Hepta- and Octanitrocubanes

Energetic Salts of Cubane-1,4-Dimethylnitrocarbamate

Several salts of cubane-1,4-dimethylnitrocarbamate (CMNC) were synthesized. The divalent CMNC is deprotonated by alkaline, alkaline earth metal, and nonmetal bases to form the corresponding salts. The compounds were characterized and analyzed by multinuclear NMR and IR spectroscopy, mass spectrometry, elemental analysis, single crystal X-ray, and thermoanalytical techniques. The energies of formation for the salts were calculated using Gaussian. Detonation performances were calculated with the Explo5 (V6.03) computer code. The sensitivities toward impact and friction were determined and compared to the neutral CMNC.

Theoretical advances in understanding and enhancing the thermostability of energetic materials

The quest for thermally stable energetic materials is pivotal in advancing the safety of applications ranging from munitions to aerospace. This perspective delves into the role of theoretical methodologies in interpreting and advancing the thermal stability of energetic materials. Quantum chemical calculations offer an in-depth understanding of the molecular and electronic structure properties of energetic compounds related to thermal stability. It is also essential to incorporate the surrounding interactions and their impact on molecular stability. Ab initio molecular dynamics (AIMD) simulations provide detailed theoretical insights into the reaction pathways and the key intermediates during thermal decomposition in the condensed phase. Analyzing the kinetic barrier of rate-determining steps under various temperature and pressure conditions allows for a comprehensive assessment of thermal stability. Recent advances in machine learning have demonstrated their utility in constructing potential energy surfaces and predicting thermal stability for newly designed energetic materials. The machine learning-assisted high-throughput virtual screening (HTVS) methodology can accelerate the discovery of novel energetic materials with improved properties. As a result, the newly identified and synthesized energetic molecule ICM-104 revealed excellence in performance and thermostability. Theoretical approaches are pivotal in elucidating the mechanisms underlying thermal stability, enabling the prediction and design of enhanced thermal stability for emerging EMs. These insights are instrumental in accelerating the development of novel energetic materials that optimally balance performance and thermal stability.

Synthesis of C-C bonded trifluoromethyl-based high-energy density materials via the ANRORC mechanism

A trifluoromethyl group substituted C-C bonded nitrogen rich energetic material 3-(3-nitro-1H-pyrazol-4-yl)-5-(trifluoromethyl)-1,2,4-oxadiazole (4), its hydroxyl amine (5) and 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazol-2-ium (6) salts and hydrazinium 5-(3-nitro-1H-pyrazol-4-yl)-3-(trifluoromethyl)-1,2,4-triazol-1-ide (7) were synthesized and fully characterized using infrared spectroscopy (IR), multinuclear magnetic resonance (NMR) spectroscopy (1H, 13C, and 19F), high-resolution mass spectrometry (HRMS), elemental analysis (EA) and differential scanning calorimetry (DSC) studies. Furthermore, compounds 4 and 7 were confirmed using single-crystal X-ray diffraction studies (SC-XRD). All compounds possess good density (1.70-1.80 g cm-3), detonation velocity (6432-7144 m s-1), pressure (16.38-20.31 GPa), and thermal stability (>170 °C). They are insensitive towards mechanical stimuli, impact (IS > 35 J) and friction (FS > 288 N). Overall, due to their balanced performance, these compounds can be a better replacement for presently used explosives such as trinitrotoluene (TNT).

Chlorinated Cubane-1,4-dicarboxylic Acids

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative).

