Cheng Shen

A series of energetic metal pentazolate hydrates

Singly or doubly bonded polynitrogen compounds can decompose to dinitrogen (N2) with an extremely large energy release. This makes them attractive as potential explosives or propellants, but also challenging to produce in a stable form. Polynitrogen materials containing nitrogen as the only element exist in the form of high-pressure polymeric phases, but under ambient conditions even metastability is realized only in the presence of other elements that provide stabilization. An early example is the molecule phenylpentazole, with a five-membered all-nitrogen ring, which was first reported in the 1900s and characterized in the 1950s. Salts containing the azide anion (N3−) or pentazenium cation (N5+) are also known, with compounds containing the pentazole anion, cyclo-N5−, a more recent addition. Very recently, a bulk material containing this species was reported and then used to prepare the first example of a solid-state metal–N5 complex. Here we report the synthesis and characterization of five metal pentazolate hydrate complexes [Na(H2O)(N5)]·2H2O, [M(H2O)4(N5)2]·4H2O (M = Mn, Fe and Co) and [Mg(H2O)6(N5)2]·4H2O that, with the exception of the Co complex, exhibit good thermal stability with onset decomposition temperatures greater than 100 °C. For this series we find that the N5− ion can coordinate to the metal cation through either ionic or covalent interactions, and is stabilized through hydrogen-bonding interactions with water. Given their energetic properties and stability, pentazole–metal complexes might potentially serve as a new class of high-energy density materials or enable the development of such materials containing only nitrogen. We also anticipate that the adaptability of the N5− ion in terms of its bonding interactions will enable the exploration of inorganic nitrogen analogues of metallocenes and other unusual polynitrogen complexes.

Molecular Design and Property Prediction for a Series of Novel Dicyclic Cyclotrimethylene Trinitramines (RDX) Derivatized as High Energy Density Materials

Quantum chemistry calculations and thermodynamics methods were carried out to screen out novel high energy density materials (HEDMs) from several new derivatives with dicyclic structures of Cyclotrimethylene trinitramine (RDX). Their volumes, densities, heats of formation, detonation properties and impact sensitivities have been calculated with thermodynamics methods under DFT B3LYP 6-31++g (d, p) level and all of these compounds exhibit good performance as HEDMs. Especially, R4 has given outstanding values as a potential HEDM. Its crystal density (2.07 g/cm(3)), heat of detonation (1.67 kJ/g), detonation velocity (10051m/s), and detonation pressure (48.5 GPa) are even higher than those of CL-20 while its impact sensitivity (h50, 16 cm) remains a relative safety value. The results indicate that the derivative work in common explosives is a good strategy which can design novel HEDMs with high energetic properties and low sensitivity. And furthermore, some mature processes can be used to synthesize them.

Combination of four oxadiazole rings for the generation of energetic materials with high detonation performance, low sensitivity and excellent thermal stability

Energetic materials, which are comprised of four oxadiazole rings and linked by three different bridges ([–NH–NH–], [–NN–], and [–NN(O)–]) are developed. All synthesized compounds were fully characterized and five of them were further determined by single-crystal X-ray diffraction. As supported by X-ray data, closed packing and extensive hydrogen-bonding interactions result in high density, low sensitivity, and excellent thermal stability. It is worth pointing out that the [–NN–] compound 3 has a decomposition temperature of 322 °C, which, to our knowledge, is the highest known value for all compounds consisting of 1,2,4- and 1,2,5-oxadiazole rings. Dihydrazinium salt 14 exhibits excellent detonation performance (D = 9042 m s−1, P = 35.0 GPa, and IS > 40 J), superior even to RDX. This novel design strategy, which combines four oxadiazole rings into one molecule, promises a fine balance between high detonation performance and low sensitivity and opens a new chapter in oxadiazole chemistry.

1-Nitro-2-trinitromethyl substituted imidazoles: a new family of high performance energetic materials

A new series of 1-nitro-2-trinitromethyl substituted imidazoles were designed and synthesized. All the compounds were characterized by multinuclear NMR and IR spectroscopies, elemental analysis (EA), and differential scanning calorimetry (DSC). X-ray structure determination of compounds 11–15, 17 and 19 showed that their densities range from 1.59 g cm−3 to 1.86 g cm−3 and gave insights into their structural characteristics showing the presence of extensive hydrogen-bonding interactions. Most of these new materials exhibit positive heats of formation (HOF = 145.7–344.8 kJ mol−1), acceptable oxygen balances and sensitivity values (IS = 10.4–32.5 J, FS = 85–240 N). Detonation velocities (D) and pressures (P) were calculated with EXPLO5 V6.01 based on the calculated HOF and densities indicating that some of these trinitromethyl materials (D = 8688–8764 m s−1, P = 34.4–35.1 GPa) are comparable to 1,3,5-trinitroperhydro-1,3,5-triazine (RDX, D = 8795 m s−1, P = 34.9 GPa). Among the new derivatives, 17 (ρ = 1.82 g cm−3, ΔHf = 145.7 kJ mol−1, D = 8764 m s−1, P = 35.1 GPa, IS = 14.5 J, OB = 5.0%) shows potential as a high performance energetic material.

A series of high-energy coordination polymers with 3,6-bis(4-nitroamino-1,2,5-oxadiazol-3-yl)-1,4,2,5-dioxadiazine, a ligand with multi-coordination sites, high oxygen content and detonation performance: syntheses, structures, and performance

In this study, 3,6-bis(4-nitroamino-1,2,5-oxadiazol-3-yl)-1,4,2,5-dioxadiazine (H2BNOD), with a relatively high oxygen content (37.41%) and good detonation performance (density = 1.817 g cm−3, detonation velocity = 8490 m s−1), is used to prepare three new high-energy coordination polymers (CPs), {Ag2(BNOD)(DMF)2}n (1), {Ag2(BNOD)}n (1a), and {Cu(BNOD)(H2O)6}n (2), and a metal salt, Co(BNOD)(H2O)6 (3). Crystal structure analyses indicated that 1 is a 2D energetic coordination polymer (E-CP) with a three-dimensional wavy layer structure; 1a is a compact 3D E-CP without any solvent molecules. 2 exhibits a zigzag 1D chain structure, while the ionic salt 3 has a layer-by-layer structure (0D). Thermal analysis indicated that 1 and 1a exhibit good, as well as similar, thermostability (200 °C) owing to their compact framework structures. The enthalpy of formation is calculated from the constant-volume combustion energy. The four compounds exhibit detonation velocities (D) ranging from 7141 to 10 084 m s−1, detonation pressures (P) ranging from 25.10 to 58.04 GPa, and heat of detonation (Q) values from 1.11 to 1.91 kcal g−1. The impact sensitivities of the energetic salts were between 5 and 12 J, and their friction sensitivities ranged from 120 to 180 N, at the same level as those of RDX and HMX. Among these four compounds, 1a exhibits outstanding performance (D = 10 084 m s−1, P = 58.04 GPa and Q = 1.91 kcal g−1) with a compact 3D CP structure.

Author Correction: A series of energetic metal pentazolate hydrates

In this Letter, under Methods section ‘[Na(H2O)(N5)]⋅2H2O (2)’, the description “the intermediate product arylpentazole (5.000 g, 26.18 mmol)” should have read “the intermediate product sodium salt of arylpentazole (5.000 g, 21.64 mmol)”. In the legend of Fig. 3, we add that “All temperature points in the stability study were onset temperatures.” to avoid misunderstanding. These corrections have been made online.