal density. Some NATNOs (9748 m/s for NATNO, 9841 m/s for NATNO-1, 9818 m/s for NATNO-2, 9906 m/s for NATNO-3, and 9592 m/s for NATNO-4) were potential high detonation velocity energy materials. These study results not only indicate that the NATNOs have relatively stable properties and excellent detonation properties but also prove that the strategy of nitro amino position isomerization coupled with N-oxide is an effective means to develop new energetic materials.

Can a heavy trinitromethyl group always result in a higher density?

Density is an important property of energetic materials and is believed to increase with the addition of heavy trinitromethyl groups, as shown in previous literature. However, this study determined that the introduction of these groups produced a decrease in density, as evidenced by the lower density of 1-trinitromethyl-4-amino-3,5-dinitropyrazole ((TN-116), 1.899 g cm^-3) compared to that of its precursor (4-amino-3,5-dinitropyrazole (LLM-116), 1.900 g cm^-3). Mechanistic studies indicated that the reduced density was due to the significantly weaker H-bonding and π-π interactions of TN-116, which produced looser stacking compared to that of LLM-116.

Graphene Oxide-Intercalated Tetrazole-Based Coordination Polymers: Thermally Stable Hybrid Energetic Crystals with Enhanced Photosensitivity

High-energy-density photosensitive pyrotechnics with good thermal stability have been in increasing demand in recent years. In this paper, graphene oxide (GO)-intercalated energetic coordination polymers (ECPs) are prepared with improved thermostability but great photosensitivity by using high nitrogen compounds azotetrazole (AT) and 5,5'-bistetrazole-1,1'-diolate dehydrate (BTO) as ligands. The decomposition activation energy (E_a) of Cu-AT has been increased from 135.7 to 151.9 kJ·mol^-1 after intercalating 5 wt% GO, and in the meantime, the exothermic peak temperature (T_p) was increased by 12.6 °C. However, the decomposition E_a of Cu-BTO decreased under the effect of the same amount of GO with little effect on T_p. This confirms that GO has stabilization effects on the Cu-AT crystal, whereas the catalytic effects on Cu-BTO would dominate after dehydration with its crystal lattice collapse. Also, when the content of GO was 3%, the resultant GO_0.03-Cu-AT exhibits a higher density (2.88 g·cm^-3) and good thermostability (T_p = 293.7 °C). This ECP shows excellent low-energy laser ignition performance, which can be ignited with an energy of less than 1 mJ at a wavelength of 976 nm. Low-energy laser initiation is considered to be a safer but more reliable method than the traditional electrical-based ones.

Coordinative Combination of Nitroamine and Gem-Dinitromethyl with Fused Ring for Enhanced Oxygen Balances and Detonation Properties

Oxygen balance and heat of formation are closely related to the nitrogen and oxygen content in a molecule and have a significant effect on the detonation performance of energetic materials. Here a new family of 1,2,4-triazolo [4,3-b][1,2,4,5]-tetrazine containing gem-dinitromethyl and nitroamine with high nitrogen-oxygen content was synthesized and characterized. Moreover, the structure of the guanidine salt (3) and TATOT salt (4) were confirmed by single-crystal X-ray diffraction. The nitrogen and oxygen content of ammonium salt 2 reached 82.5%, with a high density (1.805 g cm^-3) and high detonation properties (D = 8900 m s^-1; P = 32.4 GPa), which were similar to those of RDX.

