Pushing the Limits of Oxygen Balance in 1,3,4-Oxadiazoles

Construction of heterocycle-triazolotriazine framework energetic compounds: towards novel high-performance explosives

In this paper, three neutral heterocycle-triazolotriazine compounds featuring multiple amino groups and nitro groups were designed and synthesized. Among them, compounds 2 and 6 exhibit high detonation performance (Dv = 8180 m s-1, 8650 m s-1; P = 26.40 GPa, 31.5 GPa), low sensitivities (IS > 40 J, FS > 360 N) and high thermal stabilities (Td = 319 °C, 320 °C) suggesting their potential as alternatives to the traditional thermal-stable explosive HNS (Dv = 7612 m s-1, P = 24.3 GPa, IS = 5 J, FS = 240 N; Td = 318 °C). Meanwhile, compound 4 displays excellent properties (Dv = 8810 m s-1, IS = 15 J, FS = 240 N, Td = 215 °C, ρ = 1.84 g cm-3) which is superior to traditional explosive RDX (Dv = 8795 m s-1, IS = 7.5 J, FS = 120 N, Td = 208 °C, ρ = 1.80 g cm-3) making it a promising candidate as a novel secondary explosive. This research not only advances the field of triazolotriazine-based energetic materials but also explores their potential applications as heat-resistant or high-energy explosives.

2,2'-Bisdinitromethyl-5,5'-bistetrazole: A High-Performance, Multi-Nitro Energetic Material with Excellent Oxygen Balance

Bistetrazoles are highly sought after for developing innovative high-energy density materials. The 1,1'-substituted bistetrazoles, exemplified by TKX-50, have outstanding performance. However, the research of high-perfomance 2,2'-substituted bistetrazoles remains limited. In this work, dinitromethyl groups were introduced into bistetrazole structures as 2,2'-substituted bistetrazoles (BDBTZ), which was extensively characterized through NMR, thermal analysis, and single crystal X-ray diffraction, exhibiting excellent oxygen balance, moderate sensitivity, acceptable thermal stability, high crystal density, and excellent detonation performance.

Assembling of Nitropyrazoles into Tetranitroacetimidic Acid (TNAA): A Pathway to High-Performance Energetic Oxidizers through Dual C/N-Functionalization

In this work, incorporating nitropyraozles into tetranitroacetimidic acid (TNAA) resulted in two analogues of isomeric TNAA-like compounds (3 and 5). These compounds exhibit excellent densities, detonation performance, and high specific impulse, which are promising high-energy oxidizers that are comparable to AP and ADN. This structural modification strategy may have the potential to contribute significantly to the development of versatile, high-performance energetic oxidizers.

Design, Synthesis, and Herbicidal Activity of Novel Tetrahydrophthalimide Derivatives Containing Oxadiazole/Thiadiazole Moieties

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) has a high status in the development of new inhibitors. To develop novel and highly effective PPO inhibitors, active substructure linking and bioisosterism replacement strategies were used to design and synthesize novel tetrahydrophthalimide derivatives containing oxadiazole/thiadiazole moieties, and their inhibitory effects on Nicotiana tobacco PPO (NtPPO) and herbicidal activity were evaluated. Among them, compounds B11 (Ki = 9.05 nM) and B20 (Ki = 10.23 nM) showed significantly better inhibitory activity against NtPPO than that against flumiclorac-pentyl (Ki = 46.02 nM). Meanwhile, compounds A20 and B20 were 100% effective against three weeds (Abutilon theophrasti, Amaranthus retroflexus, and Portulaca oleracea) at 37.5 g a.i./ha. It was worth observing that compound B11 was more than 90% effective against three weeds (Abutilon theophrasti, Amaranthus retroflexus, and Portulaca oleracea) at 18.75 and 9.375 g a.i./ha. It was also safer to rice, maize, and wheat than flumiclorac-pentyl at 150 g a.i./ha. In addition, the molecular docking results showed that compound B11 could stably bind to NtPPO and it had a stronger hydrogen bond with Arg98 (2.9 Å) than that of flumiclorac-pentyl (3.2 Å). This research suggests that compound B11 could be used as a new PPO inhibitor, and it could help control weeds in agricultural production.

