The CN7− Anion

Sequential, Electrochemical-Photochemical Synthesis of 1,2,4-Triazolo-[4,3-a]pyrazines

1,2,4-triazolo-[4,3-a]pyrazine was prepared via a two-step electrochemical, photochemical process. First, a 5-substituted tetrazole is electrochemically coupled to 2,6-dimethoxypyrazine to yield 1,5- and 2,5- disubstituted tetrazoles. Subsequent photochemical excitation of the 2,5-disubstituted tetrazole species using an ultraviolet lamp releases nitrogen gas and produces a short-lived nitrilimine intermediate. Subsequent cyclization of the nitrilimine intermediate yields a 1,2,4-triazolo-[4,3-a]pyrazine backbone. The scope of this reaction was explored using various tetrazoles and pyrazines. Materials produced were identified using chemical analytical techniques and computationally studied for potential application as an insensitive energetic material.

Replacement of Toxic Hydrazines in Satellite Propulsion with Greener Dinitramide-Based Energetic Ionic Liquid Candidates

Satellite propulsion uses liquid mono or bi-propellants composed of a hydrazine in combination with a strong oxidant. However, hydrazines are highly toxic. As a result, many research efforts for more environmentally compatible propellants have been made over the past decade. In this study we evidence green formulations that retain high propulsive performances. They are based on the dinitramide anion. From an initial library of 37 ammonium dinitramides 3 best candidates were selected after evaluation of their potential syntheses, calculated theoretical performances, experimental synthesis optimizations and decomposition temperatures. These three salts were then formulated to obtain acceptable sensitivities and melting points, which eventually led to only one formulation being retained: a 40 : 60 mixture of dimethylammonium dinitramide and ammonium dinitramide phlegmatized by 10 % of glycerol.

Radiolytic evaluation of a new technetium redox control reagent for advanced used nuclear fuel separations

Technetium is a problematic radioisotope for used nuclear fuel (UNF) and subsequent waste management owing to its high environmental mobility and coextraction in reprocessing technologies as the pertechnetate anion (TcO4-). Consequently, several strategies are under development to control the transport of this radioisotope. A proposed approach is to use diaminoguanidine (DAG) for TcO4- and transuranic ion redox control. Although the initial DAG molecule is ultimately consumed in the redox process, its susceptibility to radiolysis is currently unknown under envisioned UNF reprocessing conditions, which is a critical knowledge gap for evaluating its overall suitability for this role. To this end, we report the impacts of steady-state gamma irradiation on the rate of DAG radiolysis in water, aqueous 2.0 M nitric acid (HNO3), and in a biphasic solvent system composed of aqueous 2.0 M HNO3 in contact with 1.5 M N,N-di-(2-ethylhexyl)isobutyramide (DEHiBA) dissolved in n-dodecane. Additionally, we report chemical kinetics for the reaction of DAG with key transients arising from electron pulse radiolysis, specifically the hydrated electron (eaq-), hydrogen atom (H˙), and hydroxyl (˙OH) and nitrate (NO3˙) radicals. The DAG molecule exhibited significant reactivity with the ˙OH and NO3˙ radicals, indicating that oxidation would be the predominant degradation pathway in radiation environments. This is consistent with its role as a reducing agent. Steady-state gamma irradiations demonstrated that DAG is readily degraded within a few hundred kilogray, the rate of which was found to increase upon going from water to HNO3 containing solutions and solvents systems. This was attributed to a thermal reaction between DAG and the predominant HNO3 radiolysis product, nitrous acid (HNO2), k(DAG + HNO2) = 5480 ± 85 M-1 s-1. Although no evidence was found for the radiolysis of DAG altering the radiation chemistry of the contacted DEHiBA/n-dodecane phase in the investigated biphasic system, the utility of DAG as a redox control reagent will likely be limited by significant competition with its degradation by HNO2.

