Assembly of 1D Helical Energetic Coordination Polymers Using a Flexible Bridged Furazan-triazole Cation.

Two new energetic coordination compounds with 1D helical chain structures have been synthesized. First, the polyamine precursor 4,5-diamino-2-((4-amino-1,2,5-oxadiazole-3-yl)methyl)-2,4-dihydro-3H-1,2,4-triazole-3-imino chloride salt (TATAF-Cl) is obtained by incorporating 4-(chloromethyl)-1,2,5-oxadiazol-3-amine with 4H-1,2,4-triazole-3,4,5-triamine. Using a simple hydrothermal method, two energetic complexes, Ag(TATAF)(ClO4)2 (ECP-1) and Ag(TATAF)(NO3)2·H2O (ECP-2), with a helical 1D MOF structure of furazan and triazole were synthesized. Compounds ECP-1 and ECP-2 have relatively high nitrogen and oxygen content (N + O%: 52.04%, 61.04%), excellent crystal density (2.229 g cm-3, 2.116 g cm-3 at 298 K) and high heat of detonation (1.18 kcal g-1, 1.06 kcal g-1), good detonation performance (P: 35.34 GPa, 29.52 GPa; Dv: 8412 m s-1, 7794 m s-1), and moderate sensitivity (IS: 8 J, 13 J; FS: 72 N, 64 N). Structurally, the Ag+ of the two ECPs is coordinated with two energetic cations, two perchlorates, or one nitrate via tetragonal coordination to form a single helical structure that is interspersed up and down in two directions.

Improvement of Thermal Stability and Sensitivity of Furazan/Furoxan via Ring Closure Generation of Vicinal Amino-Nitro Structure.

Energetic compounds that display high thermal stability and insensitivity properties are essential for applications in mining, gas drilling, etc. In this work, a novel 4-nitro-5-aminoisoxazole energetic moiety oriented to enhance thermal stability and decrease the sensitivity of furazan/furoxan analogues was constructed. The generation of a vicinal amino-nitro structure can be effectively realized in one step by a green and mild ring-closing reaction of nitroacetonitrile potassium salt with chloroxime in aqueous solution. Seven new energetic compounds with good thermal stability (Td: 155.8∼270.3 °C) and low sensitivity (IS: >40 J, FS: 96∼192 N) were synthesized. The nitro-furazan and isoxazole combined product exhibits the advantages of both skeletons, with energetic properties (Dv = 8350 m s-1, P = 30.1 GPa) that may find value in insensitive energetic materials. This strategy promises to achieve a balance between energy levels and stability of furazan/furoxan analogues and offers a new way for the design and synthesis of highly thermally stable compounds that meet special applications.

Intramolecular Hydrogen Bonds Assisted Construction of Planar Tricyclic Structures for Insensitive and Highly Thermostable Energetic Materials.

Safety is fundamental for the practical development and application of energetic materials. Three tricyclic energetic compounds, namely, 1,3-di(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (ATDT), 5'-nitro-3-(1H-tetrazol-5-yl)-2'H-[1,3'-bi(1,2,4-triazol)]-5-amine (ATNT), and 1-(3,4-dinitro-1H-pyrazol-5-yl)-3-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (ATDNP), were effectively synthesized through a simple two-step synthetic route. The introduction of intramolecular hydrogen bonds resulted in excellent molecular planarity for the three new compounds. Additionally, they exhibit regular crystal packing, leading to numerous intermolecular hydrogen bonds and π-π interactions. Benefiting from planar tricyclic structural features, ATDT, ATNT, and ATDNP are insensitive (IS > 60 J, FS = 360 N) when exposed to external stimuli. Furthermore, ATNT (Td = 361.1 °C) and ATDNP (Td = 317.0 °C) exhibit high decomposition temperatures and satisfying detonation performance. The intermolecular hydrogen bonding that produced this planar tricyclic molecular structure serves as a model for the creation of innovative multiple heterocycle energetic materials with excellent stability.

High-Performance Azo Cathodes Enabled by N-Heteroatomic Substitution for Zinc Batteries with a Self-Charging Capability.

