Energetic Cocrystals Research Articles

Theoretical investigations on N2H5N5/PDO cocrystal via a first‐principles study

AbstractThe exploration of cyclo‐N5ˉ‐based energetic cocrystals represents a noteworthy avenue within pentazolate chemistry, focusing on leveraging cocrystallization to enhance stability. Recently, a novel cocrystal explosive, N2H5N5/PDO, was developed by combining N2H5N5 with pyrazine 1,4‐dioxide (PDO), exhibiting promising detonation characteristics and reduced sensitivity. This study endeavors to elucidate how the structure and noncovalent interactions impact the performance of N2H5N5/PDO through a first‐principles investigation. The results indicate that the enhanced hydrogen bonding and wave‐like crystal packing structure within the cocrystal effectively bolster its stability compared to N2H5N5. The N···H and O···H interactions, in conjunction with π–π interactions, emerge as critical elements driving cocrystal formation. Compared to the pure N2H5N5, the detonation performance of the cocrystal exhibits a slight decline, albeit with a noticeable reduction in sensitivity.

Some CL-20 based energetic cocrystals - A review

Some CL-20 based energetic cocrystals - A review

Two Novel CL-20 Cocrystals with Different Performances Obtained by Molecular Similarity Combined with Hydrogen Bonding Pairing Energy: An Effective Strategy to Design and Screen Energetic Cocrystals

Two Novel CL-20 Cocrystals with Different Performances Obtained by Molecular Similarity Combined with Hydrogen Bonding Pairing Energy: An Effective Strategy to Design and Screen Energetic Cocrystals

Temperature-dependent decomposition of the CL-20/MTNP cocrystal after phase separation.

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane)-based cocrystals are attractive energetic cocrystals with a potential for high energy and low sensitivity, which account for nearly one-third of energetic cocrystals. The applications of cocrystal explosives require in-depth understanding of their thermal kinetics behaviors. Although thermal kinetics of the decomposition of CL-20-based cocrystals having no melting point have been studied, relevant research of CL-20-based cocrystals having a melting point, which are also the most frequently observed type, is still rare. In this study, the CL-20/MTNP (1-methyl-3,4,5-trinitropyrazole) cocrystal was chosen as a typical CL-20-based cocrystal having a melting point to investigate its thermal kinetics behavior. The thermal decomposition of CL-20/MTNP was identified to be a typical heterogeneous reaction with phase separation before decomposition. Due to the presence of intermolecular hydrogen bonds between CL-20 and molten MTNP after phase separation, the thermal decomposition behavior of CL-20/MTNP was strongly temperature-dependent. The complex decomposition reaction was separated into its three constituent pathways to simplify the kinetic analysis. On the basis of in-depth understanding of the decomposition process, the best functions of mechanism and kinetic parameters for each process of CL-20/MTNP decomposition were obtained using the model-fitting method. Finally, important thermal safety indicators, such as TMRad and SADT were simulated by combining the established kinetic models. This study provides further insights into the entire reaction process of the CL-20/MTNP cocrystal and would help in its better applications.

Syntheses and properties of energetic cyclo-pentazolate cocrystals.

As a new type of polynitrogen species that is stable at room temperature, the pentazolate anion (cyclo-N5-) has attracted much attention in the field of high-energy density materials, but its energy and stability are unbalanced. Cocrystallisation can balance their properties to some extent by forming new chemical compositions from existing cyclo-N5- compounds through non-covalent interactions. This article reviews the research progress of cyclo-N5- cocrystals in recent years, including synthetic methods, cocrystals of metal-N5- compounds, and cocrystals of nonmetallic pentazolate salts. The cocrystals of metal-N5- compounds mainly include metal-N5- solvates, cocrystals composed of metal-N5- compounds and amines/MSM, and metal-containing composite salts. The cocrystals of nonmetallic pentazolate salts include cocrystals composed of cyclo-N5- salts and solvents, cocrystals composed of cyclo-N5- salts and N-heterocyclic molecules, and non-metallic composite salts. The fascinating crystal structures (in some cases topological structures), stable forms, and physicochemical properties of representative cocrystals were highlighted. In addition, the future directions that need to be focused on in this field were pointed out, including the development of more preparation methods, especially those suitable for scaling up; higher precision calculation or testing of enthalpy of formation; improvement of their thermal stabilities; creation of cocrystals of cyclo-N5- salts and high-density, high-oxygen balance, high-energy oxidizers; and exploration of the formation mechanism.