Recent Progress on Nitrogen-Rich Energetic Materials Based on Tetrazole Skeleton

Development of nitrogen-rich energetic materials has gained much attention because of their remarkable properties including large nitrogen content and energy density, good thermal stability, low sensitivity, good energetic performance, environmental friendliness and so on. Tetrazole has the highest nitrogen and highest energy contents among the stable azoles. The incorporation of diverse explosophoric groups or substituents into the tetrazole skeleton is beneficial to obtain high-nitrogen energetic materials having excellent energetic performance and suitable sensitivity. In this review, the development of high-nitrogen energetic materials based on tetrazole skeleton is highlighted. Initially, the property and utilization of nitrogen-rich energetic materials are presented. After showing the advantage of the tetrazole skeleton, the high-nitrogen energetic materials based on tetrazole are classified and introduced in detail. Based on different types of energetic materials (EMs), the synthesis and properties of nitrogen-rich energetic materials based on mono-, di-, tri- and tetra-tetrazole are summarized in detail.

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.

K3C6N7O3·2H2O: A Multifunctional Nonlinear Optical Cyamelurate Crystal with Colossal π-Conjugated Orbitals

The delocalized π-conjugated units are considered as an advantageous gene for improving the optical nonlinearity of acentric crystals. For the first time, we synthesized a new acentric SHG-active metal cyamelurate crystal K₃C₆N₇O₃·2H₂O (I) by a facile solution method, containing a colossal planar π-conjugated (C₆N₇O₃)^3- unit. It displays a strong second-order harmonic generation (SHG) of 4 × KDP and a giant anisotropic birefringence of 0.446 at 1064 nm. The theoretical calculations reveal that such substantial improvement is contributed from the strong molecular susceptibility of (C₆N₇O₃)^3- units and their near-perfect coplanar arrangement. Moreover, I exhibits a broadband ultraviolet photoluminescence at 366 nm, suggesting its multifunctional capacity and great potential for compact highly integrated optoelectronic devices.

An Efficient Synthesis and Preliminary Investigation of Novel 1,3-Dihydro-2H-benzimidazol-2-one Nitro and Nitramino Derivatives

The preparation and properties of a series of novel 1,3-dihydro-2H-benzimidazol-2-one nitro and nitramino derivatives are described. A detailed crystal structure of one of the obtained compounds, 4,5,6-trinitro-1,3-dihydro-2H-benzimidazol-2-one (TriNBO), was characterized using low temperature single crystal X-ray diffraction, namely an orthorhombic yellow prism, space group 'P 2 21 21', experimental crystal density 1.767 g/cm³ (at 173 K). Methyl analog, 5-Me-TriNBO-monoclinic red plates, space group, P 21/c, crystal density 1.82 g/cm³. TriNBO contains one activated nitro group at the fifth position, which was used for the nucleophilic substitution in the aminolysis reactions with three monoalkylamines (R=CH₃, C₂H₅, (CH₂)₂CH₃) and ethanolamine. The 5-R-aminoderivatives were further nitrated with N₂O₅/ HNO₃ and resulted in a new group of appropriate nitramines: 1,3-dihydro-2H-5-R-N(NO₂)-4,6-dinitrobenzimidazol-2-ones. Thermal analysis (TGA) of three selected representatives was performed. The new compounds possess a high melting point (200-315 °C) and thermal stability and can find a potential application as new thermostable energetic materials. Some calculated preliminary energetic characteristics show that TriNBO, 5-Me-TriNBO, 5-methylnitramino-1,3-dihydro-2H-4,6-dinitrobenzimidazol-2-one, and 5-nitratoethylnitramino-1,3-dihydro-2H-4,6-dinitrobenzimidazol-2-one possess increased energetic characteristics in comparison with TNT and tetryl. The proposed nitrocompounds may find potential applications as thermostable high-energy materials.

Tuning the Properties of 5‐Azido and 5‐Nitramino‐tetrazoles by Diverse Functionalization – General Concepts for Future Energetic Materials

5‐Azido and 5‐nitraminotetrazole backbones are established heterocyclic motifs in the research field of energetic materials synthesis. Despite the high energy content of the compounds, the problem with many derivatives is that their sensitivities are far too high. Functionalization of one of the ring nitrogen atoms is the aim of this study to adjust the sensitivity by inserting nitratoethyl, azidoethyl and methyl groups. In this context, derivatives of 2‐(2‐azidoethyl)‐5‐nitraminotetrazoles (2, 2  a–2  d), as well as 1‐nitrato and 1‐azidoethyl substituted 5‐azidotetrazole (7 and 10) and the methylation products of 5‐azidotetrazole (5‐azido‐1‐methyl‐tetrazole, 11 and 5‐azido‐2‐methyl‐tetrazole, 12) were prepared. The obtained nitrogen‐rich compounds were extensively characterized through multinuclear NMR spectroscopy and IR spectroscopy. The structural confinement was checked by X‐ray diffraction experiments. The pure samples (verified by elemental analysis) were investigated regarding their behavior toward friction, impact (BAM methods) and electrostatic discharge as well as heating (DTA and DSC). For all metal‐free compounds the detonation properties were computed with the EXPLO5 code using their density and heat of formation, calculated based on CBS‐4 M level of theory.

