1,5-Di(nitramino)tetrazole: High Sensitivity and Superior Explosive Performance

Synthesis and Performance Evaluation of Zwitterionic C-N Bonded Triazole-Tetrazole-Based Primary Explosives

Developing advanced metal-free nitrogen-enriched primary explosives is challenging due to the inherent risks associated with their synthesis and handling. However, there is an urgent need to develop novel lead-free, nitrogen-rich primary explosives that offer balanced energetic properties. C-N bonded bicyclic compound 3-azido-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (4), its salts, and 3,5-diazido-1H-1,2,4-triazole (8) were synthesized from inexpensive starting materials resulting in a fine blend of sensitivity and stability. These compounds exhibit high nitrogen content (79.78 to 83.43%), good thermal stability (129-210 °C), excellent detonation performance (VOD: 8592-9361 ms-1, DP: 27.1-33.8 GPa), and acceptable sensitivity (IS: 2.5-30 J, FS: 72-288 N). The hot needle tests of compounds 4 and 8 exhibit excellent ignition performance. All of the newly synthesized compounds were fully characterized using infrared spectroscopy (IR), high-resolution mass spectroscopy (HRMS), multinuclear magnetic spectroscopy (NMR), elemental analysis (EA), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), and 2, 4, and 8 were confirmed by single-crystal X-ray crystallographic studies. The molecular electrostatic potential (ESP), noncovalent interactions reduced density gradient (NCI-RDG) method, and QTAIM analysis were performed to investigate the intermolecular interactions. Together with promising performance properties, ease of synthesis, and ignitability, they are highly suitable candidates to pave new avenues for future applications.

Encapsulating Azolates Within Cationic Metal-Organic Frameworks for High-Energy-Density Materials

Despite the synthesis of numerous cationic metal-organic frameworks (CMOFs), their counter anions have been primarily limited to inorganic Cl-, NO3 -, ClO4 -, BF4 -, and Cr2O7 2-, which have weak coordination abilities. In this study, a series of new CMOFs is synthesized using azolates with strong coordination abilities as counter anions, which are exclusively employed as ligands for coordinating with metals. Owing to the unique nitrogen-rich composition of azolates, the CMOFs demonstrate significant potential as high-energy-density materials. Notably, CMOF(CuTNPO) has an exceptionally high heat of detonation of 7375 kJ kg-1, surpassing even that of the state-of-art CL-20 (6536 kJ kg-1). To further validate the advantages of employing azolates as counter anions, analogues with azolates serving as ligands are also synthesized. The comparison study indicates that encapsulating azolates within the cationic frameworks confers both high energy and safety properties. X-ray data and quantum calculations indicate that their enhanced performance stems from stronger H─bonds and π-π interactions. This study introduces new roles for azolates in MOFs and expands possibilities for structural diversity and potential applications of framework materials.

Tuning Green Explosives through SNAr Chemistry

Reactivity and regioselectivity of SNAr-type fluorine substitution with azide in polyfluorosubstituted nitrobenzenes was studied both theoretically and experimentally. The obtained polyazido-substituted nitrobenzene derivatives were extensively characterized by NMR, IR, HPLC, X-ray, and DFT methods. It was found that the substitution with the azide nucleophile occurs first at the para- and the ortho-positions to the NO2-group and that transazidation reactions also occur here. Thermal decomposition of prepared azidonitrobenzenes was studied both in controlled (kinetic decay) and uncontrolled (explosion) modes. In case of the controlled thermal decomposition of ortho-azidonitrobenzenes, benzofuroxans were found as major products of the reaction unless another azido group was adjacent to the furoxan moiety. The bursting power of azidonitrobenzenes was found to rise gradually with the number of the azide substituents in the aromatic ring.

