Metal-Determined Explosive Characteristics of M(NO3)2(1-AT)x of Thermal and Laser Ignition (M2+ = Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+; x = 2 or 3)

Optical and thermal ignition are two common pathways to initiate the explosion of primary explosives, where laser ignition is a more reliable and safer initiation method. Caused by the current-applied laser igniter with the wavelength of 1064 or 915 nm, the energetic complexes with strong absorption in the near-infrared (NIR) region are possibly applied as laser-ignited explosives. Recently, [Cu(NO3)2(1-AT)3] complex has been synthesized with excellent NIR absorption properties, where 1-amino-5H-tetrazole (1-AT) has been proved to be a promising laser-ignited energetic ligand. To confirm the structure-thermal/optical explosive characteristics, based on the structure of synthesized [Cu(NO3)2(1-AT)3], the commonly used transition-metal cations (M2+ = Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) have been selected to construct the series of complexes of M(NO3)2(1-AT)x (x = 2 or 3) theoretically. Car-Parrinello molecular dynamics (CPMD) method has been applied to unveil the role of center metals in the initiation and growth pathways. Time-dependent density functional theory (TD-DFT) method is used to explore their charge-transfer (CT) characteristics. The optical characteristic of the metal complex is mainly determined by the behaviors of the 3d electrons of center metals in excitation, where the activity of β-d electrons is an important factor to affect the NIR characteristic of complexes.

Polyiodo Azole-Based Metal-Organic Framework Energetic Biocidal Material for Synergetic Sterilization Applications

Biological hazards caused by bacteria, viruses, and toxins have become a major survival and development issue facing the international community. However, the traditional method of disinfection and sterilization is helpless in dealing with viruses that spread quickly and are highly infectious. Metal-organic framework (MOF) biocidal materials hold promise as superior alternatives to traditional sterilization materials because of their stable framework structures and unique properties. Now, we demonstrate for the first time the synthesis of a MOF (TIBT-Cu) containing Cu metal centers and tetraiodo-4,4'-bi-1,2,4-triazole as the main ligand. This novel MOF biocidal material has good thermal stability (Td = 278 °C), excellent mechanical sensitivity, and a high bacteriostatic efficiency (>99.90%). Additionally, the particles produced by the combustion of TIBT-Cu are composed of active iodine substances and CuO particles, which can act synergistically against harmful microorganisms such as bacteria and viruses. This study provides a new perspective for the preparation of highly effective bactericidal materials.

A Physical Organic Approach towards Statistical Modeling of Tetrazole and Azide Decomposition

Nitrogen atom-rich heterocycles and organic azides have found extensive use in many sectors of modern chemistry from drug discovery to energetic materials. The prediction and understanding of their energetic properties are thus key to the safe and effective application of these compounds. In this work, we disclose the use of multivariate linear regression modeling for the prediction of the decomposition temperature and impact sensitivity of structurally diverse tetrazoles and organic azides. We report a data-driven approach for property prediction featuring a collection of quantum mechanical parameters and computational workflows. The statistical models reported herein carry predictive accuracy as well as chemical interpretability. Model validation was successfully accomplished via tetrazole test sets with parameters generated exclusively in silico. Mechanistic analysis of the statistical models indicated distinct divergent pathways of thermal and impact-initiated decomposition.

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.

Understanding Explosive Sensitivity with Effective Trigger Linkage Kinetics

We present a simple linear model for ranking the drop weight impact sensitivity of organic explosives that is based explicitly on chemical kinetics. The model is parameterized to specific heats of explosion, Q, and Arrhenius kinetics for the onset of chemical reactions that are obtained from gas-phase Born-Oppenheimer molecular dynamics simulations for a chemically diverse set of 24 molecules. Reactive molecular dynamics simulations sample all possible decomposition pathways of the molecules with the appropriate probabilities to provide an effective reaction barrier. In addition, the calculations of effective trigger linkage kinetics can be accomplished without prior physical intuition of the most likely decomposition pathways. We found that the specific heat of explosion tends to reduce the effective barrier for decomposition in accordance with the Bell-Evans-Polanyi principle, which accounts naturally for the well-known correlations between explosive performance and sensitivity. Our model indicates that sensitive explosives derive their properties from a combination of weak trigger linkages that react at relatively low temperatures and large specific heats of explosion that further reduce the effective activation energy.

