Conjugated Energetic Salts Based on Fused Rings: Insensitive and Highly Dense Materials

A Reversible Nitroamino-Based Switch Modulates Hydrogen-Bonding Networks in Energetic Materials

The regulation of hydrogen-bonding networks in molecular switches is critical for adaptive materials. However, most of the reported molecular switches are not capable of modulating hydrogen-bonding networks in energetic materials, limiting high-demand applications in explosives. In this work, the first high-energy nitroamino-based molecular switch is reported. It can control the complex hydrogen-bonding systems of energetic materials by reversible cycling for property modulation. Through alkali-acid stimulation, the nitroamino-based switch undergoes dynamic transitions, which reconfigure H-bond networks and separate twin crystals (in x-ray verification). Supported by crystallography and theoretical modeling (e.g., the density of states), this switching mechanism modulates molecular planarity (Δθ > 60°) and optimizes the energy-stability balance, obtaining a compound 6-β with comprehensive properties comparable to classical explosives (e.g., RDX and HMX). By linking hydrogen-bonding engineering and energetic materials science through the nitroamino-based molecular switch, it facilitates superior energetic compounds that can be applied to defense equipment. In addition, our work establishes the nitroamino-based switch as a generalized tool for molecular engineering, bridging dynamic hydrogen-bonding control and self-assembly materials design.

Intramolecular Cyclization and Energetic Group Modifications for Thermally Stable and Low-Sensitivity Monocyclic Dinitromethyl Zwitterionic Pyrazoles

Zwitterionic energetic materials offer a unique combination of high performance and stability, yet their synthesis and stability enhancement remain key challenges. In this study, we report the synthesis of a highly stable (dinitromethyl-functionalized zwitterionic compound, 1-(amino(iminio)methyl)-4,5-dihydro-1H-pyrazol-5-yl)dinitromethanide (4), with a thermal decomposition temperature of 215 °C, surpassing that of most previously reported energetic monocyclic zwitterions (Td < 150 °C). This compound was synthesized via intramolecular cyclization of a trinitromethyl-functionalized hydrazone precursor. Further chemical modifications, including nitration and fluorination, enabled zwitterion-to-zwitterion transformations, resulting in the formation of nitramines 10 and 12. Additionally, the perchlorate salt (8) of 4 was synthesized, along with ammonium (13), guanidinium (14), and potassium (15) salts derived from 10, all retaining zwitterionic properties. Physicochemical evaluations reveal that zwitterion 12 exhibits excellent thermal stability (Td = 181 °C) and an optimal balance between high energy output (detonation velocity: 8329 m s-1, detonation pressure: 29.4 GPa) and reduced sensitivity (impact sensitivity: 35 J, friction sensitivity: 320 N). Notably, potassium salt 15 demonstrates superior thermal stability (Td = 233 °C), exceeding that of RDX. These results expand the design framework for energetic zwitterions and contribute to the development of high-energy, low-sensitivity energetic materials.

Too fast and too furious: thermoanalytical and quantum chemical study of the thermal stability of 4,4'-dinitro-3,3'-diazenofuroxan

