1,2,4‐Triazole Links and N ‐Azo Bridges Yield Energetic Compounds

Halogenated PETN derivatives: interplay between physical and chemical factors in explosive sensitivity

Determining the factors that influence and can help predict energetic material sensitivity has long been a challenge in the explosives community. Decades of literature reports identify a multitude of factors both chemical and physical that influence explosive sensitivity; however no unifying theory has been observed. Recent work by our team has demonstrated that the kinetics of "trigger linkages" (i.e., the weakest bonds in the energetic material) showed strong correlations with experimental drop hammer impact sensitivity. These correlations suggest that the simple kinetics of the first bonds to break are good indicators for the reactivity observed in simple handling sensitivity tests. Herein we report the synthesis of derivatives of the explosive pentaerythritol tetranitrate (PETN) in which one, two or three of the nitrate ester functional groups are substituted with an inert group. Experimental and computational studies show that explosive sensitivity correlates well with Q (heat of explosion), due to the change in the number of trigger linkages removed from the starting material. In addition, this correlation appears more significant than other observed chemical or physical effects imparted on the material by different inert functional groups, such as heat of formation, heat of explosion, heat capacity, oxygen balance, and the crystal structure of the material.

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.

N-Functionalization of 5-Aminotetrazoles: Balancing Energetic Performance and Molecular Stability by Introducing ADNP

5-aminotetrazole is one of the most marked high-nitrogen tetrazole compounds. However, the structural modification of 5-aminotetrazole with nitro groups often leads to dramatically decreased molecular stability, while the N-bridging functionalization does not efficiently improve the density and performance. In this paper, we report on a straightforward approach for improving the density of 5-aminotetrazole by introducing 4-amino-3,5-dinitropyrazole. The following experimental and calculated properties show that nitropyrazole functionalization competes well with energetic performance and mechanic sensitivity. All compounds were thoroughly characterized using IR and NMR spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Two energetic compounds (DMPT-1 and DMPT-2) were further confirmed by implementing single-crystal X-ray diffraction studies. Compound DMPT-1 featured a high crystal density of 1.806 g cm-3, excellent detonation velocity (vD = 8610 m s-1), detonation pressure (P = 30.2 GPa), and impact sensitivity of 30 J.

Experimental and Computational Studies on Bio-Inspired Flavylium Salts as Sensitizers for Dye-Sensitized Solar Cells

Six new bio-inspired flavylium salts were synthesized and investigated by a combined computational and experimental study for dye-sensitized solar cell applications. The compounds were characterized by FT-IR, UV-Vis, NMR spectroscopy, and LC-MS spectrometry techniques. The pH-dependent photochromic properties of the flavylium dyes were investigated through a UV-Vis spectroscopy study and revealed that they follow the same network of chemical reactions as anthocyanins upon pH changes. The structural and electronic properties of the dyes were investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Geometry optimization calculation revealed that all dyes, regardless of the specie, flavylium cations or quinoidal bases, present a planar geometry. The photovoltaic performances of the dyes, in both flavylium and quinoidal base forms, were evaluated by the HOMO and LUMO energies and by calculating the light-harvesting efficiencies, the free energy change of electron injection, and the free energy change regeneration. The MO analysis showed that all dyes can inject electrons into the conduction band of the TiO₂ upon excitation and that the redox couple can regenerate the oxidized dyes. The results obtained for the free energy change of electron injection suggest that the quinoidal bases should inject electrons into the semiconductor more efficiently than the flavylium cations. The values for the free energy change regeneration showed that the redox electrolyte can easily regenerate all dyes. Dipole moment analysis was also performed. DSSCs based on the dyes, in both flavylium and quinoidal base forms, were assembled, and their photovoltaic performances were evaluated by measuring the open-circuit voltage, the short circuit current density, the fill factor, and the energy conversion efficiency. Results obtained by both experimental and computational studies showed that the overall performances of the DSSCs with the quinoidal forms were better than those obtained with the flavylium cations dyes.