A novel energetic cocrystal of DATNBI/TNT with low sensitivity and an unexpected polymorphic transition

A novel type of 4,4′,5,5′-tetranitro-1H,1′H-(2,2′-biimidazole)-1,1′-diamine (DATNBI)/TNT energetic cocrystal (cocrystal-1) was prepared by the solvent evaporation method. The molar ratio of the cocrystal is 1:2 and the crystal density is 1.784 g cm−3 at 23°C. It belongs to the triclinic system with space group P 1. The thermal stability, mechanical sensitivity and detonation performance of cocrystal-1 were studied. Compared with DATNBI, the mechanical sensitivity (H 50 and FS, friction sensitivity) and thermal stability (T d, detonation temperature) of cocrystal-1 were significantly improved (H 50, FS and T d of DATNBI and cocrystal-1 are, respectively, 27.8 cm, 160 N, 240°C and 65.6 cm, >360 N, 253°C). Combining these results with other characterizations, it was found that cocrystal-1 exhibited a polymorphic transformation, phase separation and melting of the two single components in succession. The ability to control the properties and understand the structural stability of this explosive cocrystal is of great value.

Supramolecular self-assembly of micro spherical CL-20/TNT energetic Co-crystal

We reported an ultrasonic-assisted emulsion approach for the synthesis of micro spherical CL-20/TNT energetic co-crystal via supramolecular self-assembly. It was demonstrated that the architected CL-20/TNT co-crystal displays advanced thermal properties and improved sensitivity performance. For the micro spherical CL-20/TNT co-crystal with mean practical size = 6.8 μm, it has only one decomposing peak at 254.8 °C and higher impact sensitivity (H50: 57.8 cm) and lower friction (41%). Herein, for the first time, organic energetic co-crystal of micro spheres was synthesized by simultaneously tailoring the energy level and safety based on the intermolecular hydrogen-bonding interactions. This novel strategy is expected to provide new opportunities for exploring the synthesis of various organic micro spherical co-crystals towards their applications.

Characterization and properties of a new insensitive explosive co-crystal composed of trinitrotoluene and pyrene

A new energetic co-crystal of trinitrotoluene (TNT) and pyrene (PYRN) with a 1:1 molar ratio was prepared by a slow solvent evaporation technique. Co-crystal physicochemical properties have also been examined using optical microscopy, powder X-ray diffraction, single crystal X-ray diffraction, and differential scanning calorimetry. The results of single-crystal X-ray diffraction and non-covalent interaction calculations showed that non-covalent interactions (donor–acceptor π-π interaction) govern the structures of the TNT:PYRN co-crystal. The experimental and theoretical outcomes supported each other in the study. Thermal stability, impact sensitivity, and detonation performance of the co-crystal were investigated. DSC measurement indicates that the co-crystal has a melting point of 167 °C and a decomposition temperature of 293 °C, indicating outstanding thermal stability. The co-crystal was found to be less impact-sensitive than TNT using the BAM fall hammer instrument. Furthermore, the calculated detonation velocity and detonation pressure of the co-crystal are 5.29 km·s−1 and 8.48 G Pa, respectively. As an outcome, the TNT:PYRN co-crystal may be a promising intermediate energy explosive with low sensitivity and, as such, may be a desirable explosive alternative in the future instead of TNT for low-vulnerability formulations.