Novel energetic materials (EM) often combine two intrinsically counter trends, viz., a high energy density and mediocre safety parameters, like thermal stability and sensitivity toward mechanical stimuli. A rational design of promising EMs requires a proper understanding of their thermal stability at both macroscopic and molecular levels. In the present contribution, we studied in detail the thermal stability of 4,4'-dinitro-3,3'-diazenofuroxan (DDF), an ultrahigh-performance energetic material with a reliable experimental detonation velocity being very close to 10 km s-1. To this end, we employed a set of complementary thermoanalytical (DSC and TGA in the solid state along with advanced thermokinetic models, optical microscopy, and gas products detection) and theoretical techniques (DLPNO-CCSD(T) quantum chemical calculations). According to the DSC measurements, the solid-state thermolysis of DDF turned out to be a complex three-step process. The decomposition commences at ∼85 °C and the most intense heat release occurs at ∼130 °C depending on the heating rate. In order to properly describe the kinetics of DDF thermolysis beyond the simple Kissinger and Friedman methods, we applied a "top-down" kinetic approach resulting in the formal model comprised of three independent stages. A flexible Kolmogorov-Johnson-Mehl-Avrami-Erofeev equation was applied for the first decomposition stage along with the extended Prout-Tompkins equation for the second and third processes, respectively. The formal exponent in the former equation turned out to be close to a second order, thus suggesting a two-dimensional nuclei-growth model for the first stage. We rationalized this fact with the aid of optical microscopy experiments tracking the changes in the morphology of a solid DDF sample. Then, we complemented the formal macroscopic kinetics with some mechanistic patterns of the primary decomposition channels from quantum chemical calculations. The three reactions involving all important moieties of the DDF molecule turned out to compete very closely: viz., the nitro-nitrite isomerization, radical C(heterocycle)-N(bridge) bond scission and molecular decomposition comprised of the consequent N-O and C-C bond scissions in a furoxane ring. The DLPNO-CCSD(T) activation barriers of all these reactions were close to ∼230 kJ mol-1. Most importantly, the calculations provide some mechanistic details missing in thermoanalytical experiment and formal kinetic models. Apart from this, we also determined a mutually consistent set of thermochemical and phase change data for DDF.

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.

Automated ECL Aptasensing Platform from an Intrarticular Radical Annihilation Route for Distinguishing Glioma Stages

Nowadays, continuous efforts have been devoted to designing stable and high-efficiency electrochemiluminescence (ECL) emitters as alternatives for tris(2,2'-bipyridine)-ruthenium(II) (Ru(bpy)32+) in medical research. Herein, a novel ECL emitter was obtained by coordinating crystalline covalent triazinyl frameworks (cCTFs) with Ru2+ (termed Ru-cCTFs), which exhibited strong ECL emission by the ligand to metal charge transfer (LMCT) route. After its integration with 4-mercaptopyridine (SH-Py), the resultant SH-Py-Ru-cCTFs achieved 2.3-fold enhancement in the ECL efficiency by employing Ru(bpy)32+ as a standard, which involved a dynamic "intrarticular radical annihilation" ECL pathway. On such foundation, an automated ECL (A-ECL) aptasensor was constructed with an "on-off-on" model and magnetic separation upon linkage of the SH-Py-Ru-cCTFs with streptavidin (SA) magnetic beads (MBs). This automatic assay of miRNA-182 showed a wider linear range from 1.0 to 100.0 fM with a correlation coefficient (R2) of 0.994, a lower limit of detection (LOD) down to 0.28 fM, and faster operation within 41 min. Impressively, this bioassay facilely distinguished the stages of glioma disease from clinical blood samples with high accuracy. Hence, this research sheds light on how to develop advanced ECL luminophores and an automatic method, showing substantial insights into pathogenesis research of gliomas.

Large-Scale Synthesis of High-Purity Isoguanosine and Resolution of its Crystal Structure by Microcrystal Electron Diffraction

Isoguanosine (isoG) is a natural structural isomer of guanosine (G) with significant potential for applications in ionophores, genetics, gel formation, and cancer therapy. However, the cost of commercially available isoG on a gram scale is relatively high. To date, a detailed method for the large-scale preparation of high-purity isoG has not been reported. This study presented a simple and convenient approach for the large-scale synthesis of isoG through the diazotization of 2,6-diaminopurine riboside with sodium nitrite and acetic acid at room temperature. Further, this method could synthesize isoG derivatives (2'-fluoro-isoguanosine (1) and 2'-deoxy-isoguanosine (2)) from 2,6-diaminopurine nucleoside derivatives using diazotization. The structural information of natural and modified nucleosides is crucial for the modification and substitution of DNA/RNA. This study obtained the single-crystal structure of isoG for the first time and analyzed it in detail using microcrystal electron diffraction. The three-dimensional supramolecular structure of isoG adopted similarly base-pair motifs from π-π stacking interaction of diverse layers, intramolecular hydrogen bonding, and distinct hydrogen bonding interactions from sugar residues. This study has contributed to further isoG modification and its applications in medicinal chemistry and 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.

