Energetic Metal-organic Frameworks Research Articles

Novel energetic metal-organic frameworks assembled from the energetic combination of furazan and tetrazole.

Two novel 2D energetic metal-organic frameworks (MOFs), namely, [Pb(BTF)(H2O)2]n (1) and [Ba(BTF)(H2O)4]n (2), that possess the combined advantages of tetrazole and furazan rings were successfully synthesized. Their crystal structures were determined by single-crystal X-ray diffraction and fully characterized by elemental analysis and FT-IR spectroscopy. Their thermal stability and sensitivity were also investigated. The MOFs have good thermal stability (Tdec > 250 °C) and are insensitive to impact (IS > 25 J) and friction (FS > 360 N), and also have good oxygen balance (Ω > -20%). Crystal structure analyses reveal that the two compounds have densities up to 3.382 g cm-3 and 2.336 g cm-3, respectively, and excellent physicochemical properties. Tetrazole and furazan rings as ligands can commendably increase the densities and oxygen balance of energetic MOFs, thereby enhancing their detonation performance. We anticipate that this work will open a new direction for the development of energetic MOFs. Moreover, (1) exhibits outstanding catalytic performance for ammonium perchlorate (AP). When the supramolecular complex was added in 10 wt% amount, the high-temperature decomposition peak of AP advanced by 95 °C and the reaction rates enhanced by lowering the activation energy.

Energetic metastable n-Al@PVDF/EMOF composite nanofibers with improved combustion performances

Combustion is a kind of reacting process involves fluid mechanics and chemical reactions at the same time. In the past decades, little attention has been paid to the improvement on the heat and mass transfer rate of EMs, especially for metastable intermixed composites (MICs). In this paper, an Al-based MIC (EF@EMOF) with modified chemical kinetics as well as improved heat and mass transfer rate was prepared by precisely designing the reaction process and introducing energetic metal organic frameworks (EMOF) with high specific surface area as the reactants. The overall reaction process includes the activation of n-Al by eliminating Al2O3, decomposition of EMOF producing metal oxide, followed by exothermic reactions between the activated n-Al with metal oxide and PVDF. Results show that obtained MIC has significantly increased heat release (3464 J g−1), burning rate (more than 5 times faster than that of mechanically mixed one), and improved combustion efficiency. Furthermore, it is found that the decomposition of EMOF as well as the etching reaction generates massive gas products on the interface layer which avoid the sintering and form lots of holes. Those holes, in return, provide new channels for the further reaction, thus significantly improving the energy output and chemical reaction kinetics.

Energetic Metal-Organic Frameworks Incorporating NH3OH+ for New High-Energy-Density Materials.

Energetic metal-organic frameworks (E-MOFs) have witnessed increasing development over the past several years. However, as a highly energetic cation, NH3OH+ has never been explored to construct transition-metal-based E-MOFs. Herein, we report the first examples of NH3OH+-containing E-MOFs with bis(tetrazole)methane (H2btm) as a ligand and copper and manganese as central metal ions, [(NH3OH)2(Cu(btm)2)]n and [(NH3OH)2(Mn(btm)2)]n. Crystal structure determinations reveal that both E-MOFs show two-dimensional layered structures. Experimental results suggest that they have high thermal decomposition temperatures (>200 °C). Among them, Cu-based E-MOFs possesses outstanding thermal stability (Tdec = 230.3 °C), which surpasses those of known NH3OH+-containing compounds. They also have high energy density; in particular, the Cu-based E-MOF affords a high heat of combustion (11447 kJ kg-1) and high heat of detonation (713.8 kJ mol-1) beyond the most powerful organic explosives in use today. Additionally, the two E-MOFs show completely different sensitivity properties: the Mn-based E-MOF is an insensitive high-energy-density material (IS > 40 J; FS > 360 N; EDS > 20 J), while the Cu-based E-MOF can be classified as a sensitive energetic material (IS = 13 J; FS = 216 N; EDS = 10.25 J), demonstrating their diverse applications in different fields. Our research proposes a unique class of high-energy-density materials.