High-Performance Aluminum Fuels Induced by Monolayer Self-Assembly of Nano-Sized Energetic Fluoride Vesicles on the Surface

Surface modification is frequently used to solve the problems of low combustion properties and agglomeration for aluminum-based fuels. However, due to the intrinsic incompatibility between the aluminum powder and the organic modifiers, the surface coating is usually uneven and disordered, which significantly deteriorates the uniformity and performances of the Al-based fuels. Herein, a new approach of monolayer nano-vesicular self-assembly is proposed to prepare high-performance Al fuels. Triblock copolymer G-F-G is produced by glycidyl azide polymer (GAP) and 2,2'-(2,2,3,3,4,5,5-Octafluorohexane-1,6-diyl) bis (oxirane) (fluoride) ring-open addition reaction. By utilizing G-F-G vesicular self-assembly in a special solvent, the nano-sized vesicles are firmly adhered to the surface of Al powder through the long-range attraction between the fluorine segments and Al. Meanwhile, the electrostatic repulsion between vesicles ensures an extremely thin coating thickness (≈15 nm), maintaining the monolayer coating structure. Nice ignition, combustion, anti-agglomeration, and water-proof properties of Al@G-F-G(DMF) are achieved, which are superior among the existing Al-based fuels. The derived Al-based fuel has excellent comprehensive properties, which can not only inspire the development of new-generation energetic materials but also provide facile but exquisite strategies for exquisite surface nanostructure construction via ordered self-assembly for many other applications.

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.

Synthesis and Energetic Characterization of Borane-Amines on High-Nitrogen Heterocycles

Borane-amines have garnered attention over the last several decades in a variety of applications, ranging from hydrogen storage materials to hypergolic fuel systems. An investigation into the synthesis of borane-amines with high-nitrogen content heterocycles was undertaken in this work. Borane-amines were formed by the reaction of BH3·Me2S in tetrahydrofuran (THF) with the requisite nitrogen-containing heterocycle and isolated by placing the crude reaction mixture in hexanes to precipitate the product. X-ray crystallography, thermogravimetric analysis (TGA), high resolution mass spectroscopy (HRMS), 1H NMR, 13C NMR, and 11B NMR were utilized for product characterization, while impact and friction sensitivity testing were conducted to identify sensitivity in the synthesized compounds. Most isolated borane-amines, except one, were found to decompose in the atmosphere and were more sensitive to mechanical stimuli than their starting materials; however, all synthesized compounds were found to be hypergolic in the presence of white fuming nitric acid (WFNA).

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.

Nitroiminotriazole (NIT) based potential solid propellants: synthesis, characterization, and applications

Nitroimino (R = N-NO2) energetic material is a unique class of high energy density materials (HEDM). Synthesis and characterization of insensitive nitroimino compounds are a major challenge. Here triazole-based nitroimino compounds and their high-nitrogen green energetic salts in excellent yields are described. These materials exhibit high positive heats of formation (7.84 to 735.29 kJ mol-1), good densities (1.66 to 1.98 g cm-3), suitable detonation properties (P = 22.02 to 31.88 GPa; D = 7472 to 8936 ms-1) and high ballistic properties (Isp 205.66 to 295.35 s; C* = 1065 to 1832 ms-1) with good thermal (Td = 136-378 °C) and mechanical stabilities (IS = 10-40 J and FS = 120-360 N).

Synthesis and Characterization of High-Energy Anti-Perovskite Compounds Cs3X[B12H12] Based on Cesium Dodecahydro-Closo-Borate with Molecular Oxoanions (X- = [NO3]-, [ClO3]- and [ClO4]-)