Asymmetric assembly of pyrazole and 1,2,3-triazole with a methylene bridge: regioisomerism and energetic properties

An asymmetric N-bridged strategy was employed to link two different energetic building blocks. The resulting compounds not only exhibit good crystal density and low sensitivity, but also demonstrate the key features of physiochemical properties and regioisomeric structures that enrich the horizon of regiochemistry of energetic compounds.

Quantum chemical studies on structural, spectroscopic, nonlinear optical, and thermodynamic properties of the 1,2,4-triazole compound

In this study, the structure of 4-[4-(diethylamino)-benzylideneamino]-5-benzyl-2H-1,2,4-triazol-3(4H)-one (DBT) was examined through spectroscopic and theoretical analyses. In this respect, the geometrical, vibrational frequency, 1H and 13C-nuclear magnetic resonance (NMR) chemical shifts, thermodynamic, hyperpolarizability, and electronic properties including the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energies of DBT as a potential non-linear optical (NLO) material were investigated using density functional theory at the B3LYP level with the 6-311G basis set. 1H and 13C-NMR chemical shifts of DBT with the gauge-invariant atomic orbital and continuous set of gauge transformation methods (in the solvents) were estimated, and the computed chemical shift values displayed excellent alignment with observed ones. Time-dependent density-functional theory (TD-DFT) calculations with the integral equation formalism polarizable continuum model within various solvents and gas phases in the ground state were used to evaluate UV-vis absorption and fluorescence emission wavelengths. Thermodynamic parameters including enthalpy, heat capacity, and entropy for DBT were also calculated at various temperatures. Moreover, calculations of the NLO were carried out to obtain the title compound’s electric dipole moment and polarizability properties. To illustrate the effect of the theoretical method on the spectroscopic and structural properties of DBT, experimental data of structural and spectroscopic parameters were used. The correlational analysis results were observed to indicate a strong relationship between the experimental and theoretical results.

New Promises from an Old Friend: Iodine-Rich Compounds as Prospective Energetic Biocidal Agents

For a very long time, frequent occurrences of biocrises have wreaked havoc on human beings, animals, and the environment. As a result, it is necessary to develop biocidal agents to destroy or neutralize active agents by releasing large amounts of strong biocides which are obtained upon detonation. Iodine is an efficient biocidal agent for bacteria, fungi, yeasts, viruses, spores, and protozoan parasites, and it is the sole element in the periodic table that can destroy microbes without contaminating the environment. Based on chemical biology, the mechanism of iodine as a bactericide may arise from oxidation and iodination reactions of cellular proteins and nucleic acids. However, because of the high vapor pressure causing elemental iodine to sublime readily at room temperature, it is inconvenient to use this material in its normal solid state directly as a biocidal agent under ambient conditions. Iodine-rich compounds where iodine is firmly bonded in molecules as a C-I or I-O moiety have been observed to be among the most promising energetic biocidal compounds. Gaseous products comprised of large amounts of iodine or iodine-containing components as strong biocides are released in the decomposition or explosion of iodine-rich compounds. Because of the detonation pressure, the iodine species are distributed over a large area greatly improving the efficacy of the system and requiring considerably less effort compared to traditional biocidal methods. The commercially available tetraiodomethane and tetraiodoethene, which possess superb iodine content also have the disadvantages of volatility, light sensitivity, and chemically reactivity, and therefore, are not suitable for use directly as biocidal agents. It is absolutely critical to synthesize new iodine-rich compounds with good thermal and chemical stabilities.In this Account, we describe our strategies for the syntheses of energetic iodine-rich compounds while maintaining the maximum iodine content with concomitant stability and routes for the synthesis of oxygen-containing iodine-rich compounds to improve the oxygen balance and achieve both high-energy and high-iodine content. In the other work, which involves cocrystals, iodine-containing polymers were also summarized. It is hoped that this Account will provide guidelines for the design and syntheses of new iodine-rich compounds and a route for the development of inexpensive, more efficient, and safer iodine-rich antibiological warfare agents of the future.

