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.

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.

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Understanding the structure–property relationship in a material is of great importance in materials science. To study the effect of ligand backbones and anionic groups on the properties of energetic cationic metal–organic frameworks (CMOFs) and to disclose their structure–property relationships, we designed and synthesized a series of CMOFs based on either 4,4′-bi-1,2,4-triazole (btrz) or its azo analogous, 4,4′-azo-1,2,4-triazole (atrz) as ligand, and either perchlorate [ClO4 –] or nitroformate [C­(NO2)3 –, NF–] anion as extra-framework anion. Surprisingly, the effect of ligand backbones on the CMOFs is inverse that of the backbones on traditional energetic compounds, while the effect of the anionic groups follows the traditional group law. We found that btrz-based CMOFs exhibit higher densities and better chemical and thermal stabilities than those of their corresponding atrz-based CMOFs, although btrz has a lower density and a lower stability than atrz. In particular, the density of btrz-Fe is more than 0.11 g cm–3 higher than that of its atrz-based analogue (atrz-Fe). Moreover, the decomposition temperature of btrz-Zn (363 °C) is 80 °C higher than that of atrz-Zn, even higher than that of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), making it a potential heat-resistant explosive. The effect mechanisms were also discussed according to the experimental results. This investigation is significant for understanding the structure–property relationship in energetic CMOFs. Moreover, it also brings about new design rules for future high-performance energetic materials.

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(NO)] 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(NO) 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)[C(NO)](HO)·atrz·2HO} (2b, ρ = 1.76 g cm, atrz = 4,4'-azo-1,2,4-triazole) is increased by 0.12 g cm compared to its 3D precursor {2a, [Cu(atrz)(NO)·2HO], ρ = 1.64 g cm}, and its heat of detonation is also enhanced to more than 1900 kJ kg. 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.