Refinement of sensitive azides via in situ generated azole-based metal-organic frameworks towards stable energetic materials

Energetic materials (EMs) have been widely employed in both military and civilian areas for nearly two centuries. The introduction of high-energy azide anions to assemble energetic metal-organic frameworks (EMOFs) is an efficient strategy to enhance energetic properties. However, azido-based EMOFs always suffer low stabilities to external mechanical stimulation. Herein, we employed an in situ hydrothermal reaction as a technique to refine azide anions with a neutral triazole-cyano-based ligand TrzAt (TrzAt = 2-(1H-1,2,4-triazol-1-yl)acetonitrile) to yield two tetrazole-based EMOFs, namely, [ZnBr(trmetz)]n1 and [Cd(trmetz)2]n2 (Htrmetz = 5-(1,2,4-triazol-1-ylmethyl)-1H-tetrazole). Compound 1 features a closely packed 2D layered network, while compound 2 exhibits a 3D architecture. With azide anions inlaid into a nitrogen-rich and chelating ligand in the EMOFs, compounds 1 and 2 present remarkable decomposition temperatures (Tdec ≥ 300 °C), low impact sensitivities (IS ≥ 32 J) and low friction sensitivities (FS ≥ 324 N). The calculated heat of detonation (ΔHdet) values of 1 and 2 are 3.496 and 4.112 kJ g-1, respectively. In particular, the ΔHdet value of 2 is higher than that of traditional secondary explosives such as 2,4,6-trinitrotoluene (TNT, ΔHdet = 3.720 kJ g-1). These results indicate that EMOFs 1 and 2 may serve as potential replacements for traditional secondary explosives. This work provides a simple and effective strategy to obtain two EMOFs with satisfactory energy densities and reliable stabilities through an in situ hydrothermal technique for desensitization of azide anions.

Coordination polymerization of nitrogen-rich linkers and dicyanamide anions toward energetic coordination polymers with low sensitivities

The design and synthesis of energetic materials (EMs) with high energy and reliable stabilities has attracted much attention in the field of EMs. In this work, we employed a strategy of the coordination polymerization of mild dicyanamide ions (DCA^-), two isomeric ligands 1-methyl-5-aminotetrazole (1-MAT) and 2-methyl-5-aminotetrazole (2-MAT) to construct energetic coordination polymers (ECPs). Four new ECPs {[Co(DCA)₂(1-MAT)₂]·H₂O}_n1, [Cu(DCA)₂(1-MAT)]_n2, [Cd(DCA)₂(1-MAT)₂]_n3 and [Cd(DCA)₂(2-MAT)₂]_n4 were successfully synthesized through solvent evaporation routes. Compounds 1 and 4 display 1D chains, while 2 and 3 exhibit 2D-layered structures. Compounds 1-3 with the 1-MAT ligand all exhibit reliable thermal stabilities (> 200 °C). The calculated heats of detonation (ΔH_det) of 1-3 are all higher than 1.4 kJ g^-1, which are higher than traditional explosive TNT (1.22 kJ g^-1) and the reported ECP AgMtta (HMtta = 5-methyl-1H-tetrazole, ΔH_det = 1.32 kJ g^-1). Furthermore, sensitivity testing demonstrates that 1-4 features low mechanical sensitivity to external mechanical action in contrast with the extremely sensitive azide-based ECPs [Cu₃(2-MAT)₂(N₃)₆]_n. In addition, compound 2 shows hypergolic properties via an 'oxidizer-fuel' drop experiment, demonstrating its application prospects in the field of propellants. This work details an approach of synthesizing multipurpose ECPs with reliable stabilities by introducing mild dicyanamide anions into nitrogen-rich skeletons.

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.

Auxiliary ligand-directed synthesis of 3D energetic coordination polymer from discrete complex: enhanced energy density, thermal stability and energy performance

A discrete complex was manipulated into a 3D energetic coordination polymer with enhanced stability and energy performance through the incorporation of an auxiliary ligand.