Toward Advanced High-Performance Insensitive FOX-7-like Energetic Materials via Positional Isomerization

For an energetic molecule with a definite elemental composition, the substituent type and position are the most important factors to influence its detonation performance and mechanical sensitivities. In this work, two pairs of FOX-7-like energetic isomers based on (2 and HTz-FOX; 5 and 6) were synthesized and characterized. Through positional isomerization, advanced high-performance insensitive explosives were obtained. Compounds 2 and 5 with an amino group adjacent to the electron-withdrawing side of the ethene bridge show both higher thermal stability and lower mechanical sensitivities (2: Td = 258 °C, impact sensitivity (IS) = 25 J, and friction sensitivity (FS) = 300 N; 5: Td = 264 °C, IS = 30 J, and FS = 320 N). In addition, 2 shows ultrahigh detonation performance (Dv = 9224 m s-1 and P = 31.1 GPa). These promising physicochemical properties are comparable to those of HMX (Dv = 9193 m s-1, P = 37.8 GPa, Td = 275 °C, IS = 7.4 J, and FS = 120 N), which suggests that 2 may be a promising energetic material in future applications.

Tri-explosophoric groups driven fused energetic heterocycles featuring superior energetic and safety performances outperforms HMX

The design and synthesis of novel energetic compounds with integrated properties of high density, high energy, good thermal stability and sensitivities is particularly challenging due to the inherent contradiction between energy and safety for energetic compounds. In this study, a novel structure of 4-amino-7,8-dinitropyrazolo-[5,1-d] [1,2,3,5]-tetrazine 2-oxide (BITE-101) is designed and synthesized in three steps. With the help of the complementary advantages of different explosophoric groups and diverse weak interactions, BITE-101 is superior to the benchmark explosive HMX in all respects, including higher density of 1.957 g·cm^-3, highest decomposition temperature of 295 °C (onset) among CHON-based high explosives to date and superior detonation velocity and pressure (D: 9314 m·s^-1, P: 39.3 GPa), impact and friction sensitivities (IS: 18 J, FS: 128 N), thereby showing great potential for practical application as replacement for HMX, the most powerful military explosive in current use.

Asymmetric assembly of pyrazole and 1,2,3-triazole with a methylene bridge: regioisomerism and energetic properties

An asymmetric N-bridged strategy was employed to link two different energetic building blocks. The resulting compounds not only exhibit good crystal density and low sensitivity, but also demonstrate the key features of physiochemical properties and regioisomeric structures that enrich the horizon of regiochemistry of energetic compounds.

The ionic salts with super oxidizing ions O2+ and N5+: Potential candidates for high-energy oxidants

As an important component of energetic materials, high-energy oxidant is one of the key materials to improve their energy. The oxidizability of oxidant directly determines the intensity of combustion or explosion reaction. It is generally believed that when the nature of reductant is certain, the stronger the oxidizability, the more intense the reaction. Dioxygenyl cation (O₂⁺) and pentazenium cation (N₅⁺) are two kinds of super oxidizing ions, which oxidizability are comparable to that of fluorine. A series of high energetic ionic salts with O₂⁺, N₅⁺ and various anions as active components are designed, and the results show that: 1) Most ionic salts have appropriate thermodynamic stability, high density (up to 2.201 g/cm³), high enthalpy of formation (up to 1863.234 kJ/mol) and excellent detonation properties (up to 10.83 km/s, 45.9 GPa); 2) The detonation velocity value of O₂ (nitrotetrazole-N-oxides) and O₂B(N₃)₄ exceed 10.0 km/s, and the detonation pressure exceed 45.0 GPa because of the O₂⁺ salts have higher crystal density (g/cm³) and oxygen balance than that of N₅⁺salts; 3) With a higher nitrogen content than O₂⁺, the N₅⁺ salts have higher enthalpy of formation, which exceed 330 kJ/mol than that of O₂⁺ salts; 4) The linear spatial structure of N₅⁺ leads the salts to reduce their density. Encouragingly, this study proves that these super oxidizing ions have the potential to become high-energy oxidants, which could be a theoretical reference for the design of new high energetic materials.