Three novel anti-perovskite compounds, formulated as Cs3X[B12H12] (X- = [NO3]-, [ClO3]-, and [ClO4]-), were successfully synthesized through the direct mixing of aqueous solutions containing Cs2[B12H12] and CsX (X-: [NO3]-, [ClO3]-, [ClO4]-), followed by isothermal evaporation. All three compounds crystallize in the orthorhombic space group Pnma, exhibiting relatively similar unit-cell parameters (e.g., Cs3[ClO3][B12H12]: a = 841.25(5) pm, b = 1070.31(6) pm, c = 1776.84(9) pm). The crystal structures were determined using single-crystal X-ray diffraction, revealing a distorted hexagonal anti-perovskite order for each. Thermal analysis indicated that the placing oxidizing anions X- into the 3 Cs+ + [B12H12]2- blend leads to a reduction in the thermal stability of the resulting anti-perovskites Cs3X[B12H12] as compared to pure Cs2[B12H12], so thermal decomposition commences at lower temperatures, ranging from 320 to 440 °C. Remarkably, the examination of the energy release through DSC studies revealed that these compounds are capable of setting free a substantial amount of energy, up to 2000 J/g, upon their structural collapse under an inert-gas atmosphere (N2). These three compounds represent pioneering members of the first ever anti-perovskite high-energy compounds based on hydro-closo-borates.

A promising perovskite primary explosive

A primary explosive is an ideal chemical substance for performing ignition in military and commercial applications. For over 150 years, nearly all of the developed primary explosives have suffered from various issues, such as troublesome syntheses, high toxicity, poor stability or/and weak ignition performance. Now we report an interesting example of a primary explosive with double perovskite framework, {(C6H14N2)2[Na(NH4)(IO4)6]}n (DPPE-1), which was synthesized using a simple green one-pot method in an aqueous solution at room temperature. DPPE-1 is free of heavy metals, toxic organic components, and doesn't involve any explosive precursors. It exhibits good stability towards air, moisture, sunlight, and heat and has acceptable mechanical sensitivities. It affords ignition performance on par with the most powerful primary explosives reported to date. DPPE-1 promises to meet the challenges existing with current primary explosives, and this work could trigger more extensive applications of perovskite.

Crown-hydroxylamines are pH-dependent chelating N,O-ligands with a potential for aerobic oxidation catalysis

Despite the rich coordination chemistry, hydroxylamines are rarely used as ligands for transition metal coordination compounds. This is partially because of the instability of these complexes that undergo decomposition, disproportionation and oxidation processes involving the hydroxylamine motif. Here, we design macrocyclic poly-N-hydroxylamines (crown-hydroxylamines) that form complexes containing a d-metal ion (Cu(II), Ni(II), Mn(II), and Zn(II)) coordinated by multiple (up to six) hydroxylamine fragments. The stability of these complexes is likely to be due to a macrocycle effect and strong intramolecular H-bonding interactions between the N-OH groups. Crown-hydroxylamine complexes exhibit interesting pH-dependent behavior where the efficiency of metal binding increases upon deprotonation of the hydroxylamine groups. Copper complexes exhibit catalytic activity in aerobic oxidation reactions under ambient conditions, whereas the corresponding complexes with macrocyclic polyamines show poor or no activity. Our results show that crown-hydroxylamines display anomalous structural features and chemical behavior with respect to both organic hydroxylamines and polyaza-crowns.

Regulating the Coordination Environment by Using Isomeric Ligands: Enhancing the Energy and Sensitivity of Energetic Coordination Compounds

Transforming the energy storage structure is an effective approach to achieve a balance between the detonation performance and the sensitivity of energetic compounds, with a goal of high energy and low sensitivity. Building upon previous work, this study employed an isomeric compound 1H-pyrazole-3-carbohydrazide (3-PZCA) as a ligand and creatively designed the energetic coordination compound (ECC) Ag(3-HPZCA)2(ClO4)3 (ECC-1). It is a novel material with a dual structure of ionic salts and coordination compounds, which represents the first report of such a structure in Ag(I)-based ECCs. With its unique structures, ECC-1 exhibits a larger [ClO4-] content, a higher oxygen balance constant (OB = 0%), and superior mechanical sensitivity (IS = 13 J and FS = 40 N). Theoretical calculations indicate that ECC-1 has a higher detonation performance compared to previous work. Furthermore, the explosive experiment testing results demonstrate that it can be ignited by lower-threshold lasers and possesses excellent initiation capability and explosive power, making it suitable not only as a primary explosive but also as a secondary explosive.