Synthesis, crystal structure, and thermal properties of Ni(NH3)4(AFT)2

Ni(NH3)4(AFT)2 [NiC6H16N18O2, AFT = 4-amino-3-(5-tetrazolate)furazan] is synthesized and characterized by elemental analysis and Fourier-transform infrared spectroscopy for the first time. X-ray diffraction measurements are used to determine the crystal structure of compound 1. The results demonstrate that compound 1 crystallized in the orthorhombic crystal system. The nickel(II) ion is six-coordinated by N atoms from two AFT-ligands and four NH3 molecules. Its thermal properties are investigated by differential scanning calorimetry and thermogravimetry-derivative thermogravimetry methods, with the results demonstrating that the differential scanning calorimetry curve exhibits two endothermic and one exothermic processes. The endothermic processes are in the range of 130–510 °C with a peak temperature of 188 °C. The temperature from 230 to 400 °C is the exothermic process in which the peak temperature is 314.58 °C. In addition, Kissinger’s and Ozawa-Doyle’s methods are used for calculating the non-isothermal kinetics parameters. Moreover, the apparent activation energy ( E), safety, and thermal stability parameters ( TSADT, TTIT, Tb) for Ni(NH3)4(AFT)2 are calculated. In addition, the calculated thermodynamic functions ( ∆S≠, ∆H≠, and ∆G≠) for the exothermic decomposition process of Ni(NH3)4(AFT)2 are 55.07 J mol−1 K−1, 196.18 kJ mol−1, and 164.90 kJ mol−1, respectively.

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N₂ is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

Azo- and methylene-bridged mixed azoles for stable and insensitive energetic applications

A simple synthetic strategy for the preparation of high nitrogen content azo- and methylene bridged mixed energetic azoles was used.

A Review on the Reactivity of 1-Amino-2-Nitroguanidine (ANQ)

1-Amino-2-nitroguanidine (ANQ) is a high-energy nitrogen-rich compound with good detonation properties and low sensitivities. ANQ has only a central carbon atom with three small groups around it, including an amino, a hydrazine and a nitroxyl group. Though the molecular structure of ANQ is very simple, its reactivity is surprisingly abundant. ANQ can undergo various reactions, including reduction reaction, acylation reaction, salification reaction, coordination reaction, aldimine condensation reaction, cyclization reaction and azide reaction. Many new energetic compounds were purposely obtained through these reactions. These reactions were systematically summarized in this review, and detonation properties of some energetic compounds were compared. In the field of energetic materials, ANQ and some derivatives exhibit good application prospects.

Synthesis of high-performance insensitive energetic materials based on nitropyrazole and 1,2,4-triazole

A new family of symmetric nitropyrazole and 1,2,4-triazole derivatives and its energetic salts were obtained. The positive effect of ternary hydrogen bonds improve the performances of target compounds.

2,4,4,6,8,8-Hexanitro-2,6-diazaadamantane: A High-Energy Density Compound with High Stability

A novel high-performance energetic compound of the polynitroazaadamantane family, 2,4,4,6,8,8-hexanitro-2,6-diazaadamantane, was designed and synthesized from 1,5-cyclooctadiene by two routes. Based on the experimental and calculated results, it exhibits a surprisingly high density (1.959 g cm^-3), high thermal stability (onset decomposition temperature of 235 °C), high positive heat of formation, and excellent detonation properties. These fascinating properties, which are comparable to those of CL-20, show great promise for potential applications as a high-energy density material.

