Development and Evolution of Energetic Cocrystals

Dinitramide salts based on nitropyrazole-diaminotriazole hybrid: novel ionic energetic materials with high-energy and low-sensitivity

In this study, employing a simple anion exchange strategy and straightforward three-step synthetic route, a pair of promising nitrogen-rich heterocyclic cation and oxygen-rich anion were assembled together to generate two novel dinitramide energetic salts, both of which exhibit prominent detonation performance comparable to benchmark explosive RDX while possessing significantly lower mechanical sensitivity than RDX, thereby highlighting them as promising candidates for advanced secondary explosives. This work has directly led to a practical protocol for the design of chloride-free environmentally friendly IEMs, and accelerates the development of organic explosives with high-energy and low-sensitivity.

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.

Constructing Porous Energetic Spherulites via Solvation-Growth Coupling for Enhanced Combustion

The fabrication of materials with hierarchical structures has garnered great interest, owing to the potential for significantly enhancing their functions. Herein, a strategy of coupling molecular solvation and crystal growth is presented to fabricate porous spherulites of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), an important energetic material. With the addition of polyvinylpyrrolidone in the antisolvent crystallization, the metastable solvate of CL-20 is formed and grows spherulitically, and spontaneously desolvates to obtain the porous spherulite when filtration, in which the characteristic peak of the nitro group of CL-20 shifts detected by the in situ micro-confocal Raman spectroscopy. The effect of polyvinylpyrrolidone is thought to induce the solvation of CL-20, confirmed by density functional theory calculations, meanwhile acting on the (020) face of CL-20 to trigger spherulitic growth, demonstrated through infrared spectroscopy and Rietveld refinement of powder X-ray diffraction. Moreover, compared to common CL-20 crystals, porous spherulites exhibit enhanced combustion with increases of 6.24% in peak pressure, 40.21% in pressurization rate, and 9.63% in pressure duration effect, indicating the capability of hierarchical structures to boost the energy release of energetic crystals. This work demonstrates a new route via solvation-growth coupling to construct hierarchical structures for organic crystals and provides insight into the structure-property relations for material design.

Utilizing "Latent" Carbon: Repositioning Hydrogen-Bonded Synthons and Assemblies via Halogen Bonding to π-Systems

Molecules bearing carboxylic acid, amide, and hydroxyl groups are ubiquitous in crystal engineering, where robust hydrogen-bonded synthons centred on these functionalities enable reliable crystal structure design. We now show that halogen bonding to the carbon π-system of such molecules, traditionally ignored in crystal engineering, permits the recognition and directional assembly of the resulting hydrogen-bonded structural subunits, leaving the archetypal hydrogen-bonded ring, ladder, and chain homosynthons intact, but repositioned in space. When applied to heteromolecular synthons, this enables rearranging more complex hydrogen-bonded motifs and the evolution of binary cocrystals into ternary ones through "latent" carbon-based recognition sites, demonstrating a rational approach to build higher-order solid-state supramolecular assemblies.

Molecular dynamics simulation of DNAN/DNB cocrystal PBXs

CONTEXT

The DNAN/DNB eutectic is a high-energy explosive eutectic with superior safety and thermal stability compared to traditional melt-cast explosives. However, the addition of polymer binders can effectively enhance its mechanical properties, allowing for continued production demands without the need for changes to existing factory equipment. In this paper, a model of the DNAN/DNB eutectic explosive was established, and five different types of polymers-cis-1,4-polybutadiene (BR), ethylene-vinyl acetate copolymer (EVA), polyethylene glycol (PEG), fluorinated polymer (F2603), and polyvinylidene fluoride (PVDF)-were added to the (1 0 - 1), (1 0 1), and (0 1 1) cleavage planes, respectively, to form polymer-bonded explosives (PBXs). The stability, trigger bond length, mechanical properties, and detonation performance of the various polymer-bound PBXs were predicted retrogressively. Among the five PBX models, the DNAN/DNB/PEG model exhibited the highest binding energy and the shortest trigger bond length, indicating a significant improvement in stability, compatibility, and sensitivity compared to the original eutectic. Additionally, although the detonation performance of DNAN/DNB decreased after the addition of binders, the final results were still satisfactory. Overall, the DNAN/DNB/PEG model demonstrated excellent comprehensive performance, proving that among the many polymer binders, PEG is the optimal choice for DNAN/DNB.