An Intramolecular-Lock Facilitates Planar Tricyclic Fused Energetic Compounds

Exploiting novel fused cyclic frameworks through simple and efficient methods has provided a blueprint for developing advanced explosives. In this study, six new [5,6,5]-tricyclic fused energetic compounds (I-VI) were synthesized through an intramolecular cyclization strategy involving a C-NH2 directed cyclization reaction. The work not only boosts the development of fused cyclic energetic compounds but also highlights their potential applications as secondary or heat-resistant explosives.

Host-Guest Technique for Designing Highly Energetic Compounds with the Nitroamino Group

A new energetic material, 2-azido-4,7-nitroamino-1H-imidazo[4,5-d]pyridazine (ANIP) with a highly sensitive azido group and its host-guest compounds (ANIP/H2O and ANIP/H2O2), and energetic salts were obtained. With the guest and protons in host molecules, an abundant hydrogen bond system can be formed. This results in high crystal density and good sensitivity, which suggests that the host-guest strategy is a promising way to balance the contradiction between energy and sensitivity and provides a new path to obtain a new generation of high energetic materials.

Design and Synthesis of Bistetrazole-Based Energetic Salts Bearing the Nitrogen-Rich Fused Ring

A series of bistetrazole-based energetic salts bearing a nitrogen-rich fused ring were designed and synthesized. Among them, compounds 4-10 showed good detonation properties and excellent thermostability. By treating nitrogen-rich fused ring 3 with concentrated hydrochloric acid, a new type of Dimroth rearrangement was observed that afforded compound 12 efficiently. This new transformation herein constitutes a valuable addition to the Dimroth rearrangement.

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.

Highly Selective Nitroamino Isomerization Guided by Proton Transport Dynamics: Full-Nitroamino Imidazole[4,5-d]pyridazine Fused-Ring System

Due to the advantage of the hydrogen bond system formed by nitroamino isomerization, by the calculations of hydrogen transfer in reported nitroamino explosives, the proton transport dynamics was first proposed to predict the nitroamino isomerization of energetic materials. With the calculated results of zero-point energy, the full-nitroamino fused energetic materials, 2,4-nitroamino-7-nitroimino-1,5-dihydro-4H-imidazolo[4,5-d]pyridazine (FNPI-1) and 2,2',7,7'-tetranitromino-4,4'-azo-imidazolo[4,5-d]pyridazine (FNPI-2) were designed and successfully synthesized. The highly selective nitroamino isomerization of neutral compound FNPI-1 is shown by X-ray diffraction. After the hydrogen transfer occurs, the intermolecular hydrogen bonds will greatly promote tight stacking, which enhances the density and thus a series of comprehensive properties of energetic materials. The theoretical calculations of zero-point energy explain perfectly the selectivity of hydrogen transfer between the nitroamino groups and the fused-ring skeleton for FNPI-1. The hydrogen atom transfer and selective isomerization of nitroamino energetic materials can be accurately predicted following proton transport dynamics, which provides computational bases and new ideas for the efficient design of fully nitroamino-based explosives.

Coordinative Combination of Nitroamine and Gem-Dinitromethyl with Fused Ring for Enhanced Oxygen Balances and Detonation Properties

Oxygen balance and heat of formation are closely related to the nitrogen and oxygen content in a molecule and have a significant effect on the detonation performance of energetic materials. Here a new family of 1,2,4-triazolo [4,3-b][1,2,4,5]-tetrazine containing gem-dinitromethyl and nitroamine with high nitrogen-oxygen content was synthesized and characterized. Moreover, the structure of the guanidine salt (3) and TATOT salt (4) were confirmed by single-crystal X-ray diffraction. The nitrogen and oxygen content of ammonium salt 2 reached 82.5%, with a high density (1.805 g cm^-3) and high detonation properties (D = 8900 m s^-1; P = 32.4 GPa), which were similar to those of RDX.