Redox-active azo compounds are emerging as promising cathode materials due to their multi-electron redox capacity and fast redox response. However, their practical application is often limited by low output voltage and poor thermal stability. Herein, we use a heteroatomic substitution strategy to develop 4,4'-azopyridine. This modification results in a 350 mV increase in reduction potential compared to traditional azobenzene, increasing the energy density at the material level from 187 to 291 Wh kg-1. The introduced heteroatoms not only raise the melting point of azo compounds from 68 °C to 112 °C by forming an intermolecular hydrogen-bond network but also improves electrode kinetics by reducing energy band gaps. Moreover, 4,4'-azopyridine forms metal-ligand complexes with Zn2+ ions, which further self-assemble into a robust superstructure, acting as a molecular conductor to facilitate charge transfer. Consequently, the batteries display a good rate performance (192 mAh g-1 at 20 C) and an ultra-long lifespan of 60,000 cycles. Notably, we disclose that the depleted batteries spontaneously self-charge when exposed to air, marking a significant advancement in the development of self-powered aqueous systems.

Can Catenated Nitrogen Compounds with Amine-like Structures Become Candidates for High-Energy-Density Compounds?

The worthwhile idea of whether amine-like catenated nitrogen compounds are stable enough to be used as high-energy materials was proposed and answered. Abstracting the NH3 structure into NR3 (R is the substituent) yields a new class of amine-like catenated nitrogen compounds. Most of the azole ring structures have a high nitrogen content and stability. Inspired by this idea, a series of new amine-like catenated nitrogen compounds (A1 to H5) were designed, and their basic energetic properties were calculated. The results showed that (1) amine-like molecular structures are often characterized by low density; however, the density of these compounds increases as the number of nitrogens in the azole ring increases; (2) these catenated nitrogen compounds generally have extremely high enthalpies of formation (882.91-2652.03 kJ/mol), and the detonation velocity of some compounds exceeds 9254.00 m/s; (3) the detonation performance of amine-like catenated nitrogen compounds designed based on imidazole and pyrazole rings is poor due to their low nitrogen content; and (4) the bond dissociation enthalpy of trigger bonds of most compounds is higher than 84 kJ/mol, indicating that these compounds have a certain thermodynamic stability. In summary, amine-like catenated nitrogen compounds have the potential to become energetic compounds with excellent detonation properties and should be considered to be synthesized by experimental chemists.

Modulating the Conduction Band of MOFs by Introducing Tiny TiO2 Nanoparticles for Enhanced Photocatalytic Performance: Importance of the Loading Position.

The preparation of TiO2 and metal-organic framework (MOF) into composite photocatalysts has been proven to be a mature and effective strategy to achieve stronger catalytic activity. In this work, we focus on exploring the significant effects and mechanisms of the relative positions of decorated titanium oxide nanoparticles and MOFs on the final catalytic activity. We first used a simple in situ method to encapsulate tiny TiO2 nanoparticles into a Zr-MOF (PCN-222), where Zr-Ti bonds were created at the interface of the two components. Thanks to the strong interfacial interaction forces, band bending occurred in TiO2@PCN-222 and a more negative conduction band (Δ = 0.26 V) with better electron transport properties was obtained. The results of photocatalytic CO2 reduction experiments under visible light showed a 78% increase (142 µmol g-1 h-1) in the production rate of HCOO-. Surprisingly, the loading of TiO2 nanoparticles on the MOF surface (TiO2@PCN-222) resulted in a significant decrease of 56% in the catalyst yield activity due to poor adsorption and electron transfer properties. This work demonstrates the possibility of tuning the band structure and catalytic activity of MOFs with the help of changing the position of the dopant and shows the importance of the rational design of MOF-based composites.

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.

Regulation of stability and density of energetic materials via isomerism.

Selective regulation of stability and density via isomerism is a promising strategy for developing energetic materials. In this work, we selectively introduced dinitromethyl groups at different positions of 4-nitro-1,2,3-triazole. The regional heterogeneity endows a high crystal density by virtue of the dense packing; on the other hand, it changes the charge distribution in the molecule, and reinforces the hydrogen bonding interactions, all of which stabilize the material. The resulting compounds exhibit excellent detonation properties and impact sensitivity that are comparable to those of HMX (Dv = 9250 m s-1 and IS = 10 J).