METHODS

Within the Materials Studio software, molecular dynamics (MD) simulations were employed to predict the properties of the DNAN/DNB eutectic PBX. The MD simulation timestep was set to 1 fs, with a cumulative simulation duration of 2 ns. A 2 ns MD simulation was conducted using the isothermal-isobaric ensemble (NPT). The COMPASS force field was applied, and the temperature was fixed at 295 K.

Tuning energetic properties through co-crystallisation - a high-pressure experimental and computational study of nitrotriazolone: 4,4'-bipyridine

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4'-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar.

Sensitizing Explosives Through Molecular Doping

Cocrystallization assembles multicomponent crystals in defined ratios that are held together by intermolecular interactions. While cocrystals have seen extensive use in the pharmaceutical industry for solving issues with stability and solubility, extension to the field of energetic materials for improved properties has proven difficult. Predicting successful coformers remains a challenge for systems lacking well-understood synthons that promote reliable intermolecular assembly. Herein, an alternative method is investigated for altering energetic properties that operates in the absence of well-defined interactions by molecular doping. An impact sensitive primary explosive, cyanuric triazide (CTA), was selected as the dopant to test if less impact sensitive secondary explosives could gain increased sensitization to impact when CTA is inserted into their crystal lattices. Molecular doping was successful in sensitizing three melt-castable energetics: 2,4,6-trinitrotoluene (TNT), 2,4-dinitroanisole (DNAN), and 1,3,3-trinitroazetidine (TNAZ). CTA could also be incorporated as a stabilized inclusion to sensitize DNAN further. These results demonstrate how the judicious choice of dopant can lead to specific property improvements, providing a method for creating energetic materials with new properties to access metal-free primary explosives and physical hot spot models for explosive ignition.

Structural Landscape of α-Acetamidocinnamic Acid Cocrystals with Bipyridine-Based Coformers: Influence of Crystal Packing on Their Thermal and Photophysical Properties

Controlling the supramolecular synthon outcome in systems with different functionalities has been a key factor for the design of supramolecular materials, which also affected their physicochemical properties. In this contribution, we have analyzed the structural landscape of α-acetamidocinnamic acid (HACA) aiming to find its synthon outcome from the competitivity between its acidic and amidic groups. We prepared four multicomponent forms including one dihydrate (HACA·2H2O) and three cocrystals bearing different bipyridine coformers with formulas (HACA)2(1,2-bpe) (1), (HACA)2(4,4'-azpy) (2), and (HACA)2(4,4'-bipy)3 (3) (1,2-bpe = 1,2-bis(4-pyridyl)ethylene; 4,4'-azpy = 4,4'-azopyridine; 4,4'-bipy = 4,4'-bipyridine). First, we applied a virtual screening approach to assess the feasibility of cocrystal formation. Then, we synthesized the cocrystals, via liquid-assisted grinding (LAG) (1 and 2) or solvothermal (3) techniques, and single crystals of HACA, and their four multicomponent forms were obtained showing different synthons and crystal packings. Besides, a Cambridge Structural Database (CSD) search of the cocrystals presenting bipyridine-type coformers and molecules with acid and amide functionalities was performed, and the observed synthon occurrences as well as the possibility of synthon modification by tuning the H-donor/H-acceptor propensity of the acidic and amidic groups were shown. Finally, we measured their thermal and photophysical properties, which were correlated with their structural features.