Trinitromethyl-Substituted 1H-1,2,4-Triazole Bridging Nitropyrazole: A Strategy of Utterly Manipulable Nitration Achieving High-Energy Density Material

Nitro groups have been demonstrated to play a decisive role in the development of the most powerful known energetic materials. Two trinitromethyl-substituted 1H-1,2,4-triazole bridging nitropyrazoles were first synthesized by straightforward routes and were characterized by chemical (MS, NMR, IR spectroscopy, and single-crystal X-ray diffraction) and experimental analysis (sensitivity toward friction, impact, and differential scanning calorimetry-thermogravimetric analysis test). Their detonation properties (detonation pressure, detonation velocity, etc.) were predicted by the EXPLO5 package based on the crystal density and calculated heat of formation with Gaussian 09. These new trinitromethyl triazoles were found to show suitable sensitivities, high density, and highly positive heat of formation. The combination of exceedingly high performances superior to those of HMX (1,3,5,7-tetranitrotetraazacyclooctane), and its straightforward preparation highlights compound 8 as a promising high-energy density material (HEDM). This work supports the effectivity of utterly manipulable nitration and provides a generalizable design synthesis strategy for developing new HEDMs.

Molecular-Simulation-Inspired Synthesis of [6]-Prismane via Photoisomerisation of Octafluoro[2.2]paracyclophane

Prismanes have been attracting interest for nearly 50 years because of their geometric symmetry, highly strained structures, and unique applications due to their high carbon densities and bulky structures. Although [3]-, [4]-, and [5]-prismanes have been synthesised, [6]-prismanes and their derivatives remain elusive. Herein, fluorine chemistry, molecular mechanics, molecular orbital package, and density functional theory calculations were used to design and implement the photoisomerisation of octafluoro[2.2]paracyclophane (selected based on the good overlap of its lowest unoccupied molecular orbitals and short distance between the benzene rings) into octafluoro-[6]-prismane. Specifically, a dilute solution of the above precursor in CH3CN/H2O/dimethyl sulfoxide (DMSO) (2:1:8, v/v/v) solution was irradiated with ultraviolet light, with the formation of the desired product confirmed through the use of nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. The product was thermally stable in solution but not under work-up conditions, which complicated the further analysis and single-crystal preparation. The key criteria for successful photoisomerisation were the presence of fluorine substituents in the cyclophane structure and DMSO in the solvent system. A more stable derivative design requires the isolation of prismane products. The proposed fluorination-based synthetic strategy is applicable to developing novel high-strain molecules/materials with three-dimensional skeletons.

Manipulating nitration and stabilization to achieve high energy

Nitro groups have played a central and decisive role in the development of the most powerful known energetic materials. Highly nitrated compounds are potential oxidizing agents, which could replace the environmentally hazardous used materials such as ammonium perchlorate. The scarcity of azole compounds with a large number of nitro groups is likely due to their inherent thermal instability and the limited number of ring sites available for bond formation. Now, the formation of the first azole molecule bonded to seven nitro groups, 4-nitro-3,5-bis(trinitromethyl)-1H-pyrazole (4), by the stepwise nitration of 3,5-dimethyl-1H-pyrazole is reported. Compound 4 exhibits exceptional physicochemical properties with a positive oxygen balance (OBCO2 = 13.62%) and an extremely high calculated density (2.04 g cm-3 at 100 K). This is impressively high for a C, H, N, O compound. This work is a giant step forward to highly nitrated and dense azoles and will accelerate further exploration in this challenging field.

From Tetranitromethane to Gem-Dinitro-Bridged Nitrogen-Rich Heterocyclic Compound: Achieving High Heat of Detonation

Improving the detonation performance of tetranitromethane (TNM) by introducing energetic moieties is an intriguing area in the field of energetic materials. Incorporation of a mono nitrogen-rich skeleton into TNM usually results in unsatisfactory detonation performance. Now, we reported the design and synthesis of an advanced TNM-like molecule (3) containing nitrogen-rich triazole and nitro-triazinane moieties. In addition, two of its analogues (4 and 5) were also obtained. Taking advantage of the positive heat of formation brought by triazole and triazinane rings and high-density properties donated by many nitro groups, 3 shows promising heat of detonation (Q = 5859 kJ kg-1), which is 2.8 times of TNM and higher than most of its mono ring-modified derivatives (Q: 2076 to 5594 kJ kg-1). The detonation velocity and detonation pressure of 3 (Dv = 8964 m s-1 and P = 35.7 GPa) are competitive with those of RDX (Q = 5763 kJ kg-1, Dv = 8782 m s-1, and P = 34.7 GPa). Structural modification by using triazole and nitro-triazinane rings may be helpful in exploring more TNM derivatives and other types of high-performance explosives.