Increasing the Energy Limit of Single Triazole–Tetrazole: HNANTT Modified with Its Energetic Coordination Polymers, Co-Crystals, and Energetic Salts

Increasing the Energy Limit of Single Triazole–Tetrazole: HNANTT Modified with Its Energetic Coordination Polymers, Co-Crystals, and Energetic Salts

Surface-Induced Thermal Decomposition of Energetic Cocrystal CL-20/MTNP Based on In Situ Morphology and Crystal Structure Characterizations

Surface-Induced Thermal Decomposition of Energetic Cocrystal CL-20/MTNP Based on In Situ Morphology and Crystal Structure Characterizations

Scaled-up production and quality controlling techniques of energetic cocrystals: challenges and prospects

Cocrystallization techniques have become extremely important methods for obtaining novel high-energy insensitive energetic materials, and it has attracted great attention for the development of high-energy explosives and propellants, etc. in recent years. Several scale-up cocrystallization techniques including solvent-nonsolvent, semibatch reaction, bead milling, and spray drying methods et al. have been applied for obtaining the energetic cocrystals, and the preparation processes of these methods were also shown. The types and quality of raw materials and solvents, the synthetic times, morphology, and size of these cocrystals were described and compared by using different synthetic techniques in the review. Moreover, the principle, advantages and disadvantages of scale-up preparation methods were shown. More importantly, the preparation efficiency, the ratio between the quality of raw materials and the volume of solvent, and yield of different methods were also exhibited and discussed, which can provide key information and experiences for the future application of the materials. Finally, future research trends are suggested from different perspectives involving the formation mechanisms in the preparation process by using intermolecular interaction simulation, experimental study, and thermodynamic calculations, the optimization of traditional scale-up techniques, and the exploitation of novel methods for the energetic cocrystals.

4,4′-Azobis(1,2,4-triazole): A Versatile Molecular Scaffold to Develop Tailor-Made Energetic Materials

Energetic materials containing azoles are appealing in terms of their high nitrogen content and presence of functional groups that can participate in different non-covalent bonding interactions. One such interesting compound is 4,4′-azobis(1,2,4-triazole) (ATRZ), which has formidable energetic parameters. Based on the presence of hydrogen-bond acceptor and metal coordination sites, a number of tailor-made energetic materials have been derived by employing ATRZ as the molecular precursor. In this review, we discuss the use of this high-energy molecular scaffold in the development of different energetic cocrystals, coordination polymers, and composites and discuss their properties in the context of state-of-the-art energetic materials.

Thermally Stable and Insensitive Energetic Cocrystals Comprising Nitrobarbituric Acid Coformers

Four novel energetic cocrystals of 5-nitropyrimidine-2,4,6(1H,3H,5H)-trione/nitro barbituric acid (NBA) with energetic coformers 1H-tetrazol-5-amine (AmTz), 5-(4-nitro-1H-pyrazol-3-yl)-4H-1,2,4-triazol-3-amine (NPTA), 1,3-diaminoguanidinehydrochloride (DAG), and 7H-[1,2,4]triazolo[4,3-b][1,2,4]triazole-3,6,7-triamine (TATOT) were synthesized for the first time and confirmed by single-crystal X-ray diffraction. Three cocrystals, NBA:AmTz, NBA:NPTA, and NBA:DAG, were obtained in a stoichiometry of 1:1, while NBA:TATOT was obtained with 1:2 stoichiometry. All the presented molecules were synthesized from commercially available inexpensive starting materials in one or two steps. All the cocrystals possess high densities (1.71–1.80 g cm–3), excellent thermal stability (222–310 °C), and low impact and friction sensitivity (>40 J and >360 N), which suggest that they are a better replacement for TNT as a core explosive and are close to RDX and HMX as a formulating energetic material. The strong stabilizing hydrogen bonding and vdW interactions are preserved among all the components of cocrystals. These interactions also play a significant role in cocrystal formation. These cocrystals combine the stability of AmTz, NPTA, DAG, and TATOT with the energetic performance of NBA into a homogeneous energetic material.

Designing and property prediction of a novel three-component CL-20/HMX/TNAD energetic cocrystal explosive by MD method.