Perchlorate-Free Energetic Oxidizers Enabled by Ionic Cocrystallization

The search for a suitable replacement for the ubiquitous oxidizer ammonium perchlorate (AP) is a top priority to enable more sustainable solid rocket motors. The oxidizing salts ammonium nitrate (AN) and ammonium dinitramide (ADN) are regarded as potential green replacements for AP, but suffer from a plethora of handling and processing issues including poor stability and a needle-like crystal morphology which inhibits dense packing; these prevent their widespread use. In the present work, ionic cocrystallization is leveraged to produce the first cocrystals of these oxidizing salts with an energetic coformer and the first such cocrystals to maintain a positive oxygen balance. The azole-based energetic molecule 5,5'-dinitro-2H,2H'-3,3″-bi-1,2,4-triazole (DNBT) is successfully cocrystallized with AN to yield the cocrystal 2AN:DNBT. Differential scanning calorimetry data confirms that AN, which in its pure form suffers from a problematic solid-state phase transition, is stabilized in the cocrystal. Application of this cocrystallization strategy to ADN produces 2ADN:DNBT, which has the highest oxygen balance of any organic cocrystal.

Combining the advantages of 1,3,4-oxadiazole and tetrazole enables achieving high-energy insensitive materials

Combining the advantages of energetic heterocycles to achieve high-energy insensitive explosives is a significant challenge. Herein, based on high-energy tetrazole rings and highly stable 1,3,4-oxadiazole rings, a series of novel nitrogen rich energetic compounds 5-9 were successfully constructed. The related compounds were fully characterized by EA, FT-IR, NMR, DSC, and MS, and compounds 6-9 were further confirmed by X-ray single crystal diffraction. Among them, the energetic ion salts 6-8 show high thermal stability (Tdec > 250 °C) and low mechanical sensitivity (IS > 40 J, FS > 360 N), as well as good energy properties (7552-8050 m s-1, 19.4-23.3 GPa). In particular, the azo compound 9 exhibits competent comprehensive performances (Tdec = 226.2 °C, D = 8502 m s-1, P = 28.9 GPa, IS = 32 J, FS = 320 N). These results suggest that the strategy of integrating tetrazole and 1,3,4-oxadiazole and employing an azo structure as a bridging unit are effective approaches to construct high-energy insensitive materials.

Polymorphism and Multi-Component Crystal Formation of GABA and Gabapentin

This study exploits the polymorphism and multi-component crystal formation of γ-amino butanoic acid (GABA) and its pharmaceutically active derivative, gabapentin. Two polymorphs of GABA and both polymorphs of gabapentin are structurally revisited, together with gabapentin monohydrate. Hereby, GABA form II is only accessible under special conditions using additives, whereas gabapentin converts to the monohydrate even in the presence of trace amounts of water. Different accessibilities and phase stabilities of these phases are still not fully clarified. Thus, indicators of phase stability are discussed involving intermolecular interactions, molecular conformations, and crystallization environment. Calculated lattice energy differences for polymorphs reveal their similar stability. Quantification of the hydrogen bond strengths with the atoms-in-molecules (AIM) model in conjunction with non-covalent interaction (NCI) plots also shows similar hydrogen bond binding energy values for all polymorphs. We demonstrate that differences in the interacting modes, in an interplay with the intermolecular repulsion, allow the formation of the desired phase under different crystallization environments. Salts and co-crystals of GABA and gabapentin with fumaric as well as succinic acid further serve as models to highlight how strongly HBs act as the motif-directing force in the solid-phase GABA-analogs. Six novel multi-component entities were synthesized, and structural and computational analysis was performed: GABA fumarate (2:1); two gabapentin fumarates (2:1) and (1:1); two GABA succinates (2:1) and (1:1); and a gabapentin:succinic acid co-crystal. Energetically highly attractive carboxyl/carboxylate interaction overcomes other factors and dominates the multi-component phase formation. Decisive commonalities in the crystallization behavior of zwitterionic GABA-derivatives are discussed, which show how they can and should be understood as a whole for possible related future products.

Fluorine-Containing Functional Group-Based Energetic Materials

Molecules featuring fluorine-containing functional groups exhibit outstanding properties with high density, low sensitivity, excellent thermal stability, and good energetic performance due to the strong electron-withdrawing ability and high density of fluorine. Hence, they play a pivotal role in the field of energetic materials. In light of current theoretical and experimental reports, this review systematically focuses on three types of energetic materials possessing fluorine-containing functional groups F- and NF2 - substituted trinitromethyl groups (C(NO2 )2 F, C(NO2 )2 NF2 ), trifluoromethyl group (CF3 ), and difluoroamino and pentafluorosulfone groups (NF2 , SF5 ) and investigates the synthetic methods, physicochemical parameters, and energetic properties of each. The incorporation of fluorine-containing functional moieties is critical for the development of novel high energy density materials, and is rapidly being adopted in the design of energetic materials.