Synthesis and Characterization of Binary, Highly Endothermic, and Extremely Sensitive 2,2'-Azobis(5-azidotetrazole)

2,2'-Azobis(5-azidotetrazole) (C₂N₁₆, 3), a highly energetic nitrogen-rich binary CN compound was obtained in a three-step synthesis through the formation of 5-azidotetrazole (1), subsequent amination using O-tosylhydroxylamine to give 2-amino-5-azidotetrazole (2), and oxidative azo coupling of 2 using tBuOCl as an oxidant in MeCN. A nitrogen:carbon ratio of 8:1, eight nitrogen atoms in a row, and a nitrogen content of over 90% was unknown for a binary heterocyclic compound until now. The successful isolation was confirmed through X-ray diffraction as well as by vibrational and ¹³C NMR spectroscopy. C₂N₁₆ can explode instantly and shows mechanical sensitivities far higher than quantitatively measurable. Nevertheless, it features interesting energetic performances, which were calculated using different quantum-chemical methods.

Infrared multiple photon dissociation action spectroscopy of protonated unsymmetrical dimethylhydrazine and proton-bound dimers of hydrazine and unsymmetrical dimethylhydrazine

The gas-phase structures of protonated unsymmetrical 1,1-dimethylhydrazine (UDMH) and the proton-bound dimers of UDMH and hydrazine are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by a free electron laser and an optical parametric oscillator laser system. To identify the structures present in the experimental studies, the measured IRMPD spectra are compared to spectra calculated at the B3LYP-GD3BJ/6-311+G(d,p) level of theory. These comparisons show that protonated UDMH binds the proton at the methylated nitrogen atom (α) with two low-lying α conformers probably being populated. For (UDMH)₂H⁺, the proton is shared between the methylated nitrogen atoms with several low-lying α conformers likely to be populated. Higher-lying conformers of (UDMH)₂H⁺ in which the proton is shared between α and β (unmethylated) nitrogen atoms cannot be ruled out on the basis of the IRPMD spectrum. For (N₂H₄)₂H⁺, there are four low-lying conformers that all reproduce the IRMPD spectrum reasonably well. As hydrazine and UDMH see usage as fuels for rocket engines, such spectra are potentially useful as a means of remotely monitoring rocket launches, especially in cases of unsuccessful launches where environmental hazards need to be assessed.

Solid Propellant Formulations: A Review of Recent Progress and Utilized Components

The latest developments in solid propellants and their components are summarized. Particular attention is given to emerging energetic binders and novel, 'green' oxidizing agents and their use in propellant formulations. A brief overview of the latest reports on fuel additives is included. Finally, a summary of the state of the art and challenges in its development are speculated on.

Selective Synthesis and Characterization of the Highly Energetic Materials 1-Hydroxy-5H-tetrazole (CHN4 O), its Anion 1-Oxido-5H-tetrazolate (CN4 O- ) and Bis(1-hydroxytetrazol-5-yl)triazene

For the first time, an adequate selective synthesis, circumventing the formation of 2-hydroxy-5H-tetrazole, of 1-hydroxy-5H-tetrazole (HTO), as well as the synthesis of bis(1-hydroxytetrazol-5-yl)triazene (H₃ T) are reported. Several salts thereof were synthesized and characterized which resulted in the formation of new primary and secondary explosives containing the 1-oxidotetrazolate unit. Molecular structures are characterized by single-crystal X-ray diffraction, ¹ H and ¹³ C NMR, IR, and elemental analysis. Calculation of the detonation performance using the Explo5 code confirmed the energetic properties of 1-hydroxy-5H-tetrazole. The detonation properties can be adjusted to the requirements for those of a secondary explosive by forming the hydroxylammonium (6) or hydrazinium (7) salts, or to meet the requirements of a primary explosive by forming the silver salt 4, which shows a fast DDT on contact with a flame. The sensitivities of all compounds towards external stimuli such as impact, friction, and electrostatic discharge were measured.