A solvent-free dense energetic metal-organic framework (EMOF): to improve stability and energetic performance via in situ microcalorimetry

It is a tremendous challenge to prepare solvent-free dense energetic metal-organic frameworks (EMOFs), hence also to improve their stability and energetic performance. In this study, based on in situ microcalorimetry, an interpenetrating EMOF without solvent molecules, [Cu(tztr)]_n (1, H₂tztr = 3-(tetrazol-5-yl)triazole) was obtained, possessing high stability (T_dec = 360 °C) and outstanding energetic properties (ΔH_det = 7.53 kcal cm^-3, D = 8.429 km s^-1, P = 40.02 GPa).

In situ synthesized 3D metal-organic frameworks (MOFs) constructed from transition metal cations and tetrazole derivatives: a family of insensitive energetic materials

The combination of the hydrothermal method with in situ synthesis has been successfully employed to prepare a family of tetrazole-based energetic metal-organic frameworks (EMOFs) ([Ag(Mtta)]_n, 1; [Cd₅(Mtta)₉]_n, 2; [Pb₃(bta)₂(O)₂(H₂O)]_n, 3; and [Pb(tztr)₂(H₂O)]_n, 4) through [2 + 3] cycloaddition of azide anions and nitrile groups. All the synthesized EMOFs were characterized by single crystal X-ray diffraction, IR spectroscopy, elemental analysis (EA), different scanning calorimetry (DSC), and thermogravimetry (TG). Both complexes 1 and 4 consist of reticular two-dimensional (2D) layers that are linked by π-π overlap interactions between the ligands in neighbouring layers to form 3D supramolecular structures. In contrast, complexes 2 and 3 are 3D frameworks. The in situ formation of ligands bta and tztr has been described for the first time. Remarkably, thermogravimetric measurements demonstrated that the EMOFs 1-4 possess excellent thermostabilities with high decomposition temperatures up to 354, 389, and 372 °C for 1, 2, and 4, respectively. Sensitivity tests revealed that all the EMOFs are extremely insensitive.

Self-assembled energetic 3D metal–organic framework [Na8(N5)8(H2O)3]n based on cyclo-N5–

A new 3D zeolite-like MOF [Na₈(N₅)₈(H₂O)₃]_n with an enhanced stability has been successfully synthesized by the self-assembly of Na⁺ with cyclo-N₅⁻ ligands.

A highly stable and tightly packed 3D energetic coordination polymer assembled from nitrogen-rich tetrazole derivatives

A tightly packed 3D energetic cadmium(ii) coordination polymer was synthesized with high stability and remarkable energetic performance.

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.

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.

An enhanced extended hook method to realize tetranuclear metal clusters embedded in energetic metal–organic framework channels

Rare tetranuclear Zn clusters were successfully embedded into energetic 3D metal–organic framework channels by an extended bifunctional tetrazolate–carboxylate hook ligand.

3D Nitrogen-rich metal–organic frameworks: opportunities for safer energetics

3D Nitrogen-rich MOFs as newly emerged energetic materials have experienced rapid development in the last few years. This Frontier Article highlights the most up-to-date progress in this field.

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.

Fluorescence and photochromic properties of a series of new Zn(ii)/Cd(ii) coordination compounds with a flexible semi-rigid tetrazole–viologen derivative

Diverse luminescence has been realized in four Zn(ii)/Cd(ii) coordination compounds. The isolated binuclear compound displays fluorescence and second-order nonlinear optical property variation in the photochromic process.

Rendering non-energetic microporous coordination polymers explosive

A stable microporous coordination polymer is transformed into a sensitive primary explosive by simple infiltration with an organic oxidizer.

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.

Coordination polymers based on a glycine-derivative ligand

The combination of a glycine-derivative supramolecular salt with lanthanide(iii) chloride hydrates under hydrothermal conditions (120 °C, 48 h) produced a family of isotypical materials formulated as [Ln(bodt)(Hbodt)].