Constructing Highly Reliable and Adaptive Primary Explosive Composites for Micro-Initiator Assisting by a Hybrid Template of Metal-Organic Frameworks and Cross-Linked Polymers.

Primary explosive, as a reliable initiator for secondary explosives, is the central component of micro-initiators for modern aerospace systems and military operations. However, they are typically prepared as powders, posing potential safety risks because of the inevitable particles scattering issues in the actual working environments. Here, the fabrication of a highly adaptive bulk material of copper azide (CA)-based safe primary explosive for micro-initiators is demonstrated. This bulk material, as derived by a complete azidation reaction of the carbonized metal-organic framework/cross-linked polymer hybrid template, enables the firm embedding of active CA species in a cross-linked carbon network (denoted as CA-C). Interestingly, this CA-C bulk material demonstrates multifarious mechanical stabilities (e.g., good shock and vibration resistance, and anti-overload capacity) in the simulated working conditions. Meanwhile, the CA contents in the CA-C bulk material reached as high as 70.3%, ensuring its detonation power. As a proof of concept, CA-C bulk material assembling in a micro-detonator can efficiently detonate the secondary explosive of CL-20 under laser irradiation. This work hereby advances the fabrication of safe and powerful primary explosives for the fulfillment of safe micro-initiator in a broad range of applications in aerospace systems.

Copper Azide Nanoparticle-Encapsulating MOF-Derived Porous Carbon: Electrochemical Preparation for High-Performance Primary Explosive Film.

It is highly desired but still remains challenging to design a primary explosive-based nanoparticle-encapsulated conductive skeleton for the development of powerful yet safe energetic films employed in miniaturized explosive systems. Herein, a proof-of-concept electrochemical preparation of metal-organic frameworks (MOFs) derived porous carbon embedding copper-based azide (Cu(N3 )2 or CuN3 , CA) nanoparticles on copper substrate is described. A Cu-based MOF, i.e., Cu-BTC is fabricated based on anodized Cu(OH)2 nanorods, as a template, to achieve CA/C film through pyrolysis and electrochemical azidation. Such a CA/C film, which is woven by numerous ultrafine nanofibers, favorably demonstrates excellent energy release (945-2090 J g-1 ), tunable electrostatic sensitivity (0.22-1.39 mJ), and considerable initiation ability. The performance is superior to most reported primary explosives, since the CA nanoparticles contribute to high brisance and the protection of the porous carbon network. Notably, the growth mechanism of the CA/C film is further disclosed by detailed experimental investigation and density functional theory (DFT) calculation. This work will offer new insight to design and develop a CA-based primary explosive film for applications in advanced explosive systems.

1-(Azidomethyl)-5H-Tetrazole: A Powerful New Ligand for Highly Energetic Coordination Compounds.

Highly energetic 1-(azidomethyl)-5H-tetrazole (AzMT, 3) has been synthesized and characterized. This completes the series of 1-(azidoalkyl)-5H-tetrazoles represented by 1-(azidoethyl)-5H-tetrazole (AET) and 1-(azidopropyl)-5H-tetrazole (APT). AzMT was thoroughly analyzed by single-crystal X-ray diffraction experiments, elemental analysis, IR spectroscopy and multinuclear (1 H, 13 C, 14 N, 15 N) NMR measurements. Several energetic coordination compounds (ECCs) of 3d metals (Mn, Fe, Cu, Zn) and silver in combination with anions such as (per)chlorate, mono- and dihydroxy-trinitrophenolate were prepared, giving insight into the coordination behavior of AzMT as a ligand. The synthesized ECCs were also analyzed by X-ray diffraction experiments, elemental analysis, and IR spectroscopy. Differential thermal analysis for all compounds was conducted, and the sensitivity towards external stimuli (impact, friction, and ESD) was measured. Due to the high enthalpy of formation of AzMT (+654.5 kJ mol-1 ), some of the resulting coordination compounds are extremely sensitive, yet are able to undergo deflagration-to-detonation transition (DDT) and initiate pentaerythritol tetranitrate (PETN). Therefore, they are to be ranked as primary explosives.

