3,3′-Dinitroamino-4,4′-azoxyfurazan and Its Derivatives: An Assembly of Diverse N–O Building Blocks for High-Performance Energetic Materials

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.

Enhancing the detonation performance of azobistriazole energetic derivatives via inducing N-oxide groups

The N-oxide strategy plays a crucial role in regulating the performance and safety of energetic materials. This study mainly addresses the question of how the N-oxide group affects the properties of azobistriazole and its derivatives. Our findings indicate that the N-oxide group can increase the density of the system, and its effect on the enthalpy of formation depends on the specific situation. The N-oxide groups can effectively improve the density and energetic properties. Some of the energetic derivatives containing N-oxide groups have a density as high as 2.097 g cm-3 (D3-NO(2)) and a detonation velocity as high as 10 275 m s-1 (C6-NO(2)). The effect of N-oxide groups on the enthalpy of formation depends on the specific circumstances. The effect of N-oxide groups on the stability of azobistriazole energetic derivatives is relatively complex. Among them, the N-oxide group on the triazole ring has an opposite effect on the bond dissociation enthalpy of functional groups. When the N-oxide group is on the 1,2,3-triazole ring, it can improve C-R (R is equal to C(NO2)3, NF2, NHNO2, NO2, and ONO2 respectively) bond dissociation enthalpy, and when it is on the 1,2,4-triazole ring, it will reduce the C-R bond dissociation enthalpy. When the N-oxide group is located on the azo bond, the bond dissociation enthalpy of the azo bond will be significantly reduced. This article systematically explores the effect of N-oxide groups on the properties of azobistriazole energetic derivatives, which will help people better utilize N-oxide groups to design and synthesize new energetic materials.

Trinitromethyl-Substituted 1H-1,2,4-Triazole Bridging Nitropyrazole: A Strategy of Utterly Manipulable Nitration Achieving High-Energy Density Material

Nitro groups have been demonstrated to play a decisive role in the development of the most powerful known energetic materials. Two trinitromethyl-substituted 1H-1,2,4-triazole bridging nitropyrazoles were first synthesized by straightforward routes and were characterized by chemical (MS, NMR, IR spectroscopy, and single-crystal X-ray diffraction) and experimental analysis (sensitivity toward friction, impact, and differential scanning calorimetry-thermogravimetric analysis test). Their detonation properties (detonation pressure, detonation velocity, etc.) were predicted by the EXPLO5 package based on the crystal density and calculated heat of formation with Gaussian 09. These new trinitromethyl triazoles were found to show suitable sensitivities, high density, and highly positive heat of formation. The combination of exceedingly high performances superior to those of HMX (1,3,5,7-tetranitrotetraazacyclooctane), and its straightforward preparation highlights compound 8 as a promising high-energy density material (HEDM). This work supports the effectivity of utterly manipulable nitration and provides a generalizable design synthesis strategy for developing new HEDMs.

Pressure-induced luminescence evolution of 3,3'-diamino-4,4'-azofurazan: Role of restricting chemical bond vibration and conformational modification

The luminescence and electronic structure of 3,3'-Diamino-4,4'-azofurazan (DAAzF) were studied under high pressure conditions through experimental and calculation approaches. The transition of π* → π was primarily responsible for DAAzF's broad light emission. Upon applying pressure to DAAzF, high-pressure-stiffened hydrogen-bond interactions enable the restriction of the stretching vibration of NH2 group. The reduced energy loss through nonradiative rotational relaxation and molecular motions lead to a ∼20 times luminescent enhancement of DAAzF from 1 atm to 8.9 GPa. With the further strengthening of interlayer hydrogen bond interactions at higher pressure, the deviation of hydrogen atoms in amino groups from the molecular plane lessens the radiation transition efficiency. In addition, the bending of the C-C-N=N bond further leads to molecular conformation changes at approximately 20.7 GPa, which induces an abrupt redshift and moderate quenching of the luminescence. Furthermore, the band gap of DAAzF is significantly influenced by pressure. As the color undergoes a transition from yellow to red, and becomes darker as the pressure increases, the absorption edge shifted towards red. At 3.4, 9, and 21 GPa, three conformational variations were identified in conjunction with electronic structural alterations.