Ambient-Pressure Recoverable Polynitrogen Solids Assembled by Pentazolate Rings with High Energy Density

Crystal structure predictions and first-principles calculations were used to predict three polynitrogen solids (aP8-N, aP12-N, and oP24-N) that possess competitive enthalpies as compared to the synthesized open-chain N₈ phase at pressures in the range of 0-60 GPa. aP8-N, aP12-N, and oP24-N contain edge-shared, N₂-linked, and N-bridged pentazolate rings and form molecular N₈, molecular N₁₂, and quasi-one-dimensional N_∞ ribbons, respectively. The calculations of formation enthalpies show that the three polynitrogen solids can be synthesized by compressing cyclo-N₅ salts in hydrogen-saturated environments. Molecular simulations suggest that the three polynitrogen solids have the ability of quench recoverability under ambient conditions once being synthesized at high pressure. With estimated energy densities in the range of 5.6-6.5 kJ/g, these three polynitrogen phases show notable promise for applications as high-energy-density materials.

Series of Azido and Fused-Tetrazole Explosives: Combining Good Thermal Stability and Low Sensitivity

The introduction of azido groups into the energetic skeleton has the advantages of increasing the energy level. In this work, a series of azido compounds with good stability and low sensitivity as well as tetrazole-fused compounds based on energetic salts are synthesized. The detonation pressures and velocities of these new compounds fall in the ranges of 18.9-27.3 GPa and 7153-8450 m s^-1, respectively. The detonation velocity of the tetrazole-fused compounds based on the potassium salts 3, 6, and 7 are 7810, 7153, and 7989 m s^-1, respectively. Also, their decomposition temperatures (244, 237, and 240 °C, respectively) are higher than that of traditional explosive RDX (204 °C). Notably, two representative compounds 2 and 5 possess higher decomposition temperature (2: 196 °C and 5: 178 °C) and overall detonation properties (2: D = 8129 m s^-1 and P = 26.6 GPa and 5: D = 8336 m s^-1 and P = 27.3 GPa) as well as relativity lower sensitivities (2: IS = 12 J and FS = 240 N and 5: IS = 10 J and FS = 144 N) than that of primary explosive 2-diazo-4,6-dinitrophenol (T_d = 157 °C, D = 6900 m s^-1, P = 24.7 GPa, IS = 1 J, and FS = 24.7 N). Moreover, the initiation capacity of compounds 2 and 5 was also assessed through the initiation tests. The results indicate that the two compounds could be a promising environmentally friendly primary explosive.

2-(1,2,4-triazole-5-yl)-1,3,4-oxadiazole as a novel building block for energetic materials

The exploration of novel nitrogen-rich heterocyclic building blocks is of importance in the field of energetic materials. A series of 2-(1,2,4-triazole-5-yl)-1,3,4-oxadiazole derivatives based on a new energetic skeleton have been first synthesized by a simple synthetic strategy. All three compounds are well-characterized by IR spectroscopy, NMR spectroscopy and thermal analysis. The compounds 5 and 8 are further characterized by single-crystal X-ray diffraction analysis. 8 and its salts (8a-8c) possess relative high decomposition temperature and low sensitivity, while 5 exhibits low decomposition temperature and high sensitivity. According to EXPLO5 calculation results of detonation performance, both 5 and 8 display acceptable detonation velocities (D) of 8450 m/s and 8130 m/s and detonation pressures (P) of 31.6 GPa and 29.2 GPa, respectively. Furthermore, 5 containing a rare diazonium ylide structure shows high impact sensitivity (4.5 J), making it has a potential as a primary explosive.

