Manipulating nitration and stabilization to achieve high energy

Construction of 3-Nitro-1H-pyrazole-5-yl-Bridged/Fused 4,5-Diamino-4H-1,2,4-triazoles Achieving High-Energy Insensitive Energetic Materials

Aminotriazole is a privileged structural motif in the design of various thermostable and insensitive energetic materials. A series of 3-nitro-1H-pyrazole-5-yl-bridged/fused 4,5-diamino-4H-1,2,4-triazoles was prepared via the cycloaddition of carboxyl pyrazole as a raw material. These newly synthesized compounds and their corresponding salts were fully characterized by chemical analysis (single-crystal X-ray diffraction, infrared, NMR, and mass spectroscopy) as well as experimental tests (thermostability and sensitivities). Their detonation properties (detonation velocity, detonation pressure, etc.) were determined with the EXPLO5 program on the basis of crystal density and calculated heat of formation with the Gaussian 09 suite. These pyrazole-triazoles show very high thermostabilities (Td > 320 °C) and low mechanical sensitivities (IS ≥ 25 J, FS ≥ 288 N) due to intermolecular hydrogen bonding interactions in polycyclic triazoles. In particular, tricyclic 3a displays an ultrahigh decomposition temperature of 371 °C, surpassing that of 2,2',4,4',6,6'-hexanitrostilbene (HNS) and can be used as a candidate for heat-resistant explosives. Dinitroamino compounds 2 (PCJ = 38.58 GPa, Vdet = 9268 m s-1) and 2d (PCJ = 36.15 GPa, Vdet = 8913 m s-1) were found to show excellent detonation performance, with 2 being comparable to 1,3,4,7-tetranitro-1,3,5,7-tetrazocane (HMX). Furthermore, compound 1 exhibits desirable detonation properties (PCJ = 34.74 GPa, Vdet = 9284 m s-1), high thermostability (333 °C), and low sensitivities (IS > 40 J, FS > 360 N), making it a promising HMX replacement. This study supports the superiority of utilizing the polycyclic pyrazole-triazole system in the development of new high-energy insensitive energetic materials.

Mechanochemical Nitration Studies of Aminotriazole Compounds

In order to promote the green development of the nitration process of energy-containing materials and to reduce the environmental pollution and resource waste caused by the traditional nitration reaction. We used a solvent-free mechanochemical reaction to nitrify 3-amino-1,2,4-triazole and 3,5-diamino-1,2,4-triazole and successfully obtained 3-nitro-1,2,4-triazole and 3,5-dinitro-1,2,4-triazole by using sodium nitrite and molybdenum trioxide as catalysts. Several parameters affecting the nitration reaction were explored, and the structures of the products were analyzed by combining Gaussian, Multiwfn, and other computational software; also, single crystals of 3,5-dinitro-1,2,4-triazole sodium salt were cultivated and analyzed for their crystal structure and surface properties, and their copper and lead salts were obtained by reacting with metal salts. The present work provides a new idea for the development of green nitration of energy-containing materials.

Modular Assembly Drives Synthesis of High-Energy Linked/Fused Molecules

In this study, we propose a "modular assembly" strategy to synthesize a series of new trinitromethyl high-energy molecules. For a typical molecule 1, this approach reduces the number of synthetic steps from 7 to 2 and improves the yield from 1.0% to 48.3%, representing a more than 48-fold increase compared to the traditional "skeleton first, group later" method. All synthesized molecules exhibit exceptional energetic performance, with molecule 1 demonstrating a density of 1.913 g cm-3, a detonation velocity of 9151 m s-1, and a thermal decomposition temperature of 177 °C, marking it as highly promising among trinitromethyl high-energy molecules.

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.

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.