1-Trinitromethyl-3,5-dinitro-4-nitroaminopyrazole: Intramolecular Full Nitration and Strong Intermolecular H-Bonds toward Highly Dense Energetic Materials

Full nitration is one of the most effective strategies used in synthesizing high-density energetic materials, but this strategy has reached its limit because the resultant compounds cannot be further functionalized. To overcome this limitation, we present the synergistic action of full nitration and strong intermolecular H-bonding in designing and synthesizing 1-trinitromethyl-3,5-dinitro-4-nitroaminopyrazole (DNTP) with a density that exceeds those of the reported monocyclic CHON compounds. The detonation velocity and specific impulse of DNTP exceed those of 1-trinitromethyl-3,4,5-trinitropyrazole (TTP), HMX, and ADN.

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.

Trinitromethyl-Substituted 1H-1,2,4-Triazole Bridging Nitropyrazole: A Strategy of Utterly Manipulable Nitration Achieving High-Energy Density Material

Nitro groups have been demonstrated to play a decisive role in the development of the most powerful known energetic materials. Two trinitromethyl-substituted 1H-1,2,4-triazole bridging nitropyrazoles were first synthesized by straightforward routes and were characterized by chemical (MS, NMR, IR spectroscopy, and single-crystal X-ray diffraction) and experimental analysis (sensitivity toward friction, impact, and differential scanning calorimetry-thermogravimetric analysis test). Their detonation properties (detonation pressure, detonation velocity, etc.) were predicted by the EXPLO5 package based on the crystal density and calculated heat of formation with Gaussian 09. These new trinitromethyl triazoles were found to show suitable sensitivities, high density, and highly positive heat of formation. The combination of exceedingly high performances superior to those of HMX (1,3,5,7-tetranitrotetraazacyclooctane), and its straightforward preparation highlights compound 8 as a promising high-energy density material (HEDM). This work supports the effectivity of utterly manipulable nitration and provides a generalizable design synthesis strategy for developing new HEDMs.

Pushing the limits of the heat of detonation via the construction of polynitro bipyrazole

The trinitromethyl group is a highly oxidized group that is found as an active functionality in many high-energy-density materials. The most frequently used previous synthetic method for the introduction of the trinitromethyl group is the nitration of heterocyclic compounds containing an acetonyl/ethyl acetate/chloroxime group. Now a novel strategy for constructing a trinitromethyl group (5) via nitration of an ethylene bridged compound, dipyrazolo[1,5-a:5',1'-c]pyrazine (2), is reported. In addition, the other two nitrated products (3 and 4) were obtained under different nitrating conditions. Compound 5 has excellent detonation performance (Dv = 9047 m s-1, P = 35.6 GPa), and a low mechanical sensitivity (IS = 10 J, FS = 216 N), with an especially attractive heat of detonation of 6921 kJ kg-1, which significantly exceeds that of the state-of-the-art explosive CL-20 (Q: 6162 kJ kg-1).

Manipulating nitration and stabilization to achieve high energy

Nitro groups have played a central and decisive role in the development of the most powerful known energetic materials. Highly nitrated compounds are potential oxidizing agents, which could replace the environmentally hazardous used materials such as ammonium perchlorate. The scarcity of azole compounds with a large number of nitro groups is likely due to their inherent thermal instability and the limited number of ring sites available for bond formation. Now, the formation of the first azole molecule bonded to seven nitro groups, 4-nitro-3,5-bis(trinitromethyl)-1H-pyrazole (4), by the stepwise nitration of 3,5-dimethyl-1H-pyrazole is reported. Compound 4 exhibits exceptional physicochemical properties with a positive oxygen balance (OBCO2 = 13.62%) and an extremely high calculated density (2.04 g cm-3 at 100 K). This is impressively high for a C, H, N, O compound. This work is a giant step forward to highly nitrated and dense azoles and will accelerate further exploration in this challenging field.

Backbone Isomerization to Enhance Thermal Stability and Decrease Mechanical Sensitivities of 10 Nitro-Substituted Bipyrazoles

The development of novel, environmentally friendly, and high-energy oxidizers remains interesting and challenging for replacing halogen-containing ammonium perchloride (AP). The trinitromethyl moiety is one of the most promising substituents for designing high-energy density oxidizers. In this study, a backbone isomerization strategy was utilized to manipulate the properties of 10 nitro group-substituted bipyrazoles containing the largest number of nitro groups among the bis-azole backbones so far. Another advanced high-energy density oxidizer, 3,3',5,5'-tetranitro-1,1'-bis(trinitromethyl)-1H,1'H-4,4'-bipyrazole (3), was designed and synthesized. Compared to the isomer 4,4',5,5'-tetranitro-2,2'-bis(trinitromethyl)-2H,2'H-3,3'-bipyrazole (4) (Td = 125 °C), 3 possesses better thermostability (Td = 156 °C), which is close to that of ammonium dinitramide (ADN) (Td = 159 °C), and it possesses better mechanical sensitivity (impact sensitivity (IS) = 13 J and friction sensitivity (FS) = 240 N) than that of 4 (IS = 9 J and FS = 215 N), thereby demonstrating a promising perspective for practical applications.

