A Duo and a Trio of Triazoles as Very Thermostable and Insensitive Energetic Materials

Approaching the Thermostability Limit of Nitrogen-Rich Heterocyclic Perchlorate-Based Energetic Materials

In recent years, driven by ever-increasing application of energetic materials in deep-seated mineral resource exploitation and aerospace engineering, the mining of advanced safe energetic materials with significant thermal stability has drawn widespread publicity. Here, a tricyclic bridged energetic compound 2-amino-4,6-bis(3,5-diamino-4-nitropyrazol-1-yl)-1,3,5-triazine (NPX-03) was prepared using simple synthetic route. Furthermore, an interesting highly thermostable nitrogen-rich perchlorate, NPX-03·2HClO4, was prepared by the self-assembly reaction of NPX-03 and HClO4, displaying a thermal decomposition peak temperature of 375.9 °C. Moreover, NPX-03·2HClO4 exhibits good detonation velocity (D = 8187 m s-1) and insensitivity (IS = 50 J, FS > 360 N), thereby being promising candidates for advanced insensitive high-energy materials.

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.

Azo-Bridged Triazole Macrocycles: Computational Design, Energy Content, Performance, and Stability Assessment

Oxadiazole and triazole are extensively investigated heterocyclic scaffolds in the development of energetic materials. New energetic molecules were designed by replacing 1,2,5-oxadiazole with 2H-1,2,3-triazole in the reported conjugated macrocyclic systems to assess the influence on the energetic properties and stability. In addition, nitro groups were introduced in triazole units (N-functionalization) to improve the energetic performance. Energetic properties, including heat of formation, oxygen balance, density, detonation pressure and velocity, and impact sensitivity, were estimated for these triazole-based macrocycles. The replacement of 1,2,5-oxadiazole with 2H-1,2,3-triazole and 2-nitro-1,2,3-triazole significantly enhances the energy content, detonation performance, and noncovalent interactions. The theoretically computed energetic properties of triazole-based macrocycles reveal high positive heats of formation (1507-2761 kJ/mol), oxygen balance (-88.8 to -22.8%), high densities (1.87-1.90 g/cm3), superior detonation velocities (8.41-9.52 km/s), pressures (26.64-40.55 GPa), acceptable impact sensitivity (27-40 cm), and safety factor (51-290). The overall energetic assessment highlights triazole-based macrocycles as a potential framework that will be useful for developing advanced energetic materials.

Cupric coordination compounds with multiple anions: a promising strategy for the regulation of energetic materials

To seek new high energetic materials, N-methylene-C-bridged nitrogen-rich heterocycle 1-((4,5-diamino-4H-1,2,4-triazol-3-yl)methyl)-1H-1,2,4-triazol-3,5-diamine (DATMTDA) (2) was first synthesized, and two copper coordination compounds ([Cu₁₂(OH)₄(ClO₄)₄(H₂O)₄(DATMTDA)₁₂](ClO₄)₁₆·12H₂O (3) and [Cu₃(OH)(ClO₄)(DATMTDA)₃](ClO₄)₃(NO₃) (4)) based on 2 were formed by introducing different anions. These compounds were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. The crystal structures of compounds 3 and 4 are similar and crystallize in monoclinic systems with the P2₁/c space group, while the central copper atoms show different coordination behaviors. However, the structure of compounds 3 and 4 is analogous to a three dimensional structure owing to the O atom of OH^-, forming coordinate bonds with three copper cations. The NBO charge of 2 was calculated using density functional theory to understand its coordination modes. The Hirshfeld surface calculation reveals that 3 and 4 have strong intermolecular interactions. The thermal decomposition processes, non-isothermal kinetics, and enthalpies of formation and sensitivities of these compounds were investigated. By introducing one NO₃^- of compound 4 to replace one ClO₄^- in compound 3, compound 4 shows lower density and lower decomposition peak temperature but lower sensitivity and a higher formation enthalpy than compound 3. The complex 4 possesses an outstanding catalytic effect for the decomposition of AP than that of complex 3. The results illustrate the possibility of introducing various anions into energetic coordination compounds for the regulation of energetic materials.

Site-Selective Oxidative Coupling Reaction of Diamines toward Aminoazo Compounds

A selective oxidative coupling reaction of a diamine containing both C- and N-NH₂ was achieved using acidic potassium permanganate as the coupling reagent. The reaction conditions were optimized, and the reaction selectivity was illustrated by quantum calculations. Furthermore, the azo-coupled product was derivatized to four nitroamine energetic materials with excellent detonation performances.

