Synthesis and Characterization of Binary, Highly Endothermic, and Extremely Sensitive 2,2'-Azobis(5-azidotetrazole)

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.

Taming of Triazole, Tetrazole, and Azido Groups: Nitrogen-Rich Energetic Materials with High Thermal Stabilities

Nitrogen-rich energetic materials are of interest due to their potential use as high-energy-density materials in various applications. However, most compounds with a high nitrogen content show poor thermal stabilities, which may limit their use in certain applications. In pursuit of nitrogen-rich energetic materials, this study presents the synthesis and characterization of two nitrogen rich energetic compounds, namely 3-azido-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (3, C3H3N11, N%: 79.78) and (E)-1,2-bis(3-azido-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-yl) diazene (7, C6H2N22, N%: 80.62). Compounds 3 and 7 have high thermal stabilities of 216 and 221 °C, respectively, making them the most thermally stable among metal-free primary explosives. Additionally, they show good energetic performance (vD: 8345 m s-1; P: 25.17 GPa; vD: 8275 m s-1; P: 25.57 GPa), making them potential candidates for metal-free high energy primary explosive. The energetic salts of 3 and 7 were also investigated. Among them, hydrazinium salt 11 displays better energetic performance (vD: 9089 m s-1; P: 30.55 GPa), which was on par with those of cyclotetramethylene tetranitramine (HMX). This research contributes to the exploration of nitrogen-rich energetic materials with potential applications in various fields.

2,2'-Bisdinitromethyl-5,5'-bistetrazole: A High-Performance, Multi-Nitro Energetic Material with Excellent Oxygen Balance

Bistetrazoles are highly sought after for developing innovative high-energy density materials. The 1,1'-substituted bistetrazoles, exemplified by TKX-50, have outstanding performance. However, the research of high-perfomance 2,2'-substituted bistetrazoles remains limited. In this work, dinitromethyl groups were introduced into bistetrazole structures as 2,2'-substituted bistetrazoles (BDBTZ), which was extensively characterized through NMR, thermal analysis, and single crystal X-ray diffraction, exhibiting excellent oxygen balance, moderate sensitivity, acceptable thermal stability, high crystal density, and excellent detonation performance.

1-Trinitromethyl-3,5-dinitro-4-nitroaminopyrazole: Intramolecular Full Nitration and Strong Intermolecular H-Bonds toward Highly Dense Energetic Materials

Full nitration is one of the most effective strategies used in synthesizing high-density energetic materials, but this strategy has reached its limit because the resultant compounds cannot be further functionalized. To overcome this limitation, we present the synergistic action of full nitration and strong intermolecular H-bonding in designing and synthesizing 1-trinitromethyl-3,5-dinitro-4-nitroaminopyrazole (DNTP) with a density that exceeds those of the reported monocyclic CHON compounds. The detonation velocity and specific impulse of DNTP exceed those of 1-trinitromethyl-3,4,5-trinitropyrazole (TTP), HMX, and ADN.

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.

Host-Guest Technique for Designing Highly Energetic Compounds with the Nitroamino Group

A new energetic material, 2-azido-4,7-nitroamino-1H-imidazo[4,5-d]pyridazine (ANIP) with a highly sensitive azido group and its host-guest compounds (ANIP/H2O and ANIP/H2O2), and energetic salts were obtained. With the guest and protons in host molecules, an abundant hydrogen bond system can be formed. This results in high crystal density and good sensitivity, which suggests that the host-guest strategy is a promising way to balance the contradiction between energy and sensitivity and provides a new path to obtain a new generation of high energetic materials.

Single Step Synthesis of gem-Dinitro Methyl-1,2,4-triazole and Its Hydroxylamine Salt: An Alternative to the FOX-7 and Other Benchmark Explosives

gem-Dinitro methyl based high-energy-density material 5-(dinitromethylene)-4,5-dihydro-1H-1,2,4-triazole (2) and its hydroxylamine salt (4) were synthesized for the first time in a single step and characterized. Further, the structure of 2 was confirmed by single-crystal X-ray diffraction (SCXRD) studies. Interestengly, both the compounds show excellent density (> 1.83 g cm-3), detonation velocity (> 8700 m s-1), pressure (> 30 GPa) and are insensitive toward mechanical stimuli such as impact and friction sensitivity. Considering their synthetic fesibility and balanced energetic performance, compounds 2 and 4 show future prospects as potential next-generation energetic materials for the replacenent of many presently used benchmark high energy density materials such as RDX, FOX-7 and highly insensitive H-FOX.