Thermodynamic Analysis and Pyrolysis Mechanism of 4,4'-Azobis-1,2,4-triazole

The nonisothermal thermal decomposition kinetics of 4,4'-azobis-1,2,4-triazole (ATRZ) at different heating rates (5, 10, 15, and 20 °C·min-1) were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) studies. The thermal decomposition kinetic parameters such as apparent activation energy (E) and pre-exponential factor (A) were calculated by the Kissinger, Ozawa, and Šatava-Šestak methods. The E and A values calculated by the above three methods are very close, which are 391.1 kJ·mol-1/1034.92 s-1, 381.1 kJ·mol-1/1034.30 s-1, and 393.4 kJ·mol-1/1035.76 s-1, respectively. Then, the decomposition mechanism function of ATRZ is analyzed by the calculated results. The results show that the decomposition temperature of ATRZ is about 300 °C and the exothermic decomposition speed is fast. The decomposition pathway of ATRZ was analyzed by pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS). The thermal decomposition kinetic equation of the ATRZ was deduced.

A Dihydrazone as a Remarkably Nitrogen-Rich Thermostable and Insensitive Energetic Material

Hydrogen bonds (H-bonds) in energetic compounds have a very pronounced effect on physicochemical properties such as density, thermal stability, sensitivity, and solubility. Now a strategy to synthesize nitrogen-rich energetic materials with overall good properties, which stem from the synergetic effects of inter- or intramolecular H-bonds, is reported. 1,2-Dihydrazono-1,2-di(1H-tetrazol-5-5-yl)ethane (4), a new thermostable and insensitive material, is obtained from the reaction of dioxime (2) with hydrazine hydrate. The exchange of the oxime (NOH) with the hydrazone (NNH2) functionality results in the reduced acidic character and low solubility in water, which make it remarkably suitable for practical use. While the detonation velocity of 4 is comparable with RDX, it has an advantage of high nitrogen content (76%) and high thermal stability (275 °C) and is insensitive toward external stimuli.

Thermal stability of azole-rich energetic compounds: their structure, density, enthalpy of formation and energetic properties

Energetic compounds, as a type of special material, are widely used in the fields of national defense, aerospace and exploration. Their research and production have received growing attention. Thermal stability is a crucial factor for the safety of energetic materials. Azole-rich energetic compounds have emerged as a research hotspot in recent years owing to their excellent properties. Due to the aromaticity of unsaturated azoles, many azole-rich energetic compounds have significant thermal stability, which is one of the properties that researchers focus on. This review presents a comprehensive summary of the physicochemical and energetic properties of various energetic materials, highlighting the relationship between thermal stability and the structural, physicochemical, and energetic properties of azole-rich energetic compounds. To improve the thermal stability of compounds, five aspects can be considered, including functional group modification, bridging, preparation of energetic salts, energetic metal-organic frameworks (EMOFs) and co-crystals. It was demonstrated that increasing the strength and number of hydrogen bonds of azoles and expanding the π-π stacking area are the key factors to improve thermal stability, which provides a valuable way to develop energetic materials with higher energy and thermal stability.

Mechanistic Understanding and Reactivity Analyses for the Photochemistry of Disubstituted Tetrazoles

The photolysis of tetrazoles has undergone extensive research. However, there are still some problems to be solved in terms of mechanistic understanding and reactivity analyses, which leaves room for theoretical calculations. Herein, multiconfiguration perturbation theory at the CASPT2//CASSCF level was employed to account for electron correction effects involved in the photolysis of four disubstituted tetrazoles. Based on calculations of vertical excitation properties and evaluations of intersystem crossing (ISC) efficiencies in the Frank-Condon region, the combination of space and electronic effects is found in maximum-absorption excitation. Two types of ISC (¹ππ* → ³nπ*, ¹ππ* → ³ππ*) are determined in disubstituted tetrazoles, and the obtained rates follow the El-Sayed rule. Through mapping three representative types of minimum energy profiles for the photolysis of 1,5-, and 2,5-disubstituted tetrazoles, a conclusion can be drawn that the photolysis of tetrazoles exhibits reactivity characteristic of bond-breaking selectivity. Kinetic evaluations show that the photogeneration of singlet imidoylnitrene operates predominately over that in the triplet state, which can be confirmed by a double-well model in the triplet potential energy surface of 1,5-disubstituted tetrazole. Similar mechanistic explorations and reactivity analyses were also applied to the photolysis of 2,5-disubstituted tetrazole to unveil fragmentation patterns of nitrile imine generation. All computational efforts allow us to better understand the photoreactions of disubstituted tetrazoles and to provide useful strategies for regulating their unique reactivity.