Polynitro-N-aryl-C-nitro-pyrazole/imidazole Derivatives: Thermally Stable-Insensitive Energetic Materials

A wide array of methoxy-substituted-polynitro-aryl-pyrazole/imidazoles with readily oxidizable -NH₂/NO₂/NHNO₂/diazo functional groups is synthesized. Single crystal X-ray diffraction (XRD) analysis confirms the molecular structure of the compounds. Energetic properties of the synthesized compounds are determined by theoretical and experimental studies. Most of the compounds are thermally stable and insensitive to impact and friction. Some of the molecules possess better detonation velocity and detonation pressure over TNT.

Metal-Free Stereoselective Addition of Propiolic acids to Ynamides: A Concise Synthetic Route to Highly Substituted Ene-Diyne/Dienyne-(E)-N,O-Acetals

A straight forward and sustainable approach for 1,2-addition of propiolic acids to ynamide has led to bench stable sp2 (E)-enol-enamides of enediynes & dienynes. The reaction is chemo, regio, as...

Flexible organic crystals. Understanding the tractable co-existence of elastic and plastic bending

As an emerging class of flexible materials, mechanically bendable molecular crystals are broadly classified as elastic or plastic. Nevertheless, flexible organic crystals with mutually exclusive elastic and plastic traits, with contrasting structural requirements, co-existing under different stress settings are exceptional; hence, it is imperative to establish the concurring factors that beget this rare occurrence. We report a series of halogen-substituted benzil crystals showing elastic bending (within ∼2.45% strain), followed by elastoplastic deformation under ambient conditions. Under higher stress settings, they display exceptional plastic flexibility that one could bend, twist, or even coil around a capillary tube. X-ray diffraction, microscopy, and computational data reveal the microscopic and macroscopic basis for the exciting co-existence of elastic, elastoplastic, and plastic properties in the crystals. The layered molecular arrangement and the weak dispersive interactions sustaining the interlayer region provide considerable tolerance towards breaking and making upon engaging or releasing the external stress; it enables restoring the original state within the elastic strain. Comparative studies with oxalate compounds, wherein the twisted diketo moiety in benzil was replaced with a rigid and coplanar central oxalate moiety, enabled us to understand the effect of the anisotropy factor on the crystal packing induced by the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O⋯C tetral interactions. The enhanced anisotropy depreciated the elastic domain, making the oxalate crystals more prone to plastic deformation. Three-point bending experiments and the determined Young's moduli further corroborate the co-existence of the elastic and plastic realm and highlight the critical role of the underlying structural elements that determine the elastic to plastic transformation. The work highlights the possible co-existence of orthogonal mechanical characteristics in molecular crystals and further construed the concurrent role of microscopic and macroscopic elements in attaining this exceptional mechanical trait.

Structural and mechanical studies of benzil and oxalate crystals highlight the microscopic and macroscopic basis for the co-existence of orthogonal mechanical traits and the elastic to plastic transformation under different stress settings.

Nitratoethyl-5H-tetrazoles: improving the oxygen balance through application of organic nitrates in energetic coordination compounds

1- and 2-Nitratoethyl-5H-tetrazole (1-NET and 2-NET) were prepared through nitration of the respective alkyl alcohol using 100% nitric acid. A mixture of 1- and 2-hydroxyethyl-5H-tetrazole was obtained after alkylation of 1,5H-tetrazole. Also, a one-pot synthesis of 1-hydroxyethyl-5H-tetrazole was developed enabling the selective preparation of 1-NET. Both organic nitrates were characterized by ¹H, ¹³C, and ¹H-¹⁵N HMBC NMR spectroscopy. In addition, calculations using the Hirshfeld method and the EXPLO5 code were performed. Principally, 20 energetic coordination compounds involving the d-metals Mn, Cu, Zn, and Ag, each structurally characterized by low temperature single crystal X-ray diffraction, were prepared based on 1-NET and 2-NET. Of these complexes, 18 were obtained as pure bulk materials, and therefore, characterized for impact, friction, and ball drop impact sensitivity, as well as electrostatic discharge and thermal stability using differential thermal analysis. Hot plate and hot needle tests were performed mostly showing strong deflagrations making the complexes candidates for green combustion catalysts. Furthermore, successful PETN initiation experiments were carried out for several complexes and all ECCs were investigated by laser ignition experiments.

Combining 1,2,4-triazole and pyrazole frameworks for new insensitive energetic materials

A new symmetric compound 3,5-bis(3-amine-4H-1,2,4-triazole)-1H-pyrazole and a series of corresponding energetic cationic salts were synthesized.

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.