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.

Synthesis of the first remdesivir cocrystal: design, characterization, and therapeutic potential for pulmonary delivery

While cocrystal engineering is an emerging formulation strategy to overcome drug delivery challenges, its therapeutic potential in non-oral applications remains not thoroughly explored. We herein report for the first time the successful synthesis of a cocrystal for remdesivir (RDV), an antiviral drug with broad-spectrum activities against RNA viruses. The RDV cocrystal was prepared with salicylic acid (SA) via combined liquid-assisted grinding (LAG) and thermal annealing. Formation of RDV-SA was found to be a thermally activated process, where annealing at high temperature after grinding was a prerequisite to facilitate the cocrystal growth from an amorphous intermediate, rendering it elusive under ambient preparing conditions. Through powder X-ray analysis with Rietveld refinement, the three-dimensional molecular structure of RDV-SA was resolved. The thermally annealed RDV-SA produced by LAG crystalized in a non-centrosymmetric monoclinic space group P2₁ with a unit cell volume of 1826.53(17) ų, accommodating one pair of RDV and SA molecules in the asymmetric unit. The cocrystal formation was also characterized by differential scanning calorimetry, solid-state nuclear magnetic resonance, and Fourier-transform infrared spectroscopy. RDV-SA was further developed as inhaled dry powders by spray drying for potential COVID-19 therapy. The optimized RDV-SA dry powders exhibited a mass median aerodynamic diameter of 4.33 ± 0.2 μm and fine particle fraction of 41.39 ± 4.25 %, indicating the suitability for pulmonary delivery. Compared with the raw RDV, RDV-SA displayed a 15.43-fold higher fraction of release in simulated lung fluid at 120 min (p =0.0003). RDV-SA was safe in A549 cells without any in vitro cytotoxicity observed in the RDV concentration from 0.05 to 10 µM.

Mechanism of the Impact-Sensitivity Reduction of Energetic CL-20/TNT Cocrystals: A Nonequilibrium Molecular Dynamics Study

High-energy low-sensitivity explosives are research objectives in the field of energetic materials, and the formation of cocrystals is an important method to improve the safety of explosives. However, the sensitivity reduction mechanism of cocrystal explosives is still unclear. In this study, CL-20/TNT, CL-20 and TNT crystals were taken as research objects. On the basis of the ReaxFF-lg reactive force field, the propagation process of the wave front in the crystals at different impact velocities was simulated. The molecular dynamics data were used to analyze the molecular structure changes and initial chemical reactions, and to explore the sensitivity reduction mechanism of the CL-20/TNT cocrystal. The results showed that the chemical reaction of the CL-20/TNT cocrystal, compared with the CL-20 single crystal, is different under different impact velocities. At an impact velocity of 2 km/s, polymerization and separation of the component molecules weakened the decomposition of CL-20. At an impact velocity of 3 km/s, the decay rates of CL-20 and TNT in the cocrystal decreased, and the intermediate products were enhanced, such as nitrogen oxides. At an impact velocity of 4 km/s, the cocrystal had little effect on the decay rates of the molecules and formation of CO₂, but it enhanced formation of N₂ and H₂O. This may explain the reason for the impact-sensitivity reduction of the CL-20/TNT cocrystal.

General Graph Neural Network-Based Model To Accurately Predict Cocrystal Density and Insight from Data Quality and Feature Representation