Bisnitramide-Bridged N-Substituted Tetrazoles with Balanced Sensitivity and High Performance

In this study, a simple synthetic strategy for bridged bis(nitramide)-based N-substituted tetrazoles is described. All new compounds were isolated and fully characterized by sophisticated analytical techniques. The structures of the intermediate derivative and two final compounds were determined by single-crystal X-ray data. The structures of the intermediate derivative and two final compounds were determined by single crystal X-ray data. Thermostabilities and energetic properties of new bridged bisnitramide-based N-substituted tetrazoles were discussed and compared with known materials.

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.

A data-driven interpretation of the stability of organic molecular crystals

Due to the subtle balance of intermolecular interactions that govern structure-property relations, predicting the stability of crystal structures formed from molecular building blocks is a highly non-trivial scientific problem. A particularly active and fruitful approach involves classifying the different combinations of interacting chemical moieties, as understanding the relative energetics of different interactions enables the design of molecular crystals and fine-tuning of their stabilities. While this is usually performed based on the empirical observation of the most commonly encountered motifs in known crystal structures, we propose to apply a combination of supervised and unsupervised machine-learning techniques to automate the construction of an extensive library of molecular building blocks. We introduce a structural descriptor tailored to the prediction of the binding (lattice) energy and apply it to a curated dataset of organic crystals, exploiting its atom-centered nature to obtain a data-driven assessment of the contribution of different chemical groups to the lattice energy of the crystal. We then interpret this library using a low-dimensional representation of the structure-energy landscape and discuss selected examples of the insights into crystal engineering that can be extracted from this analysis, providing a complete database to guide the design of molecular materials.

N-Functionalization of 5-Aminotetrazoles: Balancing Energetic Performance and Molecular Stability by Introducing ADNP

5-aminotetrazole is one of the most marked high-nitrogen tetrazole compounds. However, the structural modification of 5-aminotetrazole with nitro groups often leads to dramatically decreased molecular stability, while the N-bridging functionalization does not efficiently improve the density and performance. In this paper, we report on a straightforward approach for improving the density of 5-aminotetrazole by introducing 4-amino-3,5-dinitropyrazole. The following experimental and calculated properties show that nitropyrazole functionalization competes well with energetic performance and mechanic sensitivity. All compounds were thoroughly characterized using IR and NMR spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Two energetic compounds (DMPT-1 and DMPT-2) were further confirmed by implementing single-crystal X-ray diffraction studies. Compound DMPT-1 featured a high crystal density of 1.806 g cm-3, excellent detonation velocity (vD = 8610 m s-1), detonation pressure (P = 30.2 GPa), and impact sensitivity of 30 J.

New 5-Aminotetrazole-Based Energetic Polymers: Synthesis, Structure and Properties

