High-Performance Energetic Characteristics and Magnetic Properties of a Three-Dimensional Cobalt(II) Metal–Organic Framework Assembled with Azido and Triazole

Tuning Green Explosives through SNAr Chemistry

Reactivity and regioselectivity of SNAr-type fluorine substitution with azide in polyfluorosubstituted nitrobenzenes was studied both theoretically and experimentally. The obtained polyazido-substituted nitrobenzene derivatives were extensively characterized by NMR, IR, HPLC, X-ray, and DFT methods. It was found that the substitution with the azide nucleophile occurs first at the para- and the ortho-positions to the NO2-group and that transazidation reactions also occur here. Thermal decomposition of prepared azidonitrobenzenes was studied both in controlled (kinetic decay) and uncontrolled (explosion) modes. In case of the controlled thermal decomposition of ortho-azidonitrobenzenes, benzofuroxans were found as major products of the reaction unless another azido group was adjacent to the furoxan moiety. The bursting power of azidonitrobenzenes was found to rise gradually with the number of the azide substituents in the aromatic ring.

Poly Tetrazole Containing Thermally Stable and Insensitive Alkali Metal-Based 3D Energetic Metal-Organic Frameworks

Poly tetrazole-containing thermally stable and insensitive alkali metal-based 3D energetic metal-organic frameworks (EMOFs) are promising high energy density materials to balance the sensitivity, stability, and detonation performance of explosives in defense, space, and civilian applications. Herein, the self-assembly of L^3- ligand with alkali metals Na(I) and K(I) was prepared at ambient conditions, introducing two new EMOFs, [Na₃(L)₃(H₂O)₆]_n (1) and [K₃(L)₃(H₂O)₃]_n (2). Single crystal analysis reveals that Na-MOF (1) exhibited a 3D wave-like supramolecular structure with significant hydrogen bonding among the layers, while K-MOF (2) also featured a 3D framework. Both EMOFs were thoroughly characterized by NMR, IR, PXRD, and TGA/DSC analyses. Compounds 1 and 2 show excellent thermal decomposition T_d = 344 and 337 °C, respectively, compared to the presently used benchmark explosives RDX (210 °C), HMX (279 °C), and HNS (318 °C), which is attributed to structural reinforcement induced by extensive coordination. They also show remarkable detonation performance (VOD = 8500 m s^-1, 7320 m s^-1, DP = 26.74 GPa, 20 GPa for 1 and 2, respectively) and insensitivity toward impact and friction (IS ≥ 40 J, FS ≥ 360 N for 1; IS ≥ 40 J, FS ≥ 360 N for 2). Their excellent synthetic feasibility and energetic performance suggest that they are the perfect blend for the replacement of present benchmark explosives such as HNS, RDX, and HMX.

Series of AzTO-Based Energetic Materials: Effect of Different π-π Stacking Modes on Their Thermal Stability and Sensitivity

π-Stacking is common in materials, but different π-π stacking modes remarkably affect the properties and performances of materials. In particular, weak interactions, π-stacking and hydrogen bonding, often have a great impact on the stability and sensitivity of high-energetic compounds. Therefore, several of energetic materials based on 1,1'-dihydroxyazotetrazole (1) with a nearly flat structure, such as the salts of aminoguanidine (2), 1,3-diaminoguanidine (3), imidazole (4), pyrazole (5) and triaminoguanidine (6), and a cocrystal of 2-methylimidazole (7), were designed and synthesized. Based on single-crystal diffraction data, thermal decomposition behaviors, and the mechanical sensitivity test, the compounds of 4, 5, and 7 with face-to-face π-π stacking display outstanding thermal stability and insensitivity.

Removal of tetracycline hydrochloride from wastewater by Zr/Fe-MOFs/GO composites

Zirconium-iron metal-organic frameworks (Zr/Fe-MOFs) and Zr/Fe-MOF/graphene oxide (GO) composites were prepared via solvothermal synthesis using ferrous sulfate heptahydrate, zirconium acetate, and 1,3,5-benzenetricarboxylic acid. The MOFs and composites were measured using scanning electron microscopy (SEM), infrared spectrometry (IR), and thermogravimetric analysis (TGA). In this study, we explored the ability of Zr/Fe-MOFs and Zr/Fe-MOF/GO composites to adsorb tetracycline hydrochloride from an aqueous solution. Additionally, we optimized the adsorption performance by varying the ratio of MOFs and MOF composites to tetracycline hydrochloride solution, the concentration of tetracycline hydrochloride solution, and the pH of the solution. The results were investigated and fit to both pseudo-first-order and pseudo-second-order kinetic models. The results of the Freundlich and Langmuir isotherm models indicate that Zr/Fe-MOFs and Zr/Fe-MOF/GO composites have heterogeneous adsorption surfaces and that tetracycline hydrochloride is adsorbed over Zr/Fe-MOFs and Zr/Fe-MOF/GO by multilayer adsorption. Overall, our findings indicate that Zr/Fe-MOFs and Zr/Fe-MOF/GO composites can effectively treat wastewater, providing an inexpensive alternative to other methods.

