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.

Composite energetic materials are widely used in mining, air bag modules and propellants, and welding because they can release a large amount of stored energy on combustion. Unfortunately, common composite formulations exhibit incomplete combustion of these agents and their toxic components, reducing the yield and causing emission of harmful gaseous products. We report a new type of formulation using an energetic metal–organic framework, [Cu(atrz)3(NO3)2]n (atrz = 4,4′-azo-1,2,4-triazole), as an active component. Its physicochemical properties such as the decomposition temperature, heat of reaction, sensitivity, and gas generation rate were measured. Compared with traditional composites, these composites exhibit superior characteristics such as low toxicity, high peak pressure, insensitivity, and high activity, and they produce very little solid residue. In light of their excellent properties, they exhibit potential as green gas generators for future applications and open up a new field for the application of MOFs.

The synthesis and energetic performances of three inner diazonium salts, 3,5-dichloro-4-diazopyrazole zwitterion (1), 4-diazo-3,5-dinitropyrazole zwitterion (2), and 4-diazo-5-nitro-pyrazol-3-one zwitterion (3), were investigated in this study. All these compounds were characterized by IR, UV/Vis, 13C and 15N NMR spectroscopy, and elemental analysis. Their structures were further confirmed by single crystal X-ray diffraction. Moreover, their thermal stabilities are determined by differential scanning calorimetry (DSC). In addition, detonation parameters (e.g. detonation velocity and pressure) of the target compounds were computed using EXPLO5 v6.01 based on the calculated heat of formation and density. The results show that compound 2 exhibits a density of 1.849 g cm−3 and a decomposition temperature (Td) of 154 °C, which are superior to those of the efficient primary explosive DDNP (2-diazo-4,6-dinitrophenol, Td = 142 °C). Compounds 1 and 3 also have moderately high decomposition temperatures of 135 and 151 °C, respectively. Besides, compounds 2 and 3 exhibit good detonation properties (2, 9038 m s−1, 35.0 GPa; 3, 8055 m s−1, 26.4 GPa), which are higher than those of the widely used primary explosives DDNP (7290 m s−1, 23.7 GPa) and Pb(N3)2 (5876 m s−1, 33.4 GPa). The moderately high thermal stabilities combined with the good detonation properties make them potential green primary explosives.

Energetic polynitro anions, such as dinitramide ion [N(NO2)2–], have attracted significant interest in the field of energetic materials due to their high densities and rich oxygen contents; however, most of them usually suffer from low stability. Conveniently stabilizing energetic polynitro anions to develop new high energy materials as well as tuning their energetic properties still represent significant challenges. To address these challenges, we herein propose a novel strategy that energetic polynitro anions are encapsulated within energetic cationic metal–organic frameworks (MOFs). We present N(NO2)2– encapsulated within a three-dimensional (3D) energetic cationic MOF through simple anion exchange. The resultant inclusion complex exhibits a remarkable thermal stability with the onset decomposition temperature of 221 °C, which is, to our knowledge, the highest value known for all dinitramide-based compounds. In addition, it possesses good energetic properties, which can be conveniently tuned by changing the mole ratio of the starting materials. The encapsulated anion can also be released in a controlled fashion without disrupting the framework. This work may shed new insights into the stabilization, storage, and release of labile energetic anions under ambient conditions, while providing a simple and convenient approach for the preparation of new energetic MOFs and the modulation of their energetic properties.

A convenient and green method for the oxidation of nitrogen-rich heterocyclic amines to nitro-substituted heteroaromatics using potassium peroxymonosulfate (2KHSO5·KHSO4·K2SO4, Oxone) in water was developed. This method has several advantages over previous methods: operational simplicity, safety, inexpensive reagents, the use of H2O as the sole solvent, and mild conditions. The utility of the present oxidative system was demonstrated by the synthesis of the important energetic compounds 3,4,5-trinitro-1H-pyrazole (TNP) and 5-amino-3-nitro-1H-1,2,4-triazole (ANTA).

Accurate prediction to the detonation performances of different kinds of energetic materials has attracted significant attention in the area of high energy density materials (HEDMs). A common approach for the estimation of CHNO explosives is the Kamlet–Jacobs (K-J) equation. However, with the development of energetic materials, the components of explosives are no longer restricted to CHNO elements. In this study, we have extended the K-J equation to the calculation of certain metal-containing explosives. A new empirical method, in which metal elements are assumed to form metallic oxides, has been developed on the basis of the largest exothermic principle. In this method, metal oxides can be deemed as inert solids that release heat other than gases. To evaluate the prediction accuracy of new method, a commercial program EXPLO5 has been employed for the calculation. The difference involved in the ways of treating products has been taken into account, and the detonation parameters from two methods were subject to close comparison. The results suggest that the mean absolute values (MAVs) of relative deviation for detonation velocity (D) and detonation pressure (P) are less than 5%. Overall, this new method has exhibited excellent accuracy and simplicity, affording an efficient way to estimate the performance of explosives without relying on sophisticated computer programs. Therefore, it will be helpful in designing and synthesizing new metallic energetic compounds.