Metastable energetic nanocomposites of MOF-activated aluminum featured with multi-level energy releases

Development of the high energy storage with controlled way of releases is always desirable but challenging. Herein, a novel design of energy-storage system based on aluminum has been demonstrated with improved energy content. This group of hybrid materials uses energetic metal–organic frameworks (EMOFs) as the precursors of the metal oxides as the oxidizers in conventional nanothermites. These metastable nanocomposites of energetic MOF-activated Al (n-Al@EMOFs) are able to undergo self-sustainable combustion with multi-level energy releases. The resulted n-Al@EMOFs show unique two-step exothermic processes with a total heat release of as highly as 4142 J g−1, which is much higher than that of conventional Al/CuO system. In addition, the strategy could also help to reduce the high susceptibility of n-Al to surface oxidation and lower the ignition temperature of the composites (301.5 °C).

Framework-Interpenetrated Nitrogen-Rich Zn(II) Metal–Organic Frameworks for Energetic Materials

Nitrogen-rich high density metal–organic frameworks (MOFs) can be used as a new type of energetic materials. The energetic MOFs provide a new method to reconcile contradiction between high energy and reliable safety in energetic materials. Framework interpenetration would be an effective approach to reduce the pore volume and meanwhile to enhance the structural/chemical stabilities of the target energetic MOFs. In this work, mixed ligands of 5-aminotetrazole (HATZ) and tetrazole (HTZ) were chosen to assemble with Zn(II) ions with the purpose to prepare interpenetrated MOF materials with insensitivity. Ultimately, a high-density 3D energetic compound, [Zn2(ATZ)2(TZ)2]n (1) was in situ isolated under simple hydrothermal conditions. In the crystal structure of 1, there existed two independent 3D diamond networks, which were formed by Zn1(II) ions/TZ– ligands and Zn2(II) ions/ATZ– ligands, respectively. These two independent 3D diamond networks were interpenetrated to each other to construct a 3D condensed high-density framework. The standard molar enthalpy of formation (ΔfHo) of 1 was deduced as 1786.45 kJ/mol (4.09 kJ/g), which to date still occupies the status of the top high ΔfHo value among the reported energetic MOF materials. Conducted sensitivity measurements demonstrated the insensitivity of 1 to external mechanical stimuli. TGA showed 1 had good thermal stability up to 332 °C, whereas the decomposition temperature of pure HATZ and HTZ ligands are 207 and 174 °C, respectively. This shows that the greater stability of 1 could be attributed to the structural reinforcement induced by the effect of coordination polymerization and framework interpenetration. Compound 1 can serve as a promising energetic material with a high level of safety because of its good energetic properties, insensitivity, and high thermal stability.

A study of two metal energetic complexes based on 4-amino-3-(5-tetrazolate)-furazan: synthesis, crystal structure, thermal behaviors and energetic performance

In this contribution, two metal energetic complexes Co(HCONHNH2)2(AFT)2·H2O (1) and [Pb(HCONHNH2)2(AFT)2]n (2) (HCONHNH2=formyl hydrazide and HAFT = 4-amino-3-(5-tetrazolate)-furazan) have been synthesized and characterized. The structures of compound 1 and 2 are characterized by single crystal X-ray diffraction. The tests show that 1 possesses One-dimensional (1D) chain structure and 2 exhibits two-dimensional (2D) energetic metal-organic framework (MOF). The thermal decomposition processes of compounds have been investigated by MS-FTIR-DSC-TG coupling technique. It's worth noting that both of them exhibit higher thermal stabilities. Moreover, gaseous products generated after thermal decomposition of compound 1 and 2 are CO2, NO2, N2O, CO, HCN, NH3, H2O, N2. The standard molar enthalpies of formation of 1 and 2 are calculated to be -4501.25 kJ·mol-1 and -1091.13 kJ·mol-1, respectively. Detonation velocity and detonation pressure are respectively 9.32 km·s−1, 42.13 GPa for 1 and 5.62 km·s−1, 18.36 GPa for 2. Surprisingly, compound 2 exhibits promising detonation velocity and detonation pressure, which are higher than those of TNT, RDX and HMX. The above-mentioned information on thermal behavior is available to analyze and evaluate the stability and thermal safety of 1 and 2. The sensitivity tests reveal they possess excellent insensitivities to impact and friction. All the characterizations show that they can be used as potential energetic materials.