A Smart Access to the Dinitramide Anion - The Use of Dinitraminic Acid for the Preparation of Nitrogen-Rich Energetic Copper(II) Complexes.

Dinitraminic acid (HN(NO2 )2 , HDN) was prepared by ion exchange chromatography and acid-base reaction with basic copper(II) carbonate allowed the in situ preparation of copper(II) dinitramide, which was reacted with twelve nitrogen-rich ligands, for example, 4-amino-1,2,4-triazole, 1-methyl-5H-tetrazole, di(5H-tetrazolyl)-methane/-ethane/-propane/-butane. Nine of the complexes were investigated by low-temperature X-ray diffraction. In addition, all compounds were investigated by infrared spectroscopy (IR), differential thermal analysis (DTA), elemental analysis (EA) and thermogravimetric analysis (TGA) for selected compounds. Furthermore, investigations of the materials were carried out regarding their sensitivity toward impact (IS), friction (FS), ball drop impact (BDIS) and electrostatic discharge (ESD). In addition, hot plate and hot needle tests were performed. Complex [Cu(AMT)4 (H2 O)](DN)2 , based on 1-amino-5-methyltetrazole (AMT), is most outstanding for its detonative behavior and thus also capable of initiating PETN in classical initiation experiments. Laser ignition experiments at a wavelength of 915 nm were performed for all substances and solid-state UV-Vis spectra were recorded to apprehend the ignition mechanism.

Alkali Metals-Based Energetic Coordination Polymers as Promising Primary Explosives: Crystal Structures, Energetic Properties, and Environmental Impact.

Coordination polymers (CPs) consisting of alkali metals (Na, K, Rb, and Cs) and a powerful nitrogen- and oxygen-rich energetic ligand (4,4'-bis(dinitromethyl)-3,3'-bisnitramide-methylene-furazanate, DBMF2- ) were developed. Molecular structures of these CPs, confirmed by single-crystal X-ray diffraction analysis, indicated that the same ligand takes on a U-shaped state for Na and an N-shaped state for K, Rb, and Cs. Explosion tests demonstrated that both Na2 DBMF and K2 DBMF efficiently detonated the secondary explosive RDX. This indicates that they are both effective primary explosives. K2 DBMF exhibits better calculated detonation performance (D: 8227 m s-1 ; P: 32.5 GPa) than the primary explosive Pb(N3 )2 . In addition, toxicity tests and evaluation of their decomposition products reveal their low impact on the environment. Both experimental results and theoretical analyses indicate that the combination of alkali metals and a powerful energetic ligand can stimulate the development of primary explosives.

Multipurpose Energetic Materials by Shuffling Nitro Groups on a 3,3'-Bipyrazole Moiety.

A family of 3,3'-bipyrazole-based energetic compounds having C-NO2 /N-NO2 functionalities was synthesized by using various nitrating conditions. These nitro derivatives of bipyrazole are significantly more dense and energetic compared to the corresponding nitropyrazole analogues while maintaining the desired thermal stability and sensitivity. Depending on the number and nature of energetic nitro groups (C-NO2 /N-NO2 ), different classes of energetic materials, such as green primary explosives, high-performance secondary explosives and heat-resistant explosives, were obtained. All the compounds were thoroughly characterized by IR, NMR [1 H, 13 C{1 H}, 15 N], elemental analysis, and differential scanning calorimetry (DSC). Four were also structurally characterized with single-crystal X-ray diffraction studies. Heats of formation and detonation performance were calculated using Gaussian 03 and EXPLO5 v6.01 programs, respectively.

Methylsemicarbazide as a Ligand in Late 3d Transition Metal Complexes.

