In Situ MOF-74-Pyrolysis-Generated Porous Carbon Supporting Spinel Cu0.15Co2.85O4/C Boosts Ammonium Perchlorate Accelerating Decomposition: Precise Cu Doping Modulating Oxygen Vacancy Concentration.

As one of the main components of solid propellant, ammonium perchlorate (AP) shows slow sluggish decomposition kinetics with unconcentrated heat release. To achieve efficient catalytical decomposition, it is a significant challenge to design reasonable catalyst structure and explore the interaction between catalyst and AP. Herein, a series of porous carbon supported spinel-typed homogeneous heterometallic composites CuxCo3-xO4/C via pyrolysis of MOF-74-Co doped Cu. On basis of precise electronic-structure-tuning through modulating Cu/Co ratio in MOF-74, Cu0.15Co2.85O4/C with 5% Cu-doping featuring oxygen vacancy concentration of 26.25% exhibits the decrease to 261.5 °C with heat release up to 1222.1 J g-1 (456.9 °C and 669.2 J g-1 for pure AP). The detail process of AP accelerated decomposition is approved by TG-DSC-FTIR-MS technique. Density functional theory calculation revealed that in the Cu0.15Co2.85O4/C, the distinctive ability for NH3 catalyzed oxidation assisted with absorption performance of active porous C boosts accelerating AP decomposition. The findings would provide an insight for perceiving and understanding AP catalytic decomposition.

Synthetic Strategies Toward Nitrogen-Rich Energetic Compounds Via the Reaction Characteristics of Cyanofurazan/Furoxan.

The structural units of amino-/cyano-substituted furazans and furoxans played significant roles in the synthesis of nitrogen-rich energetic compounds. This account focused on the synthetic strategies toward nitrogen-rich energetic compounds through the transformations based on cyanofurazan/furoxan structures, including 3-amino-4-cyanofurazan, 4-amino-3-cyano furoxan, 3,4-dicyanofurazan, and 3,4-dicyanofuroxan. The synthetic strategies toward seven kinds of nitrogen-rich energetic compounds, such as azo (azoxy)-bridged, ether-bridged, methylene-bridged, hybrid furazan/furoxan-tetrazole-based, tandem furoxan-based, hybrid furazan-isofurazan-based, hybrid furoxan-isoxazole-based and fused framework-based energetic compounds were fully reviewed, with the corresponding reaction mechanisms toward the nitrogen-rich aromatic frameworks and examples of using the frameworks to create high energetic substances highlighted and discussed. The energetic properties of typical nitrogen-rich energetic compounds had also been compared and summarized.

3,4-Bis(3-tetrazolylfuroxan-4-yl)furoxan: A Linear C-C Bonded Pentaheterocyclic Energetic Material with High Heat of Formation and Superior Performance.

The design and preparation of new nitrogen-rich heterocyclic compounds are of considerable significance for the development of high-performing energetic materials. By combining nitrogen-rich tetrazole and oxygen-rich furoxan, a linear C-C bonded pentaheterocyclic energetic compound, 3,4-bis(3-tetrazolylfuroxan-4-yl) furoxan (BTTFO), was synthesized using a facile and straightforward method. Comprehensive X-ray analysis reveals the key role of hydrogen bonds, π-π interactions, and short contacts in the formation of dense packing of BTTFO and explains why a long chain-shaped molecule has a high density. This multicyclic structure incorporating three furoxan and two tetrazole moieties results in an exceptionally high heat of formation (1290.8 kJ mol-1) and favorable calculated detonation performances (v D, 8621 m s-1, P, 31.5 GPa). The interesting structure and fascinating properties demonstrated the feasibility of a linear multicyclic approach as a high-energy-density skeleton. Additionally, the thermodynamic parameters, electrostatic potential (ESP), and frontier molecular orbitals were also studied to get a better understanding of structure-property correlations.

A promising insensitive energetic material based on a fluorodinitromethyl explosophore group and 1,2,3,4-tetrahydro-1,3,5-triazine: synthesis, crystal structure and performance.

The introduction of fluorodinitromethyl energetic groups is an efficient strategy to improve the performances of energetic materials. In this paper, an insensitive energetic compound 6-(fluorodinitromethyl)-3-nitro-1,2,3,4-tetrahydro-1,3,5-triazine (FMTNT) was designed and synthesized based on the modification of 1,3,5-triazine backbone via the nitration-rearrangement, reduction and fluorination sequence. The single crystal of FMTNT was firstly obtained and determined, meanwhile, this novel structure was also fully characterized by the methods of IR, 1H NMR, 13C NMR, 19F NMR and elemental analysis. Studies on thermal behaviors and detonation performances of FMTNT were also carried out through differential scanning calorimetry (DSC-TG) approach and EXPLO5 program, respectively. The decomposition temperature of FMTNT is found to be at 157.5 °C via thermal chemical analysis and the detonation performances were proved to be good, with a detonation velocity of 8624.8 m s-1 and detonation pressure of 29.1 Gpa. Furthermore, the experimental results showed that impact and friction sensitivity reaches 20 J and 240 N, even less sensitive than TNT, indicating a broad perspective in the application of insensitive explosives and propellants.

