Nitroaminofurazans with Azo and Azoxy Linkages: A Comparative Study of Structural, Electronic, Physicochemical, and Energetic Properties

The structural, electronic, and physicochemical properties of 4,4′-bis­(nitramino)­azofurazan and 4,4′-bis­(nitramino)­azoxyfurazan as high-energy density materials were compared. In addition, a new family of nitrogen-rich energetic salts based on these two nitroaminofurazans were synthesized and fully characterized. On the basis of experimental evidence and theoretical calculations, 4,4′-bis­(nitramino)­azoxyfurazan and its ionic derivatives were found to exhibit higher detonation velocities and pressures, and higher densities than their azofurazan analogues which supports the added value of introduction of the N-oxide moiety into energetic materials. The solid state features for the two nitroaminofurazans were studied in detail by X-ray diffraction and noncovalent interaction index which identify additional hydrogen-bonding and extensive edge-to-face π–π stacking interactions arising from the presence of the azoxy N-oxide

3,3′-Dinitroamino-4,4′-azoxyfurazan and Its Derivatives: An Assembly of Diverse N–O Building Blocks for High-Performance Energetic Materials

On the basis of a design strategy that results in the assembly of diverse N–O building blocks leading to energetic materials, 3,3′-dinitroamino-4,4′-azoxyfurazan and its nitrogen-rich salts were obtained and fully characterized via spectral and elemental analyses. Oxone (potassium peroxomonosulfate) is an efficient oxidizing agent for introducing the azoxy <i>N</i>-oxide functionality into the furazan backbone, giving a straightforward and low-cost synthetic route. On the basis of heats of formation calculated with Gaussian 03 and combined with experimentally determined densities, energetic properties (detonation velocity, pressure and specific impulse) were obtained using the EXPLO v6.01 program. These new molecules exhibit high density, moderate to good thermal stability, acceptable impact and friction sensitivities, and excellent detonation properties, which suggest potential applications as energetic materials. Interestingly, 3,3′-dinitroamino-4,4′-azoxyfurazan (<b>4</b>) has the highest calculated crystal density of 2.02 g cm^–3 at 173 K (gas pycnometer measured density is 1.96 g cm^–3 at 298 K) for <i>N</i>-oxide energetic compounds yet reported. Another promising compound is the hydroxylammonium salt (<b>6</b>), which has four different kinds of N–O moieties and a detonation performance superior to those of 1,3,5,7-tetranitrotetraazacyclooctane (HMX), and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclododecane (CL-20). Furthermore, computational results, viz., NBO charges and ESP, also support the superior qualities of the newly prepared compounds and the design strategy

Molecular Design and Property Prediction of High Density Polynitro[3.3.3]-Propellane-Derivatized Frameworks as Potential High Explosives

Research in energetic materials is now heavily focused on the design and synthesis of novel insensitive high explosives (IHEs) for specialized applications. As an effective and time-saving tool for screening potential explosive structures, computer simulation has been widely used for the prediction of detonation properties of energetic molecules with relatively high precision. In this work, a series of new polynitrotetraoxopentaaza[3.3.3]-propellane molecules with tricyclic structures were designed. Their properties as potential high explosives including density, heats of formation, detonation properties, impact sensitivity, etc., have been extensively evaluated using volume-based thermodynamic calculations and density functional theory (DFT).These new energetic molecules exhibit high densities of >1.82 g cm^–3, in which <b>1</b> gives the highest density of 2.04 g cm^–3. Moreover, most new materials show good detonation properties and acceptable impact sensitivities, in which <b>5</b> displays much higher detonation velocity (9482 m s^–1) and pressure (43.9 GPa) than HMX and has a <i>h</i>₅₀ value of 11 cm. These results are expected to facilitate the experimental synthesis of new-generation nitramine-based high explosives

Enforced Layer-by-Layer Stacking of Energetic Salts towards High-Performance Insensitive Energetic Materials

Development of modern high-performance insensitive energetic materials is significant because of the increasing demands for both military and civilian applications. Here we propose a rapid and facile strategy called the “layer hydrogen bonding pairing approach” to organize energetic molecules via layer-by-layer stacking, which grants access to tunable energetic materials with targeted properties. Using this strategy, an unusual energetic salt, hydroxylammonium 4-amino-furazan-3-yl-tetrazol-1-olate, with good detonation performances and excellent sensitivities, was designed, synthesized, and fully characterized. In addition, the expected unique layer-by-layer structure with a high crystal packing coefficient was confirmed by single-crystal X-ray crystallography. Calculations indicate that the layer-stacking structure of this material can absorb the mechanical stimuli-induced kinetic energy by converting it to layer sliding, which results in low sensitivity

Energetic Salts with π‑Stacking and Hydrogen-Bonding Interactions Lead the Way to Future Energetic Materials

Among energetic materials, there are two significant challenges facing researchers: 1) to develop ionic CHNO explosives with higher densities than their parent nonionic molecules and (2) to achieve a fine balance between high detonation performance and low sensitivity. We report a surprising energetic salt, hydroxylammonium 3-dinitromethanide-1,2,4-triazolone, that exhibits exceptional properties, viz., higher density, superior detonation performance, and improved thermal, impact, and friction stabilities, then those of its precursor, 3-dinitromethyl-1,2,4-triazolone. The solid-state structure features of the new energetic salt were investigated with X-ray diffraction which showed π-stacking and hydrogen-bonding interactions that contribute to closer packing and higher density. According to the experimental results and theoretical analysis, the newly designed energetic salt also gives rise to a workable compromise in high detonation properties and desirable stabilities. These findings will enhance the future prospects for rational energetic materials design and commence a new chapter in this field