Sensitive 1,4-Disubstituted Nitro-Containing Cubanes: Structures and Properties

The cubane cage system is characteristic and well known for its high strain energy, qualifying it as a promising precursor for energetic materials. 1,4-Disubstituted cubanes are the easiest accessible derivatives. A further developed laboratory-scale procedure for cubane-1,4-dicarboxylic acid dimethyl ester is presented. From this central precursor, the bis-trinitroethyl and bis-nitromethyl esters as well as the bis-methylcarbamate and bis-methylnitrocarbamate were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallography. In addition, their physical and energetic properties were determined and studied.

Novel fluorine-containing energetic materials: how potential are they? A computational study of detonation performance

CONTEXT

High-energy density materials (HEDMs) have emerged as a research focus due to their advantageous ultra-high detonation performance and better sensitivity. The primary aim of this study revolves around crafting HEDMs that strike a delicate balance between exceptional performance and minimal sensitivity. Density functional theory (DFT) was utilized to evaluate the geometric structures, energies, densities, energy properties, and sensitivities of 39 designed derivatives. The theoretical density (ρ) and heat of formation (HOF) were used to estimate the detonation velocity (D) and pressure (P) of the title compounds. Our study shows that the introduction of fluorine-containing substituents or fluorine-free substituents into the CHOFN backbone or the CHON backbone can significantly enhance the detonation performance of derivatives. Derivative B1 exhibits the better overall performance, including superior density, detonation performance, and sensitivity (P = 58.89 GPa, D = 8.02 km/s, ρ = 1.93 g/cm³, and characteristic height H₅₀ = 34.6 cm). Our molecular design strategy contributes to the development of more novel HEDMs with excellent detonation performance and stability. It also marks a significant step towards a material engineering era guided by theory-based rational design.

METHODS

GaussView 6.0 was used for construction of molecular system coordinates, and Gaussian 16 was used to obtain optimal structures, energies, and volumes of all compounds at the B3LYP/6-31+G(d,p) level of theory. It was characterized to be the local energy minimum on the potential energy surface without imaginary frequencies at the same theory level. Molecular weight, isosurface area, and overall variance were obtained using the Multiwfn 3.3. The detonation properties of the materials were analyzed using the C-J thermodynamic detonation theory. Our broad analysis facilitated an extensive assessment of these properties.

Structure of (R,R)-4-bromo-2-{4-[4-bromo-1-(4-toluene-sulfon-yl)-1H-pyrrol-2-yl]-1,3-di-nitro-butan-2-yl}-1-(4-toluene-sulfon-yl)-1H-pyrrole, another ostensible by-product in the synthesis of geminal-dimethyl hydro-dipyrrins

The crystal structure of (R,R)-4-bromo-2-{4-[4-bromo-1-(4-toluene-sulfon-yl)-1H-pyrrol-2-yl]-1,3-di-nitro-butan-2-yl}-1-(4-toluene-sulfon-yl)-1H-pyrrole (1, C26H24Br2N4O8S2) is presented. The title compound was isolated in suitable yield as a by-product in our synthesis of geminal-dimethyl hydro-dipyrrins. We observe an unforeseen enanti-omeric resolution both in the bulk sample and the crystal of 1, with distinct C-H⋯O (Cmeth-yl-H⋯Onitro, Csp 3-H⋯Osulfon-yl) inter-actions observed in the enanti-omers present, along with other inter-actions, namely C5-pyrrol-yl-H⋯Osulfon-yl, forming a polymer along the crystallographic c-axis direction. Whilst pyrrolic fragments are well documented in the literature, little data is found surrounding the 1,3-di-nitro-butane scaffold.

