Siping Pang

3D energetic metal-organic frameworks: synthesis and properties of high energy materials.

Metal–organic frameworks (MOFs) have attracted great attention because of their intriguing molecular topologies and potential applications in chemical separation, gas storage, drug delivery, catalysis and chemical sensor technology. Particularly, MOFs could also be potential energetic materials because of their high densities and high heats of detonation. For example, Hope-Weeks and co-workers recently reported two hydrazine-perchlorate 1D MOFs [(Ni(NH2NH2)5(ClO4)2)n (NHP), and (Co(NH2NH2)5(ClO4)2)n (CHP)] with linear polymeric structures, which were regarded as possibly the most powerful metal-based energetic materials known to date, with heats of detonation comparable with that of hexanitrohexaazaisowutzitane (CL-20; about 1.5 kcalg ). Unfortunately, these coordination polymers were highly sensitive to impact deriving from their low rigidity characteristic of such linear polymeric structures, which makes practical use infeasible. In order to decrease the sensitivities, the same authors also used a hydrazine derivative (hydrazine-carboxylate) as the ligand to construct MOFs with 2D sheet structures [((Co2(N2H4)4(N2H3CO2)2)(ClO4)2·H2O)n (CHHP) and ((Zn2(N2H4)3(N2H3CO2)2)(ClO4)2·H2O)n (ZnHHP)], which showed a considerable reduction to the sensitivity, however, concomitantly their heats of detonation decreased (Figure 1). Despite these advances, current coordination frameworks are only limited to be a 1D or 2D structure. Compared with 1D linear and 2D layered structures, three-dimensional (3D) frameworks possess more complicated connection modes, which could further enhance structural reinforcement, hence improve the stabilities and energetic properties. A lot of 3D MOFs have been synthesized with interesting magnetic, catalytic, and luminescent properties, some of them incorporate a variety of energetic moities such as nitrate anions (NO3 ), perchlorate anions (ClO4 ) into the 3D frameworks. However, their potential applications as energetic materials have not been disclosed or discussed; relevant data about energetic properties are also missing in the literature. Additionally, both reported 1D and 2D energetic MOFs based on the perchlorate anions, have been scrutinized by the US Environmental Protection Agency (EPA) because they promote thyroid dysfunction and are teratogenic. Continuing our interest in finding new highly energetic, eco-friendly energetic materials, we explore the preparation of halogen-free energetic 3D MOFs, for which two polymers [Cu(atrz)3(NO3)2]n (1) and [Ag(atrz)1.5(NO3)]n (2) were designed by replacing the hydrazine ligand with 4,4’-azo1,2,4-triazole (atrz). Here, we chose to use atrz as a ligand for the following reasons: 1) as a nitrogen-rich heterocyclic backbone, atrz possesses a high nitrogen content (N%= Figure 1. Energetic MOFs with different topologies.

A novel stable high-nitrogen energetic material: 4,4′-azobis(1,2,4-triazole)

A novel high-nitrogen compound with an N,N′-azo linkage, 4,4′-azobis(1,2,4-triazole), has been synthesized and well characterized. The solid-state structure was determined by X-ray diffraction. The experimentally determined density and enthalpy of formation matched with theoretically computed values based on the B3LYP method. The DSC result suggests that 4,4′-azobis(1,2,4-triazole) decomposes at a relatively high temperature (313.36 °C). By comparison with 3,3′-azobis(1,2,4-triazole), containing a C,C′-azo linkage, the N,N′-azo linkage was found to provide compounds with a relatively high density and high energy.

