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.

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.

Design of N-N ylide bond-based high energy density materials: a theoretical survey

The generally encountered contradiction between large energy content and stability poses great difficulty in designing nitrogen-rich high-energy-density materials. Although N-N ylide bonds have been classified as the fourth type of homonuclear N-N bonds (besides >N-N<, -N[double bond, length as m-dash]N-, and N[triple bond, length as m-dash]N), accessible energetic molecules with N-N ylide bonds have rarely been explored. In this study, 225 molecules with six types of novel structures containing N-N ylide bonds were designed using density functional theory and CBS-QB3 methods. To guide future synthesis, the effects of substitution on the thermal stability, detonation velocity, and detonation pressure of the structures were evaluated under the premise that the N-N ylide skeleton remains stable. The calculations show that the bond dissociation energy values of the N-N ylide bonds of the designed 225 structures were in the range of 61.21-437.52 kJ mol-1, except for N-1NNH2. Many of the designed structures with N-N ylide bonds exhibit high detonation properties, which are superior to those of traditional energetic compounds. This study convincingly demonstrates the feasibility of the design strategy of introducing an N-N ylide bond to develop new types of energetic materials.

Toward High-Energy and Low-Sensitivity Energetic Materials Based on a Fused [5,5,5,6]-Tetracyclic Backbone

A route for fused [5,5,5,6]-tetracyclic energetic compounds based on the facile cyclization reaction has been explored. Fused [5,5,5,6]-tetracyclic compound 4 shows a high measured density (1.924 g cm^-3), a low sensitivity (IS = 10 J, and FS = 144 N), and an excellent detonation velocity (9241 m s^-1), which are much better than those of RDX. The results indicate that compound 4 is a potential candidate as a secondary explosive and provide new insight into the construction of fused polycyclic heterocycles.

Synthesis and thermal stability of a novel polyfunctional pyridine-based derivative featuring amino, nitro, and guanidine groups

A new pyridine derivative 1-(4-amino-3,5-dinitropyridin-2-yl) guanidine (ADG) was synthesized through nitration and substitution reaction using 4-amino-2-cholopyridine as raw material. Its structure was characterized by spectroscopy, nuclear magnetic resonance, and mass spectrometry. The crystal of ADG is monoclinic, space group Pbca with crystal parameters of a = 7.23 Å, b = 14.56 Å, c = 17.93 Å, α = β= γ= 90 Å, V = 1911 Å3, μ = 0.143 mm−1, and Z = 8. This new molecule exhibits moderate density ( ρ= 1.677 g cm−3), good thermal stability with a decomposition temperature of 217 °C, and moderate detonation property with detonation pressure of 20.83 GPa and detonation velocity of 7.00 km s−1. The Hirshfeld surface analysis revealed a significant contribution of weak interactions to the packing forces for molecules. Electron localization function analysis indicates that there is substantial electron localization in regions of C–H, N–H, and N–O covalent bond sites.

Molecular design and selection of 1,2,5-oxadiazole derivatives as high-energy-density materials

A family of 1,2,5-oxadiazole-based energetic compounds were designed and their properties were investigated fully by density functional theory.