Cocrystallization technology can effectively regulate crystal structure, alter packing mode, and improve physicochemical performances of energetic materials at molecule level. CL-20/HMX cocrystal explosive has high energy density than HMX, but it also exhibits high mechanical sensitivity. To decrease the sensitivity and improve the properties of CL-20/HMX energetic cocrystal, the three-component energetic cocrystal CL-20/HMX/TNAD was designed. The properties of CL-20, CL-20/HMX, and CL-20/HMX/TNAD cocrystal models were predicted. The results show that CL-20/HMX/TNAD cocrystal models have better mechanical properties than CL-20/HMX cocrystal model, implying that the mechanical properties can be effectively improved. The binding energy of CL-20/HMX/TNAD cocrystal models is higher than CL-20/HMX cocrystal model, indicating that the three-component energetic cocrystal is more stable, and the cocrystal model with the ratio 3:4:1 is predicted to be the most stable phase. CL-20/HMX/TNAD cocrystal models have higher value of trigger bond energy than pure CL-20 and CL-20/HMX cocrystal models, meaning that the three-component energetic cocrystal is more insensitive. The crystal density and detonation parameters of CL-20/HMX and CL-20/HMX/TNAD cocrystal models are lower than CL-20, illustrating that the energy density is declined. The CL-20/HMX/TNAD cocrystal has higher energy density than RDX and can be regarded as a potential high energy explosive. This paper was performed with molecular dynamics (MD) method with the software of Materials Studio 7.0 under COMPASS force field. The MD simulation was performed under isothermal-isobaric (NPT) ensemble, the temperature and pressure was 295K and 0.0001 GPa, respectively.

A new CL‐20/1,4‐DNP cocrystal explosive with good comprehensive performance

AbstractA new energetic cocrystal of 2,4,6,8,10,12‐hexanitrohexaazaisowurtzitane (CL‐20) and 1,4‐dinitropyrazole (1,4‐DNP) with a 1 : 1 molar ratio was prepared by slow solvent evaporation. This cocrystal belongs to monoclinic system with P21/c space group formed mainly by the CH−O, CH−N, and NO2−π interactions through analyzing the structures and interactions. CL‐20/1,4‐DNP cocrystal has a melting point of 132 °C with a decomposition temperature of 253 °C, showing an excellent stability. Moreover, the impact sensitivity of the cocrystal (13.5 J) is similar to that of 1,1‐diamino‐2,2‐dinitroethene (FOX‐7, 14 J), a typical insensitive energetic material, indicating a favorable low sensitivity. Furthermore, the detonation performances of the cocrystal (8954 m/s, 35.90 GPa) are slightly superior to that of 1,3,5‐trinitro‐1,3,5‐ triazacyclohexane (RDX, 8877 m/s, 34.94 GPa), suggesting that CL‐20/1,4‐DNP cocrystal has an excellent detonation property. Therefore, the CL‐20/1,4‐DNP cocrystal may be an attractive new explosive with a good comprehensive performance and thus, may be used as a promising candidate instead of RDX for safety ammunitions in future.

Studies on ammonium dinitramide and 3,4-diaminofurazan cocrystal for tuning the hygroscopicity

Ammonium dinitramide (ADN) is a promising oxidizer with high energy characteristic, which is a relatively new environmentally friendly oxidizer without halogens and carbon elements. However, ADN has high hygroscopicity when exposed to high humidity air, restricting its applications on the solid propellants. In this paper, a novel energetic cocrystal composed of ammonium dinitramide and 3,4-diaminofurazan (DAF) was proposed and successfully synthesized by antisolvent crystallization method, and the properties of the cocrystal were systematically investigated by analytical characterization and theoretical simulation calculations. The formation of the cocrystal was confirmed by powder X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy and Raman spectroscopy, indicating that the synthesized product was a cocrystal. Through theoretical studies, the ADN/DAF cocrystal structure was predicted, and the powder X-ray diffraction, morphology, water sorption capacity of ADN/DAF cocrystal were calculated, which was consistent with experimental phenomena. The results showed that newly prepared cocrystal of ADN/DAF had lower hygroscopicity compared to pure ADN, and the water sorption capacity was reduced from 15.35% to 7.90%. This may be due to the formation of NH⋯O medium-strength hydrogen bonds between the ammonium ion of ADN and the O atom of DAF in the cocrystal, which prevents the binding of water molecules in the air and ammonium ions and reduces the probability of ADN binding to water molecules, leading to the reduction of cocrystal hygroscopicity. The newly prepared energetic cocrystal can provide theoretical and technical guidance for the study of the anti-hygroscopicity of ADN and advance the practical application of ADN.