Energetic Cocrystal, Ionic Salt, and Coordination Polymer of a Perchlorate Free High Energy Density Oxidizer: Influence of pKa Modulation on Their Formation

Cocrystal, ionic salt, and coordination polymer had prompted the development of propellants, explosives, and pyrotechnics. However, the difference between their formation based on the same coformer has rarely been studied. 5,5′-Bis(trinitromethyl)-3,3′-bi-1H-1,2,4-triazole (BTNMBT) is perchlorate-free, favorable to scale-up, and a green energetic oxidizer with high physical performance (oxygen balance: +18.4%, IS: 22.5 J, FS: 252 N, D: 9073 m s–1, P: 36.2 GPa). To investigate the influence of different coformers on the formation of BTNMBT’s cocrystal, ionic salt, and metal–organic framework, organic acid as well as organic and inorganic bases with different dissociation constants (pKa) were theoretically studied. In this work, two energetic cocrystals, energetic ionic salt, and energetic metal–organic framework were synthesized based on BTNMBT. For their formation, the basic principle is found as follows: (i) when the pKa value of organic base is far lower than both pKa values of hydrogen-protons in organ...

Four three-dimensional metal–organic frameworks assembled from 1H-tetrazole: Synthesis, crystal structures and thermal properties

Four tetrazole-based energetic metal–organic frameworks (EMOFs), {[Zn5(Tz)9](NO3)·6H2O}n (1) [Zn(Tz)2]n (2) {[Cd5(Tz)9](NO3)·6H2O}n (3) and {[Mn5(Tz)9](NO3)·6H2O}n (4) (Tz = tetrazole) have been prepared by hydro/solvo thermal conditions using 1H-tetrazole and corresponding metal salts. X-ray single crystal diffraction analyses indicated that EMOFs 1, 2, 3 and 4 possess 3D porous structure. The metal ions in 1, 3, and 4 form an acs topology net with the six nitrogen atoms from μ3-Tz and μ4-Tz ligands. The Zn2+ ions in 2 form a diamond-like structure with four μ2-Tz ligands which was reported previously. The thermal stabilities were investigated by differential scanning calorimeter (DSC) and thermogravimety (TG). The results showed that four EMOFs exhibit high thermal stability (decomposition temperature up to 324.1 °C (1), 351.4 °C (2), 279.41 °C (3) and 332.75 °C (4), respectively). The thermal stability parameters (Te.0, Tb) were calculated. In addition, the standard molar enthalpies of formation (ΔfHmΘ) were calculated on the basis of the constant-volume combustion heat (ΔU) measured by using oxygen-bomb calorimetry. Lastly, the detonation performance (D, P) and mechanical sensitivity (IS, FS) of the four EMOFs were investigated.

3D solvent-free energetic metal–organic framework (EMOF) achieved by removing inclusion molecules from a new coordination polymer

The reaction of CuCl and NaN3 with 4,4′-azo-1,2,4-triazol-5-one (H2ZTO) under solvothermal conditions produced a new 3D heteronuclear Cu(i)-Na(i) energetic metal–organic framework (EMOF), [Cu3Na(ZTO)2]n·nCH3CN (1).