C5H2N14O6: achieving azido-based materials with zero oxygen balance and good energetic performance

Through introducing nitro groups, a high-nitrogen–oxygen compound (4) was prepared. The OBco of compound 4 was improved to the value of zero, and it also exhibits good detonation performance (9018 m s−1 and 34.5 GPa).

Methyl sydnone imine and its energetic salts

First investigation of this new energetic cation, which may greatly expand the range of possible energetic salts available.

Computational study about the thermal stability and the detonation performance of nitro-substituted thymine

By replacing hydrogen atoms in thymine molecules with nitro groups, a series of new high-energy-density molecules are designed. To explore the thermal stability, the heats of formation (HOF) are calculated at the B3PW91-D3/6-311++G(2df,2p) level. The bond dissociation energy and the bond order are also calculated to predict the kinetic stability at the same level. Based on our calculations, excellent stability is confirmed for title molecules. To confirm the possibility of application as high-energy-density compounds, the molecular density (ρ), explosive heats (Q), detonation velocity (D), detonation pressure (P), free space per molecule in crystal lattice (ΔV), and characteristic drop height (H₅₀) are calculated. On the consideration of the stability and the detonation characters, E1 is confirmed as the candidates of high-energy-density compounds.

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.

In situ synthesis, crystal structures, topology and photoluminescent properties of poly[di-μ-aqua-di-aqua-[μ3-4-(1H-tetra-zol-1-id-5-yl)benzoato-κ4 O:O,O':O'']barium(II)] and poly[μ-aqua-di-aqua-[μ3-4-(1H-tetra-zol-1-id-5-yl)benzoato-κ4 O:O,O':O']strontium(II)]

Two alkaline-earth coordination compounds, [Ba(C8H4N4O2)(H2O)4] n , (I), and [Sr(C8H4N4O2)(H2O)3] n , (II), from the one-pot hydrolysis transformation of benzoyl chloride and the in situ self-assembled [2 + 3] cyclo-addition of nitrile are presented. These coordination compounds are prepared by reacting 4-cyano-benzoyl chloride with divalent alkaline-earth salts (BaCl2 and SrCl2) in aqueous solution under hydro-thermal conditions. The mononuclear coordination compounds (I) and (II) show the same mode of coordination of the organic ligands. The cohesion of the crystalline structures is provided by hydrogen bonds and π-stacking inter-actions, thus forming three-dimensional supra-molecular networks. The two compounds have a three-dimensional (3,6)-connected topology, and the structural differences between them is in the number of water mol-ecules around the alkaline earth metals. Having the same emission frequencies, the compounds exhibit photoluminescence properties with a downward absorption value from (I) to (II).

Thermochemistry and Initial Decomposition Pathways of Triazole Energetic Materials

A thorough investigation of the initial decomposition pathways of triazoles and their nitro-substituted derivatives has been conducted using the MP2 method for optimization and DLPNO-CCSD(T) method for energy. Different initial thermolysis mechanisms are proposed for 1,2,4-triazole and 1,2,3-triazole, the two kinds of triazoles. The higher energy barrier of the primary decomposition path of 1,2,4-triazole (H-transfer path, ∼52 kcal/mol) compared with that of 1,2,3-triazole (ring-open path, ∼45 kcal/mol) shows that 1,2,4-triazole is more stable, consistent with experimental observations. For nitro-substituted triazoles, more dissociation channels associated with the nitro group have been obtained and found to be competitive with the primary decomposition paths of the triazole skeleton in some cases. Besides, the effect of the nitro group on the decomposition pattern of the triazole skeleton has been explored, and it has been found that the electron-withdrawing nitro group has an opposite effect on the primary dissociation channels of 1,2,4-triazole derivatives and 1,2,3-triazole derivatives.

