Promising Thermally Stable Energetic Materials with the Combination of Pyrazole-1,3,4-Oxadiazole and Pyrazole-1,2,4-Triazole Backbones: Facile Synthesis and Energetic Performance

Theoretical advances in understanding and enhancing the thermostability of energetic materials

The quest for thermally stable energetic materials is pivotal in advancing the safety of applications ranging from munitions to aerospace. This perspective delves into the role of theoretical methodologies in interpreting and advancing the thermal stability of energetic materials. Quantum chemical calculations offer an in-depth understanding of the molecular and electronic structure properties of energetic compounds related to thermal stability. It is also essential to incorporate the surrounding interactions and their impact on molecular stability. Ab initio molecular dynamics (AIMD) simulations provide detailed theoretical insights into the reaction pathways and the key intermediates during thermal decomposition in the condensed phase. Analyzing the kinetic barrier of rate-determining steps under various temperature and pressure conditions allows for a comprehensive assessment of thermal stability. Recent advances in machine learning have demonstrated their utility in constructing potential energy surfaces and predicting thermal stability for newly designed energetic materials. The machine learning-assisted high-throughput virtual screening (HTVS) methodology can accelerate the discovery of novel energetic materials with improved properties. As a result, the newly identified and synthesized energetic molecule ICM-104 revealed excellence in performance and thermostability. Theoretical approaches are pivotal in elucidating the mechanisms underlying thermal stability, enabling the prediction and design of enhanced thermal stability for emerging EMs. These insights are instrumental in accelerating the development of novel energetic materials that optimally balance performance and thermal stability.

Synthesis and Performance Evaluation of Zwitterionic C-N Bonded Triazole-Tetrazole-Based Primary Explosives

Developing advanced metal-free nitrogen-enriched primary explosives is challenging due to the inherent risks associated with their synthesis and handling. However, there is an urgent need to develop novel lead-free, nitrogen-rich primary explosives that offer balanced energetic properties. C-N bonded bicyclic compound 3-azido-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (4), its salts, and 3,5-diazido-1H-1,2,4-triazole (8) were synthesized from inexpensive starting materials resulting in a fine blend of sensitivity and stability. These compounds exhibit high nitrogen content (79.78 to 83.43%), good thermal stability (129-210 °C), excellent detonation performance (VOD: 8592-9361 ms-1, DP: 27.1-33.8 GPa), and acceptable sensitivity (IS: 2.5-30 J, FS: 72-288 N). The hot needle tests of compounds 4 and 8 exhibit excellent ignition performance. All of the newly synthesized compounds were fully characterized using infrared spectroscopy (IR), high-resolution mass spectroscopy (HRMS), multinuclear magnetic spectroscopy (NMR), elemental analysis (EA), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), and 2, 4, and 8 were confirmed by single-crystal X-ray crystallographic studies. The molecular electrostatic potential (ESP), noncovalent interactions reduced density gradient (NCI-RDG) method, and QTAIM analysis were performed to investigate the intermolecular interactions. Together with promising performance properties, ease of synthesis, and ignitability, they are highly suitable candidates to pave new avenues for future applications.

Synthesis of C-C bonded trifluoromethyl-based high-energy density materials via the ANRORC mechanism

A trifluoromethyl group substituted C-C bonded nitrogen rich energetic material 3-(3-nitro-1H-pyrazol-4-yl)-5-(trifluoromethyl)-1,2,4-oxadiazole (4), its hydroxyl amine (5) and 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazol-2-ium (6) salts and hydrazinium 5-(3-nitro-1H-pyrazol-4-yl)-3-(trifluoromethyl)-1,2,4-triazol-1-ide (7) were synthesized and fully characterized using infrared spectroscopy (IR), multinuclear magnetic resonance (NMR) spectroscopy (1H, 13C, and 19F), high-resolution mass spectrometry (HRMS), elemental analysis (EA) and differential scanning calorimetry (DSC) studies. Furthermore, compounds 4 and 7 were confirmed using single-crystal X-ray diffraction studies (SC-XRD). All compounds possess good density (1.70-1.80 g cm-3), detonation velocity (6432-7144 m s-1), pressure (16.38-20.31 GPa), and thermal stability (>170 °C). They are insensitive towards mechanical stimuli, impact (IS > 35 J) and friction (FS > 288 N). Overall, due to their balanced performance, these compounds can be a better replacement for presently used explosives such as trinitrotoluene (TNT).