Elaborating NH-Bridged Nitrogen-Rich Energetic Materials via Base-Mediated Dimroth Rearrangement: Synthesis, Characterization, and Performance Study

The pursuit of heat-resistant energetic materials featuring high thermostability and energy has gained keen interest in recent years owing to their use in coal mining and aerospace domains. In this study, we synthesized 4-((4,6-diamino-1,3,5-triazin-2-yl) amino)-1H-1,2,3-triazole-5-carbonitrile (6) and its perchlorate and nitrate energetic salts (6a and 6b) by incorporating amino bridging (-NH-) using the Dimroth rearrangement (DR) from inexpensive starting materials as a heat-resistant energetic materials. All of the compounds were thoroughly characterized by infrared (IR), NMR, elemental analysis (EA), high-resolution mass spectrometry (HRMS), and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) studies. Compounds 6a and 6b showed good densities (1.81 and 1.80 g cm-3), detonation performance (VOD = 7505 and 8257 m s-1, DP = 23.47 and 24.41 GPa), insensitivity to mechanical stimuli (IS = 40 J and FS = >360 N), and excellent thermal stability (Td = 307 and 334 °C), surpassing presently used heat-resistant explosive HNS (318 °C). The molecular electrostatic potentials and noncovalent interactions were pursued to understand possible interaction sites and structure-directing interactions in these salts. Their facile synthetic approach, good energetic performance, and outstanding thermal stability indicate that they are the ideal combination for replacing current benchmark heat-resistant explosive HNS. Additionally, this study highlights the use of classical DR for making new energetic materials with fine-tuned properties.

Catalytic Tetrazole Synthesis via [3+2] Cycloaddition of NaN3 to Organonitriles Promoted by Co(II)-complex: Isolation and Characterization of a Co(II)-diazido Intermediate

The [3+2] cycloaddition of sodium azide to nitriles to give 5-substituted 1H-tetrazoles is efficiently catalyzed by a Cobalt(II) complex (1) with a tetradentate ligand N,N-bis(pyridin-2-ylmethyl)quinolin-8-amine. Detailed mechanistic investigation shows the intermediacy of the cobalt(II) diazido complex (2), which has been isolated and structurally characterized. Complex 2 also shows good catalytic activity for the synthesis of 5-substituted 1H-tetrazoles. These are the first examples of cobalt complexes used for the [3+2] cycloaddition reaction for the synthesis of 1H-tetrazoles under homogeneous conditions.

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.

Pushing the Limit of Oxygen Balance on a Benzofuroxan Framework: K2DNDP as an Extremely Dense and Thermally Stable Material as a Substitute for Lead Azide

Because of environmental and health impacts, there is an ongoing necessity to develop sustainable primary explosives to replace existing lead-based analogues. Now we describe a potential primary explosive, dipotassium 4,6-dinitro-5,7-dioxidobenzo[c][1,2,5]oxadiazole 1-oxide (K2DNDP), which exhibits an excellent thermal stability (Tdec = 281 °C), positive oxygen balance (+4.79%), and a calculated crystal density of ρ = 2.274 g cm-3 at 100 K. Its physicochemical properties concomitantly with its straightforward synthesis make it a potential replacement for lead-based initiators.

Zwitterionic fused pyrazolo-triazole based high performing energetic materials

A series of nitrogen-rich fused energetic materials were synthesized from commercially available inexpensive starting materials and fully characterized using 1H and 13C NMR, IR spectroscopy, elemental analysis, and DSC. The structure of zwitterionic compound 2 was supported by SCXRD data. Among all, 3 and 4 possess excellent detonation velocity (8956 and 9163 m s-1) and are insensitive towards friction (>360 N) and impact (10 J), having moderate to excellent thermal stability (171-262 °C). It is worth mentioning that the zwitterionic fused pyrazolo-triazole compound 2 and its energetic salts offer remarkable performance as new-generation thermally stable 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.