Base-Mediated Tandem [3 + 2] Cycloaddition/Ring Openning Reaction of Arylhydrazonoyl Chlorides with Arylnitroso Compounds for Synthesis of Substituted Diazene Oxides

A base-mediated tandem [3 + 2] cycloaddition/ring opening reaction of nitrilimines generated from arylhydrazonoyl chlorides with arylnitroso compounds has been developed. This protocol provides a novel and rapid approach for the synthesis of substituted azoxy compounds under mild conditions with moderate to good yields and a broad substrate scope.

Synthesis of Azoxy Compounds: from Copper Compounds to Mesoporous Silica-Encaged Ultrasmall Copper Catalysts

Azoxy compounds have aroused extensive attention due to their unique biological activities, but the chemical synthesis of these compounds often suffers from limitations due to their requirement for stoichiometric oxidants, high costs, and restricted substrate range. Herein, a series of azoxy compounds were constructed via facile coupling reactions by using cost-effective N-methoxyformamide and nitroso compounds over Cu-based catalysts, affording high product yields with excellent tolerance of functional groups. Significantly, the mesoporous silica nanosphere-encapsulated ultrasmall Cu (Cu@MSN) catalyst was developed via a one-pot synthetic method and first used for the synthesis of azoxy compounds. As compared with copper salt catalysts, the Cu@MSN catalyst exhibited remarkably enhanced catalytic activity and superior recycling stability. Such a Cu@MSN catalyst overcame the inherent drawbacks of low activity, fast deactivation, and difficult recycling of traditional metal salt catalysts in organic reactions. This work provides a green and efficient method for the construction of azoxy compounds and also creates new prospects for the application of nanoporous materials confined metal catalysts in organic synthesis.

Regulation of stability and density of energetic materials via isomerism

Selective regulation of stability and density via isomerism is a promising strategy for developing energetic materials. In this work, we selectively introduced dinitromethyl groups at different positions of 4-nitro-1,2,3-triazole. The regional heterogeneity endows a high crystal density by virtue of the dense packing; on the other hand, it changes the charge distribution in the molecule, and reinforces the hydrogen bonding interactions, all of which stabilize the material. The resulting compounds exhibit excellent detonation properties and impact sensitivity that are comparable to those of HMX (D_v = 9250 m s^-1 and IS = 10 J).

Three-Dimensional Metal-Organic Frameworks as Super Heat-Resistant Explosives: Potassium 4,4'-Oxybis[3,3'-(5-tetrazol)]furazan and Potassium (1,2,4-Triazol-3-yl)tetrazole

Heat-resistant explosives play an irreplaceable role in specialized applications. Two energetic metal-organic frameworks (EMOFs), potassium 4,4'-oxybis[3,3'-(5-tetrazol)]furazan and potassium (1,2,4-triazol-3-yl)tetrazole, featuring a three-dimensional metal-organic framework structure, were first synthesized and characterized by chemical (¹H NMR, ¹³C NMR, MS, IR spectroscopy, and single-crystal XRD) and physicochemical analyses (sensitivity toward friction, impact, electrostatic, and DSC-TGA test). The new 3D EMOFs were found to show high thermostability, highly positive heat of formation, and suitable sensitivities. The Hirshfeld surface was further analyzed in order to explore the effect on sensitivities. Their detonation properties (detonation velocity, detonation pressure, etc.) were calculated by the EXPLO5 program. K₂NTT exhibits extremely high decomposition temperatures of up to 361 °C; meanwhile, its detonation performance is comparable to that of TATB and other energetic potassium salts, which makes it a promising heat-resistant explosive.

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.