Cocrystal engineering as an effective way to modify solid-state properties has inspired great interest from diverse material fields while cocrystal density is an important property closely correlated with the material function. In order to accurately predict the cocrystal density, we develop a graph neural network (GNN)-based deep learning framework by considering three key factors of machine learning (data quality, feature presentation, and model architecture). The result shows that different stoichiometric ratios of molecules in cocrystals can significantly influence the prediction performances, highlighting the importance of data quality. In addition, the feature complementary is not suitable for augmenting the molecular graph representation in the cocrystal density prediction, suggesting that the complementary strategy needs to consider whether extra features can sufficiently supplement the lacked information in the original representation. Based on these results, 4144 cocrystals with 1:1 stoichiometry ratio are selected as the dataset, supplemented by the data augmentation of exchanging a pair of coformers. The molecular graph is determined to learn feature representation to train the GNN-based model. Global attention is introduced to further optimize the feature space and identify important atoms to realize the interpretability of the model. Benefited from the advantages, our model significantly outperforms three competitive models and exhibits high prediction accuracy for unseen cocrystals, showcasing its robustness and generality. Overall, our work not only provides a general cocrystal density prediction tool for experimental investigations but also provides useful guidelines for the machine learning application. All source codes are freely available at https://github.com/Xiao-Gua00/CCPGraph.

Construction of nano-sized FOX-7/ZIF-8 composites for fast decomposition and reduced sensitivity

Herein, novel nano-sized 1,1-diamino-2,2-dinitroethylene (C₂H₄N₄O₄, FOX-7)/zeolitic imidazolate framework-8 (ZIF-8) composites are constructed by facile liquid-assisted mechanochemical reactions. In contrast to two-step thermal decomposition of raw FOX-7, the prepared FOX-7/ZIF-8 composites demonstrate a single high-intensity exothermal decomposition attributed to the catalysis of ZIF-8. Benefiting from nano-sized energetic materials and the buffering effect of ZIF-8, the mechanical sensitives of FOX-7/ZIF-8 composites are decreased.

Recent Progress on Synthesis, Characterization, and Performance of Energetic Cocrystals: A Review

In the niche area of energetic materials, a balance between energy and safety is extremely important. To address this "energy-safety contradiction", energetic cocrystals have been introduced. The investigation of the synthesis methods, characteristics, and efficacy of energetic cocrystals is of the utmost importance for optimizing their design and development. This review covers (i) various synthesis methods for energetic cocrystals; (ii) discusses their characteristics such as structural properties, detonation performance, sensitivity analysis, thermal properties, and morphology mapping, along with other properties such as oxygen balance, solubility, and fluorescence; and (iii) performance with respect to energy contents (detonation velocity and pressure) and sensitivity. This is followed by concluding remarks together with future perspectives.

Influence of Multiple Binding Sites on the Supramolecular Assembly of N-[(3-pyridinylamino) Thioxomethyl] Carbamates

In this study, we investigated how the presence of multiple intermolecular interaction sites influences the heteromeric supramolecular assembly of N-[(3-pyridinylamino) thioxomethyl] carbamates with fluoroiodobenzenes. Three targets—R-N-[(3-pyridinylamino) thioxomethyl] carbamate (R = methyl, ethyl, and isobutyl)—were selected and crystallized, resulting in three parent structures, five co-crystals, and one co-crystal solvate. Three hydrogen-bonded parent crystal structures were stabilized by N-H···N hydrogen bonding and assembled into layers that stacked on top of one another. Molecular electrostatic potential surfaces were employed to rank binding sites (Npyr > C=S > C=O) in order to predict the dominant interactions. The N-H⋯H hydrogen bond was replaced by I⋯Npyr in 3/6 cases, I⋯C=S in 4/6 cases, and I⋯O=C in 1 case. Interestingly, the I⋯C=S halogen bond coexisted twice with I⋯Npyr and I⋯O=C. Overall, the MEPs were fairly reliable for predicting co-crystallization outcomes; however, it is crucial to also consider factors such as molecular flexibility. Finally, halogen-bond donors are capable of competing for acceptor sites, even in the presence of strong hydrogen-bond donors.

Full-nitro-nitroamino cooperative action: Climbing the energy peak of benzenes with enhanced chemical stability

More nitro groups accord benzenes with higher energy but lower chemical stability. Hexanitrobenzene (HNB) with a fully nitrated structure has stood as the energy peak of organic explosives since 1966, but it is very unstable and even decomposes in moist air. To increase the energy limit and strike a balance between energy and chemical stability, we propose an interval full-nitro-nitroamino cooperative strategy to present a new fully nitrated benzene, 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB), which was synthesized using an acylation-activation-nitration method. TNTNB exhibits a high density (d: 1.995 g cm^-3 at 173 K, 1.964 g cm^-3 at 298 K) and excellent heat of detonation (Q: 7179 kJ kg^-1), which significantly exceed those of HNB (Q: 6993 kJ kg^-1) and the state-of-the-art explosive CL-20 (Q: 6534 kJ kg^-1); thus, TNTNB represents the new energy peak for organic explosives. Compared to HNB, TNTNB also exhibits enhanced chemical stability in water, acids, and bases.