From Tetranitromethane to Gem-Dinitro-Bridged Nitrogen-Rich Heterocyclic Compound: Achieving High Heat of Detonation

Improving the detonation performance of tetranitromethane (TNM) by introducing energetic moieties is an intriguing area in the field of energetic materials. Incorporation of a mono nitrogen-rich skeleton into TNM usually results in unsatisfactory detonation performance. Now, we reported the design and synthesis of an advanced TNM-like molecule (3) containing nitrogen-rich triazole and nitro-triazinane moieties. In addition, two of its analogues (4 and 5) were also obtained. Taking advantage of the positive heat of formation brought by triazole and triazinane rings and high-density properties donated by many nitro groups, 3 shows promising heat of detonation (Q = 5859 kJ kg-1), which is 2.8 times of TNM and higher than most of its mono ring-modified derivatives (Q: 2076 to 5594 kJ kg-1). The detonation velocity and detonation pressure of 3 (Dv = 8964 m s-1 and P = 35.7 GPa) are competitive with those of RDX (Q = 5763 kJ kg-1, Dv = 8782 m s-1, and P = 34.7 GPa). Structural modification by using triazole and nitro-triazinane rings may be helpful in exploring more TNM derivatives and other types of high-performance explosives.

Energetic performance of trinitromethyl nitrotriazole (TNMNT) and its energetic salts

Little is known about trinitromethyl nitrotriazole (TNMNT) since the crystal structure, density, energetic performance, and thermal properties have not been determined. A detailed characterization of TNMNT and its hydrazinium and potassium salts and their potential as solid propellants and oxidizers has been established. TNMNT exhibits a high density (1.96 g cm-3) and positive enthalpy of formation (ΔHf = +84.79 kJ mol-1). TNMNT and its hydrazinium and potassium salts illustrate excellent detonation properties (P = 34.24 to 36.22 GPa, D = 8899 to 9031 ms-1). TNMNT and its hydrazinium salt exhibit outstanding propulsive properties (Isp = 247.28 to 271.19 s), and these are superior to AP (Isp = 156.63 s) and ADN (Isp = 202.14 s). The results suggest opening the door to utilizing TNMNT and its energetic salts in solid rocket propulsion.

Combining the advantages of 1,3,4-oxadiazole and tetrazole enables achieving high-energy insensitive materials

Combining the advantages of energetic heterocycles to achieve high-energy insensitive explosives is a significant challenge. Herein, based on high-energy tetrazole rings and highly stable 1,3,4-oxadiazole rings, a series of novel nitrogen rich energetic compounds 5-9 were successfully constructed. The related compounds were fully characterized by EA, FT-IR, NMR, DSC, and MS, and compounds 6-9 were further confirmed by X-ray single crystal diffraction. Among them, the energetic ion salts 6-8 show high thermal stability (Tdec > 250 °C) and low mechanical sensitivity (IS > 40 J, FS > 360 N), as well as good energy properties (7552-8050 m s-1, 19.4-23.3 GPa). In particular, the azo compound 9 exhibits competent comprehensive performances (Tdec = 226.2 °C, D = 8502 m s-1, P = 28.9 GPa, IS = 32 J, FS = 320 N). These results suggest that the strategy of integrating tetrazole and 1,3,4-oxadiazole and employing an azo structure as a bridging unit are effective approaches to construct high-energy insensitive materials.