Synthesis of Bridged Tetrazoles with Promising Properties and Potential Applications by a One-Step Finkelstein Reaction

Numerous nitramine bridged compounds which show promising combinations of properties have already been identified in the area of energetic materials. In this work, four new nitrazapropane bridged tetrazoles, as well as four new trinitrazaheptane tetrazoles and three oxapropane bridged tetrazoles were synthesized and fully characterized. These new compounds can all be synthesized by a simple, one-step synthesis using Finkelstein conditions. All of these new energetic materials were characterized using NMR spectroscopy, single crystal X-ray diffraction, vibrational analysis and elemental analysis. The thermal behaviour of these compounds was studied by differential thermal analysis (DTA) and partly by thermogravimetric analysis (TGA). The BAM standard method was used to determine the sensitivities towards impact (IS) and friction (FS). The enthalpies of formation were calculated at the CBS-4M level, and the energetic performances were calculated using the EXPLO5 (V6.06.01) computer code. The properties of the new compounds were compared to each other as well as to the known energetic material RDX. Moreover, the iron(II) and copper(II) perchlorate complexes with 1,3-bis-1,1-tetrazolylnitrazapropane as ligand were prepared and investigated.

Refinement of sensitive azides via in situ generated azole-based metal-organic frameworks towards stable energetic materials

Energetic materials (EMs) have been widely employed in both military and civilian areas for nearly two centuries. The introduction of high-energy azide anions to assemble energetic metal-organic frameworks (EMOFs) is an efficient strategy to enhance energetic properties. However, azido-based EMOFs always suffer low stabilities to external mechanical stimulation. Herein, we employed an in situ hydrothermal reaction as a technique to refine azide anions with a neutral triazole-cyano-based ligand TrzAt (TrzAt = 2-(1H-1,2,4-triazol-1-yl)acetonitrile) to yield two tetrazole-based EMOFs, namely, [ZnBr(trmetz)]n1 and [Cd(trmetz)2]n2 (Htrmetz = 5-(1,2,4-triazol-1-ylmethyl)-1H-tetrazole). Compound 1 features a closely packed 2D layered network, while compound 2 exhibits a 3D architecture. With azide anions inlaid into a nitrogen-rich and chelating ligand in the EMOFs, compounds 1 and 2 present remarkable decomposition temperatures (Tdec ≥ 300 °C), low impact sensitivities (IS ≥ 32 J) and low friction sensitivities (FS ≥ 324 N). The calculated heat of detonation (ΔHdet) values of 1 and 2 are 3.496 and 4.112 kJ g-1, respectively. In particular, the ΔHdet value of 2 is higher than that of traditional secondary explosives such as 2,4,6-trinitrotoluene (TNT, ΔHdet = 3.720 kJ g-1). These results indicate that EMOFs 1 and 2 may serve as potential replacements for traditional secondary explosives. This work provides a simple and effective strategy to obtain two EMOFs with satisfactory energy densities and reliable stabilities through an in situ hydrothermal technique for desensitization of azide anions.

Straightforward Synthesis of Insensitive 2-(1-Hydroxy-2,2-dinitrovinyl)guanidine and Its Guanidinium Dinitromethanide Salt as a High Energy Density Material

High energetic 2-(1-hydroxy-2,2-dinitrovinyl)guanidine and guanidinium dinitromethanide (GDNM) salt were synthesized in one and two steps using a simple and cost-effective methodology from commercially available inexpensive starting materials with a high yield. NMR, IR spectroscopy, elemental analysis, and differential scanning calorimetry studies were used to characterize compound 2a and GDNM salt. Single-crystal XRD, Hirshfeld surface analysis, and SEM analysis were used to study the crystal structure, hydrogen-bonding/noncovalent interactions, and morphology of the GDNM salt, respectively. The physicochemical and energetic properties of compound 2a and GDNM salt reveal their good energetic performance, specific impulse, and high mechanical insensitivity, which are better than that of propellants such as ADN and AP and close to that of the benchmark explosives such as RDX and FOX-7.