Inside Back Cover: Puffing Up Energetic Metal–Organic Frameworks to Large Carbon Networks with Hierarchical Porosity and Atomically Dispersed Metal Sites (Angew. Chem. Int. Ed. 7/2019)

An energetic metal–organic framework (EMOF) with pre-imbedded transition-metal ions serves as a precursor for the fabrication of large carbon networks with hierarchical pores and atomically dispersed metal sites (ADMSs). In their Communication on page 1975 ff., Q. Xu, R. Zou, and co-workers describe the high-temperature carbonization of this material: the zinc-based triazole-rich nanoparticles puff up to form sub-millimeter-scale carbon networks, while the pre-imbedded transition-metal ions are transformed into active ADMSs.

Puffing Up Energetic Metal–Organic Frameworks to Large Carbon Networks with Hierarchical Porosity and Atomically Dispersed Metal Sites

AbstractLarge carbon networks featuring hierarchical pores and atomically dispersed metal sites (ADMSs) are ideal materials for energy storage and conversion due to the spatially continuous conductive networks and highly active ADMSs. However, it is a challenge to synthesize such ADMS‐decorated carbon networks. Here, an innovative fusion‐foaming methodology is presented in which energetic metal–organic framework (EMOF) nanoparticles are puffed up to submillimeter‐scaled ADMS‐decorated carbon networks via a one‐step pyrolysis. Their extraordinary catalytic performance towards oxygen reduction reaction verifies the practicability of this synthetic approach. Moreover, this approach can be readily applicable to a wide range of unexplored EMOFs, expanding scopes for future materials design.

Puffing Up Energetic Metal-Organic Frameworks to Large Carbon Networks with Hierarchical Porosity and Atomically Dispersed Metal Sites.

Large carbon networks featuring hierarchical pores and atomically dispersed metal sites (ADMSs) are ideal materials for energy storage and conversion due to the spatially continuous conductive networks and highly active ADMSs. However, it is a challenge to synthesize such ADMS-decorated carbon networks. Here, an innovative fusion-foaming methodology is presented in which energetic metal-organic framework (EMOF) nanoparticles are puffed up to submillimeter-scaled ADMS-decorated carbon networks via a one-step pyrolysis. Their extraordinary catalytic performance towards oxygen reduction reaction verifies the practicability of this synthetic approach. Moreover, this approach can be readily applicable to a wide range of unexplored EMOFs, expanding scopes for future materials design.

In situ synthesis of energetic metal–organic frameworks [Cd5(Mtta)9]n film exhibiting excellent ignition capability

Energetic thin films have been widely used in the field of microscale energy-demanding systems. In this work, a novel energetic metal–organic frameworks [Cd5(Mtta)9]n film is fabricated on the copper substrate through an in situ synthesis method for the first time. A 5-methyl tetrazole/copper complex is deposited to modify the copper substrate through an electrochemical-assisted strategy. The [Cd5(Mtta)9]n film is then integrated on the surface of modified copper substrate by an in situ reaction of acetonitrile with sodium azide and cadmium nitrate. The morphological, structural and compositional information of the [Cd5(Mtta)9]n film is characterized by field emission scanning electron microscopy, X-ray diffraction and infrared spectrum. The thermostabilities of the [Cd5(Mtta)9]n film are studied by differential scanning calorimetry and thermogravimetry. In addition, the preliminary laser ignition test is conducted by using pulsed Nd:YAG laser. The results show that the as-prepared [Cd5(Mtta)9]n film possesses a rod-like topography. The flame height and ignition duration of [Cd5(Mtta)9]n film reach 9.0 mm and 220 µs, respectively, revealing that [Cd5(Mtta)9]n film is an excellent ignition material. This research opens up a new avenue for the preparation of novel energetic films, which provides potential applications on microelectromechanical systems to achieve functional nanoenergetics-on-a-chip.