A comparative study of the structures, thermal stabilities and energetic performances of two energetic regioisomers: 3(4)-(4-aminofurazan-3-yl)-4(3)-(4-nitrofurazan-3-yl)furoxan.

Although energetic regioisomers have attracted intensive attention due to their interesting structure-property correlation, their effective synthesis and accurate identification has remained very difficult. In this paper, we synthesized two energetic regioisomers, namely 3-(4-aminofurazan-3-yl)-4-(4-nitrofurazan-3-yl)furoxan (ANFF-34) and 4-(4-aminofurazan-3-yl)-3-(4-nitrofurazan-3-yl)furoxan (ANFF-43), via a controllable strategy with improved yields of 32% and 38%, respectively. The structures of ANFF-34 and ANFF-43 were unambiguously identified using comparative studies of 15N NMR and single-crystal X-ray diffraction. Moreover, their thermal behaviours, and non-isothermal thermodynamic parameters were systematically investigated. Both ANFF-34 (T m: 116.2 °C, T d: 255.4 °C) and ANFF-43 (T m: 106.2 °C, T d: 255.6 °C) have similar thermal decomposition processes to that of DNTF. The superior performances of ANFF-34 (ρ: 1.8 g cm-3, D: 8214 m s-1, P: 30.5 GPa, IS > 40 J) and ANFF-43 (ρ: 1.7 g cm-3, D: 7868 m s-1, P: 27.0 GPa, IS > 40 J) indicate their great potential to be used as melt-cast carrier explosives. This study provides a solid foundation for the design and synthesis of new energetic compounds through isomer effects.

The Ingenious Synthesis of a Nitro-Free Insensitive High-Energy Material Featuring Face-to-Face and Edge-to-Face π-Interactions.

Density, detonation property, and sensitivity may be the most valued features when evaluating an energetic material. By reasoning structure-property relationships, a nitro-free planar energetic material with high nitrogen and oxygen content, 7-hydroxy-difurazano[3,4-b:3',4'-f]furoxano[3″,4″-d]azepine (4), was synthesized using a unique and facile approach. The structure was fully characterized by IR and NMR spectra, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. The expected properties of 4, including a high density of 1.92 g cm-3, high detonation velocity of 8,875 m s-1, and low mechanical sensitivities (impact sensitivity, 21 J and friction sensitivity, >360 N), confirm our strategy. Interestingly, the single-crystal structures of 4 reveal expected face-to-face and edge-to-face π-interactions in the crystal stacking. The remarkable differences in crystal stacking of 4 provide unequivocal evidence that face-to-face π-π interactions contribute significantly to closer assembly and higher density.

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.

Synthesis, Characterization and Performance of Promising Energetic Materials Based on 1,3-Oxazinane.

1,3-oxazinane is an ideal framework for advanced energetic materials because of its compact skeleton and the presence of several modifiable sites. However, investigations on characterization and performance of 1,3-oxazinane energetic compounds are extremely limited. Two heterocyclic 1,3-oxazinane molecules were synthesized under different Mannich condensation processes and further reacted to form nitro- and azide-substituted energetic compounds 3,5,5-trinitro-1,3-oxazinane (TNTON) and 5-azido-3,5-dinitro-1,3-oxazinane (ADTON), in good yields. Interestingly, the two energetic molecules showed distinct physical properties. ADTON shows an impressive glass transition temperature (Tg) as low as -46 °C with high density, which is highly suitable for rate-accelerating materials. TNTON exhibits good thermal stabilities (melting point of 89 °C and a decomposition point of 231 °C) and highly insensitive behavior (38 J, 360 N). The theoretical detonation pressure of TNTON is ca. 63 % higher than that of TNT, indicating broad application prospects in melt-cast explosives.

A Family of Energetic Materials Based on 1,2,4-Oxadiazole and 1,2,5-Oxadiazole Backbones With Low Insensitivity and Good Detonation Performance.