Combining the advantages of 1,3,4-oxadiazole and tetrazole enables achieving high-energy insensitive materials

Combining the advantages of energetic heterocycles to achieve high-energy insensitive explosives is a significant challenge. Herein, based on high-energy tetrazole rings and highly stable 1,3,4-oxadiazole rings, a series of novel nitrogen rich energetic compounds 5-9 were successfully constructed. The related compounds were fully characterized by EA, FT-IR, NMR, DSC, and MS, and compounds 6-9 were further confirmed by X-ray single crystal diffraction. Among them, the energetic ion salts 6-8 show high thermal stability (Tdec > 250 °C) and low mechanical sensitivity (IS > 40 J, FS > 360 N), as well as good energy properties (7552-8050 m s-1, 19.4-23.3 GPa). In particular, the azo compound 9 exhibits competent comprehensive performances (Tdec = 226.2 °C, D = 8502 m s-1, P = 28.9 GPa, IS = 32 J, FS = 320 N). These results suggest that the strategy of integrating tetrazole and 1,3,4-oxadiazole and employing an azo structure as a bridging unit are effective approaches to construct high-energy insensitive materials.

2,2'-Azobis(1,5'-bitetrazole) with a N10 Chain and 1,5'-Bitetrazolate-2N-oxides: Construction of Highly Energetic Nitrogen-Rich Materials Based on C-N-Linked Tetrazoles

A series of high-nitrogen compounds, including a unique molecule 2,2'-azobis(1,5'-bitetrazole) with a branched N10 chain and 1,5'-bitetrazolate-2N-oxides, were synthesized successfully based on C-N-linked 1,5'-bistetrazoles using azo coupling of N-amine bonds and N-oxide introduction strategies. All compounds were characterized by NMR spectroscopy, IR spectroscopy, elemental analysis, and differential scanning calorimetry, in which the structures of five compounds were further determined by single-crystal X-ray diffraction analysis (2, T-N10B, 3a, 3b, and THX). The nitrogen contents of these five compounds range from 63.62 (THX) to 83.43% (T-N10B), which are much higher than that of CL-20 (38.34%). The heat of formation for the prepared compounds was calculated by using the Gaussian 09 program, with T-N10B having the highest value of 5.13 kJ g-1, about 6 times higher than that of CL-20 (0.83 kJ g-1). The calculated detonation performances by EXPLO5 v6.05.04 show that THX has excellent detonation performance (D = 9581 m s-1, P = 35.93 GPa) and a remarkable specific impulse (Isp = 284.9 s).

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.

Poly Tetrazole Containing Thermally Stable and Insensitive Alkali Metal-Based 3D Energetic Metal-Organic Frameworks

Poly tetrazole-containing thermally stable and insensitive alkali metal-based 3D energetic metal-organic frameworks (EMOFs) are promising high energy density materials to balance the sensitivity, stability, and detonation performance of explosives in defense, space, and civilian applications. Herein, the self-assembly of L^3- ligand with alkali metals Na(I) and K(I) was prepared at ambient conditions, introducing two new EMOFs, [Na₃(L)₃(H₂O)₆]_n (1) and [K₃(L)₃(H₂O)₃]_n (2). Single crystal analysis reveals that Na-MOF (1) exhibited a 3D wave-like supramolecular structure with significant hydrogen bonding among the layers, while K-MOF (2) also featured a 3D framework. Both EMOFs were thoroughly characterized by NMR, IR, PXRD, and TGA/DSC analyses. Compounds 1 and 2 show excellent thermal decomposition T_d = 344 and 337 °C, respectively, compared to the presently used benchmark explosives RDX (210 °C), HMX (279 °C), and HNS (318 °C), which is attributed to structural reinforcement induced by extensive coordination. They also show remarkable detonation performance (VOD = 8500 m s^-1, 7320 m s^-1, DP = 26.74 GPa, 20 GPa for 1 and 2, respectively) and insensitivity toward impact and friction (IS ≥ 40 J, FS ≥ 360 N for 1; IS ≥ 40 J, FS ≥ 360 N for 2). Their excellent synthetic feasibility and energetic performance suggest that they are the perfect blend for the replacement of present benchmark explosives such as HNS, RDX, and HMX.