Combining the furoxanylhydrazone framework with various energetic functionalities to prepare new insensitive energetic materials with 3D-cube layer stacking

We provide a new series of energetic salts and neutral compounds containing furoxanylhydrazone with 3D-cube layer stacking.

1,3,4-Oxadiazole based thermostable energetic materials: synthesis and structure–property relationship

A combination of 1,3,4-oxadiazole and pyrazole produces a series of new compounds with satisfactory energetic properties.

A promising cation of 4-aminofurazan-3-carboxylic acid amidrazone in desensitizing energetic materials

For the development of energetic materials, insensitive compounds have attracted considerable attention due to their improved safety and lower cost than those of sensitive energetic compounds during production, transportation, and application. In this study, insensitive 4-aminofurazan-3-carboxylic acid amidrazone was used as a cation to obtain four derivatives which were determined by X-ray single crystal diffraction. It is interesting to note that all four derivatives are insensitive to impact and friction, while the velocities of detonation for derivatives are superior to that of insensitive TATB (1,3,5-triamino-2,4,6-trinitrobenzene). Multi-factors analysis shows that the cation of 4-aminofurazan-3-carboxylic acid amidrazone is a promising furazan-based cation in desensitizing energetic compounds.

4-Aminofurazan-3-carboxylic acid amidrazone was used to obtain four derivatives confirmed by X-ray diffraction. The derivatives are insensitive to impact and friction, while the velocities of detonation are superior to that of 1,3,5-triamino-2,4,6-trinitrobenzene.

An efficient strategy for the preparation of insensitive energetic materials: intramolecular cyclization of picrylhydrazone into an indazole derivative

An efficient method to acheive a balance of energy and sensitivity through the intramolecular cyclization reaction of picrylhydrazone into an indazole derivative.

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.

1,2,4-Oxadiazole-Bridged Polynitropyrazole Energetic Materials with Enhanced Thermal Stability and Low Sensitivity

A family of mono or di(1,2,4-oxadiazole)-bridged polynitropyrazole derivatives with C-nitro/N-nitro functionalities is reported. All compounds were fully characterized by IR, NMR (¹ H, ¹³ C), elemental analysis and differential scanning calorimetry (DSC). The solid-state structure features were further investigated with X-ray diffraction. Of these, compounds 3,5-bis(3,4-dinitro-1H-pyrazol-5-yl)-1,2,4-oxadiazole (3 a) and 5,5'-bis(3,4-dinitro-1H-pyrazol-5-yl)-3,3'-bi(1,2,4-oxadiazole) (3 b) possess high thermal stability (3 a: T_dec =274 °C; 3 b: T_dec =272 °C), sensitivity (IS >30 J, FS >360 N) and comparable detonation properties (3 a: D_v =8741 m s^-1 , P=34.0 GPa; 3 b: D_v =8685 m s^-1 , P=33.4 Gpa) to RDX. In addition, 3,5-bis(4-nitro-1H-pyrazol-3-yl)-1,2,4-oxadiazole (4 a) and 5,5'-bis(4-nitro-1H-pyrazol-3-yl)-3,3'-bi(1,2,4-oxadiazole) (4 b) have high decomposition temperature (4 a: T_dec =314 °C; 4 b: T_dec =317 °C), low sensitivity (IS >40 J; FS>360 N) and superior detonation performances (4 a: D_v =8027 m s^-1 , P=26.4 GPa; 4 b: D_v =7991 m s^-1 , P=25.2 Gpa) than conventional heat-resistant explosive hexanitrostilbene (HNS: T_dec =318 °C; IS=5 J; FS=240 N; D_v =7612 m s^-1 , P=24.3 GPa), thus suggesting their potential application as heat-resistant explosives.

Novel strategies for synthesizing energetic materials based on BTO with improved performances

The layer-by-layer assembly of molecules is ubiquitous in nature. Highly ordered structures formed in this manner often exhibit fascinating material properties. A layer hydrogen bonding pairing approach allows the development of tunable energetic materials with targeted properties. A series of unusual energetic compounds based on 1H,1'H-5,5'-bistetrazole-1,1'-diolate (1), such as the salts of 3-amino-1,2,4-triazolium (2), aminoguanidinium (3), and hydrazinium (4), and the cocrystals of 4-amino-1H-pyrazole (5), 2-methylimidazole (6), and imidazole (7), were synthesized using this strategy. The structures of the obtained products 2-7 were fully characterized by elemental analysis, IR spectroscopy, ¹H NMR and ¹³C NMR spectroscopy, and single-crystal X-ray analysis. Their thermal decomposition behavior was studied by differential scanning calorimetry and thermogravimetry. Their mechanical sensitivities and detonation performances were also analyzed in detail. Results show that products 2-7 exhibit higher density, better detonation performances, and more excellent sensitivities than those of the same species of cation salts previously reported.