Monitoring the Micro-Structural Evolution Mechanism of Next-Generation Ultra-High-Energy All-Nitrogen Materials: A Molecular Dynamic Study

Micro-structural evolution mechanisms of next-generation ultra-high-energy all-nitrogen materials under the extreme conditions of high temperature coupled with high pressure were revealed by state-of-the-art ab initio molecular dynamics studies based on highest-nitrogen-content energetic material 2,2'-azobis(5-azidotetrazole). The results indicate that there are three primary initial uni-molecular decomposition pathways, namely, tetrazole ring opening, azido group elimination, and the breaking of the N-N bond between the azo group and azidotetrazole. In complicated global decomposition reactions, there exists the formation of nitrogen-rich clusters and all-nitrogen species. Lowering the temperature or increasing the pressure is conducive to increasing the N content in the nitrogen-rich cluster and widening the time distribution for the cluster. Abundant all-nitrogen species N₄, N₅, N₆, N₇, N₈, N₉, N₁₀, and N₁₃ were formed, and their detailed evolutionary process and construction mechanisms were enunciated. We innovatively constructed a series of next-generation ultra-high-energy all-nitrogen materials, which are expected to realize the controllable construction of next-generation ultra-high-energy all-nitrogen materials under extreme conditions.

Approaches to 1,4-Disubstituted Cubane Derivatives as Energetic Materials: Design, Theoretical Studies and Synthesis

Novel 1,4-disubstituted cubane derivatives have been designed and selected ones have been successfully synthesized and characterized by various analytical and spectroscopic techniques, including single-crystal X-ray analysis. A detailed computational study at B3LYP/6-311++G(d,p) level of theory revealed that all newly designed 1,4-disubstituted cubane derivatives possess higher densities, higher density-specific impulse and superior ballistic properties when compared to conventional fuels, for example, RP-1. These compounds also exhibit acceptable kinetic and thermodynamic stabilities which were evaluated in terms of their HOMO-LUMO energy gap and bond dissociation energies, respectively, and are superior to TEX and many other compounds containing explosophoric groups. These results provide novel insights into the possible application of cubane-based energetic materials.

Alleviating the stability–performance contradiction of cage-like high-energy-density materials by a backbone-collapse and branch-heterolysis competition mechanism

Key role of cage-like conformations in alleviating the stability–performance contradiction of HEDMs.

Synthesis of Energetic 7-Nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one Based on a Novel Hofmann-Type Rearrangement

Rearrangement reactions are efficient strategies in organic synthesis and contribute enormously to the development of energetic materials. Here, we report on the preparation of a fused energetic structure of 7-nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one (NPTO) based on a novel Hofmann-type rearrangement. The 1,2,3-triazine unit was introduced into the fused bicyclic skeleton from a pyrazole unit for the first time. The new compound of NPTO was fully characterized using multinuclear NMR and IR spectroscopy, elemental analysis as well as X-ray diffraction studies. The thermal behaviors and detonation properties of NPTO were investigated through a differential scanning calorimetry (DSC-TG) approach and EXPLO5 program-based calculations, respectively. The calculation results showed similar detonation performances between NPTO and the energetic materials of DNPP and ANPP, indicating that NPTO has a good application perspective in insensitive explosives and propellants.