An N-glycidyl-5-aminotetrazole homopolymer was synthesized herein by nucleophilic substitution of 5-aminotetrazole heterocycles for chlorine atoms in poly-(epichlorohydrin)-butanediol. Copolymers of N-glycidyl-5-aminotetrazole and glycidyl azide with a varied ratio of energetic elements were synthesized by simultaneously reacting the 5-aminotetrazole sodium salt and the azide ion with the starting polymeric matrix. The 5-aminotetrazole-based homopolymer was nitrated to furnish a polymer whose macromolecule is enriched additionally with energy-rich terminal ONO2 groups and nitrate anions. The structures of the synthesized polymers were characterized by 1H and 13C NMR and IR spectroscopies, elemental analysis and gel-permeation chromatography. The densities were experimentally measured, and thermal stability data were acquired by differential scanning calorimetry. The insertion of aminotetrazole heterocycles into the polymeric chain and their modification via nitration provides an acceptable thermal stability and a considerable enhancement in density and nitrogen content compared to azide homopolymer GAP. By the 1.3-dipolar cycloaddition reaction, we demonstrated the conceptual possibility of preparing spatially branched, energy-rich polymeric binders bearing 5-aminotetrazole and 1,2,3-triazole heterocycles starting from the plasticized azide copolymers. The presence of the aforesaid advantages makes the reported polymers attractive candidates for use as a scaffold of energetic binders.

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.

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.

Nitrogen-rich ion salts of 1-hydroxytetrazole-5-hydrazide: a new series of energetic compounds that combine good stability and high energy performance

High-efficiency explosives that combine high stability and excellent energy performance are one of the key directions of energetic materials research. In this study, a novel monocyclic hydroxytetrazole derivative (3) with high stability was prepared, and a series of insensitive energetic ionic salts were derived from it. Benefiting from their outstanding performance in terms of density, 3D hydrogen bonding and π-electron interactions, these salts are excellent in both detonation performance (D = 8709 to 9314 m s^-1 and P = 29.9 to 35.6 GPa) and thermal stability (T_d = 193.0-232.2 °C). The hydrazine salt (2) exhibits high detonation properties (D = 9314 m s^-1 and P = 35.6 GPa), due to its high density (ρ = 1.71 g cm^-3) and high heat of formation (Δ_fH = 563.2 kJ mol^-1 = 3.19 kJ g^-1). In addition, the high thermal stability (T_d = 232.0 °C) and low mechanical sensitivity (IS = 30 J and FS = 360 N) of 2 are also unmatched by HMX and TKX-50. These improved properties demonstrate the great promise of 2 as an insensitive high-energy explosive.

Supramolecular Frameworks and a Luminescent Coordination Polymer from New β-Diketone/Tetrazole Ligands

Mixed multidentate linkers with donor groups of different types can be fruitfully exploited in the self-assembly of coordination polymers (CPs) and Metal-Organic Frameworks (MOFs). In this work we develop new ligands containing a β-diketone chelating functionality, to better control the stereochemistry at the metal center, and tetrazolyl multidentate bridging groups, a combination not yet explored for networking with metal ions. The new ligands, 1,3-bis(4-(1H-tetrazol-5-yl)phenyl)-1,3-propanedione (H3L1) and 1-phenyl-3-(4-(1H-tetrazol-5-yl)phenyl)-1,3-propanedione (H2L2), are synthesized from the corresponding nitrile precursors by [2+3] dipolar cycloaddition of azide under metal-free catalytic conditions. Crystal structure analysis evidences the involvement of tetrazolyl fragments in multiple hydrogen bonding giving 2D and 1D supramolecular frameworks. Reactivity of the new ligands with different metal salts indicates good coordinating ability, and we report the preparation and structural characterization of the tris–chelate complex [Fe(HL1)3]3− (1) and the homometallic 2D CP [ZnL2(DMSO)] (2). In compound 1 only the diketonate donor is used, whereas the partially deprotonated tetrazolyl groups are involved in hydrogen bonding, giving rise to a 2D supramolecular framework of (6,3)IIa topological type. In compound 2 the ligand is completely deprotonated and uses both the diketonate donor (chelating) and the tetrazolate fragment (bridging) to coordinate the Zn(II) ions. The resulting neutral 2D network of sql topology shows luminescence in the solid state, which is red shifted with respect to the free ligand. Interestingly, it can be easily exfoliated in water to give a luminescent colloidal solution.

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.

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.

The regioselectivity of the sulfonylation of tetrazoles: a theoretical view

DFT calculations were performed to reveal the regioselectivity for the sulfonylation of tetrazoles.