Mechanism, Kinetics and Thermodynamics of Decomposition for High Energy Derivatives of [1,2,4]Triazolo[4,3-b][1,2,4,5]tetrazine

This paper presents the data of research studies on the mechanisms, kinetics and thermodynamics of decomposition of three high-energy compounds: [1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine-3,6-diamine (TTDA), 3-amino-6-hydrazino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine (TTGA) and 3,6-dinitroamino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine (DNTT). The points of change of the reaction mechanisms under thermal effects with different intensities from 0.1 to 2000 s⁻¹ have been established. The values of activation and induction energies for the limiting stages of decomposition have been obtained. The formation of nanostructured carbon nitride (α-C₃N₄) in condensed decomposition products, cyanogen (C₂N₂) and hydrogen cyanide (HCN) in gaseous products have been shown. Concentration-energy diagrams for the reaction products have been compiled. The parameters of heat resistance and thermal safety proved to be: 349.5 °C and 358.2 °C for TTDA; 190.3 °C and 198.0 °C for TTGA; 113.4 °C and 114.1 °C for DNTT. The energy and thermodynamic properties have also been estimated. This work found the activation energy of the decomposition process to be 129.0 kJ/mol for TTDA, 212.2 kJ/mol for TTGA and 292.2 kJ/mol for DNTT. The average induction energy of the catalytic process (Ecat) for TTGA was established to be 21 kJ/mol, and for DNTT-1500–1700 kJ/mol. The induction energy of the inhibition process (Eing) of TTDA was estimated to be 800–1400 kJ/mol.

Energetic Gem-dinitro Salts with Improved Thermal Stability by Incorporating with A Fused Building Block

Thermal stability is one of the most significant properties for the safety of energetic materials, finding a stable skeleton with suitable energetic groups is always a primary test. In this work, an unusual aminohydrazone cyclization strategy was used in the synthesis of a new series of gem-dinitro 1,2,4-triazolo[4,3-b][1,2,4,5]-tetrazine compounds with desirable thermal stability (≥197 °C). All of the new compounds were fully characterized by infrared (IR), NMR, differential scanning calorimetry, single crystal X-ray diffraction, and elemental analysis. The decomposition temperature of potassium salt 2 is 288 °C, reaching the level of HMX. All of these performances have demonstrated the effective synthesis strategy for innovatively combining geminal dinitro groups with fused rings.

Accelerated discovery of thermostable high-energy materials with intramolecular donor-acceptor building blocks

A domain-related data search promoted triazolotriazine-fused energetic scaffold filtration with combinatorial design to alleviate the lack of thermostable high-energy materials; 16 candidates were discovered that may show promising energy and safety performance, as well as excellent thermal stability. Novel fused triazolo-1,2,4-triazine energetic material 7-nitro-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c][1,2,4]triazin-4-amine-2-oxide (Candidate No. 4) with excellent thermal stability, high energy performance and low sensitivity was developed successfully by using a facile N-oxide synthetic method. Our findings may be applicable to a wider range of materials and prove equally powerful for searching for other high-performing energetic materials.

Tuning the Energetic Performance of CL-20 by Surface Modification Using Tannic Acid and Energetic Coordination Polymers

The energetic performance of hexanitrohexaazaisowurtzitane (CL-20) was modulated with two energetic coordination polymers (ECPs), [Cu(ANQ)₂(NO₃)₂] and [Ni(CHZ)₃](ClO₄)₂, in this study by a two-step method. First, tannic acid polymerized in situ on the surface of CL-20 crystals. Then, [Cu(ANQ)₂(NO₃)₂] and [Ni(CHZ)₃](ClO₄)₂ were hydrothermally formed on the surface of CL-20/TA, respectively. Explosion performance tests show that the impact sensitivity of the coated structure CL-20/TA/[Cu(ANQ)₂(NO₃)₂] is 58% less than that of CL-20 with no energy decrease. On the other hand, CL-20/TA/[Ni(CHZ)₃](ClO₄)₂ can be initiated by a low laser energy of 107.3 mJ (Nd:YAG, 1064 nm, 6.5 ns pulse width), whereas CL-20 cannot be initiated by even 4000 mJ laser energy. This study shows that it is feasible to modify the performance of CL-20 by introducing energetic CPs with certain properties, like high energy insensitive, laser-sensitive, etc., which could be a prospective method for designing high energy insensitive energetic materials in the future.