A Method for the Preparation of Fused Dinitromethyl High-Energy-Density Materials

This work investigates a simple synthetic method for producing fused dinitromethyl energetic compounds. Fused compound 2 has a high detonation velocity (9358 m s-1) close to that of the well-known high-energy-density explosive CL-20 (9455 m s-1), an extremely high density (1.97 cm-1), and acceptable sensitivity (IS = 8 J). The good thermal stability of 2 (Td = 181 °C) is rarely reported in the field of dinitromethyl-based high explosives. The results show that compound 2 is a promising candidate for high explosives and provide new insight into the synthesis of dinitromethyl compounds.

Attaining the Utmost Stability and Energy of Carbonyl Azides by the Synergistic Improvement of Conjugation and H-bonding

Carbonyl azides are important precursors to isocyanates and are used as energetic compounds. However, the further development of these compounds is limited by their inherently poor stability. In this study, we present a new family of carbonyl azides, 5-nitro-1H-1,2,4-triazol-3-yl-carbamoyl-azide (NTCA), which was synthesized through in situ oxidation cleavage of amino-tetrazole. Compared with its precursor (nitrocarbamoyl azide, HNCA), X-ray data and quantum calculations indicate that NTCA has much stronger conjugation (dihedral angle decreased from 13.39° to 1.35°) and more H-bonds (increase from 2 to 7 pairs). As a result, NTCA exhibits the highest thermal stability (decomposition temperature of 212 °C) and highest density (1.820 g cm-3) among all known carbonyl azides. In addition, a series of Curtius rearrangements were performed to generate substituted ionic derivatives, which also exhibit high stability and energy. This study provides an effective strategy for synthesizing carbonyl azides with high stability and energy, paving the way for future practical applications.

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.

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.

Assembling of Nitropyrazoles into Tetranitroacetimidic Acid (TNAA): A Pathway to High-Performance Energetic Oxidizers through Dual C/N-Functionalization

In this work, incorporating nitropyraozles into tetranitroacetimidic acid (TNAA) resulted in two analogues of isomeric TNAA-like compounds (3 and 5). These compounds exhibit excellent densities, detonation performance, and high specific impulse, which are promising high-energy oxidizers that are comparable to AP and ADN. This structural modification strategy may have the potential to contribute significantly to the development of versatile, high-performance energetic oxidizers.

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.

Understanding the Stability of Highly Nitrated Sensitive Pyrazole Isomers

Two energetic isomers of chemically unstable 3,5-bis(dinitromethyl)-4-nitro-1H-pyrazole (2), namely, 4-methyl-3,5-dinitro-1-(trinitromethyl)-1H-pyrazole (4) and 5-methyl-3,4-dinitro-1-(trinitromethyl)-1H-pyrazole (6), each containing five nitro groups and having the same chemical composition, exhibit major differences in their physiochemical properties. These include density, enthalpy of formation, temperature of decomposition, and sensitivity to impact and friction. Notably, both isomer 4 and isomer 6 demonstrate superior thermal stability compared to isomer 2, making them promising candidates as safer energetic materials.

Construction of Adaptive Deformation Block: Rational Molecular Editing of the N-Rich Host Molecule to Remove Water from the Energetic Hydrogen-Bonded Organic Frameworks

Energetic hydrogen-bonded organic frameworks (E-HOFs), as a type of energetic material, spark fresh vitality to the creation of high energy density materials (HEDMs). However, E-HOFs containing cations and anions face challenges such as reduced energy density due to the inclusion of crystal water. In this work, the modification of amino groups in N-rich organic units could form a smart building block of hydrogen-bonded frameworks capable of changing the volume of the void space in the molecule through adaptive deformation of E-MOF blocks, thus enabling the replacement of water. Based on the above strategy, we report an interesting example of a series of hydrogen-bonded organic frameworks (E-HOF 2a and 3a) synthesized using a facile method. The crystal structure data of all of the compounds were also obtained in this work. Anhydrous 2a and 3a exhibit higher density, good thermal stability, and low mechanical sensitivity. The strategy of covalent bond modification for the host molecules of energetic frameworks shows enormous potential in eliminating the crystalline H2O of hydration and exploring high energy density materials.

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

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