Enhanced catalysis through structurally modified hybrid 2-D boron nitride nanosheets comprising of complexed 2-hydroxy-4-methoxybenzophenone motif

Tuning the structural architecture of the pristine two dimensional hexagonal boron nitride (h-BN) nanosheets through rational surface engineering have proven advantageous in the fabrication of competent catalytic materials. Inspired by the performance of h-BN based nanomaterials in expediting key organic transformations, we channelized our research efforts towards engineering the inherent surface properties of the exclusively stacked h-BN nanosheets through the incorporation of a novel competent copper complex of a bidentate chelating ligand 2-hydroxy-4-methoxybenzophenone (BP). Delightfully, this hybrid nanomaterial worked exceptionally well in boosting the [3 + 2] cycloaddition reaction of azide and nitriles, providing a facile access to a diverse variety of highly bioactive tetrazole motifs. A deep insight into the morphology of the covalently crafted h-BN signified the structural integrity of the exfoliated h-BN@OH nanosheets that exhibited lamellar like structures possessing smooth edges and flat surface. This interesting morphology could also be envisioned to augment the catalysis by allowing the desired surface area for the reactants and thus tailoring their activity. The work paves the way towards rational design of h-BN based nanomaterials and adjusting their catalytic potential by the use of suitable complexes for promoting sustainable catalysis, especially in view of the fact that till date only a very few h-BN nanosheets based catalysts have been devised.

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.

Construction of Coplanar Bicyclic Backbones for 1,2,4-Triazole-1,2,4-Oxadiazole-Derived Energetic Materials

Combining different nitrogen-rich heterocycles into a molecule can fine-tune its energetic performance and physical properties as well as its safety for use in energetic materials. Here, 1,2,4-oxadiazole was incorporated into 1,2,4-triazole to construct new energetic backbones. 3-(5-Amino-1H-1,2,4-triazol-3-yl)-1,2,4-oxadiazol-5-amine (5) was designed and synthesized. Nitramino-functionalized N-(5-(5-amino-1,2,4-oxadiazol-3-yl)-3H-1,2,4-triazol-3-yl)nitramide (6) and N-(5-(5-(nitramino)-1,2,4-oxadiazol-3-yl)-3H-1,2,4-triazol-3-yl)nitramide (7) were also obtained, and two series of corresponding nitrogen-rich salts were prepared, leading to the creation of new energetic compounds. All derivatives were fully characterized, and five of them were further confirmed by X-ray diffraction. The theoretical calculations, energetic performance, safety, and the main decomposition gaseous products of 1,2,4-triazole-1,2,4-oxadiazole-derived energetic materials were studied. Compound 7 and its dihydroxylammonium salt (7 c) exhibited prominent detonation performance comparable to that of RDX while possessing satisfying thermal stabilities and mechanical sensitivities.

1,3,4,5-Tetraamino-1,2,4-triazolium Cation: An Energetic Moiety

The amination of 3,4,5-triamino-1,2,4-triazole with O-tosylhydroxylamine yielded the nitrogen-rich 1,3,4,5-tetraamino-1,2,4-triazolium cation as its tosylate salt. Subsequent metathesis reactions produced energetic salts with various energetic anions, including perchlorate, nitrate, nitrotetrazolate, and bistetrazolate diolate. All energetic salts possess relatively high heats of formation, thermal sensitivities, and detonation velocities and pressures. The prepared energetic salts were characterized chemically using single-crystal X-ray crystallography, elemental analysis, and ¹H NMR, ¹³C NMR, and IR spectroscopy and energetically by measuring their thermal, impact, and friction sensitivities. ¹⁵N NMR was carried out on the tosylate salt. Energetic performances were determined by a combined experimental-computational method using calculated heats of formation and experimental crystal densities.