Molecular Dynamics Simulation of Shock Response of CL-20 Co-crystals Containing Void Defects

To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane (CL-20) co-crystals, shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene (TNT), 1,3-dinitrobenzene (DNB), solvents ligands dimethyl carbonate (DMC) and gamma-butyrolactone (GBL) with void were simulated, using molecular dynamics method and reactive force field. It is found that the CL-20 co-crystals with void defects will form hot spots when impacted, significantly affecting the decomposition of molecules around the void. The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s, and the main reactions are the formation of dimer and the shedding of nitro groups. The existence of voids reduces the safety of CL-20 co-crystals, which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly. Detonation has occurred under the reflection velocity of 4 km/s, energetic co-crystals are easier to polymerize than solvent co-crystals, and are not obviously affected by voids. The results show that the energy of the wave decreases after sweeping over the void, which reduces the chemical reaction frequency downstream of the void and affects the detonation performance, especially the solvent co-crystals.

Thermal stability of azole-rich energetic compounds: their structure, density, enthalpy of formation and energetic properties.

Energetic compounds, as a type of special material, are widely used in the fields of national defense, aerospace and exploration. Their research and production have received growing attention. Thermal stability is a crucial factor for the safety of energetic materials. Azole-rich energetic compounds have emerged as a research hotspot in recent years owing to their excellent properties. Due to the aromaticity of unsaturated azoles, many azole-rich energetic compounds have significant thermal stability, which is one of the properties that researchers focus on. This review presents a comprehensive summary of the physicochemical and energetic properties of various energetic materials, highlighting the relationship between thermal stability and the structural, physicochemical, and energetic properties of azole-rich energetic compounds. To improve the thermal stability of compounds, five aspects can be considered, including functional group modification, bridging, preparation of energetic salts, energetic metal-organic frameworks (EMOFs) and co-crystals. It was demonstrated that increasing the strength and number of hydrogen bonds of azoles and expanding the π-π stacking area are the key factors to improve thermal stability, which provides a valuable way to develop energetic materials with higher energy and thermal stability.

Theoretical prediction on performance of a novel CL-20/bicyclo-HMX energetic cocrystal by MD method

Theoretical prediction on performance of a novel CL-20/bicyclo-HMX energetic cocrystal by MD method

Synthesis, Performance, and Thermal Behavior of Two Insensitive 3,4-Dinitropyrazole-Based Energetic Cocrystals

Due to the acidity and the limited applications of 3,4-dinitropyrazole (DNP), two types of nitrogen-rich energetic cocrystals (DD1 and DD2) based on DNP and 3,4-diaminofurazan (DAF) were synthesized. The magnificently grown cocrystals were thoroughly examined by Fourier transform infrared spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction, elemental analysis, and nuclear magnetic resonance. A differential scanning calorimetry analysis revealed that both cocrystals have different endothermic peaks and remarkably similar exothermic peaks. Moreover, thermogravimetric analysis demonstrates that the thermal decomposition of DD1 and DD2 seems to be three mass loss stages. Hirshfeld surface analysis suggests that O···H (hydrogen bonding) close contacts contribute the most to the stabilization of DD1 and DD2. Subsequently, the pH values of DD1 and DD2 indicate that cocrystals reduce the acidity of DNP; additionally, the inclusion of hydrogen peroxide can improve the oxygen balance of the cocrystal to a certain degree. The obtained cocrystals have high nitrogen contents and acceptable sensitivities to external stimuli (friction and impact) that prove them as promising candidates for expanding the applications of DNP in the field of energetic materials after overcoming an acidity problem.