Insensitive High-Energy Density Materials Based on Azazole-Rich Rings: 1,2,4-Triazole N-Oxide Derivatives Containing Isomerized Nitro and Amino Groups.

It is an arduous and meaningful challenge to design and develop new energetic materials with lower sensitivity and higher energy. How to skillfully combine the characteristics of low sensitivity and high energy is the key problem in designing new insensitive high-energy materials. Taking a triazole ring as a framework, a strategy of N-oxide derivatives containing isomerized nitro and amino groups was proposed to answer this question. Based on this strategy, some 1,2,4-triazole N-oxide derivatives (NATNOs) were designed and explored. The electronic structure calculation showed that the stable existence of these triazole derivatives was due to the intramolecular hydrogen bond and other interactions. The impact sensitivity and the dissociation enthalpy of trigger bonds directly indicated that some compounds could exist stably. The crystal densities of all NATNOs were larger than 1.80 g/cm3, which met the requirement of high-energetic materials for crystal density. Some NATNOs (9748 m/s for NATNO, 9841 m/s for NATNO-1, 9818 m/s for NATNO-2, 9906 m/s for NATNO-3, and 9592 m/s for NATNO-4) were potential high detonation velocity energy materials. These study results not only indicate that the NATNOs have relatively stable properties and excellent detonation properties but also prove that the strategy of nitro amino position isomerization coupled with N-oxide is an effective means to develop new energetic materials.

Enhanced Energetic Performance via the Combination of Furoxan and Oxa-[5,5]bicyclic Structures.

Three new compounds based on the combination of furoxan (1,2,5-oxadiazole N-oxide) and oxa-[5,5]bicyclic ring were synthesized. Among them, the nitro compound showed satisfactory detonation properties (Dv, 8565 m s-1; P, 31.9 GPa), which is comparable to the performance of RDX (a classic high-energy secondary explosive). Additionally, the introduction of the N-oxide moiety and oxidation of the amino group more effectively improved the oxygen balance and density (d, 1.81 g cm-3; OB%, +2.8%) of the compounds compared to furazan analogues. Combined with good density and oxygen balance as well as moderate sensitivity, this type of furoxan and oxa-[5,5]bicyclic structure will open up a platform for the synthesis and design of new high-energy materials.

The Design, Synthesis and Application of Nitrogen Heteropolycyclic Compounds with UV Resistance Properties.

Exposure to ultraviolet (UV) light is known to cause skin aging, skin damage, cancer, and eye diseases, as well as polymer material aging. Therefore, significant attention has been devoted to the research and development of UV absorbers. Considering the robust hydrogen bonding and conjugated structure present in nitrogen-containing polycyclic compounds, these compounds have been selected as potential candidates for exploring ultraviolet absorption properties. After structural optimization and the simulation of ultraviolet absorption spectra, four tris-[1,2,4]-triazolo-[1,3,5]-triazine (TTTs) derivatives, namely TTTB, TTTD, TTTJ, and TTTL, were selected as the preferred compounds and synthesized. The structure of the compound was determined using various analytical techniques, including FTIR, 1HNMR, 13CNMR, HRMS, and XRD. Subsequently, composite films of polyvinyl chloride (PVC) and TTTs were produced using a simple solvent casting technique. The PVC films were subjected to UV age testing by exposing them to an ultraviolet aging chamber. The age-resistant performance of the fabricated films was evaluated using an ultraviolet spectrophotometer and Fourier infrared spectrum instrument. The findings suggest that TTTs exhibit a noteworthy capacity for absorbing ultraviolet radiation. The TTTL compound exhibits a superior UV absorption performance compared to commercially available UV absorbers such as UV-0 and UV-327 in the market.

Asymmetrical Methylene-Bridge Linked Fully Iodinated Azoles as Energetic Biocidal Materials with Improved Thermal Stability.