Synthesis and Effects of Two Novel Rare-Earth Energetic Complexes on Thermal Decomposition of Cyclotetramethylene Tetranitramine (HMX)

In order to explore the effect of the energetic complex on the thermal decomposition HMX, two new rare-earth energetic complexes [La(tza)(NO3)2(H2O)4]n (1) and [Ce(tza)(NO3)2(H2O)4]n (2) (Htza = tetrazole-1-acetic acid) were prepared by a solvent evaporation method. The obtained products were structurally characterized by Fourier-transform infrared spectroscopy (FTIR), elemental analysis, powder X-ray diffraction (PXRD), single crystal X-ray diffraction (XRD), and thermogravimetric analysis coupled with differential scanning calorimetry (TG-DSC). In addition, the compatibility of complex 1 with cyclotetramethylene tetranitramine (HMX) was studied by DSC and FTIR, respectively. Structural analysis suggested that complex 1 exhibits an orthorhombic, P 21 21 21 space group, and the La (III) ion was 10-fold coordinated in a distorted double-capped antiprism configuration. Complex 2 featured a one-dimensional, right-handed helical infinite chain. The effect of complexes 1 and 2 on the thermal decomposition of HMX was investigated by DSC, which revealed that complex 1 showed a slightly better effect than 2 on the thermal decomposition of HMX and released more heat. Furthermore, complex 1 had good compatibility with HMX, indicating that it may act as a combustion promoter for nitrate ester plasticized polyether (NEPE) solid propellant.

Constructing Strategies and Applications of Nitrogen-Rich Energetic Metal–Organic Framework Materials

The synthesis of energetic metal–organic frameworks (EMOFs) with one-dimensional, two-dimensional and three-dimensional structures is an effective strategy for developing new-generation high-energy-density and insensitive materials. The basic properties, models, synthetic strategies and applications of EMOF materials with nitrogen-rich energetic groups as ligands are reviewed. In contrast with traditional energetic materials, EMOFs exhibit some interesting characteristics, like tunable structure, diverse pores, high-density, high-detonation heat and so on. The traditional strategies to design EMOF materials with ideal properties are just to change the types and the size of energetic ligands and to select different metal ions. Recently, some new design concepts have come forth to produce more EMOFs materials with excellent properties, by modifying the energetic groups on the ligands and introducing highly energetic anion into skeleton, encapsulating metastable anions, introducing templates and so on. The paper points out that appropriate constructing strategy should be adopted according to the inherent characteristics of different EMOFs, by combining with functional requirements and considering the difficulties and the cost of production. To promote the development and application of EMOF materials, the more accurate and comprehensive synthesis, systematic performance measurement methods, theoretical calculation and structure simulation should be reinforced.

Evolution of Oxidizing Inorganic Metal Salts: Ultrafast Laser Initiation Materials Based on Energetic Cationic Coordination Polymers

An effective and novel design strategy for ultrafast laser-initiating materials has been established on the basis of coordination chemistry for the first time in the present work. In view of the positive effect of Ag ion and perchlorate on laser sensitivity, silver perchlorate as a representative of oxidizing inorganic metal salts was used to construct energetic cationic coordination polymers (ECCPs), which solved the inconvenient situation caused by the difficulty in applying these salts directly in energetic materials because of the unavoidable hygroscopicity and the inhomogeneity of physical mixtures of oxidants and reductants. With the nonenergetic nitrogen-rich ligand 3-amino-1H-1,2,4-triazole-5-carbohydrazide (ATCA), one new laser-sensitive Ag(I)-based ECCP [Ag(ATCA)ClO₄]_n (1) was successfully synthesized with a compact helical structure proved by X-ray single-diffraction crystal data. The physicochemical property evaluation revealed that this Ag-ECCP was not only completely devoid of the undesirable properties of the silver perchlorate and displayed excellent tolerance to moisture and noncorrosive properties to metal shells, but was also endowed with good thermal stability and excellent safety for mechanical stimulation. Moreover, theoretical calculations based on the standard molar enthalpy of formation and the lead plate explosive test as the actual damage experiment have proved that the compound has a superior detonation performance (up to 6800 m s^-1 and 0.511 kcal g^-1) compared to the traditional primary explosives. More importantly, the laser-initiation-experiment-based femtosecond laser-testing system and high-speed photography demonstrated that this ECCP was an energetic material with great potential for application in the safety detonator as an ultrafast photosensitive initiating material for laser direct initiation, whose initiation delay time is as low as 73 ms using only 200 mJ initiation energy.