Modulating energetic performance through decorating nitrogen-rich ligands in high-energy MOFs

In the presence of different nitrogen-rich ligands, two energetic MOFs with formulas [Ag(tza)]_n (1) and [Ag(atza)]_n (2) (Htza = tetrazole-1-acetic acid and Hatza = (5-amino-1H-tetrazole-1-yl) acetic acid) were successfully synthesized and characterized. X-ray single crystal structure analysis shows that both 1 and 2 have 2D layer-like topologies. The experimental and theoretical evaluations reveal the promising properties of both energetic compounds, such as prominent heats of detonation, high thermal stabilities, good sensitivities and excellent detonation performances. In contrast to 1, interestingly, the introduction of the amino group in 2 leads to various coordination modes of the ligands and different stacking patterns of the frameworks, resulting in the observation of the shorter Ag-O, Ag-Ag, C-N, N-N, and N[double bond, length as m-dash]N bond lengths in 2. Consequently, 2 features superior heats of detonation and thermostability compared to 1. The nonisothermal thermokinetic parameters are obtained by using the Kissinger and Ozawa methods, while the standard molar enthalpies of formation are calculated from the determination of constant volume combustion energies. In addition, both compounds were explored as practical additives to promote the thermal decomposition of ammonium perchlorate (AP). This work may provide an effective approach for manipulating the energetic properties and thermostability of high-energy compounds via the perturbation of energetic groups.

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.

Improving properties of energetic coordination polymers through structural modulation from 1D to 3D without changes of ligands or metal nodes

Two energetic coordination polymers, Pb₂(AOT)₂·7(H₂O) (1) (AOT: 5,5′-azo-bis(1-oxidotetrazonate)) and Pb₂(AOT)O·3(H₂O) (2), were prepared at different temperatures and pressures.

Amino-tetrazole functionalized fused triazolo-triazine and tetrazolo-triazine energetic materials

In this study, two insensitive energetic compounds using fused triazolo-triazine and tetrazolo-triazine as the framework, one amino and one tetrazole as functional groups, were prepared through a two-step reaction.

A solvent-free dense energetic metal-organic framework (EMOF): to improve stability and energetic performance via in situ microcalorimetry

It is a tremendous challenge to prepare solvent-free dense energetic metal-organic frameworks (EMOFs), hence also to improve their stability and energetic performance. In this study, based on in situ microcalorimetry, an interpenetrating EMOF without solvent molecules, [Cu(tztr)]_n (1, H₂tztr = 3-(tetrazol-5-yl)triazole) was obtained, possessing high stability (T_dec = 360 °C) and outstanding energetic properties (ΔH_det = 7.53 kcal cm^-3, D = 8.429 km s^-1, P = 40.02 GPa).

Nitramino-functionalized tetracyclic oxadiazoles as energetic materials with high performance and high stability: crystal structures and energetic properties

The combination of 1,2,4-oxadiazole and nitramino-1,2,5-oxadiazole is a promising strategy for designing energetic materials with high performance and high stability.

Tetracyclic pyrazine-fused furazans as insensitive energetic materials: syntheses, structures, and properties

Tetracyclic pyrazine-fused furazans are promising candidates as insensitive energetic materials.

Dendritic Polynitrato Energetic Motifs: Development and Exploration of Physicochemical Behavior through Theoretical and Experimental Approach

Considering the fundamental and most desirable characteristics of energetic materials, a series of 1,2,3-triazole-based heterocyclic energetic motifs nicely tuned with nitrato (-ONO₂) functionality were synthesized by a microwave-assisted environmental friendly synthetic approach with good yields. Thermal stability and the nature of evolved gases on decomposition of structurally characterized energetic motifs were analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) analysis and Fourier transform infrared coupled with TGA-DSC. The explosiveness of these motifs was explored by calculation of enthalpy of formation and density employing density functional theory, and the detonation performances (detonation pressure and velocity) were explored using EXPLO5_V6.03. All of these compounds were calculated to have better oxygen balance (-36 to -52%) as compared to that of trinitrotoluene (-74%). Most of the nitrate ester derivatives were found to exhibit low impact sensitivities, high densities, good thermal stabilities, and promising detonation properties, and PN ₃ was observed to be a superior candidate in terms of its energetic characteristics. Hence, the experimental and theoretical outcomes strongly reflect that the present approach of developing dendritic high energetic materials bearing green explosive characteristics might be a potential pathway for designing and synthesizing green explosives with desired characteristics.