Molecule Empowerment and Crystal Desensitization: A Multilevel Structure-Property Analysis toward Designing High-Energy Low-Sensitivity Layered Energetic Materials

Layered energetic materials (LEMs) can effectively balance energy and mechanical sensitivity, making them a current research focus in the field of energetic materials. However, the influence of the layered stacking pattern on impact sensitivity is still unclear, leading to the lack of advanced design strategies for high-energy low-sensitivity LEMs. Herein, we first utilize novel indicators such as maximum plane separation and hydrogen bond dimension to perform high-throughput screening on over 106 candidate structures, resulting in 17 target crystals. A systematic analysis was then conducted on the relationships between the bond dissociation energy (BDE) of the weakest energy-storing bond at the molecular level, the intralayer hydrogen bond energy (HBE), and the sliding energy barrier (SEB) at the crystal level with impact sensitivity. The findings suggest that a material can have low sensitivity only if at least two of the three properties perform well, and the interlayer sliding resistance can be reduced by enhancing the intermolecular hydrogen bond interactions, which reasonably explains the experimental phenomena. More importantly, we developed a prediction model for the impact sensitivity of LEMs with a coefficient of determination of 0.88. Additionally, factors affecting HBE and SEB were identified, and a linear model was established based on molecular-level feature variables. Finally, a new strategy for designing high-energy low-sensitivity LEMs was proposed, namely, empowerment at the molecular scale and desensitization at the crystal scale. This study integrates high-throughput screening, multilevel structure-property relationship analysis, and mathematical model construction, offering new perspectives for the development of novel high-energy and low-sensitivity energetic materials.

Energetic derivatives substituted with trinitrophenyl: improving the sensitivity of explosives

The incorporation of trinitrophenyl-modified 1,3,4-oxadiazole fragments is commonly observed in high-energy molecules with heat-resistant properties. This study explores the strategy of developing heat-resistant energetic materials by incorporating trinitrophenyl and an azo group into 1,3,4-oxadiazole, which involved the synthesis and characterization of (E)-1,2-bis(5-(2,4,6-trinitrophenyl)-1,3,4-oxadiazol-2-yl)diazene (2), N-(5-(2,4,6-trinitrophenyl)-1,3,4-oxadiazol-2-yl)nitramide (3), and the energetic salts of 3. Characterization techniques employed included 1H and 13C NMR, IR and elemental analysis. Additionally, the structures of 2 and 3 were validated using single crystal X-ray analysis. To further understand the physical and chemical characteristics of these novel energetic compounds, various calculations and measurements were performed. Compound 2 exhibits excellent thermostability (Td = 294 °C), which is comparable to that of traditional heat-resistant explosive HNS (Td = 318 °C). But 2 is insensitive towards impact (>40 J) and friction (>360 N), surpassing HNS (5 J, 240 N), suggesting that compound 2 deserves further investigation as a potential heat-resistant explosive.

Copper-catalyzed aerobic annulation of hydrazones with dienones: an efficient route to pyrazole-linked hybrid molecules

A copper-catalyzed aerobic [3 + 2] annulation reaction to access various pyrazole-bound chalcones starting from readily available and cost-effective hydrazones and dienones is reported. These pyrazole-bound chalcones were further utilized effectively to prepare a series of pyrazole-linked hybrid molecules, such as pyrazole-pyrazoline, pyrazole-aziridine, and pyrazole-pyridine hybrids by efficient simple transformations. Synthetically challenging hybrid molecules were obtained in a simple, two-step process with high atom economy under aerobic copper catalysis.