Triazole-Bridged Zinc Dinuclear Complexes: Mechanochemical Synthesis, Crystal Structure, and Biological Activity

Two zinc (Zn) complexes, [Zn₂(DAT)₂Cl₄] (I) and [Zn₂(DAT)₂(NO₃)₄] (II), were prepared by grinding 3,5-diamino-1,2,4-triazole (C₂H₅N₅, DAT) with Zn precursors such as ZnCl₂ and Zn(NO₃)₂, respectively. This solid-state reaction gives the corresponding Zn complex as the sole product in over 99% yield. This mechanochemical method promotes the selective formation of Zn complexes different from those obtained using the conventional solution-based route. The crystal structures of the two complexes were analyzed by single-crystal X-ray diffraction. Complex (I) crystallizes in the monoclinic space group P2₁/c, whereas complex (II) crystallizes in the triclinic space group P _1̅. Each complex is characterized by the presence of a characteristic DAT-bridged dimer with one DAT ligand per Zn atom, and the DAT ligand provides a bridge between the two Zn metals. All Zn centers of (I) and (II) adopted a slightly distorted tetrahedral geometry. Both complexes contain a hexanuclear Zn₂N₄ ring, but their ring structures are different. Complex (I) possesses a boat geometry, while complex (II) has a nearly planar structure. The Zn-bound chlorides of complex (I) form intermolecular N-H···Cl hydrogen bonds that link neighboring molecules. In complex (II), the O atoms in the nitrate groups are hydrogen-bonded to the DAT ligand via O···H-N linkages. Both complexes exhibit blue emissions in the solid state at ambient temperature. They were evaluated as anticancer agents in HeLa, NCCIT, and MCF-7 cancer cell lines, exhibiting promising anticancer activities.

Elaboration, Characterization and Thermal Decomposition Kinetics of New Nanoenergetic Composite Based on Hydrazine 3-Nitro-1,2,4-triazol-5-one and Nanostructured Cellulose Nitrate

This research aims to develop new high-energy dense ordinary- and nano-energetic composites based on hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) and nitrated cellulose and nanostructured nitrocellulose (NC and NMCC). The elaborated energetic formulations (HNTO/NC and HNTO/NMCC) were fully characterized in terms of their chemical compatibility, morphology, thermal stability, and energetic performance. The experimental findings implied that the designed HNTO/NC and HNTO/NMCC formulations have good compatibilities with attractive characteristics such as density greater than 1.780 g/cm3 and impact sensitivity around 6 J. Furthermore, theoretical performance calculations (EXPLO5 V6.04) displayed that the optimal composition of the as-prepared energetic composites yielded excellent specific impulses and detonation velocities, which increased from 205.7 s and 7908 m/s for HNTO/NC to 209.6 s and 8064 m/s for HNTO/NMCC. Moreover, deep insight on the multi-step kinetic behaviors of the as-prepared formulations was provided based on the measured DSC data combined with isoconversional kinetic methods. It is revealed that both energetic composites undergo three consecutive exothermic events with satisfactory activation energies in the range of 139–166 kJ/mol for HNTO/NC and 119–134 kJ/mol for HNTO/NMCC. Overall, this research displayed that the new developed nanoenergetic composite based on nitrated cellulose nanostructure could serve as a promising candidate for practical applications in solid rocket propellants and composite explosives.

Hunting for Energetic Complexes as Hypergolic Promoters for Green Propellants Using Hydrogen Peroxide as Oxidizer

The development of hypergolic materials has aroused great interest due to their important applications in aerospace technology. In this work, six new energetic complexes were prepared and comprehensively characterized. All energetic complexes had isostructural characteristics, which made them ideal candidates for studying their structure-performance relationships. These energetic complexes had good thermal stabilities and excellent specific impulses. The vacuum-specific impulses were in the range 264.0-271.9 s, which was greater than most reported solid hypergolic materials. Moreover, the hypergolic performance of these compounds was examined by using 100% HNO₃ as the oxidizer, and their catalytic performance in the hypergolic reaction of typical energetic ionic liquids and 90% H₂O₂ was comprehensively studied. All compounds displayed excellent hypergolic performance with the shortest ignition delay time of 4 ms. The examined copper-containing energetic complexes displayed excellent catalytic activities for the hypergolic reaction between energetic ionic liquids and 90% H₂O₂. The shortest ignition delay time of the examined hypergolic reactions was 31 ms. The suitable physicochemical properties, excellent energetic properties, and high catalytic activity of the hypergolic reactions have demonstrated the great potential of these energetic complexes as promoters for the development of green hypergolic bipropellants.

High-Energy-Density Materials: An Amphoteric N-Rich Bis(triazole) and Salts of Its Cationic and Anionic Species

The synthesis and characterization of the N-rich bis(triazole) compound 1H,4′H-[3,3′-bis(1,2,4-triazole)]-4′,5,5′-triamine (C₄H₇N₉) with a N content of 69.6% by weight is reported. The compound exhibits a rich acid–base behavior because it can accept up to two protons, forming a monocation and a dication, and can lose one proton, forming an anion. Measurement of the acid constants has shown that there exist well-defined pH intervals in which each of the four species is predominant in solution, opening the way to their isolation and characterization by single-crystal X-ray analysis as salts with different counterions. Some energetic salts of the monocation or dication containing oxidizing inorganic counterions (dinitramide, perchlorate, and nitrate) were also prepared and characterized in the solid state for their sensitivity. In particular, the neutral compound shows a very remarkable thermal stability in air, with T_d = 347 °C, and is insensitive to impact and friction. Salts of the dication with energetic counterions, in particular perchlorate and nitrate, show increased sensitivities and reduced thermal stability. The salt of the monocation with dinitramide as the counterion outperforms other dinitramide salts reported in the literature because of its higher thermal stability (T_d = 230 °C in air) and friction insensitiveness.

