Synthesis of Advanced Pyrazole and N-N-Bridged Bistriazole-Based Secondary High-Energy Materials

Employing Nitrogen-Sulfur Synergy: 1,2,3-Triazole-Thiadiazole-Based Energetic Materials

In this study, we synthesized energetic materials integrating thiadiazole and triazole moieties. The newly developed compounds were thoroughly characterized using NMR, IR, elemental analysis, TGA-DSC, and single-crystal X-ray diffraction (for compound 3). These compounds exhibited acceptable properties, including high densities (1.88-1.92 g cm-3), moderate to good detonation performance (VOD: 6383-8128 m s-1), good thermal stability (143-238 °C), and less sensitivity to impact (>15 J) and friction (360 N). Notably, compounds 4 and 8 achieved superior detonation velocities compared to nearly all reported sulfur-based energetic materials to date. This work highlights the significance of triazole-thiadiazole frameworks in the development and fine-tuning of energetic materials.

Highly Promising Primary Explosive: A Metal-Free, Fluoro-Substituted Azo-Triazole with Unmatched Safety and Performance

A primary explosive is a perfect chemical compound for starting ignition in military and commercial uses. Over the past century, the quest for lead-free, environmentally friendly primary explosives has been a significant challenge and a long-standing goal. Here, an innovative organic primary explosive, (E)-1,2-bis(3-azido-5-(trifluoromethyl)-4H-1,2,4-triazol-4-yl)diazene (4), has been designed and synthesized through a straightforward three-step reaction from commercially available reagents. Importantly, this compound integrated two trifluoromethyl and azido groups into the N,N'-azo-1,2,4-triazole backbone to enhance the performance and safety. With this combination, it meets stringent criteria for safer, environmentally friendly primary explosives: being metal and perchlorate-free, possessing high density, excellent priming ability, and unique sensitivities to nonexplosive stimuli. It shows robust environmental resistance, good thermal stability, and effective detonation performance and also can be effectively initiated with a laser. Moreover, in the detonation test, compound 4 successfully detonated 500 mg of PETN with an ultralow minimum primer charge (MPC) of 40 mg, similar to traditional primary explosive LA (MPC: 40 mg) and outperforming organic metal-free primary explosives ICM-103 (MPC: 60 mg) and DDNP (MPC: 70 mg). The high detonation power, combined with its straightforward synthesis, cost-effectiveness, and easy large-scale manufacturing, makes it a superior alternative to currently used primary explosives such as lead azide (LA) and diazodinitrophenol (DDNP).

Employing the Trifluoromethyl Group on a 5/5 Fused Triazolo[4,3-b][1,2,4]triazole Backbone: A Viable Strategy for Attaining Balanced Energetics

In this study, we synthesized trifluoromethyl-substituted bis-triazole nitrogen-rich compounds (3-5) using a simple, cost-effective method. The newly made compounds were characterized using NMR, IR, elemental analysis, TGA-DSC, and single-crystal X-ray diffraction (for compounds 3 and 4). They demonstrated high density (1.82-1.92 g cm-3), moderate detonation performance (7567-7905 m s-1), good thermal stability (146-215 °C), and low sensitivity to impact (40 J) and friction (360 N), offering high potential nature as a cationic component in energetic salts, defense, and civilian applications.

Synthesis of 4-Amino-5-nitro-7H-pyrazolo[3,4-d][1,2,3]triazine-2-oxide and Its Heat-Resistant Derivatives

4-Amino-5-nitro-7H-pyrazolo[3,4-d][1,2,3]triazine-2-oxide (PTO) is synthesized via one step in this study. Subsequently, 4,7-diamino-5-nitro-pyrazolo[3,4-d][1,2,3]triazine-2-oxide (APTO), 4-oxo-5-nitro-7H-pyrazolo[3,4-d][1,2,3]triazine-2-oxide (OPTO), and several heat-resistant salts are synthesized through local structural modifications on PTO. Comparison of thermal stability between PTO and APTO indicates that while the amino group has a negative impact on the thermal stability of APTO, it enhances the detonation performance of APTO and effectively reduces its mechanical sensitivity. Our findings provide a practical new approach for constructing energetic materials with excellent stability.

Constructing Nitrogen-Rich Fused [5,6,5]-Tricyclic Frameworks Through Rearrangement: Heat-Resistant Zwitterionic Salt Energetic Materials

This study synthesized nitrogen-rich [5,6,5] fused compounds through a novel rearrangement reaction. Owing to its unique zwitterionic salt structure, rearrangement product 4-1 exhibits high thermal stability (Td > 250 °C), low sensitivity (IS > 40 J, FS > 360 N), and acceptable detonation velocities and pressures (νD = 8520 m s-1 and P = 32.53 GPa, respectively), which are better than those of TNT and TATB. These indicate the potential of zwitterionic salts as thermally stable energetic materials and provide new synthesis strategies for constructing fused polycyclic heterocycles through rearrangement.

Zwitterionic Energetic Materials: Synthesis, Structural Diversity and Energetic Properties

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

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

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

Elevating the energetic capabilities of metal coordination compounds by incorporating nitrate anions

In the realm of energetic materials research, there has been notable interest in energetic coordination compounds (ECCs) owing to their remarkable thermal stability and resistance to mechanical stimuli. This study successfully demonstrated the synthesis of an azole-based C-C bonded ECC1 under ambient conditions. A comprehensive characterization study, employing techniques such as IR, TGA-DSC, NMR and single-crystal X-ray diffraction analysis, was conducted. The bulk compound was investigated by PXRD analysis. In-depth exploration of its physicochemical and energetic performance revealed good detonation properties such as a detonation velocity (VOD) of 8553 m s-1 and a detonation pressure (DP) of 36.2 GPa, which surpass those of heat resistant explosives HNS and TATB. Due to its remarkable high melting and onset decomposition temperature (278/379 °C), it also outperforms the benchmark explosive HMX (279 °C) and the heat-resistant explosive HNS (318 °C) and shows a high impact sensitivity (IS) of 20 J and friction sensitivity (FS) of 360 N. The study also employed Hirshfeld surface and 2D fingerprint analysis to elucidate the close contact of atoms within the molecules. The combination of high detonation properties, thermal stability, and low sensitivity makes the synthesized ECC1 intriguing for further investigations and suggests its potential applications as a safe and high-energy-dense material.

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.

Intramolecular Hydrogen Bonds Assisted Construction of Planar Tricyclic Structures for Insensitive and Highly Thermostable Energetic Materials

Safety is fundamental for the practical development and application of energetic materials. Three tricyclic energetic compounds, namely, 1,3-di(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (ATDT), 5'-nitro-3-(1H-tetrazol-5-yl)-2'H-[1,3'-bi(1,2,4-triazol)]-5-amine (ATNT), and 1-(3,4-dinitro-1H-pyrazol-5-yl)-3-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (ATDNP), were effectively synthesized through a simple two-step synthetic route. The introduction of intramolecular hydrogen bonds resulted in excellent molecular planarity for the three new compounds. Additionally, they exhibit regular crystal packing, leading to numerous intermolecular hydrogen bonds and π-π interactions. Benefiting from planar tricyclic structural features, ATDT, ATNT, and ATDNP are insensitive (IS > 60 J, FS = 360 N) when exposed to external stimuli. Furthermore, ATNT (Td = 361.1 °C) and ATDNP (Td = 317.0 °C) exhibit high decomposition temperatures and satisfying detonation performance. The intermolecular hydrogen bonding that produced this planar tricyclic molecular structure serves as a model for the creation of innovative multiple heterocycle energetic materials with excellent stability.

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.