Symmetric Refunctionalization of Diaminodinitropyrazine with Hydrazine and Aminotetrazole: Strategy for Enhancing Detonation Performance and Safety in Energetic Materials

Two novel nitrogen-rich green energetic compounds were synthesized for the first time from readily available and cost-effective pyrazine starting materials. All newly synthesized molecules were comprehensively characterized, including infrared spectroscopy, nuclear magnetic resonance, elemental analysis, mass spectrometry, and thermogravimetric analysis-differential scanning calorimetry. All compounds have additionally been validated by single-crystal X-ray diffraction analysis. The physicochemical properties of compounds 2, 4, and 5 were thoroughly investigated. Notably, all compounds exhibit remarkable performance, such as a high density (>1.84 g cm-3), excellent detonation properties (VOD > 8582 m s-1, and DP > 31.3 GPa), outstanding thermostability (>205 °C), and high insensitivity (IS > 35 J, and FS = 360 N). These attributes are quite comparable to those of secondary benchmark explosives such as TATB, RDX, LLM-105, and FOX-7. This tuned performance evidences that the incorporation of hydrazine, nitro, and aminotetrazole into the pyrazine framework fosters robust nonbonded interactions, ultimately enhancing thermal stability and reducing sensitivity. The findings of this study not only signify that compounds 2 and 5 have excellent detonation properties and stability but also prove that the strategy of replacing amino groups with hydrazine and aminotetrazole is a practical means of developing new insensitive energetic materials.

Understanding the Stability of Highly Nitrated Sensitive Pyrazole Isomers

Two energetic isomers of chemically unstable 3,5-bis(dinitromethyl)-4-nitro-1H-pyrazole (2), namely, 4-methyl-3,5-dinitro-1-(trinitromethyl)-1H-pyrazole (4) and 5-methyl-3,4-dinitro-1-(trinitromethyl)-1H-pyrazole (6), each containing five nitro groups and having the same chemical composition, exhibit major differences in their physiochemical properties. These include density, enthalpy of formation, temperature of decomposition, and sensitivity to impact and friction. Notably, both isomer 4 and isomer 6 demonstrate superior thermal stability compared to isomer 2, making them promising candidates as safer energetic materials.

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.

Solvent Free Potassium 3,5-dinitro-6-oxo-1,6-dihydropyrazin-2-olate 3D EMOF as Thermally Stable Energetic Material

Heat-resistant explosives play a vital role in indispensable applications. For this, we have synthesized a novel, three-dimensional, solvent-free energetic metal-organic framework (EMOF) potassium 3,5-dinitro-6-oxo-1,6-dihydropyrazin-2-olate (KDNODP) straightforwardly. The synthesized EMOF was characterized through IR, NMR spectroscopy, elemental analysis, and differential scanning calorimetry studies. Furthermore, single-crystal X-ray diffraction provided a complete description of KDNODP. It exhibits a three-dimensional EMOF structure with remarkably balanced properties such as high density (2.11 g cm-3), excellent thermal stability (291 °C), good detonation performance (8127 m s-1 and 26.94 GPa) and low mechanical sensitivity (IS=35 J; FS=360 N) than the commonly used heat-resistant explosives HNS (density=1.74 g cm-3; VOD=7164 m s-1, DP=21.65 GPa, IS=5 J) as well as the similar reported energetic potassium MOFs. To gain insights into the packing and intermolecular interactions, the Hirshfeld surface and a 2D fingerprint analysis were examined. Additionally, scanning electron microscopy was used to investigate the particle size and morphological characteristics of KDNODP. These outcomes highlight a successful method for creating 3D EMOF based on a six-membered heterocycle as a potential heat-resistant energetic material.

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.