Fluorine-Containing Functional Group-Based Energetic Materials

Molecules featuring fluorine-containing functional groups exhibit outstanding properties with high density, low sensitivity, excellent thermal stability, and good energetic performance due to the strong electron-withdrawing ability and high density of fluorine. Hence, they play a pivotal role in the field of energetic materials. In light of current theoretical and experimental reports, this review systematically focuses on three types of energetic materials possessing fluorine-containing functional groups F- and NF2 - substituted trinitromethyl groups (C(NO2 )2 F, C(NO2 )2 NF2 ), trifluoromethyl group (CF3 ), and difluoroamino and pentafluorosulfone groups (NF2 , SF5 ) and investigates the synthetic methods, physicochemical parameters, and energetic properties of each. The incorporation of fluorine-containing functional moieties is critical for the development of novel high energy density materials, and is rapidly being adopted in the design of energetic materials.

Thermal stability of azole-rich energetic compounds: their structure, density, enthalpy of formation and energetic properties

Energetic compounds, as a type of special material, are widely used in the fields of national defense, aerospace and exploration. Their research and production have received growing attention. Thermal stability is a crucial factor for the safety of energetic materials. Azole-rich energetic compounds have emerged as a research hotspot in recent years owing to their excellent properties. Due to the aromaticity of unsaturated azoles, many azole-rich energetic compounds have significant thermal stability, which is one of the properties that researchers focus on. This review presents a comprehensive summary of the physicochemical and energetic properties of various energetic materials, highlighting the relationship between thermal stability and the structural, physicochemical, and energetic properties of azole-rich energetic compounds. To improve the thermal stability of compounds, five aspects can be considered, including functional group modification, bridging, preparation of energetic salts, energetic metal-organic frameworks (EMOFs) and co-crystals. It was demonstrated that increasing the strength and number of hydrogen bonds of azoles and expanding the π-π stacking area are the key factors to improve thermal stability, which provides a valuable way to develop energetic materials with higher energy and thermal stability.

Challenging the Limitations of Tetranitro Biimidazole through Introducing a gem-Dinitromethyl Scaffold

A gem-dinitromethyl group was successfully introduced into the TNBI·2H₂O structure (TNBI: 4,4',5,5'-tetranitro-2,2'-bi-1H-imidazole) to obtain 1-(dinitromethyl)-4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (DNM-TNBI). Benefiting from the transformation of an N-H proton into a gem-dinitromethyl group, the current limitations of TNBI were well solved. More importantly, DNM-TNBI has high density (1.92 g·cm^-3, 298 K), good oxygen balance (15.3%), and excellent detonation properties (D_v = 9102 m·s^-1, P = 37.6 GPa), suggesting that it has great potential as an oxidizer or a high-performance energetic material.

Theoretical design of new insensitive high energy metal complexes based on the double fused-ring insensitive ligands strategy

CONTEXT

In this work, 24 new nitrogen-rich fused-ring energetic metal complexes were designed based on the double fused-ring insensitive ligands strategy. First, 7-nitro-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c][1,2,4]triazin-4-amine and 6-amino-3-(4H,8H-bis([1,2,5]oxadiazolo)[3,4-b:3',4'-e]pyrazin-4-yl)-1,2,4,5-tetrazine-1,5-dioxide were linked together by coordinating with metals cobalt and copper. Then, three energetic groups (NH₂, NO₂, and C(NO₂)₃) were introduced into the system to modify the structure and adjust the performance. Then, their structures and properties were investigated theoretically; the effects of different metals and small energetic groups were studied also. Finally, 9 compounds which have both higher energy and lower sensitivity than the famous high energy compound compound 1,3,5,7-tetranitro-1,3,5,7-tetrazocine were selected out. In addition, it was found that copper, NO₂, and C(NO₂)₃ could increase the energy while cobalt and NH₂ would be helpful for reducing the sensitivity.

METHODS

Calculations were performed at the TPSS/6-31G(d) level by using the Gaussian 09 software.

Can a heavy trinitromethyl group always result in a higher density?

Density is an important property of energetic materials and is believed to increase with the addition of heavy trinitromethyl groups, as shown in previous literature. However, this study determined that the introduction of these groups produced a decrease in density, as evidenced by the lower density of 1-trinitromethyl-4-amino-3,5-dinitropyrazole ((TN-116), 1.899 g cm^-3) compared to that of its precursor (4-amino-3,5-dinitropyrazole (LLM-116), 1.900 g cm^-3). Mechanistic studies indicated that the reduced density was due to the significantly weaker H-bonding and π-π interactions of TN-116, which produced looser stacking compared to that of LLM-116.