Energetic propane-1,3-diaminium and butane-1,4-diaminium salts of N,N'-dinitroethylenediazanide: syntheses, crystal structures and thermal properties

The acidity of the amine H atoms and the consequent salt formation ability of ethylenedinitramine (EDNA) were analyzed in an attempt to improve the thermal stability of EDNA. Two short-chain alkanediamine bases, namely propane-1,3-diamine and butane-1,4-diamine, were chosen for this purpose. The resulting salts, namely propane-1,3-diaminium N,N'-dinitroethylenediazanide, C₃H₁₂N₂²⁺·C₂H₄N₄O₄^2-, and butane-1,4-diaminium N,N'-dinitroethylenediazanide, C₄H₁₄N₂²⁺·C₂H₄N₄O₄^2-, crystallize in the orthorhombic space group Pbca and the monoclinic space group P2₁/n, respectively. The resulting salts display extensive hydrogen-bonding networks because of the presence of ammonium and diazenide ions in the crystal lattice. This results in an enhanced thermal stability and raises the thermal decomposition temperatures to 202 and 221 °C compared to 180 °C for EDNA. The extensive hydrogen bonding present also plays a crucial role in lowering the sensitivity to impact of these energetic salts.

Optimizing the molecular structure and packing style of a crystal by intramolecular cyclization from picrylhydrazone to indazole

Crystal engineering has prompted the development of energetic materials in recent years.

Relationship between the crystal packing and impact sensitivity of energetic materials

The crystal packing structure–safety (usually represented by sensitivity) relationships of energetic materials (EMs) are requisite to set a basis for tailoring new ones with the desired safety by means of crystal engineering, because safety is one of the two most important properties of EMs for which there is always a high concern.

Experimental Charge-Density Study of the Intra- and Intermolecular Bonding in TKX-50

The intra- and intermolecular bonding in the known phase of dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate, TKX-50, has been analyzed on the basis of the experimentally determined charge density distribution from high-resolution X-ray diffraction data obtained at 20 K. This was compared to the charge density obtained from DFT calculations with periodic boundary conditions using both direct calculations and derived structure factors. Results of topological analysis of the electron density corroborate that TKX-50 is best described as a layered structure linked primarily by a number of hydrogen bonds as well as by a variety of other interactions. Additional bonding interactions were identified, including a pair of equivalent 1,5-type intramolecular closed-shell interactions in the dianion. Refinement of anharmonic motion was shown to be essential for obtaining an adequate model, despite the low temperature of the study. Although generally unusual, the implementation of anharmonic refinement provided a significant improvement compared to harmonic refinement of both traditional and split-core multipole models.

Comparative Study of Various Pyrazole-based Anions: A Promising Family of Ionic Derivatives as Insensitive Energetic Materials

In the design of advanced energetic materials, high-density explosophores play a pivotal role because of their remarkable enhancement of both density and molecular stability. Using diversified functionalization strategies, a comparative study involving various nitropyrazole anions shows that these are crucially important in determining performance and stability. A promising family of pyrazole-based energetic ionic derivatives were synthesized and characterized by NMR and IR spectroscopies, and elemental analysis. Among them, 7, 8, 11-13 exhibit favorable overall performance as energetic materials.

A theoretical prediction on the shear-induced phase transformation of TKX-50

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a new and attractive energetic material that outperforms numerous common explosives because of its excellent properties and performance, and is thus a promising candidate to replace some of them.

Enforced Layer-by-Layer Stacking of Energetic Salts towards High-Performance Insensitive Energetic Materials

Development of modern high-performance insensitive energetic materials is significant because of the increasing demands for both military and civilian applications. Here we propose a rapid and facile strategy called the "layer hydrogen bonding pairing approach" to organize energetic molecules via layer-by-layer stacking, which grants access to tunable energetic materials with targeted properties. Using this strategy, an unusual energetic salt, hydroxylammonium 4-amino-furazan-3-yl-tetrazol-1-olate, with good detonation performances and excellent sensitivities, was designed, synthesized, and fully characterized. In addition, the expected unique layer-by-layer structure with a high crystal packing coefficient was confirmed by single-crystal X-ray crystallography. Calculations indicate that the layer-stacking structure of this material can absorb the mechanical stimuli-induced kinetic energy by converting it to layer sliding, which results in low sensitivity.