Elevating the energetic capabilities of metal coordination compounds by incorporating nitrate anions

In the realm of energetic materials research, there has been notable interest in energetic coordination compounds (ECCs) owing to their remarkable thermal stability and resistance to mechanical stimuli. This study successfully demonstrated the synthesis of an azole-based C-C bonded ECC1 under ambient conditions. A comprehensive characterization study, employing techniques such as IR, TGA-DSC, NMR and single-crystal X-ray diffraction analysis, was conducted. The bulk compound was investigated by PXRD analysis. In-depth exploration of its physicochemical and energetic performance revealed good detonation properties such as a detonation velocity (VOD) of 8553 m s-1 and a detonation pressure (DP) of 36.2 GPa, which surpass those of heat resistant explosives HNS and TATB. Due to its remarkable high melting and onset decomposition temperature (278/379 °C), it also outperforms the benchmark explosive HMX (279 °C) and the heat-resistant explosive HNS (318 °C) and shows a high impact sensitivity (IS) of 20 J and friction sensitivity (FS) of 360 N. The study also employed Hirshfeld surface and 2D fingerprint analysis to elucidate the close contact of atoms within the molecules. The combination of high detonation properties, thermal stability, and low sensitivity makes the synthesized ECC1 intriguing for further investigations and suggests its potential applications as a safe and high-energy-dense material.

Single Step Synthesis of gem-Dinitro Methyl-1,2,4-triazole and Its Hydroxylamine Salt: An Alternative to the FOX-7 and Other Benchmark Explosives

gem-Dinitro methyl based high-energy-density material 5-(dinitromethylene)-4,5-dihydro-1H-1,2,4-triazole (2) and its hydroxylamine salt (4) were synthesized for the first time in a single step and characterized. Further, the structure of 2 was confirmed by single-crystal X-ray diffraction (SCXRD) studies. Interestengly, both the compounds show excellent density (> 1.83 g cm-3), detonation velocity (> 8700 m s-1), pressure (> 30 GPa) and are insensitive toward mechanical stimuli such as impact and friction sensitivity. Considering their synthetic fesibility and balanced energetic performance, compounds 2 and 4 show future prospects as potential next-generation energetic materials for the replacenent of many presently used benchmark high energy density materials such as RDX, FOX-7 and highly insensitive H-FOX.

Elaborating NH-Bridged Nitrogen-Rich Energetic Materials via Base-Mediated Dimroth Rearrangement: Synthesis, Characterization, and Performance Study

The pursuit of heat-resistant energetic materials featuring high thermostability and energy has gained keen interest in recent years owing to their use in coal mining and aerospace domains. In this study, we synthesized 4-((4,6-diamino-1,3,5-triazin-2-yl) amino)-1H-1,2,3-triazole-5-carbonitrile (6) and its perchlorate and nitrate energetic salts (6a and 6b) by incorporating amino bridging (-NH-) using the Dimroth rearrangement (DR) from inexpensive starting materials as a heat-resistant energetic materials. All of the compounds were thoroughly characterized by infrared (IR), NMR, elemental analysis (EA), high-resolution mass spectrometry (HRMS), and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) studies. Compounds 6a and 6b showed good densities (1.81 and 1.80 g cm-3), detonation performance (VOD = 7505 and 8257 m s-1, DP = 23.47 and 24.41 GPa), insensitivity to mechanical stimuli (IS = 40 J and FS = >360 N), and excellent thermal stability (Td = 307 and 334 °C), surpassing presently used heat-resistant explosive HNS (318 °C). The molecular electrostatic potentials and noncovalent interactions were pursued to understand possible interaction sites and structure-directing interactions in these salts. Their facile synthetic approach, good energetic performance, and outstanding thermal stability indicate that they are the ideal combination for replacing current benchmark heat-resistant explosive HNS. Additionally, this study highlights the use of classical DR for making new energetic materials with fine-tuned properties.

Highly Dense N-N-Bridged Dinitramino Bistriazole-Based 3D Metal-Organic Frameworks with Balanced Outstanding Energetic Performance