Chemical Descriptors for a Large-Scale Study on Drop-Weight Impact Sensitivity of High Explosives

The drop-weight impact test is an experiment that has been used for nearly 80 years to evaluate handling sensitivity of high explosives. Although the results of this test are known to have large statistical uncertainties, it is one of the most common tests due to its accessibility and modest material requirements. In this paper, we compile a large data set of drop-weight impact sensitivity test results (mainly performed at Los Alamos National Laboratory), along with a compendium of molecular and chemical descriptors for the explosives under test. These data consist of over 500 unique explosives, over 1000 repeat tests, and over 100 descriptors, for a total of about 1500 observations. We use random forest methods to estimate a model of explosive handling sensitivity as a function of chemical and molecular properties of the explosives under test. Our model predicts well across a wide range of explosive types, spanning a broad range of explosive performance and sensitivity. We find that properties related to explosive performance, such as heat of explosion, oxygen balance, and functional group, are highly predictive of explosive handling sensitivity. Yet, models that omit many of these properties still perform well. Our results suggest that there is not one or even several factors that explain explosive handling sensitivity, but that there are many complex, interrelated effects at play.

Trinitromethyl Energetic Groups Enhance High Heats of Detonation

The introduction of groups with high enthalpies of formation can effectively improve the detonation performance of the compounds. A series of novel energetic compounds (10-13) with high enthalpies of formation, high density, and high nitrogen-oxygen content were designed and synthesized by combining gem-polynitromethyl, 1,2,4-oxadiazole, furoxan, and azo groups. All the new compounds were thoroughly characterized by IR, NMR, elemental analysis, and differential scanning calorimetry. Compounds 10 and 11 were also further characterized with single-crystal X-ray diffraction. Compound 11 has high density (1.93 g cm^-3), high enthalpy of formation (993.5 kJ mol^-1), high detonation velocity (9411 m s^-1), and high heat of detonation (6889 kJ kg^-1) and is a potentially excellent secondary explosive.

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

Thermally stable energetic materials have broad applications in the deep mining, oil and natural exploration, and aerospace industries. The quest for thermally stable (heat-resistant) energetic materials with high energy output and low sensitivity has fascinated many researchers worldwide. In this study, two different series of thermally stable energetic materials and salts based on pyrazole-oxadiazole and pyrazole-triazole (3-23) with different explosophoric groups have been synthesized in a simple and straightforward manner. All the newly synthesized compounds were fully characterized by IR, ESI-MS, multinuclear NMR spectroscopy, elemental analysis, and thermogravimetric analysis-differential scanning calorimetry measurements. The structures of 3, 7, and 22 were supported by single-crystal X-ray diffraction studies. The density, heat of formation, and energetic properties (detonation velocity and detonation pressure) of all the compounds range between 1.75 and 1.94 g cm-3, 0.73 to 2.44 kJ g-1, 7689 to 9139 m s-1, and 23.3 to 31.5 GPa, respectively. All the compounds are insensitive to impact (>30 J) and friction (>360 N). In addition, compounds 4, 6, 10, 14, 17, 21, 22, and 23 show high onset decomposition temperature (Td between 238 and 397 °C) than the benchmark energetic materials RDX (Td = 210 °C), HMX (279 °C), and thermally stable HNS (318 °C). It is noteworthy that the pyrazole-oxadiazole and pyrazole-triazole backbones greatly influence their physicochemical and energetic properties. Overall, this study offers a perspective on insensitive and thermally stable nitrogen-rich materials and explores the relationship between the structure and performance.

Toward Advanced High-Performance Insensitive FOX-7-like Energetic Materials via Positional Isomerization

For an energetic molecule with a definite elemental composition, the substituent type and position are the most important factors to influence its detonation performance and mechanical sensitivities. In this work, two pairs of FOX-7-like energetic isomers based on (2 and HTz-FOX; 5 and 6) were synthesized and characterized. Through positional isomerization, advanced high-performance insensitive explosives were obtained. Compounds 2 and 5 with an amino group adjacent to the electron-withdrawing side of the ethene bridge show both higher thermal stability and lower mechanical sensitivities (2: Td = 258 °C, impact sensitivity (IS) = 25 J, and friction sensitivity (FS) = 300 N; 5: Td = 264 °C, IS = 30 J, and FS = 320 N). In addition, 2 shows ultrahigh detonation performance (Dv = 9224 m s-1 and P = 31.1 GPa). These promising physicochemical properties are comparable to those of HMX (Dv = 9193 m s-1, P = 37.8 GPa, Td = 275 °C, IS = 7.4 J, and FS = 120 N), which suggests that 2 may be a promising energetic material in future applications.