Potassium (3-Methyl-2-oxido-1,2,5-oxadiazol-4-yl)dinitromethanide

Furoxan derivatives enriched with explosophoric functionalities are promising compounds in the preparation of novel energetic materials. Herein, a previously unknown potassium (3-methyl-2-oxido-1,2,5-oxadiazol-4-yl)dinitromethanide (also referred to as potassium 4-dinitromethyl-3-methylfuroxanate) was synthesized via tandem nitration-reduction reactions of an available (furoxanyl)chloroxime. The structure of the synthesized compound was established by elemental analysis, IR, 1H, 13C and 14N NMR spectroscopy. Thermal stability and mechanical sensitivity of the prepared compound toward impact and friction were experimentally determined.

ortho-C-H Acetoxylation of Cubane Enabling Access to Cubane Analogues of Pharmaceutically Relevant Scaffolds

A novel method of introducing an oxygen functionality into a cubane core was developed using a transition-metal-catalyzed directed acetoxylation methodology via C-H activation. The obtained compounds were derivatized into cubane analogues of pharmaceutically relevant structural motifs, namely, acetylsalicylic acid and coumarin motifs, which could potentially act as bioisosteres of these scaffolds.

Isostructural rubidium and caesium 4-(3,5-di-nitro-pyrazol-4-yl)-3,5-di-nitro-pyrazolates: crystal engineering with polynitro energetic species

In the structures of the title salts, poly[[μ4-4-(3,5-di-nitro-pyrazol-4-yl)-3,5-di-nitro-pyrazol-1-ido]rubidium], [Rb(C6HN8O8)] n , (1), and its isostructural caesium analogue [Cs(C6HN8O8) n , (2), two independent cations M1 and M2 (M = Rb, Cs) are situated on a crystallographic twofold axis and on a center of inversion, respectively. Mutual inter-molecular hydrogen bonding between the conjugate 3,5-dinito-pyrazole NH-donor and 3,5-di-nitro-pyrazole N-acceptor sites of the anions [N⋯N = 2.785 (2) Å for (1) and 2.832 (3) Å for (2)] governs the self-assembly of the translation-related anions in a predictable fashion. Such one-component modular construction of the organic subtopology supports the utility of the crystal-engineering approach towards designing the structures of polynitro energetic materials. The anionic chains are further linked by multiple ion-dipole inter-actions involving the 12-coordinate cations bonded to two pyrazole N-atoms [Rb-N = 3.1285 (16), 3.2261 (16) Å; Cs-N = 3.369 (2), 3.401 (2) Å] and all of the eight nitro O-atoms [Rb-O = 2.8543 (15)-3.6985 (16) Å; Cs-O = 3.071 (2)-3.811 (2) Å]. The resulting ionic networks follow the CsCl topological archetype, with either metal or organic ions residing in an environment of eight counter-ions. Weak lone pair-π-hole inter-actions [pyrazole-N atoms to NO2 groups; N⋯N = 2.990 (3)-3.198 (3) Å] are also relevant to the packing. The Hirshfeld surfaces and percentage two-dimensional fingerprint plots for (1) and (2) are described.

Heterocyclic Nitrilimines and Their Use in the Synthesis of Complex High-Nitrogen Materials

We show the ability of a nitrilimine prepared from 3-amino-5-nitro-1,2,4-triazole to undergo various cyclization and rearrangement reactions, giving a beautiful diversity of nitrogen-rich heterocyclic products. This chemistry includes the first cyclization of a nitrilimine with a diazonium species, giving a tetrazole, a previously unknown transformation, as well as leading to the creation of several new energetic materials with backbones not available by traditional techniques. New materials prepared were characterized both chemically (multinuclear NMR, IR, mass spectrometry, and elemental analysis) and energetically, with sensitivities and performances reported.

Detonation properties and impact sensitivities of trinitromethane derivatives of three-membered heterocyclic ring compounds

We have carried out the design and theoretical investigation of a series of trinitromethane derivatives of three-membered heterocyclic ring compounds - aziridine, 1H-azirine, diaziridine, 1H-diazirine, triaziridine, 1H-triazirene, oxaziridine, oxadiaziridine, dioxaziridine, oxirane, and dioxirane - in search for new high energy density materials (HEDM). We have estimated the properties relevant to HEDMs of the proposed molecules using Density Functional Theory (B3LYP/aug-cc-pVDZ). The results show that most of the molecules have a high value of solid-phase heat of formation, crystal density, detonation velocity and pressure with satisfying values for impact sensitivities. We have identified some of these molecules, 1-(triinitromethyl)diaziridine, 2-(trinitromethyl)-1-nitro-1H-azirine, and (2-(trinitromethyl)-3-nitrooxirane) are potential candidates of energetic molecules among the 60 molecules we investigated. As most of them are having a high positive oxygen balance, they can be recommended for use as oxidisers in solid propellants.