Due to the inherent conflict between energy and safety, the construction of energetic materials or energetic metal-organic frameworks (E-MOFs) with balanced thermal stability, sensitivity, and high detonation performance is challenging for chemists worldwide. In this regard, in recent times self-assembly of energetic ligands (high nitrogen- and oxygen-containing small molecules) with alkali metals were probed as a promising strategy to build high-energy materials with excellent density, insensitivity, stability, and detonation performance. Herein, based on the nitrogen-rich N,N'-([4,4'-bi(1,2,4-triazole)]-3,3'-dial)dinitramide (H2BDNBT) energetic ligand, two new environmentally benign E-MOFs including potassium [K2BDNBT]n (K-MOF) and sodium [Na2BDNBT]n (Na-MOF) have been introduced and characterized by NMR, IR, TGA-DSC, ICP-MS, PXRD, elemental analyses, and SCXRD. Interestingly, Na-MOF and K-MOF demonstrate solvent-free 3D dense frameworks having crystal densities of 2.16 and 2.14 g cm-3, respectively. Both the E-MOFs show high detonation velocity (VOD) of 8557-9724 m/s, detonation pressure (DP) of 30.41-36.97 GPa, positive heat of formation of 122.52-242.25 kJ mol-1, and insensitivity to mechanical stimuli such as impact and friction (IS = 30-40 J, FS > 360 N). Among them, Na-MOF has a detonation velocity (9724 m/s) superior to that of conventional explosives. Additionally, both the E-MOFs are highly heat-resistant, having higher decomposition (319 °C for K-MOF and 293 °C for Na-MOF) than the traditional explosives RDX (210 °C), HMX (279 °C), and CL-20 (221 °C). This stability is ascribed to the extensive structure and strong covalent interactions between BDNBT2- and K(I)/Na(I) ions. To the best of our knowledge, for the first time, we report dinitramino-based E-MOFs as highly stable secondary explosives, and Na-MOF may serve as a promising next-generation high-energy-density material for the replacement of presently used secondary thermally stable energetic materials such as RDX, HNS, HMX, and CL-20.

Zwitterionic fused pyrazolo-triazole based high performing energetic materials

A series of nitrogen-rich fused energetic materials were synthesized from commercially available inexpensive starting materials and fully characterized using 1H and 13C NMR, IR spectroscopy, elemental analysis, and DSC. The structure of zwitterionic compound 2 was supported by SCXRD data. Among all, 3 and 4 possess excellent detonation velocity (8956 and 9163 m s-1) and are insensitive towards friction (>360 N) and impact (10 J), having moderate to excellent thermal stability (171-262 °C). It is worth mentioning that the zwitterionic fused pyrazolo-triazole compound 2 and its energetic salts offer remarkable performance as new-generation thermally stable energetic materials.

Synthesis of Advanced Pyrazole and N-N-Bridged Bistriazole-Based Secondary High-Energy Materials

In this work, we have synthesized 3,5-dihydrazinyl-4-nitro-1H-pyrazole (2), 9-nitro-1H-pyrazolo[3,2-c:5,1-c']bis([1,2,4]triazole)-3,6-diamine (3), and N-N-bonded N,N'-{[4,4'-bi(1,2,4-triazole)]-3,3'-diyl}dinitramide (5) and its stable nitrogen-rich energetic salts in one and two steps in quantitative yields from commercially available inexpensive starting material 4,6-dichloro-5-nitropyrimidine (1). Along with characterization via nuclear magnetic resonance, infrared, differential scanning calorimetry, and elemental analysis, the structures of 2 and 4-8 were confirmed by single-crystal X-ray diffraction. Interestingly, 5-8 show excellent thermal stability (242, 221, 250, and 242 °C, respectively) compared to that of RDX (210 °C). Detonation velocities of 2, 4, 6, and 7 range from 8992 to 9069 m s-1, which are better than that of RDX (8878 m s-1) and close to that of HMX (9221 m s-1). All of these compounds are insensitive to impact (10-35 J) and friction (360 N) sensitivity. These excellent energetic performances, stabilities, and synthetic feasibilities make compounds 2, 4, 6, and 7 promising candidates as secondary explosives and potential replacements for the presently used benchmark explosives RDX and HMX.