Cover Feature: Gem‐dinitromethyl‐substituted Energetic Metal–Organic Framework based on 1,2,3‐Triazole from in situ Controllable Synthesis (Chem. Asian J. 19/2018)

Cover Feature: <i>Gem</i>‐dinitromethyl‐substituted Energetic Metal–Organic Framework based on 1,2,3‐Triazole from in situ Controllable Synthesis (Chem. Asian J. 19/2018)

Gem-dinitromethyl-substituted Energetic Metal-Organic Framework based on 1,2,3-Triazole from in situ Controllable Synthesis.

Synthesizing energetic metal-organic frameworks at ambient temperature and pressure has been always a challenge in the research area of energetic materials. In this work, through in situ controllable synthesis, energetic metal-organic framework gem-dinitromethyl-substituted dipotassium 4,5-bis(dinitromethyl)-1,2,3-triazole with a "cage-like" crystal packing was obtained and characterized. Most importantly, for the first time, we found that it could be successfully afforded with a catalytic effect of trifluoroacetic acid. This new compound exhibited its high density (2.04 g cm-3 ) at ambient temperature, superior detonation velocity (8715 m s-1 ) to that of lead azide (5877 m s-1 ) and comparable to that of RDX (8748 m s-1 ). Its detonation products are mainly N2 (48.1 %), suggesting it is also a green energetic material. The above-mentioned performance indicates its potential applications in detonator devices as lead-free primary explosive.

Three unexpected cadmium(II)-based energetic metal–organic frameworks derived from 2-(dinitromethylene)-1,3-diazacyclopentane

One cadmium–DNDZ [DNDZ = 2-(dinitromethylene)-1,3-diazacyclopentane] complex [Cd(NH3)4(DNDZ)2 (1)] and three unexpected cadmium–ADNA [ADNA = N-(2-aminoethyl)-2,2-dinitroacetamide] metal–organic frameworks (MOFs) {[Cd(NH3)2(ADNA)2]n (2), [Cd(CH3NH2)2(ADNA)2]n (3) and [Cd(CH3CH2NH2)2(ADNA)2]n (4)} were first synthesized by reactions of cadmium nitrate and DNDZ potassium salt in different aqueous amines. DNDZ molecules underwent a ring-opening reaction resulting in the formation of a new chain-like molecule ADNA, which is found for the first time and only in the cadmium(II) coordination environment compared with the previous other metal–DNDZ complexes, so the cadmium(II) ions should have special catalysis to the ring-opening reaction. The single crystal structures of complexes 1, 3 and 4 were obtained. The central cadmium(II) ion can form a distorted octahedral structure with six coordination atoms. Thermal behaviors and impact sensitivities of the four complexes were studied. Complex 1 presents one exothermic decomposition process (248.17 °C) after two consecutive endothermic processes, but the three MOFs present only one exothermic decomposition process and their peak temperatures are close to one another (about 168 °C). The impact sensitivities of the four complexes are tested to be >20 J for 1, >16 J for 2, >17 J for 3 and >11 J for 4, respectively.

Stabilizing volatile azido in a 3D nitrogen-rich energetic metal–organic framework with excellent energetic performance

The appearance of the nitrogen-rich energetic MOFs provides another opportunity for the new-generation of high energetic explosives. In this work, an insensitive energetic nitrogen-rich ligand, 3-amino-1, 2, 4-triazole (Hatz) was imported into the system of transition-metal azides via the coordination polymerization strategy in the hope to prepare mixed-ligand nitrogen-rich high energetic MOF materials with low sensitivity and finally a solvent-free 3D energetic compacted metal-organic framework (MOF), Cd3(atz)4(N3)2 (1) was successfully isolated under hydrothermal conditions. Compound 1 was characterized by single crystal X-ray diffraction, IR spectroscopy, elemental analysis (EA), different scanning calorimetry (DSC), and thermogravimetry analysis (TGA). Topological analysis shows that the 3D framework of 1 can be abstracted into a ten-connected topological network. The volatile azido ion can be viewed as a counter anion to be stabilized in a 3D framework as the connection of Cd(II) ions with two independent atz− ligands still remains a 3D framework. Compound 1 has a high calculated density (ρ) of 2.517 g cm−3. The standard molar enthalpy of formation (ΔfHo) of 1 was calculated to be 1330.10 kJ mol−1, which is higher than those of most of the previously 3D energetic MOFs. Sensitivity tests demonstrate that 1 is insensitive to external mechanical stimuli. TGA demonstrates that 1 has an excellent thermostability which can be stable up to 372 °C. Compound 1 can be served as a high-energy-density material with a favorable level of safety due to its excellent energetic performances, low sensitivities and excellent thermostability.