Cubane and cubanoid: Structural, optoelectronic and thermodynamic properties from DFT and TD-DFT method

In this paper, we report structural, electronic and optical properties of cubane (C₈H₈) and cubanoids (cubane-like molecules) using Density Functional Theory (DFT). The cubanoids are cubanes for which Carbon atoms have been substituted by Nitrogen (N), Phosphorus (P), Boron (B), Silicon (Si), Arsenic (As), Antimony (Sb) or Bismuth (Bi) atoms. These molecules presented exceptional stability with several different symmetry point groups, being the majority T_d. All calculated vibrational frequencies are positive for any studied molecules indicating that all these structures are in a stable state. The HOMO-LUMO gaps and DOS were calculated converged towards to values between 1.87 eV and 5.61 eV, actually showing promising electronic properties (Just for comparison, the cubane energy gap is 7.50 eV). The optical absorptions were also calculated for the cubanoid structure using the Time-Dependent Density Functional Theory (TD-DFT). Their dependence on the wavelength is analyzed, where five of theses structures absorb on the visible region. Finally, the extrapolation of thermodynamic properties indicates that these cubanoid could be potentially synthesized spontaneously, where four structures, the synthesis would occur for temperatures below 400 K, while for Si₄Bi₄H₄ structure, the synthesis would occur at room temperature.

Taming CL-20 through hydrogen bond interaction with nitromethane

A novel cocrystal explosive of CL-20/nitromethane in a 1 : 2 molar.

Synthesis and energetic properties of homocubane based high energy density materials

Novel Homocubane based HED materials with high densities, HOF and density specific impulse are superior to conventional fuels RP1 and HTPB.

Decagram Synthesis of Dimethyl 1,4-Cubanedicarboxylate Using Continuous-Flow Photochemistry

The highly strained cubane system is of great interest as a scaffold and rigid linker in both pharmaceutical and materials chemistry. A straightforward approach is reported for the scale-up of a [2+2] photocycloaddition step using convenient home-made flow photoreactors to access dimethyl 1,4-cubanedicarboxylate on decagram-scale in 33–40% yield over 8 steps. The process is demonstrated on 3.4 g·h–1 input with 30 minutes residence time, enabling to reduce the process time and to avoid the use of batch photoreactors. Completion of the characterisation of the photocycloadduct and its hydrates is reported.

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.

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.

Bulk polarity of 3,5,7-trinitro-1-azaadamantane mediated by asymmetric NO2(lone pair)...NO2(π-hole) supramolecular bonding

Molecular crystals exhibiting polar symmetry are important paradigms for developing new electrooptical materials. Though accessing bulk polarity still presents a significant challenge, in some cases it may be rationalized as being associated with the specific molecular shapes and symmetries and subtle features of supramolecular interactions. In the crystal structure of 3,5,7-trinitro-1-azaadamantane, C₉H₁₂N₄O₆, the polar symmetry of the molecular arrangement is a result of complementary prerequisites, namely the C_3v symmetry of the molecules is suited to the generation of polar stacks and the inherent asymmetry of the principal supramolecular bonding, as is provided by NO₂(lone pair)...NO₂(π-hole) interactions. These bonds arrange the molecules into a trigonal network. In spite of the apparent simplicity, the structure comprises three unique molecules (Z' = 1/3 + 1/3 + 1/3), two of which are donors and acceptors of three N...O interactions and the third being primarily important for weak C-H...O hydrogen bonding. These distinct structural roles agree with the results of Hirshfeld surface analysis. A set of weak C-H...O and C-H...N hydrogen bonds yields three kinds of stacks. The orientation of the stacks is identical and therefore the polarity of each molecule contributes additively to the net dipole moment of the crystal. This suggests a special potential of asymmetric NO₂(lone pair)...NO₂(π-hole) interactions for the supramolecular synthesis of acentric materials.