Most ignition and initiation systems nowadays still contain poisonous chemicals such as lead styphnate and lead azide but also chromates and other compounds of high concern. Therefore, methylsemicarbazide (1, MSC), which can be prepared in a one-step reaction and in an extraordinary high yield of 95 %, has been evaluated as ligand in energetic coordination compounds. For the first time 25 new transition metal complexes (Mn2+ , Ni2+ , Co2+ , Cu2+ , and Zn2+ ) using methylsemicarbazide (1) as the ligand were prepared and comprehensively analyzed by, for example, XRD, IR, EA, UV/Vis and DSC/DTA/TGA. Many show a strong energetic character, which can be tuned by using different anions such as Cl- , SO42- , NO3- , ClO4- , picrate or styphnate. Selected compounds were additionally evaluated as lead-free primary explosives in initiation tests (nitropenta filled detonators) and in laser ignition systems. Especially compound 7 showed very promising results during these tests and could be a potential candidate for future applications.

C8 N26 H4 : An Environmentally Friendly Primary Explosive with High Heat of Formation.

The synthesis and characterization of the metal-free polyazido compounds 3,6-bis-(2-(4,6-diazido-1,3,5-triazin-2-yl)-hydrazinyl)-1,2,4,5-tetrazine (2) and 3,6-bis-(2-(4,6-diazido-1,3,5-triazin-2-yl)-diazenyl)-1,2,4,5-tetrazine (4) are presented. Two compounds were characterized by NMR spectra, IR spectroscopy, mass spectrometry, and differential scanning calorimetry (DSC). Additionally, the structure of 2 was confirmed by single-crystal X-ray diffraction. Compounds 2 and 4 exhibit measured densities (1.755 g cm-3 and 1.763 g cm-3 ), good thermal stabilities (194 °C and 189 °C), high heat of formation (2114 kJ mol-1 and 2820 kJ mol-1 ), and excellent detonation performance (D, 8365 m s-1 and 8602 m s-1 ; P, 26.8 GPa and 29.4 GPa). Furthermore, compounds 2 and 4 have been tested for their priming ability to detonate RDX. The results indicate that the title compound 2 is a potential environmentally friendly alternative candidate to lead-based primary explosives.

Potassium Nitraminofurazan Derivatives: Potential Green Primary Explosives with High Energy and Comparable Low Friction Sensitivities.

Lead-based primary explosives were widely applied in military and civilian ammunition, which have subsequently caused serious environmental and health-related problems. Therefore, the development of green alternatives for the lead-based primary explosives has been one of the major focuses in the field of energetic materials. Four potassium salts based on nitraminofurazan have been easily synthesized and show excellent comprehensive performances. Among them, potassium 3-dinitromethyl-4-nitraminofurazan (K2 DNMNAF, 1) showed better thermal stability (Td : 281.4 °C), higher density (2.174 g cm-3 ), and lower friction sensitivities (72 N) than that of potassium 4,5-bis(dinitromethyl)furoxanate (K2 BDNMF, Td : 218.3 °C, density: 2.130 g cm-3 , FS: 5 N, P: 27.3 GPa, vD : 7759 m s-1 ); furthermore, it displayed comparable detonation performances (P: 27.2 GPa, vD : 7758 m s-1 ). The promising properties of these salts make this kind of material a competitive alternative to lead azide as a primary explosive.

13 C and 15 N NMR spectra of high-energy polyazidocyanopyridines.

13 C and 15 N NMR spectra of high-energy 2,4,6-triazidopyridine-3,5-dicarbonitrile, 2,3,5,6-tetraazidopyridine-4-carbonitrile and 3,4,5,6-tetraazidopyridine-2-carbonitrile are reported. The assignment of signals in the spectra was performed on the basis of density functional theory calculations. The molecular geometries were optimized using the M06-2X functional with the 6-311+G(d,p) basis set. The magnetic shielding tensors were calculated by the gauge-independent atomic orbital method with the Tao-Perdew-Staroverov-Scuseria hybrid functional known as TPSSh. In all the calculations, a polarizable continuum model was used to simulate solvent effects. This approach provided accurate predictions of the 13 C and 15 N chemical shifts for all the three compounds despite complications arising due to non-coplanar arrangement of the azido groups in the molecules. It was found that the 15 N chemical shifts of the Nα atoms in the azido groups of 2,4,6-triazidopyridines correlate with the 13 C chemical shifts of the carbon atoms attached to these azido groups. Copyright © 2016 John Wiley & Sons, Ltd.