The instability and volatility of iodine is high, however, effective iodine biocidal species can be readily stored in iodinated azoles and then be released upon decomposition or detonation. Iodine azoles with high iodine content and high thermal stability are highly desired. In this work, the strategy of methylene bridging with asymmetric structures of 3,4,5-triiodo-1-H-pyrazole (TIP), 2,4,5-triiodo-1H-imidazol (TIM), and tetraiodo-1H-pyrrole (TIPL) are proposed. Two highly stable fully iodinated methylene-bridged azole compounds 3,4,5-triiodo-1-((2,4,5-triiodo-1H-imidazol-1-yl)methyl)-1H-pyrazole (3) and 3,4,5-triiodo-1-((tetraiodo-1H-pyrrol-1-yl)methyl)-1H-pyrazole (4) were obtained with high iodine content and excellent thermal stability (iodine content: 84.27% for compound 3 and 86.48% for compound 4; Td: 3: 285 °C, 4: 260 °C). Furthermore, their composites with high-energy oxidant ammonium perchlorate (AP) were designed. The combustion behavior and thermal decomposition properties of the formulations were tested and evaluated. This work may open a new avenue to develop advanced energetic biocidal materials with well-balanced energetic and biocidal properties and versatile functionality.

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

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

Boosting the Energetic Performance of Trinitromethyl-1,2,4-oxadiazole Moiety by Increasing Nitrogen-Oxygen in the Bridge.

The trinitromethyl moiety is a useful group for the design and development of novel energetic compounds with high nitrogen and oxygen content. In this work, by using an improved nitration method, the dinitromethyl precursor was successfully nitrated to the trinitromethyl product (2), and its structure was thoroughly characterized by FTIR, NMR, elemental analysis, differential scanning calorimetry, and single-crystal X-ray diffraction. Compound 2 has a high density (1.897 g cm-3), high heat of formation (984.8 kJ mmol-1), and a high detonation performance (D: 9351 m s-1, P: 37.46 GPa) that may find useful applications in the field of high energy density materials.

Coordinative Combination of Nitroamine and Gem-Dinitromethyl with Fused Ring for Enhanced Oxygen Balances and Detonation Properties.

Oxygen balance and heat of formation are closely related to the nitrogen and oxygen content in a molecule and have a significant effect on the detonation performance of energetic materials. Here a new family of 1,2,4-triazolo [4,3-b][1,2,4,5]-tetrazine containing gem-dinitromethyl and nitroamine with high nitrogen-oxygen content was synthesized and characterized. Moreover, the structure of the guanidine salt (3) and TATOT salt (4) were confirmed by single-crystal X-ray diffraction. The nitrogen and oxygen content of ammonium salt 2 reached 82.5%, with a high density (1.805 g cm-3) and high detonation properties (D = 8900 m s-1; P = 32.4 GPa), which were similar to those of RDX.

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

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

Nitration of Chitin Monomer: From Glucosamine to Energetic Compound.

The nitration of chitin monomer in a mixture of nitric acid and acetic anhydride was conducted and a highly nitrated (3R,4R,6R)-3-acetamido-6-((nitrooxy)methyl)tetrahydro-2H-pyran-2,4,5-triyl trinitrate (1) was obtained. Its structure was fully characterized using infrared spectroscopy, NMR spectroscopy, elemental analysis, and X-ray diffraction. Compound 1 possesses good density (ρ: 1.721 g·cm-3) and has comparable detonation performance (Vd: 7717 m·s-1; P: 25.6 GPa) to that of nitrocellulose (NC: Vd: 7456 m·s-1; P: 23 GPa; Isp = 239 s) and microcrystalline nitrocellulose (MCNC; Vd: 7683 m·s-1; P: 25 GPa; Isp = 250 s). However, Compound 1 has much lower impact sensitivity (IS: 15 J) than the regular nitrocellulose (NC; IS: 3.2 J) and MCNC (IS: 2.8 J). Compound 1 was calculated to exhibit a good specific impulse (Isp: 240 s), which is comparable with NC (Isp: 239 s) and MCNC (Isp: 250 s). By replacing the nitrocellulose with Compound 1 in typical propellants JA2, M30, and M9, the specific impulse was improved by up to 4 s. These promising properties indicate that Compound 1 has a significant potential as an energetic component in solid propellants.

Energetic Butterfly: Heat-Resistant Diaminodinitro trans-Bimane.