Bis(dinitropyrazolyl)methanes spruced up with hydroxyl groups: high performance energetic salts with reduced sensitivity

With an aim to improve the overall physical stability of high-performing 3,5-dinitro-functionalised bispyrazolymethanes, a hydroxyl functionality was introduced at the fourth position to obtain 1,1'-methylenebis(3,5-dinitro-1H-pyrazol-4-ol) and its energetic salts. Superior oxygen balance and energy in comparison to the amino substituent at the 4th position and enhanced sensitivity with respect to the nitro and azido substituents helped in unlocking the potential of less explored N-alkylated-4-hydroxy-3,5-dinitropyrazoles. Fine-tuning of properties via dicationic salt formation, which is not feasible in any other reported symmetrically connected pyrazole-based energetic materials, resulted in improved physical and thermal stabilities, as well as energetic performance. Hirshfeld surface analysis, electrostatic potential analysis, the study of aromaticity and weakest Mayer-bond order analysis helped further in studying the structure-property relationship of the synthesized compounds with respect to different reported methylene-bridged symmetrical compounds.

Controlling the Energetic Properties of N-Methylene-C-Linked 4-Hydroxy-3,5-dinitropyrazole- and Tetrazole-Based Compounds via a Selective Mono- and Dicationic Salt Formation Strategy

In the quest to synthesize high-performing insensitive high-energy density materials (HEDMs), the main challenge is establishing an equilibrium between energy and stability. For this purpose, we explored 4-hydroxy-3,5-dinitropyrazole- and tetrazole-based energetic scaffolds connected via a N-methylene-C bridge. The hydroxy functionality between nitro groups on the pyrazole ring promotes physical stability via inter- and intramolecular hydrogen bonding and contributes to oxygen balance, supporting better energetic performance. Due to two acidic sites (OH and NH) with different reactivities, a series of monocationic and dicationic salts were synthesized, and their overall performance was compared. All compounds synthesized in this study have high physical stability with impact sensitivity >40 J and friction sensitivity >360 N. Monocationic salts were generally found to have better thermal stability with respect to their corresponding dicationic energetic salts, which showed better energetic performance. The salt formation strategy effectively improved the thermal stability of 2 (Td = 168 °C), where most energetic salts have decomposition temperatures higher than 220 °C. All of the compounds were characterized through IR, multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), and elemental analysis. The structure-property relationship was studied using Hirshfeld surface analysis, noncovalent interaction (NCI) analysis, and electrostatic potential studies.

Straightforward Synthesis of Insensitive 2-(1-Hydroxy-2,2-dinitrovinyl)guanidine and Its Guanidinium Dinitromethanide Salt as a High Energy Density Material

High energetic 2-(1-hydroxy-2,2-dinitrovinyl)guanidine and guanidinium dinitromethanide (GDNM) salt were synthesized in one and two steps using a simple and cost-effective methodology from commercially available inexpensive starting materials with a high yield. NMR, IR spectroscopy, elemental analysis, and differential scanning calorimetry studies were used to characterize compound 2a and GDNM salt. Single-crystal XRD, Hirshfeld surface analysis, and SEM analysis were used to study the crystal structure, hydrogen-bonding/noncovalent interactions, and morphology of the GDNM salt, respectively. The physicochemical and energetic properties of compound 2a and GDNM salt reveal their good energetic performance, specific impulse, and high mechanical insensitivity, which are better than that of propellants such as ADN and AP and close to that of the benchmark explosives such as RDX and FOX-7.

Energetic coordination compounds: self-assembled from the nitrogen-rich energetic C-C bonded pyrazoles and triazoles