Energetic Salts with π‑Stacking and Hydrogen-Bonding Interactions Lead the Way to Future Energetic Materials

Among energetic materials, there are two significant challenges facing researchers: 1) to develop ionic CHNO explosives with higher densities than their parent nonionic molecules and (2) to achieve a fine balance between high detonation performance and low sensitivity. We report a surprising energetic salt, hydroxylammonium 3-dinitromethanide-1,2,4-triazolone, that exhibits exceptional properties, viz., higher density, superior detonation performance, and improved thermal, impact, and friction stabilities, then those of its precursor, 3-dinitromethyl-1,2,4-triazolone. The solid-state structure features of the new energetic salt were investigated with X-ray diffraction which showed π-stacking and hydrogen-bonding interactions that contribute to closer packing and higher density. According to the experimental results and theoretical analysis, the newly designed energetic salt also gives rise to a workable compromise in high detonation properties and desirable stabilities. These findings will enhance the future prospects for rational energetic materials design and commence a new chapter in this field

Taming of 3,4-Di(nitramino)furazan

Highly energetic 3,4-di­(nitramino)­furazan (<b>1</b>, DNAF) was synthesized and confirmed structurally by using single-crystal X-ray diffraction. Its highly sensitive nature can be attributed to the shortage of hydrogen-bonding interactions and an interactive nitro chain in the crystal structure. In order to stabilize this structure, a series of corresponding nitrogen-rich salts (<b>3</b>–<b>10</b>) has been prepared and fully characterized. Among these energetic materials, dihydrazinium 3,4-dinitraminofurazanate (<b>5</b>) exhibits a very promising detonation performance (<i>νD</i> = 9849 m s^–1; <i>P</i> = 40.9 GPa) and is one of the most powerful explosives to date. To ensure the practical applications of <b>5</b>, rather than preparing the salts of <b>1</b> through acid-base reactions, an alternative route through the nitration of <i>N</i>-ethoxycarbonyl-protected 3,4-diaminofurazan and aqueous alkaline workup was developed

Micellization/Demicellization Self-Assembly Change of ABA Triblock Copolymers Induced by a Photoswitchable Ionic Liquid with a Small Molecular Trigger

To date, the demonstration of photoinduced micellization/demicellization of ABA-type triblock copolymers in ionic liquids (ILs) has been based on photoresponsive polymers. Herein, rather than the photoresponsive polymers, a small molecular trigger, an azobenzene-based IL, is employed for the first time to achieve a photocontrollable micellization. ABA-type triblock copolymers were synthesized in which the A block (either poly­(2-phenylethyl methacrylate) or poly­(benzyl methacrylate)) has a lower critical solution temperature (LCST) in imidazolium-based ILs, while the B block (poly­(methyl methacrylate)) is compatible with ILs; these triblock copolymers are denoted as PMP and BMB, respectively. Solutions of the azobenzene-based IL containing the copolymers exhibited different micellization temperatures in the dark and under UV irradiation. For PMP, at a temperature between the two micellization temperatures, UV irradiation induced a “unimer-to-micelle” transition, while for BMB, UV irradiation induced a “micelle-to-unimer” transition. The main difference in the chemical structures of the copolymers is the number of methylene spacers (1 or 2) between the aromatic ring and ester of the A blocks. NMR analysis showed that the chemical shifts of the ILs were shifted in opposite directions on UV irradiation, indicating that azobenzene isomerization can affect the solvation interactions between the polymers and the ILs

New Roles for 1,1-Diamino-2,2-dinitroethene (FOX-7): Halogenated FOX‑7 and Azo-bis(diahaloFOX) as Energetic Materials and Oxidizers

The syntheses and full characterization of two new halogenated 1,1-diamino-2,2-dinitroethene (FOX-7) compounds and three halogenated azo-bridged FOX-7 derivatives are described. Some of these new structures demonstrate properties that approach those of the commonly used secondary explosive RDX (cyclo-1,3,5-trimethylene-2,4,6-trinitramine). All the compounds display hypergolic properties with common hydrazine-based fuels and primary aliphatic amines (ignition delay times of 2–53 ms). This is a new role that has yet to be reported for FOX-7 and its derivatives. Their physical and energetic properties have been investigated. All compounds were characterized by single-crystal X-ray crystallography, elemental analysis, infrared spectra, and differential scanning calorimetry. These new molecules as energetic materials and hypergolic oxidizers contribute to the expansion of the chemistry of FOX-7

New Roles for 1,1-Diamino-2,2-dinitroethene (FOX-7): Halogenated FOX‑7 and Azo-bis(diahaloFOX) as Energetic Materials and Oxidizers

The syntheses and full characterization of two new halogenated 1,1-diamino-2,2-dinitroethene (FOX-7) compounds and three halogenated azo-bridged FOX-7 derivatives are described. Some of these new structures demonstrate properties that approach those of the commonly used secondary explosive RDX (cyclo-1,3,5-trimethylene-2,4,6-trinitramine). All the compounds display hypergolic properties with common hydrazine-based fuels and primary aliphatic amines (ignition delay times of 2–53 ms). This is a new role that has yet to be reported for FOX-7 and its derivatives. Their physical and energetic properties have been investigated. All compounds were characterized by single-crystal X-ray crystallography, elemental analysis, infrared spectra, and differential scanning calorimetry. These new molecules as energetic materials and hypergolic oxidizers contribute to the expansion of the chemistry of FOX-7