Due to a significant and prolific activity in the field of design and synthesis of new energetic molecules, it becomes increasingly difficult to introduce new explosophore structures with attractive properties. In this work, we synthesized a trans-bimane-based energetic material-3,7-diamino-2,6-dinitro-1H,5H-pyrazolo-[1,2-a]pyrazole-1,5-dione (4), the structure of which was comprehensively analyzed by a variety of advanced spectroscopic methods and by X-ray crystallo-graphy (with density of 1.845 g·cm-3 at 173 K). Although obtained crystals of 4 contained solvent molecules in their structure, state-of-the-art density functional theory (DFT) computational techniques allowed us to predict that solvent-free crystals of this explosive would preserve a similar tightly packed planar layered molecular arrangement, with the same number of molecules of 4 per unit cell, but with a smaller unit cell volume and therefore higher energy density. Explosive 4 was found to be heat resistant, with an onset decomposition temperature of 328.8 °C, and was calculated to exhibit velocity of detonation in a range of 6.88-7.14 km·s-1 and detonation pressure in the range of 19.14-22.04 GPa, using for comparison both HASEM and the EXPLO 5 software. Our results indicate that the trans-bimane explosophore could be a viable platform for the development of new thermostable energetic materials.

Synthesis of Denser Energetic Metal-Organic Frameworks via a Tandem Anion-Ligand Exchange Strategy.

High-density materials have attracted extensive attention because of their broad applications. However, strategies for improving the densities of MOFs and preparing denser MOFs remain almost unexplored. Herein, we propose a tandem anion-ligand exchange strategy for synthesizing denser MOFs by using three-dimensional cationic MOFs (3D CMOFs) with pillared layered structures as precursors and high-density anions and small monotopic ligands as exogenous guests. By means of this strategy, we choose the high-density nitroformate ion [C(NO2)3-] as an exogenous anion and water as an exogenous ligand to successfully synthesize two layered CMOFs. Single-crystal X-ray diffraction showed that after this transformation, the extra-framework anions are replaced with the C(NO2)3- anions, and the distances between adjacent layers in the two-dimensional (2D) networks are more than 3.70 Å shorter than those of their 3D precursors. The resultant materials exhibit higher densities, higher heats of detonation, higher nitrogen and oxygen contents, and lower metal contents. In particular, the density of {Cu(atrz)2[C(NO2)3]2(H2O)2·atrz·2H2O}n (2b, ρ = 1.76 g cm-3, atrz = 4,4'-azo-1,2,4-triazole) is increased by 0.12 g cm-3 compared to its 3D precursor {2a, [Cu(atrz)3(NO3)2·2H2O]n, ρ = 1.64 g cm-3}, and its heat of detonation is also enhanced to more than 1900 kJ kg-1. The resultant 2D layered CMOFs are also new potential high-energy density materials. This work may provide new insights into the design and synthesis of high-density MOFs. Moreover, we anticipate that the approach reported here would be useful for the preparation of new MOFs, in particular, which are otherwise difficult or unfeasible through traditional synthetic routes.

Joint experimental and theoretical studies of the surprising stability of the aryl pentazole upon noncovalent binding to ß-cyclodextrin.

Herein, binding of the ß-cyclodextrin (ß-CD) host to the unstable aryl pentazole guest has been confirmed experimentally and theoretically. After the confinement of aryl pentazole, electron density reorganization was studied by M06-2X dispersion-corrected DFT and further reflected in the characteristic shift in the NMR spectra. Among the host-guest complexes, the inclusion complex is favored with the phenyl ring expectedly encapsulated within the cavity through noncovalent interactions such as hydrogen bonding, C-Hπ, and the special Csp2-HH-Csp3 bonding discovered by the NBO, QTAIM, and NCI-RDG theories. The host-guest binding renders the enhancement of the nitrogen-ring aromatic character; this has been analyzed by employing nucleus-independent chemical shift (NICS)-based profiles. The non-covalent interaction largely enhances the thermal stability of the guest through a change of the decomposition reaction path whether the guest is encapsulated or not by the host. By comparison of the structures of B1-B4, the enhancement could be assigned to the ion-type transition structure stabilized by the C-H bonds of the host.