Effects of oxidizing molecules on the thermal decomposition of TTDO by ab initio molecular dynamics simulations

Oxidizing molecules play a very important role in improving the comprehensive properties of energetic materials. Recently, a series of energetic cocrystals containing 2,4,6-triamino-1,3,5-triazine-1,3-dioxide (TTDO) and oxidizing molecule have been successfully prepared. Therefore, ab initio molecular dynamics were used to simulate the thermal decomposition process of TTDO, TTDO:H₂O₂, TTDO:HNO₃, and TTDO:HClO₄ crystals at 3000 K to study the role of oxidizing molecules during the thermal decomposition of TTDO. The initial decomposition paths of the TTDO crystal include N-H bond breaking, C-N bond breaking, and intramolecular and intermolecular H transfers. The formation mechanisms of H₂O, N₂, and CO₂ in the four crystals are completely different. The key formation mechanism of H₂O is the combination of O with OH, that of N₂ is the formation of the -N-N- structure, and that of CO₂ is to form the intermediate CO-R with carbonyl structure that form the fragment with the -O-C-O- structure. All the oxidizers H₂O₂, HNO₃, and HClO₄ involve in the formation of H₂O, N₂, and CO₂. The formation mechanisms of urea during the decomposition process of the four crystals are completely different, but the key step is to produce the structure of -N-CO-N-. An analysis of N_x shows that H₂O₂, HNO₃ and HClO₄ affect not only the types of N_x, but also its formation mechanisms. Among them, HNO₃ has the greatest influence on N_x.

A novel energetic cocrystal composed of CL-20 and 1-methyl-2,4,5-trinitroimidazole with high energy and low sensitivity

A cocrystal explosive comprising 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1-methyl-2,4,5-trinitroimidazole (MTNI) (molar ratio, 1:1) was synthesized. The structure of the cocrystal was characterized by single-crystal X-ray diffraction. Its structure was further determined by powder X-ray diffraction, infrared spectroscopy and differential scanning calorimetry which showed that its morphology was different from the morphology of the mechanical mixture of two raw materials. The decomposition temperature of the cocrystal is lower than that of CL-20 and MTNI. The calculated detonation performance is slightly lower than that of HMX, but the cocrystal has excellent sensitivity performance relative to that of CL-20, even lower than that of RDX. These features make this cocrystal ideal to be used in applications with low-sensitivity requirements.

DFT Quantum-Chemical Calculation of Thermodynamic Parameters and DSC Measurement of Thermostability of Novel Benzofuroxan Derivatives Containing Triazidoisobutyl Fragments

New derivatives of benzofuroxan containing triazidoisobutyl fragments, opening the way for the creation of highly effective compositions with an increased value of energy characteristics, were synthesized for the first time. Such compounds are also an excellent platform for further modification and for the preparation of new biologically-active compounds containing tetrazole and triazole fragments. Calculations of heats of formation performed with the DFT (density functional theory) method showed that the studied compounds are high-energetic density ones, the enthalpies of formation of which are comparable to the enthalpies of formation of similar benzofuroxan derivatives and exceeds experimental enthalpy of formation of CL-14 (5,7-diamino-4,6-dinitrobenzofuroxan). The analysis of DSC indicates a sufficiently high thermal stability of the synthesized azidobenzofuroxans, which are acceptable for their use as components in the creation of highly efficient compositions with an increased value of energy characteristics.

Pressure-stabilized high-energy-density material YN10

Polynitrogen compounds have been intensively studied for potential applications as high energy density materials, especially in energy and military fields. Here, using the swarm intelligence algorithm in combination with first-principles calculations, we systematically explored the variable stoichiometries of yttrium-nitrogen compounds on the nitrogen-rich regime at high pressure, where a new stable phase of YN₁₀adoptingI4/msymmetry was discovered at the pressure of 35 GPa and showed metallic character from the analysis of electronic properties. In YN₁₀, all the nitrogen atoms weresp²-hybridized in the form of N₅ring. Furthermore, the gravimetric and volumetric energy densities were estimated to be 3.05 kJ g^-1and 9.27 kJ cm^-1respectively. Particularly, the calculated detonation velocity and pressure of YN₁₀(12.0 km s^-1, 82.7 GPa) was higher than that of TNT (6.9 km s^-1, 19.0 GPa) and HMX (9.1 km s^-1, 39.3 GPa), making it a potential candidate as a high-energy-density material.

Simple methods for the introduction of nitrate ester, amino and diazo-oxide substituents into dinitromethylpyrazole

The oxygen balance and detonation properties of dinitromethylpyrazole were tuned according to the good reactivity of the chlorine group.