An energetic, N-rich compound that, depending on the pH, can exist as neutral, singly protonated, doubly protonated, and deprotonated species is shown.

Synthesis of nitrogen-rich and thermostable energetic materials based on hetarenecarboxylic acids

Two series of both nitrogen-rich and thermostable energetic materials as well as their energetic salts based on hetarenecarboxylic acids are now described. Among these new compounds, neutral compounds 3 and 10 have higher nitrogen contents (69.66% and 63.05%) than their energetic salts, which suggests that they could be used as green energetic materials. In addition, compound 3 shows a good decomposition temperature (T_d = 281 °C), which is close to that of TNT (T_d = 295 °C). Nitrogen-rich salt 6 exhibits better integrated energetic-properties (D = 8913 m s^-1, IS = 24 J, FS = 320 N) than RDX (D = 8795 m s^-1, IS = 7.5 J, FS = 120 N).

Design of functionalized bridged 1,2,4-triazole N-oxides as high energy density materials and their comprehensive correlations

The demand for high energy density materials (HEDMs) remains a major challenge. Density functional theory (DFT) methods were employed to design a new family of bridged 1,2,4-triazole N-oxides by the manipulation of the linkage and oxygen-containing groups. The optimized geometry, electronic properties, energetic properties and sensitivities of new 40 molecules in this study were extensively evaluated. These designed compounds exhibit high densities (1.87-1.98 g cm^-3), condensed-phase heat of formation values (457.31-986.40 kJ mol^-1), impressive values for detonation velocity (9.28-9.49 km s^-1) and detonation pressure (21.22-41.31 GPa). Their sensitivities (impact, electrostatic, and shock) were calculated and compared with 1,3,5-triamino-2,4,6-trinitrobenzene (TABT) and 4,6-dinitrobenzofuroxan (DNBF). Some new compounds 4,4'-trinitro-5,5'-bridged-bis-1,2,4-triazole-2,2'-diol (TN1-TN8) and 4,4'-dinitro-5,5'-ammonia-bis-1,2,4-triazole-2,2'-diol (DN3) were distinguished from this system, making them promising candidates for HEDMs. In addition, we found that the gas-relative parameters (detonation heat, oxygen balance, φ) were as important as the density, which were highly correlated to the detonation properties (P, D). Their comprehensive correlations should also be considered in the design of new energetic molecules.

Anatomies for the thermal decomposition behavior and product rule of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole

High-performance energetic materials are mainly used in the military, aerospace industry and chemical fields. The ordinary technology of producing energetic materials cannot avoid the domination of its unique needs. At present, revealing the underlying mechanism of the formation of high-energy materials is of great significance for improving their quality characteristics. We pay special attention to the decomposition and reactive molecular dynamics (RMD) simulation of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole (DNBT). Various forms were captured in the simulation, and the form is determined by the temperature of the initial reactant. By observing the heating pattern and morphological changes under the initial thermal equilibrium, interesting temperature jumps were found in 325 K and 350 K. Observation of continuous heating (simulated temperatures are 2600 K, 2900 K, 3200 K and 3500 K) shows that DNBT has the maximum heating rate at 3500 K. In addition, N₂ occupies this dominant position in the product, moreover, N₂ and NO₂ respectively dominate the gas phase products during the initial heating process. According to the transition state analysis results of the intermediates, we found 4 interesting intermediate products, which were determined by high frequency reaction under the 4 simulated temperatures and performed with transition state calculations. It shows that the selection of reactant temperature and its activity is the key to orderly decomposition of DNBT. It is expected that these findings will be widely used in comprehensive decomposition devices and to improve the concept of learning military and industrial technology.

The performance and behavior of DNBT under RMD simulation at high temperature (2600 K, 2900 K, 3200 K and 3500 K).

Combining 1,2,4-triazole and pyrazole frameworks for new insensitive energetic materials

A new symmetric compound 3,5-bis(3-amine-4H-1,2,4-triazole)-1H-pyrazole and a series of corresponding energetic cationic salts were synthesized.

Effect of multiple oxadiazole rings with nitro and nitramino functionalities on energetic properties: computational analysis of the structure–property relationship

The oxadiazole ring is an essential nitrogen-containing heterocycle and a valuable building block that is used in developing numerous functionalized energetic compounds.