Modulating Energetic Characteristics of Multicomponent 1D Coordination Polymers: Interplay of Metal-Ligand Coordination Modes

The energetic properties of multicomponent explosive materials can be altered for high detonation capabilities and minimized safety risk by changing their building components. We synthesized energetic coordination polymers (ECPs) using a 5,5'-bis(tetrazole)-1,1'-diolate linker and a N,N-dimethylacetamide (DMA) solvent, together with Cu and Mn metal cations. The new compounds, ECP-1 and ECP-2, contain two different types of 1D chain structures, straight and helical. We have conducted comprehensive studies on these ECP structures, energetic properties, and sensitivity and found excellent insensitivity owing to the long chain-to-chain distances created by the DMA solvent molecules. The results indicate that the metals as well as solvents used are crucial components influencing both the structure and energetic properties.

Energetic host–guest inclusion compounds: an effective design paradigm for high-energy materials

Due to the stringent requirements of performance, safety, and cost for the development of new energetic materials (EMs), the synthesis of host–guest inclusion compounds is an attractive way to fully exploit the application potential of existing EMs.

Two novel TNB energetic cocrystals with low melting point: a potential strategy to construct melt cast explosive carriers

Two novel low melting-point cocrystals with high performances were obtained by cocrystallizing TNB with 1,4-DNI and DNMT, namely TNB/1,4-DNI (1) and TNB/DNMT (2).

Microchannel-confined crystallization: shape-controlled continuous preparation of a high-quality CL-20/HMX cocrystal

Shape-controlled continuous preparation of a high-quality CL-20/HMX cocrystal has been realized through a microchannel-confined crystallization strategy.

Recent advances in studying the nonnegligible role of noncovalent interactions in various types of energetic molecular crystals

This highlight summarizes the research progress on the considerable effects of noncovalent interactions on diverse types of energetic materials and enlighten us to explore new factors that affect the key performance of explosives.

Optimized energetic HNTO/AN co-crystal and its thermal decomposition kinetics in the presence of energetic coordination nanomaterials based on functionalized graphene oxide and cobalt

The present research aims to select the optimal molar ratio of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) and ammonium nitrate (AN) to produce an energetic co-crystal. For a comparison purpose, the heat release, cost, density and hygroscopicity of the different co-crystals were evaluated. The obtained results indicated that HNTO/AN at the 1 : 3 ratio exhibited a higher heat release, better thermal stability, low water content and a reasonable cost, compared to other co-crystals. This new co-crystal was fully characterized through powder X-ray diffraction (XRD), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC), confirming that this latter displayed similar characteristics to those of the co-crystal with a 1 : 1 ratio, which was recently developed. On the other hand, the catalytic activity of two energetic coordination polymers of triaminoguanidine-cobalt (T-Co) complexes, with or without graphene oxide (GO-T-Co-T), on the thermolysis of the developed co-crystal has been also assessed by DSC under non-isothermal conditions. It is revealed that these catalysts have greatly decreased the decomposition temperature of the HNTO/AN cocrystal. Moreover, because of the complete decomposition in the case of the (HNTO/AN)/GO-T-Co-T composite, the heat release has been increased as well. Isoconversional integral kinetic methods were exploited to determine the kinetic parameters of the different systems. According to the obtained results, these catalysts have a strong catalytic action on the decomposition of the co-crystal AN/HNTO for which the activation energy and the pre-exponential factor are considerably lowered. Consequently, the developed co-crystal and the energetic catalysts could be considered as potential ingredients for the next generation of composite solid propellant formulations.