Monitoring the Micro-Structural Evolution Mechanism of Next-Generation Ultra-High-Energy All-Nitrogen Materials: A Molecular Dynamic Study

Micro-structural evolution mechanisms of next-generation ultra-high-energy all-nitrogen materials under the extreme conditions of high temperature coupled with high pressure were revealed by state-of-the-art ab initio molecular dynamics studies based on highest-nitrogen-content energetic material 2,2'-azobis(5-azidotetrazole). The results indicate that there are three primary initial uni-molecular decomposition pathways, namely, tetrazole ring opening, azido group elimination, and the breaking of the N-N bond between the azo group and azidotetrazole. In complicated global decomposition reactions, there exists the formation of nitrogen-rich clusters and all-nitrogen species. Lowering the temperature or increasing the pressure is conducive to increasing the N content in the nitrogen-rich cluster and widening the time distribution for the cluster. Abundant all-nitrogen species N₄, N₅, N₆, N₇, N₈, N₉, N₁₀, and N₁₃ were formed, and their detailed evolutionary process and construction mechanisms were enunciated. We innovatively constructed a series of next-generation ultra-high-energy all-nitrogen materials, which are expected to realize the controllable construction of next-generation ultra-high-energy all-nitrogen materials under extreme conditions.

High-performing, insensitive and thermally stable energetic materials from zwitterionic gem-dinitromethyl substituted C-C bonded 1,2,4-triazole and 1,3,4-oxadiazole

A series of gem-dinitromethyl substituted zwitterionic C-C bonded azole based energetic materials (3-8) were designed, synthesized, and characterized through NMR, IR, EA, and DSC studies. Further, the structure of 5 was confirmed with SCXRD and those of 6 and 8 with ¹⁵N NMR. All the newly synthesized energetic molecules exhibited higher density, good thermal stability, excellent detonation performance, and low mechanical sensitivity to external stimuli such as impact and friction. Among all, compounds 6 and 7 may serve as ideal secondary high energy density materials due to their remarkable thermal decomposition (200 °C and 186 °C), insensitivity to impact (>30 J), velocity of detonation (9248 m s^-1 and 8861 m s^-1) and pressure (32.7 GPa and 32.1 GPa). Additionally, the melting and decomposition temperatures of 3 (T_m = 92 °C, T_d = 242 °C) indicate that it can be used as a melt-cast explosive. The novelty, synthetic feasibility, and energetic performance of all the molecules suggest that they can be used as potential secondary explosives in defence and civilian fields.

Phase transition-induced initial decomposition of nitrogen-rich binary CN compound 2,2'-azobis(5-azidotetrazole) and its precursor 2-amino-5-azidotetrazole via tetrazole ring opening under external electric fields: a comparative DFT-D study

A comparative DFT-D study was performed to investigate the external electric field-induced crystal structures, electronic features, Hirshfeld surfaces, vibrational properties and initial decomposition mechanisms of nitrogen-rich binary CN compound 2,2'-azobis(5-azidotetrazole) (C₂N₁₆) and its precursor 2-amino-5-azidotetrazole (CH₂N₈). The results show that there exist phase transitions at the critical points of 0.006 a.u. and 0.008 a.u. for CH₂N₈ and C₂N₁₆, respectively, which are embodied in various properties of these compounds and induce their initial decomposition of the tetrazole ring opening via the breaking of N-N single bonds. The analysis of band gaps and density of states suggests the external electric field-induced enhancing ability for electron transition from the occupied orbitals to empty ones and N-N bond breaking may be the initial decomposition pathway for them. The variations in Hirshfeld surfaces indicate the spatial change and adjustment of non-bonding interactions in the two crystals. The discussions on vibrational properties indicate that IR characteristic peaks of all vibrational modes in the two crystals show a gradual red shift toward a low frequency region. The external electric field-induced initial decomposition pathways of both crystals are tetrazole ring opening via the breaking of a N-N single bond. Our findings provide insights for a comprehensive understanding of external electric field-induced phase transition and initial decomposition mechanisms of nitrogen-rich binary CN energetic compounds.