Prospective Symbiosis of Green Chemistry and Energetic Materials

A global increase in environmental pollution demands the development of new "cleaner" chemical processes. Among urgent improvements, the replacement of traditional hydrocarbon-derived toxic organic solvents with neoteric solvents less harmful for the environment is one of the most vital issues. As a result of the favorable combination of their unique properties, ionic liquids (ILs), dense gases, and supercritical fluids (SCFs) have gained considerable attention as suitable green chemistry media for the preparation and modification of important chemical compounds and materials. In particular, they have a significant potential in a specific and very important area of research associated with the manufacture and processing of high-energy materials (HEMs). These large-scale manufacturing processes, in which hazardous chemicals and extreme conditions are used, produce a huge amount of hard-to-dispose-of waste. Furthermore, they are risky to staff, and any improvements that would reduce the fire and explosion risks of the corresponding processes are highly desirable. In this Review, useful applications of almost nonflammable ILs, dense gases, and SCFs (first of all, CO₂ ) for nitration and other reactions used for manufacturing HEMs are considered. Recent advances in the field of energetic (oxygen-balanced and hypergolic) ILs are summarized. Significant attention is paid to the SCF-based micronization techniques, which improve the energetic performance of HEMs through an efficient control of the morphology and particle size distribution of the HEM fine particles, and to useful applications of SCFs in HEM processing that makes them less hazardous.

Strategy for designing stable and powerful nitrogen-rich high-energy materials by introducing boron atoms

One of the most important aims in the development of high-energy materials is to improve their stability and thus ensure that they are safe to manufacture and transport. In this work, we theoretically investigated open-chain N₄B₂ isomers using density functional theory in order to find the best way of stabilizing nitrogen-rich molecules. The results show that the boron atoms in these isomers are aligned linearly with their neighboring atoms, which facilitates close packing in the crystals of these materials. Upon comparing the energies of nine N₄B₂ isomers, we found that the structure with alternating N and B atoms had the lowest energy. Structures with more than one nitrogen atom between two boron atoms had higher energies. The energy of N₄B₂ increases by about 50 kcal/mol each time it is rearranged to include an extra nitrogen atom between the two boron atoms. More importantly, our results also show that boron atoms stabilize nitrogen-rich molecules more efficiently than carbon atoms do. Also, the combustion of any isomer of N₄B₂ releases more heat than the corresponding isomer of N₄C₂ does under well-oxygenated conditions. Our study suggests that the three most stable N₄B₂ isomers (BN13, BN24, and BN34) are good candidates for high-energy molecules, and it outlines a new strategy for designing stable boron-containing high-energy materials. Graphical abstract The structural characteristics, thermodynamic stabilities, and exothermic properties of nitrogen-rich N₄B₂ isomers were investigated by means of density functional theory.

Nitrogen-Rich Tetranuclear Metal Complex as a New Structural Motif for Energetic Materials

For designing energetic materials (EMs), the most challenging issue is to achieve a balance between energetic performance and reliable stability. In this work, we employed an efficient and convenient method to synthesize a new class of EMs: nitrogen-rich tetranuclear metal complexes [M(Hdtim)(H₂O)₂]₄ (M = Zn 1, Mn 2; H₃dtim = 1H-imidazol-4,5-tetrazole) with the N content of >46%. The structural analyses illustrate that isomorphous compounds 1 and 2 feature isolated hollow ellipsoid tetranuclear units, which are linked by both π-π interactions and hydrogen-bonding interactions to give a 3D supramolecular architecture. Compounds 1 and 2 exhibit prominent energetic characteristics: excellent detonation performances and reliable thermal, impact, and friction stabilities. Being nitrogen-rich tetrazolate compounds, the enthalpies of combustion of 1 (-11.570 kJ g^-1) and 2 (-12.186 kJ g^-1) are higher than those of classical EMs, RDX and HMX, and they possess high positive heats of formation. Sensitivity tests demonstrate that 1 and 2 are insensitive to external mechanical action. Excellent energetic performances and low sensitivities promote 1 and 2 to serve as a new class of promising EMs with a desirable level of safety.

Structures and properties of energetic cations in energetic salts

Energetic cations play important roles in energetic performance, which may attribute to the diverse backbones and substituted groups of energetic cations. This review emphasizes the roles of backbones and substituted groups in the energetic performance of energetic salts.

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.