Boosting the Energetic Performance of Trinitromethyl-1,2,4-oxadiazole Moiety by Increasing Nitrogen-Oxygen in the Bridge

The trinitromethyl moiety is a useful group for the design and development of novel energetic compounds with high nitrogen and oxygen content. In this work, by using an improved nitration method, the dinitromethyl precursor was successfully nitrated to the trinitromethyl product (2), and its structure was thoroughly characterized by FTIR, NMR, elemental analysis, differential scanning calorimetry, and single-crystal X-ray diffraction. Compound 2 has a high density (1.897 g cm⁻³), high heat of formation (984.8 kJ mmol⁻¹), and a high detonation performance (D: 9351 m s⁻¹, P: 37.46 GPa) that may find useful applications in the field of high energy density materials.

2-(1,2,4-triazole-5-yl)-1,3,4-oxadiazole as a novel building block for energetic materials

The exploration of novel nitrogen-rich heterocyclic building blocks is of importance in the field of energetic materials. A series of 2-(1,2,4-triazole-5-yl)-1,3,4-oxadiazole derivatives based on a new energetic skeleton have been first synthesized by a simple synthetic strategy. All three compounds are well-characterized by IR spectroscopy, NMR spectroscopy and thermal analysis. The compounds 5 and 8 are further characterized by single-crystal X-ray diffraction analysis. 8 and its salts (8a-8c) possess relative high decomposition temperature and low sensitivity, while 5 exhibits low decomposition temperature and high sensitivity. According to EXPLO5 calculation results of detonation performance, both 5 and 8 display acceptable detonation velocities (D) of 8450 m/s and 8130 m/s and detonation pressures (P) of 31.6 GPa and 29.2 GPa, respectively. Furthermore, 5 containing a rare diazonium ylide structure shows high impact sensitivity (4.5 J), making it has a potential as a primary explosive.

Enhancement of Energetic Performance through the Construction of Trinitromethyl Substituted β-Bis(1,2,4-oxadiazole)

Halogen-free substitutions of ammonium perchlorate (AP), which meet the requirements of high density, high performance, and acceptable stability, have been a subject of scientific research for many years. In this work, by regrouping atoms in trinitromethyl substituted bis(1,2,4-oxadiazole), a novel oxidizer, trinitromethyl substituted β-bis(1,2,4-oxadiazole) (3), was designed and synthesized. It possesses an improved density (ρ = 2.002 g cm^-3 at 170 K, ρ = 1.942 g cm^-3 at 298 K) and thermal stability (T_d = 142.8 °C) in comparison to its regioisomer 5,5'-bis(trinitromethyl)-3,3'-bi(1,2,4-oxadiazole) (E). The properties for 3 were studied by both experimental and theoretical methods. The high positive oxygen balance of +7.3% and high specific impulse of 250 s also make compound 3 a promising candidate for an energetic oxidizer.

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.

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.

Pushing the Limit of Nitro Groups on a Pyrazole Ring with Energy-Stability Balance

Polynitro compounds exhibit high density and good oxygen balance, which are desirable for energetic material applications, but their syntheses are often very challenging. Now, the design and syntheses of a new three-dimensional (3D) energetic metal-organic framework (EMOF) and high-energy-density materials (HEDMs) with good thermal stabilities and detonation properties based on a polynitro pyrazole are reported. Dipotassium 3,5-bis(dinitromethyl)-4-nitro-1H-pyrazole (5) exhibits a 3D EMOF structure with good thermal stability (202 °C), a high density of 2.15 g cm^-3 at 100 K (2.10 g cm^-3 at 298 K) in combination with superior detonation performance (D_v = 7965 m s^-1, P = 29.3 GPa). Dihydrazinium 3,5-bis(dinitromethyl)-4-nitro-1H-pyrazole (7) exhibits a good density of 1.88 g cm^-3 at 100 K (1.83 g cm^-3 at 298 K) and superior thermal stability (218 °C), owing to the presence of 3D hydrogen-bonding networks. Its detonation velocity (8931 m s^-1) and detonation pressure (35.9 GPa) are considerably superior to those of 1,3,5-trinitro-1,3,5-triazine (RDX). The results highlight the syntheses of a 3D EMOF (5) and HEDM (7) with five nitro groups as potential energetic materials.

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.