Construction of a Thermally Stable and Highly Energetic Metal–Organic Framework as Lead-Free Primary Explosives

Two energetic compounds, 4,8-dinitraminodifurazano[3,4-b,e]pyrazine (1) and its potassium-based energetic metal–organic framework (E-MOF) (2), were prepared, and their crystal structures were confirmed by single-crystal X-ray diffraction analysis. Compound 1 cocrystallizes with water molecules and shows a three-dimensional (3D) sandwich-like supramolecular structure, which is rare in the known energetic organic compounds. Compound 2 has a pillared layered structure with a pcu topology. The layered structure in the 3D framework featuring sql topology was constructed from inorganic chains {K2O} and nitroamine groups. The crystal density of 2 is up to 2.114 g cm–3. This potassium-based E-MOF shows high thermal stability, high detonation velocity, and high impact and friction sensitivities, which make it a potential high-performing primary explosive.

New roles of metal–organic frameworks: Fuels for aluminum-free energetic thermites with low ignition temperatures, high peak pressures and high activity

Aluminum-based thermites are widely used in gas generators, propulsions, explosives, and welding because these materials can release a large amount of stored energy on combustion. However, one of the biggest problems in the traditional aluminum-based thermite systems is excessive oxidation of the aluminum particle before combustion, resulting in a decrease of the active aluminum content. Here, we report a new-concept aluminum-free thermites based on an energetic metal–organic framework [Cu(atrz)3(NO3)2]n (MOF(Cu), atrz = 4,4′-azo-1,2,4-triazole) as a fuel. Compared with the traditional aluminum-based thermites, these new thermites exhibit superior performances such as low electrostatic discharge sensitivities, low ignition temperatures, high heats of reaction, high peak pressures, high activity, and production of very few solid residues. It is anticipated that this work will open a new field for the application of MOFs, while laying the groundwork for the development of new energetic materials.

Thermal decomposition of energetic MOFs nickel hydrazine nitrate crystals from an ab initio molecular dynamics simulation

We report the initiation mechanisms and subsequent chemical decompositions of energetic metal-organic frameworks (MOFs) nickel hydrazine nitrate (NHN) crystal at high temperatures and high temperatures coupled with high pressures by ab initio molecular dynamics simulations. The initial decomposition step is the collapse of the MOF cage at 518 K and 518 K coupled with 1, 2, and 3 GPa. But their cleavage steps are different. It is found that the pressure decelerates the initial decomposition of the NHN crystal. The decomposition mechanisms of the NHN crystal at 518 K coupled with 20.2 GPa are much different from those at 518 K coupled with low pressures. The results indicate that the temperature is the foremost factor that affected the decomposition of the NHN crystal. At 4000 K and 4000 K coupled with 20.2 GPa, the initial decomposition mechanisms of NHN are both the cage collapse by several NiN bond breaking. The variation tends and the release times of H2O are similar at the two cases. In the early decomposition stage, NHN decomposed very fast and drastically. But the later decomposition was slow. During 1.0 ps, there are ten H2O released fast at the two extreme conditions. Then the population of H2O keeps nearly stable during the later decomposition stage. At 7.959 ps, last one H2O was formed. Our results may provide useful information for understanding the chemical decompositions of energetic metal-organic frameworks compounds.