Design and synthesis of new compounds with both high detonation performances and good safety properties have always been a formidable task in the field of energetic materials. By introducing -ONO2 and -NHNO2 moieties into 1,2,4-oxadiazole- and 1,2,5-oxadiazole-based backbones, a new family of energetic materials, including ammonium 3-nitramino-4-(5-hydroxymethyl-1,2,4-oxadiazol-3-yl)-furazan (4), 3,3'-bis[5-nitroxymethyl-1,2,4-oxadiazol-3-yl]-4,4'-azofuroxan (6), [3-(4-nitroamino-1,2,5-oxadiazol-3-yl)-1,2,4-oxadiazol-5-yl]-methylene nitrate (8), and its energetic ionic salts (10-12), were synthesized and fully characterized. The energetic and physical properties of the materials were investigated through theoretical calculations and experimental determination. The results show that the oxadiazole-based compounds exhibit high enthalpy of formations, good detonation performances, and extraordinary insensitivities. In particular, the hydrazinium salt (11) shows the best energetic properties (11: d = 1.821 g cm-3; P = 35.1 GPa, v D = 8,822 m s-1, IS = 40 J, FS > 360N). The ESP and Hirshfeld surface analysis indicated that a large number of hydrogen bonds as well as π-π stacking interactions within molecules might be the key reason for their low sensitivities and high energy-density levels.

Experimental and theoretical studies on stability of new stabilizers for N-methyl-P-nitroaniline derivative in CMDB propellants.

Although N-methyl-P-nitroaniline (MNA) was a quite effective stabilizer in composite modified double base (CMDB) propellants, it undergoes crystallization easily from nitroglycerin (NG) during storage. In order to improve its solubility in nitroglycerin (NG) and the stability in propellants, several new stabilizers including N-ethyl-p-nitroaniline (ENA), N-n-propyl-p-nitroaniline (n-PNA), N-i-propyl-p-nitroaniline (i-PNA), N-n-butyl-p-nitroaniline (n-BNA) and N-t-butyl-p-nitroaniline (t-BNA) were designed and synthesized to replace MNA by increasing the carbon chain length. The interaction between NG and different stabilizers was simulation by Materials Studio 5.5 and the stability and the high temperature stability performance of those new stabilizers in propellants were calculated by Gaussian 09. It was found that both the solubility of new stabilizers in NG and the stability and the high temperature stability performance of those in propellants were improved when the carbon chain length of substitution groups on nitrogen atom was increased. Thus, the n-BNA was a most potential stabilizer. Then all properties of the stabilizers were studied experimentally, which was agreement well with the theoretical analysis.

Copper-based energetic MOFs with 3-nitro-1H-1,2,4-triazole: solvent-dependent syntheses, structures and energetic performances.

The persistent challenge in the field of energetic materials is how to synthesize energetic compounds with high density, high heat of detonation and outstanding detonation performance by gathering the maximum number of energetic groups in the smallest volume. The self-assembly of energetic groups with metal ions is crucially influenced by the solvent conditions. Here, the reaction of Cu(NO3)2·3H2O with 3-nitro-1H-1,2,4-triazole (Hntz) in aqueous ammonia under hydrothermal conditions via a self-assembly strategy yielded the Cu(i) energetic compound [Cu(ntz)]n (1). In order to further enhance the energetic property, an N3- anion was introduced into the system and two Cu(ii) energetic compounds, [Cu(ntz)(N3)(DMF)]n (2) and [Cu(ntz)(N3)(H2O)]n (3), were successfully synthesized under different solvent conditions. Structural analyses show that compound 1 features a compacted 3D structure framework and compounds 2-3 exhibit 1D butterfly-like chain structures. The experimental results reveal that 1 possesses attractive thermal stability up to 315.0 °C and 1-3 present excellent insensitivity. Importantly, the heat of detonation of compound 2 has been factually improved due to the abundant energetic bonds in the coordinated DMF molecules compared to 1 and lots of energies are taken away during the release of the coordinated solvent molecules in the low temperature range resulting in the obvious decreases in detonation pressure and detonation velocity for compounds 2-3, which further exemplifies that the subtle change of reaction conditions may have a crucial effect on the resultant detonation performance. In addition, the detonation performances of 1-3 calculated by both a simple method for metal-containing explosives developed by Pang et al. and the commercial program EXPLO5 v6.01, are discussed in detail.

High Energy Density Materials Incorporating 4,5-Bis(dinitromethyl)-Furoxanate and 4,5-Bis(dinitromethyl)-3-Oxy-Furoxanate.

3-Oxy-furoxanate is immobilized in a heterometallic energetic metal-organic framework (MOFs). Two furoxan-based MOFs ([Ag2 K4 (BDOFO)(BDFO)2 (H2 O)6 ]n , [K2 (BDFO)]n ) and a salt ([(BDFO2- )(NH2 NH3 + )2 (H2 O)]n (BDOFO2- =4,5-bis(dinitromethyl)-3-oxy-furoxanate, BDFO2- =4,5-bis(dinitromethyl)-furoxanate) are synthesized and their energetic performance evaluated. This study outlines the systematic investigation of detonation performance of 3-oxy-furoxan and its derivatives.