Highly Stable Energetic Coordination Polymer Assembled with Co(II) and Tetrazole Derivatives

A solvothermal reaction of Co(CH₃COO)₂·4H₂O and 5-mercapto-1-methyl-tetrazole (Hmmtz) in methanol (MeOH) yielded a one-dimensional solvent-free energetic coordination polymer, namely, [Co(mmtz)₂] _n 1, which was structurally characterized. The enthalpy of formation (Δ_f H°) of 1 (907 kJ mol^-1) is much larger than that of commercial 2,4,6-trinitrotoluene (-59 kJ mol^-1). The impact sensitivity and the friction sensitivity are greater than 40 J and 360 N, respectively, indicating that compound 1 exhibits a potential application as a safe explosive. Temperature-dependent molar magnetic susceptibilities show that weak antiferromagnetic behavior exists in 1.

A difunctional azido-cobalt(ii) coordination polymer exhibiting slow magnetic relaxation behaviour and high-energy characteristics with good thermostability and insensitivity

A novel one-dimensional azido-cobalt(ii) compound, [Co2(1-mbt)2(N3)4]n (1) (1-mbt = 1-((2-propyl-imidazol-1-yl)methyl)-benzo[1,2,3]triazole), was solvothermally synthesized. X-ray crystal structure analysis demonstrates that two crystallographically independent Co(ii) atoms in the asymmetrical unit of compound 1 exhibit a rectangular pyramid geometry. The 3D supermolecular network of 1 consists of well-isolated 1D metal chains in which the azido bridging ligands assume an unusual pattern of combination with the Co(ii) centre as the sign of [-EE-EO-EO-EO-]n. The various coordination modes of the azido anion are responsible for different magnetic exchanges between the adjacent Co(ii) ions. The end-to-end (EE) mode mediates the antiferromagnetic coupling, whereas the end-on (EO) manner contributes to the ferromagnetic interaction. Magneto-structural relationships are discussed with the aid of theoretical calculations which are employed to find the potential single-ion magnetic anisotropy and reproduce the observed magnetic coupling properly. Alternating current magnetic susceptibility measurements reveal that 1 features a typical behaviour of field-induced slow magnetic relaxation. Energetic characterization evidences that the resulting compound possesses satisfactory detonation properties, superior lack of sensitivity and thermostability owing to the high nitrogen content (N% = 40.10%) and a coherent intrachain configuration. The kinetic parameters of the exothermic processes for 1 are investigated by the Kissinger method and the Ozawa method. We note that 1 has potential application prospects as a new generation of environmentally friendly high-energy materials based on this nitrogen-rich and oxygen-free system. In addition, the compound is developed as a practical additive to promote the thermal decomposition of ammonium perchlorate (AP) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The finding in this work highlights an example of effective development of advanced magneto-energetic materials.

Rational assembly of functional Co-MOFs via a mixed-ligand strategy: synthesis, structure, topological variation, photodegradation properties and dye adsorption

Four novel Co(ii) metal–organic frameworks were synthesized employing a rational design approach under solvothermal conditions.

Explosives in the Cage: Metal-Organic Frameworks for High-Energy Materials Sensing and Desensitization

An overview of the current status of coordination polymers and metal-organic frameworks (MOFs) pertaining to the field of energetic materials is provided. The explosive applications of MOFs are discussed from two aspects: one for detection of explosives, and the other for explosive desensitization. By virtue of their adjustable pore/cage sizes, high surface area, tunable functional sites, and rich host-guest chemistry, MOFs have emerged as promising candidates for both explosive sensing and desensitization. The challenges and perspectives in these two areas are thoroughly discussed, and the processing methods for practical applications are also discussed briefly.

SMM behaviour and magnetocaloric effect in heterometallic 3d–4f coordination clusters with high azide : metal ratios

We present the synthesis and characterization of heterometallic compounds with a very large azide to metal ratio and fascinating magnetic properties.