Full-nitro-nitroamino cooperative action: Climbing the energy peak of benzenes with enhanced chemical stability

More nitro groups accord benzenes with higher energy but lower chemical stability. Hexanitrobenzene (HNB) with a fully nitrated structure has stood as the energy peak of organic explosives since 1966, but it is very unstable and even decomposes in moist air. To increase the energy limit and strike a balance between energy and chemical stability, we propose an interval full-nitro-nitroamino cooperative strategy to present a new fully nitrated benzene, 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB), which was synthesized using an acylation-activation-nitration method. TNTNB exhibits a high density (d: 1.995 g cm^-3 at 173 K, 1.964 g cm^-3 at 298 K) and excellent heat of detonation (Q: 7179 kJ kg^-1), which significantly exceed those of HNB (Q: 6993 kJ kg^-1) and the state-of-the-art explosive CL-20 (Q: 6534 kJ kg^-1); thus, TNTNB represents the new energy peak for organic explosives. Compared to HNB, TNTNB also exhibits enhanced chemical stability in water, acids, and bases.

Cobalt Metal-Organic Frameworks with Aggregation-Induced Emission Characteristics for Fluorometric/Colorimetric Dual Channel Detection of Nitrogen-Rich Heterocyclic Compounds

Nitrogen-rich heterocyclic compounds (NRHCs) are an emerging type of explosive, and their quantification is important in national security inspection and environmental monitoring. Up until now, designing an efficient NRHCs sensing strategy was still in the early stages. Herein, a new metal-organic framework (MOF) with aggregation-induced emission (AIE) characteristics is synthesized with fluorometric/colorimetric responses for rapid and selective detection of NRHCs. The nonemissive probe is designed with tetraphenylethylene derivative as the linker and Co as the node, quencher, and color-changing agent. Cobalt AIE-MOF exhibits a turn-on emission enhancement due to the competitive coordination substitution between NRHCs and the scaffold as well as the following AIE process of the liberative linkers. Meanwhile, the color appearance of the probe changes from blue to yellow based on the dissociation of the original Co coordinating system. Using this dual-mode probe, single- and dual-ring NRHCs are successfully detected from 5 μM to 7.5 mM within 25 s. The cobalt AIE-MOF exhibits excellent selectivity of NRHCs against a variety of interferences, providing a promising tool for designing a multichannel detection strategy.

Theoretical insight into density and stability differences of RDX, HMX and CL-20

In this work, density and stability differences of RDX, HMX and CL-20 are exploited and addressed through static calculations from views of monomolecular parameters, intermolecular interactions (by the proposed BEC method) and crystal packing.

Host–guest energetic materials: a promising strategy of incorporating small insensitive molecule into the lattice cavities of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane to enhance the safety on the premise of maintaining the excellent energy density

A novel HNIW-MA host–guest explosive was constructed by embedding the mall molecules into the lattice cavities of HNIW, and it enhances the safety on the premise of maintaining its energy density.

Smart Host-Guest Energetic Material Constructed by Stabilizing Energetic Fuel Hydroxylamine in Lattice Cavity of 2,4,6,8,10,12-Hexanitrohexaazaisowurtzitane Significantly Enhanced the Detonation, Safety, Propulsion, and Combustion Performances

The host-guest inclusion strategy has become a promising method for developing novel high-energy density materials (HEDMs). The selection of functional guest molecules was a strategic project, as it can not only enhance the detonation performance of host explosives but can also modify some of their suboptimal performances. Here, to improve the propulsion and combustion performances of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW), a novel energetic-energetic host-guest inclusion explosive was obtained by incorporating energetic rocket fuel, hydroxylamine (HA), into the lattice cavities of HNIW. Based on their perfect space matching, the crystallographic density of HNIW-HA was determined to be 2.00 g/cm³ at 296 K, which has reached the gold standard regarding the density of HEDMs. HNIW-HA also showed higher thermal stability (T_d = 245.9 °C) and safety (H₅₀ = 16.8 cm) and superior detonation velocity (D_V = 9674 m/s) than the ε-HNIW. Additionally, because of the excellent combustion performance of HA, HNIW-HA possessed higher propulsion performances, including combustion speed (S_C = 39.5 mg/s), combustion heat (Q_C = 8661 J/g), and specific impulse (I_sp = 276.4 s), than ε-HNIW. Thus, the host-guest inclusion strategy has potential to surpass the limitations of energy density and suboptimal performances of single explosives and become a strategy for developing multipurpose intermolecular explosives.