Taming CL-20 through hydrogen bond interaction with nitromethane

A novel cocrystal explosive of CL-20/nitromethane in a 1 : 2 molar.

Octanitropyrazolopyrazole: a gem-trinitromethyl based green high-density energetic oxidizer

Environmental concerns demand the replacement of ammonium perchlorate (AP) by a green oxidizer in composite propellants. Herein, we report the synthesis and characterization of a novel green high-density energetic oxidizer octanitropyrazolopyrazole (ONPP). With its high specific impulse (256 s), high density (1.997 g cm-3) and good thermal stability (160 °C), ONPP can potentially replace AP.

Derivatives of 3,6-Bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine: Excellent Energetic Properties with Lower Sensitivities

To find a balance between energy and safety, a series of compounds based on azo-, azoxy-, 1,4,2,5-dioxadiazene-, and 3,6-diamino-1,2,4,5-tetrazine-bridged bis(aminofurazan) were designed and synthesized. These compounds were analyzed by nitro group charges (Q_nitro) and bond dissociation energy (BDE) calculations, which are related to sensitivity and stability. Based on the calculated results, derivatives of 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the largest values for -Q_nitro and BDE of all of the bis(aminofurazan) compounds. This shows that compounds based on 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the lowest sensitivities and best stabilities, which has been substantiated by experiments. Additionally, their explosive properties remain essentially competitive with compounds based on azo-, azoxy-, and 1,4,2,5-dioxadiazene-bridged bis(aminofurazan). Hirshfeld surface calculations were also performed to better understand the relationship between the molecular structure and stability/sensitivity. This work highlights the value of 3,6-diamino-1,2,4,5-tetrazine as a linker to achieve good balance between safety and energy.

gem-Dinitromethyl-Functionalized 5-Amino-1,3,4-oxadiazolate Derivatives: Alternate Route, Characterization, and Property Analysis

A new, safer, and more cost-effective methodology to synthesize salts based on gem-dinitromethyl-functionalized 5-amino-1,3,4-oxadiazolate is given. Cyclization, deprotection, nitration, and neutralization reactions were conducted to obtain products in high yield. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis, and differential scanning calorimetry. Crystal structure analysis, property tests, and theoretical calculations confirm good detonation performance and high mechanical stabilities of the salts.

A new oxygen-rich energetic salt dihydrazine tetranitroethide: a promising explosive alternative with high density and good performance

A novel high-energy salt with good oxygen balance, dihydrazine tetranitroethide (5), has been synthesized and characterized by FT-IR spectroscopy, NMR spectroscopy, elemental analysis, and X-ray single crystal diffraction. Compound 5 exhibits high crystal density (1.81 g cm-3) and impressive detonation velocity (9508 m s-1) and detonation pressure (37.9 GPa), showing potential applications as a high performance explosive and a promising additive of propellants.

Combination of gem-dinitromethyl functionality and a 5-amino-1,3,4-oxadiazole framework for zwitterionic energetic materials

A series of zwitterionic energetic materials was reported, which exhibited higher densities and better detonation performances than common energetic salts.

All-nitrogen ion-based compounds as energetic oxidizers: a theoretical study on [N5+][NO3−], [N5+][N(NO2)2−], [NO2+][N5−] and NO2–N3

The first four all-nitrogen pieces based energetic oxidizers, [N₅⁺][NO₃⁻], [N₅⁺][N(NO₂)₂⁻], [NO₂⁺][N₅⁻] and NO₂–N₃ (N₄O₂), were studied.

A novel energetic framework combining the advantages of furazan and triazole: a design for high-performance insensitive explosives

Combining energetic furazan and triazole rings to achieve a series of high performance and insensitive energetic compounds.

Bis(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)methanone: An Applicable and Very Dense Green Oxidizer

Ammonium perchlorate (AP) is most often used as a practical solid rocket propellant because of its excellent performance. However, AP has many shortcomings, including instability, high negative enthalpy of formation, and claimed health and environmental issues resulting from its combustion products. The pursuit of highly dense, high-performance, and environmentally friendly oxidizers as solid propellants has long attracted scientists around the world. In this work, bis(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)methanone (3) was obtained from bis(3-nitro-1H-1,2,4-triazol-5-yl)methane (1) with chloroacetone followed by nitration. The structure of 3 was confirmed by elemental analysis and single-crystal X-ray diffraction. By introducing the carbonyl moiety, the density of 3 was increased to 1.945 g/cm³ and the decomposition temperature increased to 164 °C. Compound 3 is a green energetic oxidizer that has a positive oxygen balance (+8.7%), a high specific impulse (218 s), and an acceptable sensitivity (9 J, 240 N), making it a practical replacement for AP in solid rocket propellant formulations.