Fabrication of nanoscale core–shell structured lead azide/porous carbon based on a metal–organic framework with high safety performance

Carbon-based lead azide with nano-scale lead azide coated with a carbon shell (LA/C) was prepared using a lead-containing MOF material. The prepared LA/C exhibits excellent electrostatic sensitivity (1.84 J), higher LA content (85%), and better ignition ability (22 cm) compared to other reported modified LA materials.

Host–guest energetic materials: a promising strategy of incorporating small insensitive molecule into the lattice cavities of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane to enhance the safety on the premise of maintaining the excellent energy density

A novel HNIW-MA host–guest explosive was constructed by embedding the mall molecules into the lattice cavities of HNIW, and it enhances the safety on the premise of maintaining its energy density.

A low-dimensional N-rich coordination polymer as an effective fluorescence sensor for 2,4,6-trinitrophenol detection in an aqueous medium

Stable one-dimensional coordination polymer is used as a highly selective sensor for the detection of TNP.

Molecular Dynamics Simulations of the Thermal Decomposition of 3,4-Bis(3-nitrofurazan-4-yl)furoxan

When stimulated, for example, by a high temperature, the physical and chemical properties of energetic materials (EMs) may change, and, in turn, their overall performance is affected. Therefore, thermal stability is crucial for EMs, especially the thermal dynamic behavior. In the past decade, significant efforts have been made to study the thermal dynamic behavior of 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF), one of the new high-energy-density materials (HEDMs). However, the thermal decomposition mechanism of DNTF is still not specific or comprehensive. In this study, the self-consistent-charge density-functional tight-binding method was combined with molecular dynamics (MD) simulations to reveal the differences in the thermal decomposition of DNTF under four heating conditions. The O-N (O) bond would fracture first during DNTF initial thermal decomposition at medium and low temperatures, thus triggering the cracking of the whole structure. At 2000 and 2500 K, NO₂ loss on outer ring I is the fastest initial thermal decomposition pathway, and it determines that the decomposition mechanism is different from that of a medium-low temperature. NO₂ is found to be the most active intermediate product; large molecular fragments, such as C₂N₂O, are found for the first time. Hopefully, these results could provide some insights into the decomposition mechanism of new HEDMs.

Combination multi-nitrogen with high heat of formation: theoretical studies on the performance of bridged 1,2,4,5-tetrazine derivatives

A series of bridged tetrazine derivatives (BDDT) were designed by using different bridges to connect two molecules of 1,2,4, 5-tetrazine oxides and then combining different substituents. At the same time, we used DFT-wB97/6-31 + G** method to regularly predict the HOMO-LUMO, heats of formation (HOF), detonation properties, thermal stability, and thermodynamic property orbitals of BDDT compounds. By studying the comprehensive relationship between different substituents and bridging and performance, it is shown that -N(NO₂)₂ and -C(NO₂)₃ are not only excellent groups to improve the heat of formation and detonation properties, but also can cause the compound to have a superior oxygen balance. And that the incorporation of the -N = N- and -NH-N = N- is helpful to enhance their thermal stabilities and HOF. -CH₂-CH₂- and -CH₂-NH- are good for improving the HOMO-LUMO energy gaps. Performances with positive HOF (1170-1590 kJ mol^-1), remarkable density (1.88-1.93 g cm^-3), outstanding detonation properties (D = 9.15-9.80 km s^-1, P = 38.24-44.40 GPa), and acceptable impact sensitivity lead C5, D8, E5, E7, F5, and F7 to be the potential candidates of HEDMs.

1,2-Bis(5-(trinitromethyl)-1,2,4-oxadiazol-3-yl)diazene: a water stable, high-performing green oxidizer

Trinitromethane moieties are very important for the design and development of high performing dense green oxidizers. The novel oxidizer 1,2-bis(5-(trinitromethyl)-1,2,4-oxadiazol-3-yl)diazene, 14 is stable in water in contrast to 1,2,4-oxadiazoles with other electron withdrawing substituents at the C5-position. Compound 14 is a CNO-based oxidizer with positive oxygen balance (+6.9%), moderate thermostability, and mechanical insensitivity that may find useful applications in the field of green rocket propallant.