Multisubstituted Imidazolo[4,5-d]pyridazine Fused Ring System Resulting from Nitroamine-Nitroimine Tautomerism

A series of multisubstituted imidazolo[4,5-d]pyridazine fused ring compounds was synthesized in which nitroamine-nitroimine tautomerism is exhibited. The electrostatic potential indicates that the nitroimino group has the lowest negative value, second only to the nitro group, culminating in the nitroamino area, which has the highest positive value. In addition, a strong hydrogen bond system which arises from the newly formed nitroimino tautomer suggests that the nitroimino is more stable than its nitroamino analogue.

Design and properties of a new family of wing-like and propeller-like multi-tetrazole molecules as potential high-energy density compounds

Density functional theory (DFT) methods were employed to design a new family of wing-like and propeller-like multi-tetrazole molecules based on the combination of N-center multi-tetrazole and various energetic groups. The optimized geometry, electronic properties, and thermodynamics were calculated for investigating the molecular stability and chemical reactivity. Their energetic parameters including density, heats of formation, detonation properties, and impact sensitivity were extensively evaluated, and the effects of energetic groups were investigated as well. These newly designed wing-like and propeller-like multi-tetrazole molecules exhibit acceptable oxygen balance, moderate impact sensitivities, high density, excellent heats of formation, and good detonation performance. Especially, B3, B4, B5, and B6 are very helpful for enhancing their detonation performance (D ≥ 9500 m·s^-1, P ≥ 41 GPa) are promising candidates for new environmentally friendly HEDMs.

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.

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

The development of energetic materials with high energy and low sensitivity has attracted immense interests due to their widespread applications in aerospace technology and national defense. In this work, a promising self-assembly strategy was developed to prepare three high-energy materials (1-3) through the introduction of oxidant molecules into the crystal voids of the parent materials. The structures of these new materials were comprehensively examined by infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffraction. In these materials, three unique layer structures with hcb, sql, and interrupted sql topologies were observed, which were formed by the fused-ring-based energetic components. Windows with hexagonal, square, and rectangular structures were observed within these layer structures, which were occupied by H₂O₂, NO₃^-, and ClO₄^-, respectively. Oxidant molecules interacted with parent molecules via hydrogen bonds to form crystal structures of these materials. Moreover, the energetic property of these materials was estimated by computing methods. The calculation results revealed that these self-assembly materials exhibit excellent energetic properties. The highest energetic performance was observed for compound 3. The detonation velocity, detonation pressure, and specific impulse values were up to 9339 m·s^-1, 42.5 GPa, and 308 s, respectively, which were greater than those of HMX. Furthermore, these materials exhibited good sensitivity, which was closely related to their unique crystal structures. The high performance of these materials indicated that the self-assembly strategy should be a promising method for the development of novel energetic materials.

Investigation of electronic and vibrational properties of dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate under high-pressure conditions

Dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50), a newly found ionic energetic material with excellent performance and low sensitivity, has attracted much attention. In this work, the high-pressure response of vibrational properties in conjunction with structural and electronic properties are investigated to understand its stability under hydrostatic and uniaxial compressions. From our calculations, the band gap of TKX-50 broadens up to 0.5 GPa, then gradually shrinks at 0.5-10 GPa due to the unusual evolution of the a-axis. Analysis of the Mulliken population implies that the pressure dependence of the band gap is weak due to the inhibition of charge transfer under hydrostatic pressure. The Raman spectra of TKX-50 under uniaxial and hydrostatic compressions were simulated. The results suggest that TKX-50 undergoes multiple possible structural transformations under uniaxial compressions through discontinuous modifications of bond lengths in the cation moieties, whereas it maintain structural stability up to 10 GPa under hydrostatic conditions. Overall, the investigation of the electronic properties and uniaxial compression responses increases knowledge of TKX-50 under high-pressure conditions.