Energetic salts based on 1-amino-1,2,3-triazole and 3-methyl-1-amino-1,2,3-triazole

High-density energetic salts that contain nitrogen-rich anions and the 1-amino-1,2,3-triazole (ATZ) or 3-methyl-1-amino-1,2,3-triazole (MAT) cation were synthesized. All salts were fully characterized by IR spectroscopy, multinuclear (1H, 13C) NMR spectroscopy, differential scanning calorimetry (DSC), and impact sensitivity. 1-Amino-1,2,3-triazolium 5-nitrotetrazolate, 3-methyl-1-amino-1,2,3-triazolium 5-nitrotetrazolate, and 3-methyl-1-amino-1,2,3-triazolium azotetrazolate crystallize in the triclinic space group P, as determined by single-crystal X-ray diffraction. Their densities are 1.688, 1.588, and 1.550 g cm−3, respectively. The measured densities of the other organic energetic salts range between 1.56 and 1.86 g cm−3. The detonation pressure (P) values calculated for these salts range from 21.2 to 37.3 GPa, and the detonation velocities (D) range from 7239 to 9082 m s−1, making the salts potentially energetic materials.

Design and synthesis of energetic materials towards high density and positive oxygen balance by N-dinitromethyl functionalization of nitroazoles

A new N-functionalized strategy of nitrogen heterocycles was utilized for the synthesis of nitroazole-based energetic materials, giving rise to a new family of highly dense and oxygen-rich energetic materials. They were characterized by IR spectroscopy, NMR spectroscopy, elemental analysis, DSC, and X-ray diffraction. These new molecules exhibit high densities, moderate to good thermal stabilities, acceptable impact and friction sensitivities, and excellent detonation properties, which suggest potential applications as energetic materials or oxidizers. Interestingly, among tetrazole-based CHNO energetic materials compound 5 has the highest measured density of 1.97 g cm−3 to date. 5c is the first and the only heterocyclic CHNO energetic salt with a positive OB until now. Compounds 5 and 6 exhibit excellent detonation properties (38.5 GPa, 9.22 km s−1; 37.0 GPa, 9.05 km s−1), comparable to the highly explosive HMX. With high OB, the specific impulses of 5, 5b, 5c, and 6c are superior to those of AP and ADN as neat compounds, and the ratio of oxidizer/aluminium/PBAN (%) is 80:20:0 or 80:13:7. Furthermore, computational results, BDEs, Mulliken charges and Wiberg bond orders also support the superior qualities of the newly prepared compounds and the design strategy.

Nitrogen-rich salts based on 5-hydrazino-1H-tetrazole: a new family of high-density energetic materials

High-density energetic salts that contain nitrogen-rich anions and the 5-hydrazino-1H-tetrazolium cation were synthesized. All salts were fully characterized by vibrational spectroscopy (IR), multinuclear (1H, 13C) NMR spectroscopy, elemental analysis, differential scanning calorimetry (DSC), and impact sensitivity. Four compounds were characterized by single X-ray diffraction. The results show that the extensive hydrogen bonding interactions between the cations and anions form a complex 3D network, which contributes greatly to the high density of the 5-hydrazinotetrazolium salts. It was also found that the incorporation of hydrazino groups into a heterocyclic ring increases the heat of formation and overall nitrogen content of the entire molecule. Some of these salts exhibit reasonable physical properties, such as good thermal stability (Td = 173.7–198.6 °C), reasonable impact sensitivities (IS = 4–40 J), and excellent specific impulses (Isp = 196.1–288.7 s). In addition, detonation properties of the energetic salts obtained with EXPLO 5.05 identify them as competitively energetic compounds, and in some cases are superior to those of HMX.

A Simple Method for the Prediction of the Detonation Performances of Metal-Containing Explosives

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.