Novel insensitive energetic-cocrystal-based BTO with good comprehensive properties

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared a structurally unusual 1H,1′H-5,5′-bistetrazole-1,1′-diolate (BTO) based energetic cocrystal, which we also confirmed by single-crystal X-ray diffraction and powder-crystal X-ray diffraction. The obtained cocrystal crystallizes in a triclinic system, P-1 space group, with a density of 1.72 g cm⁻³. The properties including the thermal stability, sensitivity and detonation performance of the cocrystal were analyzed in detail. In addition, the thermal decomposition behavior of the cocrystal was studied by differential calorimetry and thermogravimetry tandem infrared spectroscopy. The results indicated that the cocrystal exhibits strong resistance to thermal decomposition up to 535.6 K. The cocrystal also demonstrates a sensitivity of >50 J. Moreover, its formation enthalpy was estimated to be 2312.0 kJ mol⁻¹, whereas its detonation velocity and detonation pressure were predicted to be 8.213 km s⁻¹ and 29.1 GPa, respectively, by applying K–J equations. Therefore, as expected, the obtained cocrystal shows a good comprehensive performance, which proves that a high degree of layer-by-layer stacking is essential for the structural density, thermal stability and sensitivity.

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared an unusual energetic cocrystal, which confirmed by single-crystal X-ray diffraction.

Functionalization of fluorodinitroethylamino derivatives based on azole: a new family of insensitive energetic materials

In this study, we report the synthesis of a new family of fluorodinitroethyl-substituted aminoazole derivatives, which might be of interest for applications as insensitive energetic materials.

Pursuing reliable thermal analysis techniques for energetic materials: decomposition kinetics and thermal stability of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50)

Reliable kinetics of thermolysis for a novel explosive dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) was obtained using a variety of thermoanalytical and kinetic methods and verified by modeling of adiabatic self-heating.

Isomerization Pathways of ONCNO: Unstable or Metastable?

Fulminates containing the CNO(-) ion have been widely utilized as high-energy density materials (HEDMs) for more than 120 years. Yet no purely covalently bound CNO molecule, i.e., nitrile oxide, is known to behave as an HEDM. In this study, we performed a thorough investigation of the potential energy surface of nitrile oxide ONCNO and related isomers, applying various sophisticated methods including G4, CBS-QB3, W1BD, CCSD(T)/CBS, and CASPT2/CBS. The Gibbs free energy calculations showed that the decomposition of ONCNO to the considerably endothermic products CNO + NO is favored compared to that into the highly exothermic products CO2 + N2. Thus, ONCNO fails to be the long expected nitrile oxide HEDM. However, with the rate-determining barrier of 23.3 kcal mol(-1) at the W1BD level, ONCNO should be experimentally accessible.

Nitrogen-rich 4,4′-azo bis(1,2,4-triazolone) salts—the synthesis and promising properties of a new family of high-density insensitive materials

4,4′-Azo-bis(1,2,4-triazolone) (ZTO) based salts from alkaline (Li⁺, K⁺, Na⁺, and Cs⁺), alkaline earth metal salts (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) and hydrazinium salt were synthesized in a simple, straightforward manner and were characterized by IR and NMR spectroscopy, elemental analysis.

Studies on sodium polymers based on di(1H-tetrazol-5-yl)methanone oxime

[Na(Hbto)(H₂O)₂·2H₂O]_n (1), [(NH₃OH)₂Na₂(bto)₂(H₂O)₄·H₂O]_n (2) and [(NH₃OH)Na(bto)(H₂O)₂]_n (3), eco-friendly coordination polymers, have been synthesized.

Nitrogen-rich energetic salts of 1H,1′H-5,5′-bistetrazole-1,1′-diolate: synthesis, characterization, and thermal behaviors

A series of nitrogen-rich heterocyclic 1H,1′H-5,5′-bistetrazole-1,1′-diolate salts with excellent thermal stabilities, impact sensitivities and promising detonation performances was synthesized.

Electrophilic iodination: a gateway to high iodine compounds and energetic materials

Preparation of polyiodopyrazoles and subsequent highly oxygenated nitro compounds.

Monocyclic and bicyclic CO4: how stable are they?

For the first time the barriers for the CO₂-elimination from 11 and 12 energy-rich CO₄ were located, they amount to 28.7 and 14.7 kcal mol⁻¹ at the CASPT2(18e,12o)/CBS level of theory, and 23.5 and 21.1 kcal mol⁻¹ at the UCCSD(T)/CBS level of theory.