Boosting intermolecular interactions of fused cyclic explosives: the way to thermostable and insensitive energetic materials with high density

Improving the packing efficiency of explosives by strong intermolecular interactions can acquire high density while avoiding the expense of stability.

Strong intermolecular interaction induced methylene-bridged asymmetric heterocyclic explosives

Methylene-bridged asymmetric heterocyclic explosives were designed and synthesized to attempt the possibility of realizing energetic materials with high-energy and adequate sensitivity.

Modern trends in “Green” primary energetic materials

The evergrowing demand for cleaner, high-performing energetic materials (EMs) has led to a quest for replacement of currently used toxic metal-based traditional energetic compounds such as lead azide and lead styphnate.

Hydrogen bond system generated by nitroamino rearrangement: new character for designing next generation energetic materials

Hydrogen bond systems stabilize molecules and shorten intermolecular distances to give higher density and lower sensitivity.

Methyl sydnone imine and its energetic salts

First investigation of this new energetic cation, which may greatly expand the range of possible energetic salts available.

Nitro-, Cyano-, and Methylfuroxans, and Their Bis-Derivatives: From Green Primary to Melt-Cast Explosives

In the present work, we studied in detail the thermochemistry, thermal stability, mechanical sensitivity, and detonation performance for 20 nitro-, cyano-, and methyl derivatives of 1,2,5-oxadiazole-2-oxide (furoxan), along with their bis-derivatives. For all species studied, we also determined the reliable values of the gas-phase formation enthalpies using highly accurate multilevel procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach and isodesmic reactions with the domain-based local pair natural orbital (DLPNO) modifications of the coupled-cluster techniques. Apart from this, we proposed reliable benchmark values of the formation enthalpies of furoxan and a number of its (azo)bis-derivatives. Additionally, we reported the previously unknown crystal structure of 3-cyano-4-nitrofuroxan. Among the monocyclic compounds, 3-nitro-4-cyclopropyl and dicyano derivatives of furoxan outperformed trinitrotoluene, a benchmark melt-cast explosive, exhibited decent thermal stability (decomposition temperature >200 °C) and insensitivity to mechanical stimuli while having notable volatility and low melting points. In turn, 4,4′-azobis-dicarbamoyl furoxan is proposed as a substitute of pentaerythritol tetranitrate, a benchmark brisant high explosive. Finally, the application prospects of 3,3′-azobis-dinitro furoxan, one of the most powerful energetic materials synthesized up to date, are limited due to the tremendously high mechanical sensitivity of this compound. Overall, the investigated derivatives of furoxan comprise multipurpose green energetic materials, including primary, secondary, melt-cast, low-sensitive explosives, and an energetic liquid.

Polynitro-acetone, dimethyl ether, and dimethylamine: a series of potential green and powerful oxidants for propellants

With the purpose of searching novel, green and energetic oxidants, polynitro-acetone, polynitro-dimethyl ether, and polynitro-dimethylamine are designed as potential powerful oxidants and energetic materials in this work. Their optimized molecular geometries and electronic structures are calculated using density functional theory at m062x/6-311G++(d,p) level. Based on these results, heat of formation (HOF), detonation energy (Q), detonation velocity (D), and detonation pressure (P) are further evaluated. It is found that the oxygen-rich and chlorine-free compounds with 5 to 6 NO₂ groups in molecule can be used as the potential energetic oxidants with high oxygen balance, while those with 3 to 4 NO₂ groups are suitable for high-density energetic materials. Furthermore, stability correlations of all the compounds are established according to calculated bond order, natural bond orbital (NBO), bond dissociation enthalpies (BDE), and energy gaps (ΔE_LUMO-HOMO). Finally, burning rate is also calculated to show their potential application as oxidants in propellants. Graphical abstract.