Nitrogen-rich salts based on polyamino substituted N,N′-azo-1,2,4-triazole: a new family of high-performance energetic materials

A new family of nitrogen-rich energetic salts based on 3,3′-diamino-4,4′-azo-1,2,4-triazole containing an N,N′-azo linkage has been synthesized and fully characterized by IR, 1H and 13C NMR spectrum, elemental analysis, differential scanning calorimetry (DSC) and sensitivities toward impact, friction and electrostatics. The crystal structures of chloride 2, nitrate 3, perchlorate 4 and isomerization product 10 have been determined by single-crystal X-ray diffraction analysis. All the salts exhibit high thermal stabilities with decomposition temperatures of over 200 °C, except for nitroformate 6. The measured densities of salts 2–7 fall in the range of 1.71 to 1.99 g cm−1. Theoretical performance calculations (Gaussian 03 and EXPLO5) provided detonation pressures and velocities for energetic salts in the ranges 26.3 to 45.7 GPa and 8042 to 9580 m s−1, respectively. Moreover, these salts exhibit reasonable impact sensitivities (IS = 8–40 J) and friction sensitivities (FS = 90–360 N); these salts also exhibit excellent thermal stabilities, high detonation properties and reasonable sensitivities, which, in some cases, are superior to those of TNT, TATB and HMX, and present a favorable balance between the energy and stability of energetic materials. In addition, these salts exhibit excellent specific impulses (265 to 301 s), which make them competitive energetic materials.

Energetic Salts Based on an Oxygen-Containing Cation: 2,4-Diamino-1,3,5- triazine-6-one

A family of energetic salts with high thermal stability and low impact sensitivity based on an oxygen-containing cation, 2,4-diamino-1,3,5-triazine-6-one, were synthesized and fully characterized by IR and multinuclear ((1)H, (13)C) NMR spectroscopy, elemental analysis, and differential scanning calorimetry. Insights into their sensitivities towards impact, friction, and electrostatics were gained by submitting the materials to standard tests. The structures of 2,4-diamino-1,3,5-triazine-6-one nitrate, 2,4-diamino-1,3,5-triazine-6-one sulfate, 2,4-diamino-1,3,5-triazine-6-one perchlorate, 2,4-diamino-1,3,5-triazine-6-one 5-nitrotetrazolate were determined by single-crystal X-ray diffraction; their densities are 1.691, 1.776, 1.854, and 1.636 g cm(-3), respectively. Most of the salts decompose at temperatures over 180 °C; in particular, the salts 2,4-diamino-1,3,5-triazine-6-one nitrate and 2,4-diamino-1,3,5-triazine-6-one perchlorate, which decompose at 303.3 and 336.4 °C, respectively, are fairly stable. Furthermore, most of the salts exhibit excellent impact sensitivities (>40 J), friction sensitivities (>360 N), and are insensitive to electrostatics. The measured densities of these energetic salts range from 1.64 to 2.01 g cm(-3) . The detonation pressure values calculated for these salts range from 14.6 to 29.2 GPa, and the detonation velocities range from 6536 to 8275 m s(-1) ; these values make the salts potential candidates for thermally stable and insensitive energetic materials.

Trinitromethyl/trinitroethyl substituted CL-20 derivatives: structurally interesting and remarkably high energy

A series of trinitromethyl/trinitroethyl substituted derivatives of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5,5,0, 03.11,05.9] dodecane (CL-20) were designed and investigated by theoretical methods. Intramolecular interactions between the trinitromethyl/trinitroethyl and the cage were investigated. The effects of trinitromethyl/trinitroethyl groups on stability of the parent compound are discussed. The results reveal a mutual influence of bond length and dihedral angle between the trinitromethyl and the cage. Compared to CL-20, the sensitivity of derivatives is barely affected. Properties such as density, heat of formation and detonation performance of these novel compounds were also predicted. The introduction of the trinitromethyl group can significantly enhance the oxygen balance, density and detonation properties of the parent compound. The remarkable energy properties make these novel cage compounds competitive high energy density materials.

A Highly Energetic N-Rich Zeolite-Like Metal-Organic Framework with Excellent Air Stability and Insensitivity

A stable N‐rich aromatic ligand is employed to prepare energetic zeolite‐like metal‐organic frameworks. IFMC‐1 shows excellent air stability, and the lowest sensitivity toward impact, friction, and electrostatic discharge and the highest predicted heat of detonation among the reported coordination polymers, and even commercial materials (such as trinitrotoluene (TNT)).