Self-Assembly of Nitrogen-Rich Heterocyclic Compounds with Oxidants for the Development of High-Energy Materials

Construction and Modification of Nitrogen-Rich Polycyclic Frameworks: A Promising Fused Tricyclic Host-Guest Energetic Material with Heat Resistance, High Energy, and Low Sensitivity

The construction and modification of novel energetic frameworks to achieve an ideal balance between high energy density and good stability are a continuous pursuit for researchers. In this work, a fused [5,6,5]-tricyclic framework was utilized as the energetic host to encapsulate the oxidant molecules for the first time. A series of new pyridazine-based [5,6] and [5,6,5] fused polycyclic nitrogen-rich skeletons and their derivatives were designed and synthesized. Two strategies, amino oxidation and host-guest inclusion, were used to modify the skeleton in only one step. All compounds exhibit good comprehensive properties (Td (onset) > 200 °C, ρ > 1.85 g cm-3, Dv > 8400 m s-1, IS > 20 J, FS > 360 N). Benefiting from the pyridazine-based fused tricyclic structure with more hydrogen bonding units and larger conjugated systems, the first example of [5,6,5]-tricyclic host-guest energetic material triamino-9H-pyrazolo[3,4-d][1,2,4]triazolo[4,3-b]pyridazine-diperchloric acid (10), shows high decomposition temperature (Td (onset) = 336 °C), high density and heats of formation (ρ = 1.94 g cm-3, ΔHf = 733.4 kJ mol-1), high detonation performance (Dv = 8820 m s-1, P = 36.2 GPa), high specific impulse (Isp = 269 s), and low sensitivity (IS = 30 J, FS > 360 N). The comprehensive performance of 10 is superior to that of high-energy explosive RDX and heat-resistant explosives such as HNS and LLM-105. 10 has the potential to become a comprehensive advanced energetic material that simultaneously satisfies the requirements of high-energy and low-sensitivity explosives, heat-resistant explosives, and solid propellants. This work may give new insights into the construction and modification of a nitrogen-rich polycyclic framework and broaden the applications of fused polycyclic framework for the development of host-guest energetic materials.

Optimization of performance and sensitivity: preparation of two Ag(I)-based ECPs by using isomeric ligands

For energetic compounds, their structure determines their performance, and even minor variations in their structure can have a significant impact on their performance. The application scenarios for energetic materials are diverse, and their performance requirements vary as well. To investigate the influence of different substituent positions on the performance of primary explosives, we prepared two Ag(I)-based complexes, [Ag(2-IZCA)ClO4]n (ECPs-1) and [Ag(4-IZCA)ClO4]n (ECPs-2), using structurally isomeric ligands, 1H-imidazole-2-carbohydrazide (2-IZCA) and 1H-imidazole-4-carbohydrazide (4-IZCA). The structures were confirmed using infrared, elemental analysis, and single-crystal X-ray diffraction. Experimental results demonstrate that both ECPs exhibit good thermal stability. However, compared to ECPs-1, ECPs-2 exhibits a lower thermal initial decomposition temperature (Td = 210 °C), lower mechanical sensitivity (IS = 27 J, FS = 84 N), and more concentrated energy output. Although theoretical predictions suggest similar detonation velocities and pressures for both compounds, actual detonation performance tests indicate that ECPs-2 has stronger explosive power and initiating capability, with potential for use as a laser initiator (E = 126 mJ). The simple preparation method and inexpensive starting materials enrich the research on primary explosives.

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.

Effects of pressure on structural, electronic, optical, and mechanical properties of nitrogen-rich energetic material: 6-azido-8-nitrotetrazolo[1,5-b]pyridazine-7-amine (3at)

CONTEXT AND RESULTS

6-Azido-8-nitrotetrazolo[1,5-b]pyridazine-7-amine (3at) is a promising green energetic material, which meets the development requirements of environment-friendly explosives. By discussing the relationship between lattice parameters and pressure, it is found that the compression ratio indicates anisotropy of compressibility. And bond lengths get shorter under pressure, resulting in stronger intermolecular bonds. The N₃ group rotates under pressure. And then, the optical properties basically change regularly with the change of pressure. As the pressure increases, the absorption range widens. In the low energy interval, it shows transparency, and then with the increase of energy and pressure, it shows better optical activity. With the increase of pressure and energy, the absorption coefficient increases, representing that the optical activity becomes high. Finally, according to the analysis of mechanical properties, 3at exhibited brittle behavior at 0 GPa and 100 GPa, while at 10 to 90 GPa, the values of ν and B/G are malleable.

COMPUTATIONAL AND THEORETICAL TECHNIQUES

Based on density functional theory, the crystal parameters, electronic properties, optical properties, and elastic and mechanical properties of 3at under different pressures were studied theoretically. The GGA-PW91+OBS method was used to calculate the physical parameters under pressure, such as lattice parameters, energy band structures, dielectric function, refractive index, absorption coefficient, and elastic constants. Physical properties under (3at) pressure are predicted.

Synthesis, thermal behaviors, and energetic properties of asymmetrically substituted tetrazine-based energetic materials

1,2,4,5-tetrazine ring is a common structure for the construction of energy-containing compounds, and its high nitrogen content and large conjugation effect give it the advantage of a good balance between energy and mechanical stability as a high-nitrogen energy-containing material. However, most of the reported works about tetrazine energetic materials (EMs) are symmetrically substituted tetrazines due to their easy accessibility. A small number of reports show that asymmetrically substituted tetrazines also have good properties, such as high density and generation of enthalpy and energy. Herein, two asymmetrically substituted tetrazines and their five energetic salts were prepared and fully characterized by IR spectroscopy, NMR spectra, elemental analysis, and differential scanning calorimetry (DSC). The structure of the two compounds was further confirmed by single-crystal X-ray diffraction studies. The thermal behaviors and thermodynamic parameters were determined and calculated. In addition, the energetic properties and impact sensitivities of all the compounds were obtained to assess their application potential. The results show that compounds 2–4 and 7–9 show higher detonation velocities than TNT, and the hydrazinium salt 9 possesses the best detonation properties (D = 8,232 m s⁻¹ and p = 23.6 GPa). Except for 4 and 3, all the other compounds are insensitive, which may be applied as insensitive explosives. Noncovalent interaction analysis was further carried out, and the result shows that the strong and high proportion of hydrogen bonds may contribute to the low-impact sensitivity.

Energetic host–guest inclusion compounds: an effective design paradigm for high-energy materials

Due to the stringent requirements of performance, safety, and cost for the development of new energetic materials (EMs), the synthesis of host–guest inclusion compounds is an attractive way to fully exploit the application potential of existing EMs.

1,2-Bis(5-(trinitromethyl)-1,2,4-oxadiazol-3-yl)diazene: a water stable, high-performing green oxidizer

Trinitromethane moieties are very important for the design and development of high performing dense green oxidizers. The novel oxidizer 1,2-bis(5-(trinitromethyl)-1,2,4-oxadiazol-3-yl)diazene, 14 is stable in water in contrast to 1,2,4-oxadiazoles with other electron withdrawing substituents at the C5-position. Compound 14 is a CNO-based oxidizer with positive oxygen balance (+6.9%), moderate thermostability, and mechanical insensitivity that may find useful applications in the field of green rocket propallant.