Novel polynitro azoxypyrazole-based energetic materials with high performance

Novel polynitro azoxypyrazole-based energetic compounds 1,2-bis (4-nitro-1H-pyrazol-5-yl) diazene 1-oxide (3) and 1,2-bis (1,4-dinitro-1H-pyrazol-3-yl) diazene 1-oxide (4) were synthesized from 5-amino-pyrazole-4-carbonitrile by optimized reactions. Their structures were characterized by elemental analysis and single-crystal X-ray diffraction techniques. Compound 3 exhibits high thermal stability (239 °C), low mechanical sensitivity (IS = 22 J, FS = 240 N) and moderate detonation performance (D_v = 8272 m s^-1, P = 28.1 GPa). Compound 4 shows moderate thermal stability (161 °C), decent mechanical sensitivity and higher detonation performance (D_v = 9228 m s^-1, P = 38.7 GPa) compared to that of RDX. These newly developed strategies for constructing novel energetic compounds enrich the content of the ever-expanding energetic materials.

Energetic isomers of bridged oxadiazole nitramines: the effect of asymmetric heterocyclics on stability and energetic properties

Energetic isomers often exhibit different properties. To understand the effect of arrangement and connection of isomers on energetic properties and sensitivity, in this study, we designed and synthesized a series of oxadiazole nitramine compounds including N-(5-(5-(nitramino)-1,3,4-oxadiazol-2-yl)-1,2,4-oxadiazol-3-yl)nitramide (NOON) and its ionic derivatives. NOON exhibits comparable performance (D = 8888 m s^-1, P = 34.1 GPa) to highly explosive RDX. A comparative study of detonation properties, sensitivity, and thermal stability of the three oxadiazole nitramine isomers (NOON, ICM-101, and DNBO) is carried out. The results show that due to the proton transformation, strong intramolecular hydrogen bonding interaction, and formation of six-membered ring conformation, the 2-nitramino-1,3,4-oxadiazole building block exhibits better detonation properties and higher thermal stability than its isomer 2-nitramino-1,2,4-oxadiazole.

Selective Synthesis of Bis(3-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)-4,4'-azo- and -azoxyfurazan Derivatives

In this paper, we report the synthesis of two new derivatives, bis(3-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)-4,4'-azo- and -azoxyfurazans by selective oxidation of 4-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)-1,2,5-oxadiazol-3-amine. Ammonium salts of these derivatives were prepared, and all of them were fully characterized by multinuclear NMR, FTIR spectroscopy, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. All of the new compounds have high measured crystal densities, and the energetic properties have been investigated.

How stable can the pentanitrogen cation be in kinetics?

For the 22 year-old pentanitrogen cation N5+ (01), we surprisingly found that the previously reported transition states (TSs) do not correspond to N2-extrusion. We located the real N2-extrusion TS, which can well reconcile the hitherto remaining inconsistency between the gas-phase and salt-like forms of 01 both in structure and energetics.

Improved Detonation Performance Via Coordination Substitution: Synthesis and Characterization of Two New Green Energetic Coordination Polymers

In this work, a new energetic coordination polymer (ECP), [Cu(HBTI)(H₂O)]_n (1) (H₃BTI = 4,5-bistetrazole-imidazole), was synthesized by a hydrothermal method. Due to the existence of coordination water molecules in 1, however, its energy density was limited, which led to the insufficient detonation performance. To further improve its detonation performance, [Cu(H₂BTI)(NO₃)]_n (2) was then obtained by substituting the coordinated water molecule in 1 with nitrate through the coordination substitution reaction under acidic conditions. The structures of two ECPs were respectively characterized using X-ray single-crystal diffraction, and the theoretical density of 2 (2.227 g·cm^-3) was greater than 1 (1.851 g·cm^-3). Thermogravimetric analyses showed that 2 has a one-step rapid weight loss process compared with the two-step slow weight loss process of 1. The theoretical calculations indicated that the detonation performances of 2 were better than those of 1. Moreover, the promotion effects of two ECPs on the combustion decomposition of ammonium perchlorate were studied using a differential scanning calorimetry method.

Strong intermolecular interaction induced methylene-bridged asymmetric heterocyclic explosives

Methylene-bridged asymmetric heterocyclic explosives were designed and synthesized to attempt the possibility of realizing energetic materials with high-energy and adequate sensitivity.