In energetic materials research, energetic coordination compounds (ECCs) have received much attention due to their high thermal stability and insensitivity to mechanical stimuli. The energetic characteristics of ECCs can be modified by combining various metal cations, potent anions, and ligands. In this study, we have synthesized two energetic ligands, 5-(4-nitro-1H-pyrazol-3-yl)-1H-1,2,4-triazol-3-amine (NPTA) and (Z)-N-(5-(4-nitro-1H-pyrazol-3-yl)-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)nitramide (NPTN), from a commercially viable starting material and reacted them with nitrate salts of various 3d metals (e.g., Ni, Co, Zn) to obtain six new ECCs, [Ni(NPTA)(H2O)3]2·2NO3 (1), [Co(NPTA)(H2O)3]2·2NO3 (2), [Zn(NPTA)(H2O)3]2·2NO3 (3), [Ni(NPTN)(H2O)3]2 (4), [Co(NPTN)(H2O)3]2 (5), and [Zn(NPTN)(H2O)3]2 (6) under ambient conditions. All the newly prepared ECCs were characterised through PXRD, IR, SEM, and TGA-DSC analysis. Furthermore, single crystal analysis proved that 1-6 are dimeric complexes. Moreover, 1-6 show excellent density ranges from 1.94 to 2.06 g cm-3 and remarkable thermal stability (216-352 °C), and are highly insensitive towards impact (>40 J) and friction (>360 N), describing their potential as high performing energetic materials. All the ECCs revealed good enthalpy of combustion (-6.3 to -9.94 kJ g-1). Additionally, the Hirshfeld surface and 2D fingerprint analysis were used to understand the close contact of atoms within the molecules. High crystal densities, thermal stabilities and low sensitivities make the synthesized ECCs interesting for further studies and potential applications as safe high-energy dense materials.

Structural, vibrational and electronic properties of nitrogen-rich 2,4,6-triazide-1,3,5-triazine under high pressure

CONTEXT AND RESULTS

2,4,6-triazide-1,3,5-triazine (TAT) has received widespread attention for its great potential to synthesize or convert to nitrogen-rich high energy density materials (HEDMs). The TAT structure alteration in the compression process up to 30 GPa has characteristics as follows: (a) [N₃] groups straighten; (b) [N₃] groups gather toward the six-membered C-N heterocycles. At about 5 GPa, Raman peak split at 700 cm^-1 was observed both in calculation and in-situ Raman experiment, which is caused by pressure-induced intramolecular stress. Besides, the broad band of the amorphous two-dimensional C=N network (centered at 1630 cm^-1) occurred at about 12 GPa. Meantime, the study on electronic features suggests the pressure-induced deformation in TAT molecular structure cause the discontinuous change of band gap at about 4.5 GPa and 8.0 GPa, respectively.

COMPUTATIONAL AND THEORETICAL TECHNIQUES

The static compression process of TAT was explored in the range of 0-30 GPa by using dispersion corrected density functional theory (DFT-D) calculations combined with in-situ Raman experiment. The GGA/PBE+G06 method that has less errors than other calculation methods was used to predict the geometry structure, vibrational properties and electronic structure of TAT under pressure.

Poly Tetrazole Containing Thermally Stable and Insensitive Alkali Metal-Based 3D Energetic Metal-Organic Frameworks

Poly tetrazole-containing thermally stable and insensitive alkali metal-based 3D energetic metal-organic frameworks (EMOFs) are promising high energy density materials to balance the sensitivity, stability, and detonation performance of explosives in defense, space, and civilian applications. Herein, the self-assembly of L^3- ligand with alkali metals Na(I) and K(I) was prepared at ambient conditions, introducing two new EMOFs, [Na₃(L)₃(H₂O)₆]_n (1) and [K₃(L)₃(H₂O)₃]_n (2). Single crystal analysis reveals that Na-MOF (1) exhibited a 3D wave-like supramolecular structure with significant hydrogen bonding among the layers, while K-MOF (2) also featured a 3D framework. Both EMOFs were thoroughly characterized by NMR, IR, PXRD, and TGA/DSC analyses. Compounds 1 and 2 show excellent thermal decomposition T_d = 344 and 337 °C, respectively, compared to the presently used benchmark explosives RDX (210 °C), HMX (279 °C), and HNS (318 °C), which is attributed to structural reinforcement induced by extensive coordination. They also show remarkable detonation performance (VOD = 8500 m s^-1, 7320 m s^-1, DP = 26.74 GPa, 20 GPa for 1 and 2, respectively) and insensitivity toward impact and friction (IS ≥ 40 J, FS ≥ 360 N for 1; IS ≥ 40 J, FS ≥ 360 N for 2). Their excellent synthetic feasibility and energetic performance suggest that they are the perfect blend for the replacement of present benchmark explosives such as HNS, RDX, and HMX.