Facile synthesis of thermally stable tetrazolo[1,5-b][1,2,4]triazine substituted energetic materials: synthesis and characterization

Various thermally stable energetic materials with high nitrogen content, low sensitivity and better detonation performance were synthesized. The versatile functionalization of 1,2,4-triazine involving the introduction of oxadiazole and tetrazole is discussed. All the compounds were fully characterized using IR, multinuclear NMR spectroscopy, elemental analysis, and high-resolution mass spectrometry. Compounds 2, 3, 9 and 12 were further verified using single-crystal X-ray analysis. Compound 9 can be considered a melt-cast explosive due to its lower onset melting temperature (112 °C). The detonation velocity, pressure, density, and heat of formation of all the synthesized compounds range between 7056 and 8212 m s^-1, 17.57 and 23.78 GPa, 1.70 and 1.81 g cm^-1, and 43 and 644 kJ mol^-1, respectively. Due to the high nitrogen percentage (53 to >72%), these molecules can be used in car airbag applications. Due to the high thermal stability (>220 °C) and lower sensitivity, these compounds can be potentially used as high-performing thermally stable secondary energetic materials.

(2-Vinyltetrazolyl)furoxans as New Potential Energetic Monomers

A regioselective approach toward the synthesis of a set of new (2-vinyltetrazolyl)furoxans as potential energetic monomers has been realized. All target energetic materials were thoroughly characterized by spectral and analytical methods. Moreover, crystal structures of two representative heterocyclic systems were studied by single-crystal X-ray diffraction. Prepared high-energy substances have high combined nitrogen-oxygen content (63-71 %), high enthalpies of formation and good detonation parameters (D: 6.7-7.8 km s-1; P: 18-28 GPa). Mechanical sensitivities of the synthesized vinyltetrazoles range these explosives from highly sensitive to completely insensitive. Using calculations of molecular electrostatic potentials (ESP), structural factors influencing the impact sensitivity were revealed. Overall, newly synthesized (2-vinyltetrazolyl)furoxans are of interest as promising energetic monomers due to the presence of the vinyl moiety and explosophoric heterocyclic combination, while their performance exceeds that of benchmark explosive TNT.

Promising Thermally Stable Energetic Materials with the Combination of Pyrazole-1,3,4-Oxadiazole and Pyrazole-1,2,4-Triazole Backbones: Facile Synthesis and Energetic Performance

Thermally stable energetic materials have broad applications in the deep mining, oil and natural exploration, and aerospace industries. The quest for thermally stable (heat-resistant) energetic materials with high energy output and low sensitivity has fascinated many researchers worldwide. In this study, two different series of thermally stable energetic materials and salts based on pyrazole-oxadiazole and pyrazole-triazole (3-23) with different explosophoric groups have been synthesized in a simple and straightforward manner. All the newly synthesized compounds were fully characterized by IR, ESI-MS, multinuclear NMR spectroscopy, elemental analysis, and thermogravimetric analysis-differential scanning calorimetry measurements. The structures of 3, 7, and 22 were supported by single-crystal X-ray diffraction studies. The density, heat of formation, and energetic properties (detonation velocity and detonation pressure) of all the compounds range between 1.75 and 1.94 g cm-3, 0.73 to 2.44 kJ g-1, 7689 to 9139 m s-1, and 23.3 to 31.5 GPa, respectively. All the compounds are insensitive to impact (>30 J) and friction (>360 N). In addition, compounds 4, 6, 10, 14, 17, 21, 22, and 23 show high onset decomposition temperature (Td between 238 and 397 °C) than the benchmark energetic materials RDX (Td = 210 °C), HMX (279 °C), and thermally stable HNS (318 °C). It is noteworthy that the pyrazole-oxadiazole and pyrazole-triazole backbones greatly influence their physicochemical and energetic properties. Overall, this study offers a perspective on insensitive and thermally stable nitrogen-rich materials and explores the relationship between the structure and performance.

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.

Construction of Highly Thermostable and Insensitive Three-Dimensional Energetic Salts Based on [1,2,5]Oxadiazolo[3,4-d]pyrimidine

A novel method for accessing energetic salts of a fused-ring skeleton based on [1,2,5]oxadiazolo[3,4-d]pyrimidine and three alkali metals, sodium (Na), potassium (K), and cesium (Cs), was developed. All three compounds were fully characterized, and their structures were confirmed by single-crystal X-ray analysis. They were highly thermally stable (>290 °C) and had high density, good detonation properties, and insensitive properties, which suggested possible heat-resistant explosive applications.

Synthesis of heterocyclic (triazole, furoxan, furazan) fused pyridazine di-N-oxides via hypervalent iodine oxidation

Use of a mild PIDA oxidation strategy to access heterocyclic (triazole, furoxan, furazan) fused pyridazine di-N-oxides.