Experimental and Computational Studies on N-alkylation Reaction of N-Benzoyl 5-(Aminomethyl)Tetrazole

The N-alkylation reaction of N-benzoyl 5-(aminomethyl)tetrazole (5-AMT) with benzyl bromide was carried out in the presence of K2CO3 as a base. Two separable regioisomers were obtained, thus their purification led to determine the proportion of each of them, and their structures were attributed essentially based on 1H and 13C NMR spectroscopy in addition to the elemental analysis and MS data. In order to confirm the results obtained at the synthesis level, a computational study was carried out by application of density functional theory (DFT) using the Becke three-parameter hybrid exchange functional and the Lee-Yang-Parr correlation functional (B3LYP).

Molding fabrication of copper azide/porous graphene with high electrostatic safety by self-assembly of graphene oxide

In the wake of the development of micro-initiation systems, traditional lead-based primary explosives hardly satisfy the needs of high energy output. Copper azide (CA), one of the most promising primary explosives, is restricted in practical applications because of its high electrostatic sensitivity and the method of charge in micro-initiation systems. To tackle these issues, two synthetic paths of CA based on a porous graphene skeleton are proposed. First, a viscous homogeneous mixed solution is rapidly frozen in liquid nitrogen to form a spherical copper-containing precursor material. The copper azide/carbon/graphene composite (CA/C/GA) was fabricated by freeze-drying, high-temperature thermal decomposition andin situazidation. Second, A cylindrical copper/graphene gel formed by high-temperature hydrothermal self-assembly is served as a precursor material. Also, hydrogen reduction andin situazidation procedures were utilized to synthesize copper azide@graphene foam (CA@GF). Detailed characterization indicates that the excellent performance of composite materials is ascribed to the excellent electrical and thermal conductivity of graphene material. The electrostatic sensitivities of CA/C/GA and CA@GF were 3.6 mJ and 2.5 mJ, respectively, and the flame sensitivity was 50 cm. The course of fabrication is environmentally friendly and easy to perform and it may be well-matched with the charge of the micro-detonation system.

Series of AzTO-Based Energetic Materials: Effect of Different π-π Stacking Modes on Their Thermal Stability and Sensitivity

π-Stacking is common in materials, but different π-π stacking modes remarkably affect the properties and performances of materials. In particular, weak interactions, π-stacking and hydrogen bonding, often have a great impact on the stability and sensitivity of high-energetic compounds. Therefore, several of energetic materials based on 1,1'-dihydroxyazotetrazole (1) with a nearly flat structure, such as the salts of aminoguanidine (2), 1,3-diaminoguanidine (3), imidazole (4), pyrazole (5) and triaminoguanidine (6), and a cocrystal of 2-methylimidazole (7), were designed and synthesized. Based on single-crystal diffraction data, thermal decomposition behaviors, and the mechanical sensitivity test, the compounds of 4, 5, and 7 with face-to-face π-π stacking display outstanding thermal stability and insensitivity.

Pressure-Induced In Situ Construction of P-CO/HNIW Explosive Composites with Excellent Laser Initiation and Detonation Performance

Laser initiation is a popular research topic in the energetic community. Particularly, the direct ignition of secondary explosives by laser ignitors is considered to be an advanced strategy for enhancing safety and promoting the miniaturization of weapons. Here, to improve the laser sensitivity of secondary explosives, P-CO synthesized under high pressure was employed as a coating for HNIW owing to its laser sensitivity and excellent energetic properties. In this operation, HNIW underwent an obvious isostructural phase transition from the ε-phase to the γ'-phase in the pressure range of 1.0-4.8 GPa. Subsequently, sub-nanoscale HNIW-based composites were formed when CO in situ polymerized to P-CO on the surfaces of HNIW at 5.1 GPa. This HNIW-based composite could be ignited at a much lower laser power (0.49-0.65 W) compared with pure HNIW (2.75-2.98 W) when excited by an Nd:YAG laser with a wavelength of 1064 nm. Additionally, the DFT calculations demonstrated that the arrangement density between HNIW and P-CO was significantly enhanced as the pressure increased. Thus, the introduction of advanced materials into explosive formulations through high-pressure technology is a novel and feasible strategy for developing multipurpose energetic materials.