Correlated RNN Framework to Quickly Generate Molecules with Desired Properties for Energetic Materials in the Low Data Regime

Motivated by the challenging of deep learning on the low data regime and the urgent demand for intelligent design on highly energetic materials, we explore a correlated deep learning framework, which consists of three recurrent neural networks (RNNs) correlated by the transfer learning strategy, to efficiently generate new energetic molecules with a high detonation velocity in the case of very limited data available. To avoid the dependence on the external big data set, data augmentation by fragment shuffling of 303 energetic compounds is utilized to produce 500,000 molecules to pretrain RNN, through which the model can learn sufficient structure knowledge. Then the pretrained RNN is fine-tuned by focusing on the 303 energetic compounds to generate 7153 molecules similar to the energetic compounds. In order to more reliably screen the molecules with a high detonation velocity, the SMILE enumeration augmentation coupled with the pretrained knowledge is utilized to build an RNN-based prediction model, through which R² is boosted from 0.4446 to 0.9572. The comparable performance with the transfer learning strategy based on an existing big database (ChEMBL) to produce the energetic molecules and drug-like ones further supports the effectiveness and generality of our strategy in the low data regime. High-precision quantum mechanics calculations further confirm that 35 new molecules present a higher detonation velocity and lower synthetic accessibility than the classic explosive RDX, along with good thermal stability. In particular, three new molecules are comparable to caged CL-20 in the detonation velocity. All the source codes and the data set are freely available at https://github.com/wangchenghuidream/RNNMGM.

Facile Synthesis of Energetic Nanoparticles of Copper Azide with High Initiation Ability for Micro-Initiator Applications Using Layered Copper Hydroxide

Copper azide (CA) is one of the preferred primary explosives in the micro-initiating device, and it is of conducive significance to develop high-content CA-modified materials. In this work, we reported two types of CA composites with CA nanorods embedded in carbon nanosheets (CA/C) and CA distributed on salicylic acid (CA/SA) using layered copper hydroxide nanosheets intercalated with salicylic acid as the precursor. The detailed characterizations demonstrated that CA/C exhibits eximious electrostatic sensitivity (1.06 mJ) due to the inherent structural characteristics of CA/C such as the limitation of the free movement of CA by the layered structure and preeminent electrical conductivity of carbon nanosheets. Surprisingly, CA/C with nearly 1.0 mg in the miro-initiating device can reliably detonate Hexanitrohexaazaisowurtzitane (CL-20). CA/C exhibits extremely high CA content (93%), excellent ignition ability, and detonation ability, and its performance is superior to pure CA and most CA-modified materials reported previously. CA/SA also has an excellent detonation ability and its electrostatic sensitivity is as low as 0.92 mJ. These findings provide a new perspective for the development of high-performance primary explosives for the micro-initiating device.

Programming a Metal-Organic Framework toward Excellent Hypergolicity

Exploring novel hypergolic fuels for modern space propulsion is highly desired. However, the analysis and understanding of the structure and hypergolic performance at the molecular level are still insufficient. To understand the factors that dictate hypergolicity, we conducted a comparative study on a series of metal-organic frameworks (MOFs) characterized by the same topology but with varied ligand structures. The ignition delay (ID) time trend was found to be imidazole < triazole < tetrazole, and the rapid ID time was 8 ms. By combining experimental studies and density functional theory (DFT) calculations, we found that propargyl and cyanoborohydride groups that functioned as dual hypergolic triggers contributed to the hypergolicity, and a distinct electronic structure was detrimental to ID time. The structure-performance relationships presented herein can potentially provide some fundamental insights into the field of developing high-performance hypergolic fuels.

Polynitro-N-aryl-C-nitro-pyrazole/imidazole Derivatives: Thermally Stable-Insensitive Energetic Materials

A wide array of methoxy-substituted-polynitro-aryl-pyrazole/imidazoles with readily oxidizable -NH₂/NO₂/NHNO₂/diazo functional groups is synthesized. Single crystal X-ray diffraction (XRD) analysis confirms the molecular structure of the compounds. Energetic properties of the synthesized compounds are determined by theoretical and experimental studies. Most of the compounds are thermally stable and insensitive to impact and friction. Some of the molecules possess better detonation velocity and detonation pressure over TNT.