Self-assembly of silver(i)-based high-energy metal–organic frameworks (HE-MOFs) at ambient temperature and pressure: synthesis, structure and superior explosive performance

Two HE-MOFs, {Ag₂(DNMAF)(H₂O)₂}_n (1) and {Ag₂(DNMAF)}_n (2), were prepared using K₂DNMAF in a mild self-assembly strategy.

Coligand modifications fine-tuned the structure and magnetic properties of two triple-bridged azido-Cu(ii) chain compounds exhibiting ferromagnetic ordering and slow relaxation

Two triple-bridged azido-Cu(ii) compounds with different benzoates as coligands exhibit distinct magnetic properties.

A substituent effect of phenylacetic acid coligand perturbed structures and magnetic properties observed in two triple-bridged azido-Cu(ii) chain compounds with ferromagnetic ordering and slow magnetic relaxation

Two triple-bridged azido-Cu(ii) chains exhibit distinct magnetic behaviors.

A novel 3D energetic MOF of high energy content: synthesis and superior explosive performance of a Pb(ii) compound with 5,5'-bistetrazole-1,1'-diolate

The development of high-performance insensitive energetic materials is important because of the increasing demand for these materials in military and civilian applications. A novel 3D energetic metal-organic framework (MOF) of exceptionally high energy content, [Pb(BTO)(H2O)]n, was synthesized and structurally characterized by single crystal X-ray diffraction, featuring a three-dimensional parallelogram porous framework, where BTO represents 5,5'-bistetrazole-1,1'-diolate. The thermal stability and energetic properties were determined, exhibiting good thermostability (Td = 309.0 °C), excellent detonation pressure (P) of 53.06 GPa, a detonation velocity (D) of 9.204 km s(-1), and acceptable sensitivity to confirmed impact (IS = 7.5 J). Notably, the complex possesses unprecedented superior density than the reported energetic MOFs. The results highlight this new MOF as a potential energetic material.

Nitrogen-Rich Energetic Metal-Organic Framework: Synthesis, Structure, Properties, and Thermal Behaviors of Pb(II) Complex Based on N,N-Bis(1H-tetrazole-5-yl)-Amine

The focus of energetic materials is on searching for a high-energy, high-density, insensitive material. Previous investigations have shown that 3D energetic metal-organic frameworks (E-MOFs) have great potential and advantages in this field. A nitrogen-rich E-MOF, Pb(bta)·2H₂O [N% = 31.98%, H₂bta = N,N-Bis(1H-tetrazole-5-yl)-amine], was prepared through a one-step hydrothermal reaction in this study. Its crystal structure was determined through single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, and elemental analysis. The complex has high heat denotation (16.142 kJ·cm^-3), high density (3.250 g·cm^-3), and good thermostability (T_dec = 614.9 K, 5 K·min^-1). The detonation pressure and velocity obtained through theoretical calculations were 43.47 GPa and 8.963 km·s^-1, respectively. The sensitivity test showed that the complex is an impact-insensitive material (IS > 40 J). The thermal decomposition process and kinetic parameters of the complex were also investigated through thermogravimetry and differential scanning calorimetry. Non-isothermal kinetic parameters were calculated through the methods of Kissinger and Ozawa-Doyle. Results highlighted the nitrogen-rich MOF as a potential energetic material.

Synthesis, crystal structure and properties of a new 1D polymeric nitrogen-rich energetic complex {TAG[Li(BTO)(H2O)]}n based on 1H,1′H-5,5′-bitetrazole-1,1′-diolate

The novel polymer {TAG[Li(BTO)(H₂O)]}_n, based on 1H,1′H-5,5′-bitetrazole-1,1′-diolate, opened up a new field on BTO-based energetic materials and anionic metal–organic frameworks.

High performance 5-aminotetrazole-based energetic MOF and its catalytic effect on decomposition of RDX

The energetic compound [Ag₂(5-ATZ)(N₃)] (1) features a compacted 3D framework structure, remarkable thermostability above 300 °C and perfect detonation performance. Remarkably, 1 can accelerate effectively the thermal decomposition of RDX.

An Ag(i) energetic metal–organic framework assembled with the energetic combination of furazan and tetrazole: synthesis, structure and energetic performance

A novel 3D Ag(i) energetic MOF assembled with a furazan derivative (4,4′-oxybis[3,3′-(1H-5-tetrazol)]furazan) shows low sensitivity, good thermostability and ultrahigh detonation pressure and detonation velocity.