Coupling complementary strategy to flexible graph neural network for quick discovery of coformer in diverse co-crystal materials

Cocrystal engineering have been widely applied in pharmaceutical, chemistry and material fields. However, how to effectively choose coformer has been a challenging task on experiments. Here we develop a graph neural network (GNN) based deep learning framework to quickly predict formation of the cocrystal. In order to capture main driving force to crystallization from 6819 positive and 1052 negative samples reported by experiments, a feasible GNN framework is explored to integrate important prior knowledge into end-to-end learning on the molecular graph. The model is strongly validated against seven competitive models and three challenging independent test sets involving pharmaceutical cocrystals, π-π cocrystals and energetic cocrystals, exhibiting superior performance with accuracy higher than 96%, confirming its robustness and generalization. Furthermore, one new energetic cocrystal predicted is successfully synthesized, showcasing high potential of the model in practice. All the data and source codes are available at https://github.com/Saoge123/ccgnet for aiding cocrystal community.

First and Second Dissociation Enthalpies in Bi-Component Crystals Consisting of Maleic Acid and L-Phenylalanine

The energetics of the stepwise dissociation of a A:B₂ bi-component crystal, according to A:B₂(cr) → A:B(cr) + B(cr) and A:B(cr) → A(cr) + B(cr), was investigated using MA:Phe₂ and MA:Phe (MA = maleic acid; Phe = L-phenylalanine) as model systems. The enthalpy changes associated with these sequential processes and with the overall dissociation reaction A:B₂(cr) → A(cr) + 2B(cr) were determined by solution calorimetry. It was found that they are all positive, indicating that there is a lattice enthalpy gain when MA:Phe₂ is formed, either from the individual precursors or by adding Phe to MA:Phe. Single-crystal X-ray diffraction (SCXRD) analysis showed that MA:Phe₂ is best described as a protic salt containing a maleate anion (MA⁻) and two non-equivalent L-phenylalanine units, both linked to MA⁻ by NH···O hydrogen bonds (H-bond): one of these units is protonated (HPhe⁺) and the other zwitterionic (Phe^±). Only MA⁻ and HPhe⁺ molecules are present in the MA:Phe lattice. In this case, however, NH···O and OH···O H-bonds are formed between each MA⁻ unit and two HPhe⁺ molecules. Despite these structural differences, the enthalpy cost for the removal of the zwitterionic Phe^± unit from the MA:Phe₂ lattice to yield MA:Phe is only 0.9 ± 0.4 kJ mol⁻¹ higher than that for the dissociation of MA:Phe, which requires a proton transfer from HPhe⁺ to MA⁻ and the rearrangement of L-phenylalanine to the zwitterionic, Phe^±, form. Finally, a comparison of the dissociation energetics and structures of MA:Phe and of the previously reported glycine maleate (MA:Gly) analogue indicated that parameters, such as the packing coefficient, density, hydrogen bonds formed, or fusion temperature, are not necessarily good descriptors of dissociation enthalpy or lattice enthalpy trends when bi-component crystals with different molecular composition are being compared, even if the stoichiometry is the same.

Assessment of Computational Tools for Predicting Supramolecular Synthons

The ability to predict the most likely supramolecular synthons in a crystalline solid is a valuable starting point for subsequently predicting the full crystal structure of a molecule with multiple competing molecular recognition sites. Energy and informatics-based prediction models based on molecular electrostatic potentials (MEPs), hydrogen-bond energies (HBE), hydrogen-bond propensity (HBP), and hydrogen-bond coordination (HBC) were applied to the crystal structures of twelve pyrazole-based molecules. HBE, the most successful method, correctly predicted 100% of the experimentally observed primary intermolecular-interactions, followed by HBP (87.5%), and HBC = MEPs (62.5%). A further HBC analysis suggested a risk of synthon crossover and synthon polymorphism in molecules with multiple binding sites. These easy-to-use models (based on just 2-D chemical structure) can offer a valuable risk assessment of potential formulation challenges.

Halogen bonds as a tool in the design of high energetic materials: evidence from crystal structures and quantum chemical calculations

Combined crystallographic and quantum chemical study was performed to reveal the influence of halogen bonding on the sensitivity towards detonation of high-energy molecules.