Kinetics and mechanism of decomposition induced by solvent evolution in ICM-101 solvates: solvent-evolution-induced low-temperature decomposition

[2,2'-Bi(1,3,4-oxadiazole)]-5,5'-dinitramide (ICM-101), a high-energy-density material, was reported in recent years. ICM-101 is the first energetic material with the 2,2'-bi(1,3,4-oxadiazole) structure as the main ring structure. The molecular structure of ICM-101 shows excellent planar characteristics, providing a new option for the design of high-energy-density materials. However, during crystal preparation, ICM-101 easily interacts with solvents and forms the corresponding solvates. Interestingly, during thermal decomposition, when the solvent escapes from ICM-101 solvates, it induces the decomposition of ICM-101. In this study, the decomposition of ICM-101 induced by solvent evolution was evaluated in detail, and the decomposition kinetic equation was established. The mechanism of solvent-evolution-induced decomposition in ICM-101 solvates was further studied, and it was found that solvent evolution might produce defects in the crystals of ICM-101 solvates, and induce the decomposition of ICM-101 on the defects.

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.

Synthesis of Thermally Stable and Insensitive Energetic Materials by Incorporating the Tetrazole Functionality into a Fused-Ring 3,6-Dinitropyrazolo-[4,3-c]Pyrazole Framework

A series of fused-ring energetic materials, i.e., 3,6-dinitro-1,4-di(1H-tetrazol-5-yl)-pyrazolo[4,3-c]pyrazole (DNTPP, compound 2) and its ionic derivatives (compounds 3-8), were designed and synthesized in this study. The molecular structures of compounds 2, 3, 6, 7·2H₂O, and 8 were confirmed using single-crystal X-ray diffraction. Their physicochemical and energetic properties, such as density, thermal stability, heat of formation, sensitivity, and detonation properties (e.g., detonation velocity and detonation pressure), were also evaluated. The results indicate that DNTPP and most of its ionic derivatives are extremely thermally stable and insensitive toward mechanical stimuli. In particular, the thermal decomposition temperature of compound 3 is up to 329 °C, while compounds 7 and 8 are very insensitive (impact sensitivity: >20 J; friction sensitivity: >360 N). Compounds 2, 3, and 6 possess good comprehensive properties, including excellent thermal stability, remarkable low sensitivities, and favorable detonation performance. These features show that DNTPP and its ionic derivatives have considerable promise as thermally stable and insensitive energetic materials.

First-principle calculations of electronic, vibrational, and thermodynamic properties of 1,3-diamino-2,4,6-trinitrobenzene

Energy-containing materials have aroused people's widespread concern because of its admirable performance in recent years. In this paper, the electronic structure, vibrational, and thermodynamic properties of 1,3-diamino-2,4,6-trinitrobenzene (DATB) are systematically investigated by adopting the first-principle calculations. We find that lattice parameters are in excellent agreement with the previous calculated and experimental values. The vibration spectra are described in detail and the peaks in the Raman and infrared spectra are assigned to different vibration modes. Phonon dispersion curves indicate that the DATB is dynamically stable. According to the vibrational properties, the thermodynamic functions such as enthalpy (H), constant volume heat capacity (C_V), Helmholtz free energy (F), Debye temperature (Θ), and entropy (S) are analyzed. No corresponding experimental values have been found so far, and therefore, knowledge of these properties will provide a reference and guidance for the follow-up research.