Exploring Complex Reaction Networks Using Neural Network-Based Molecular Dynamics Simulation

Ab initio molecular dynamics (AIMD) is an established method for revealing the reactive dynamics of complex systems. However, the high computational cost of AIMD restricts the explorable length and time scales. Here, we develop a fundamentally different approach using molecular dynamics simulations powered by a neural network potential to investigate complex reaction networks. This potential is trained via a workflow combining AIMD and interactive molecular dynamics in virtual reality to accelerate the sampling of rare reactive processes. A panoramic visualization of the complex reaction networks for decomposition of a novel high explosive (ICM-102) is achieved without any predefined reaction coordinates. The study leads to the discovery of new pathways that would be difficult to uncover if established methods were employed. These results highlight the power of neural network-based molecular dynamics simulations in exploring complex reaction mechanisms under extreme conditions at the ab initio level, pushing the limit of theoretical and computational chemistry toward the realism and fidelity of experiments.

Accelerated discovery of thermostable high-energy materials with intramolecular donor-acceptor building blocks

A domain-related data search promoted triazolotriazine-fused energetic scaffold filtration with combinatorial design to alleviate the lack of thermostable high-energy materials; 16 candidates were discovered that may show promising energy and safety performance, as well as excellent thermal stability. Novel fused triazolo-1,2,4-triazine energetic material 7-nitro-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c][1,2,4]triazin-4-amine-2-oxide (Candidate No. 4) with excellent thermal stability, high energy performance and low sensitivity was developed successfully by using a facile N-oxide synthetic method. Our findings may be applicable to a wider range of materials and prove equally powerful for searching for other high-performing energetic materials.

Full-nitro-nitroamino cooperative action: Climbing the energy peak of benzenes with enhanced chemical stability

More nitro groups accord benzenes with higher energy but lower chemical stability. Hexanitrobenzene (HNB) with a fully nitrated structure has stood as the energy peak of organic explosives since 1966, but it is very unstable and even decomposes in moist air. To increase the energy limit and strike a balance between energy and chemical stability, we propose an interval full-nitro-nitroamino cooperative strategy to present a new fully nitrated benzene, 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB), which was synthesized using an acylation-activation-nitration method. TNTNB exhibits a high density (d: 1.995 g cm^-3 at 173 K, 1.964 g cm^-3 at 298 K) and excellent heat of detonation (Q: 7179 kJ kg^-1), which significantly exceed those of HNB (Q: 6993 kJ kg^-1) and the state-of-the-art explosive CL-20 (Q: 6534 kJ kg^-1); thus, TNTNB represents the new energy peak for organic explosives. Compared to HNB, TNTNB also exhibits enhanced chemical stability in water, acids, and bases.

Nitrification Progress of Nitrogen-Rich Heterocyclic Energetic Compounds: A Review

As a momentous energetic group, a nitro group widely exists in high-energy-density materials (HEDMs), such as trinitrotoluene (TNT), 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), etc. The nitro group has a significant effect on improving the oxygen balance and detonation performances of energetic materials (EMs). Moreover, the nitro group is a strong electron-withdrawing group, and it can increase the acidity of the acidic hydrogen-containing nitrogen-rich energetic compounds to facilitate the construction of energetic ionic salts. Thus, it is possible to design nitro-nitrogen-rich energetic compounds with adjustable properties. In this paper, the nitration methods of azoles, including imidazole, pyrazole, triazole, tetrazole, and oxadiazole, as well as azines, including pyrazine, pyridazine, triazine, and tetrazine, have been concluded. Furthermore, the prospect of the future development of nitrogen-rich heterocyclic energetic compounds has been stated, so as to provide references for researchers who are engaged in the synthesis of EMs.

Interfacial engineered RDX/TATB energetic co-particles for enhanced safety performance and thermal stability

1,3,5-trinitro-1,3,5-triazinane (RDX) has attracted considerable attentions in energy related fields. However, the safety performance of RDX needs to be improved in terms of various external stimulations. Herein, such issues of...