Energetic Metal-Organic Frameworks Incorporating NH3OH+ for New High-Energy-Density Materials

Energetic metal-organic frameworks (E-MOFs) have witnessed increasing development over the past several years. However, as a highly energetic cation, NH₃OH⁺ has never been explored to construct transition-metal-based E-MOFs. Herein, we report the first examples of NH₃OH⁺-containing E-MOFs with bis(tetrazole)methane (H₂btm) as a ligand and copper and manganese as central metal ions, [(NH₃OH)₂(Cu(btm)₂)]_n and [(NH₃OH)₂(Mn(btm)₂)]_n. Crystal structure determinations reveal that both E-MOFs show two-dimensional layered structures. Experimental results suggest that they have high thermal decomposition temperatures (>200 °C). Among them, Cu-based E-MOFs possesses outstanding thermal stability (T_dec = 230.3 °C), which surpasses those of known NH₃OH⁺-containing compounds. They also have high energy density; in particular, the Cu-based E-MOF affords a high heat of combustion (11447 kJ kg^-1) and high heat of detonation (713.8 kJ mol^-1) beyond the most powerful organic explosives in use today. Additionally, the two E-MOFs show completely different sensitivity properties: the Mn-based E-MOF is an insensitive high-energy-density material (IS > 40 J; FS > 360 N; EDS > 20 J), while the Cu-based E-MOF can be classified as a sensitive energetic material (IS = 13 J; FS = 216 N; EDS = 10.25 J), demonstrating their diverse applications in different fields. Our research proposes a unique class of high-energy-density materials.

Theoretical screening of bistriazole-derived energetic salts with high energetic properties and low sensitivity

We designed four series of energetic anions by replacing nitro group (NO₂) with trinitromethyl group (C(NO₂)₃) or by inserting N-bridging groups (-NH-, -NH-NH-, -N[double bond, length as m-dash]N-, -N[double bond, length as m-dash]N(O)-) into the bistriazole frameworks. The properties of 40 energetic salts, based on the bistriazole-derived anions and hydroxylammonium cation, were studied by density functional theory (DFT) and volume-based thermodynamics calculations (VBT). It is found that the newly designed energetic salts have good detonation properties due to their larger nitrogen content and better oxygen balance. And one of their corresponding hydroxylammonium salts exhibits better detonation performance (D = 10.06 km s^-1 and P = 48.58 GPa) than CL-20 (D = 9.54 km s^-1 and P = 43.36 GPa). Moreover, 10 energetic salts not only exhibit excellent energetic properties superior to CL-20, but also have lower sensitivity than CL-20 (h ₅₀ = 13.81 cm). In addition, we rationally selected salt B6 from the 10 salts to predict its crystal structure under pressures. By converting energetic molecules with excellent detonation properties into energetic ions, some highly bistriazole-derived energetic salts with both excellent performance and low sensitivity could be developed strategically.

New Strategy for Enhancing Energetic Properties by Regulating Trifuroxan Configuration: 3,4-Bis(3-nitrofuroxan-4-yl)furoxan

It is of current development to construct high-performance energetic compounds by aggregation of energetic groups with dense arrangement. In this study, a hydrogen-free high-density energetic 3,4-bis(3-nitrofuroxan-4-yl)furoxan (BNTFO-I) was designed and synthesized in a simple, and straightforward manner. Its isomer, 3,4-bis(4-nitrofuroxan-3-yl)furoxan (BNTFO-IV), was also obtained by isomerization. The structures of BNTFO-I and BNTFO-IV were confirmed by single-crystal X-ray analysis for the first time. Surprisingly, BNTFO-I has a remarkable calculated crystal density of 1983 g cm-3 at 296 K, which is distinctly higher than BNTFO-IV (1.936 g cm-3, 296 K), and ranks highest among azole-based CNO compounds yet reported. It is noteworthy that BNTFO-I exhibits excellent calculated detonation properties (vD, 9867 m s-1, P, 45.0 GPa). The interesting configuration differences of BNTFO-I and BNTFO-IV provide insight into the design of new advanced energetic materials.