Kangcai Wang

Bis(4-nitraminofurazanyl-3-azoxy)azofurazan and Derivatives: 1,2,5-Oxadiazole Structures and High-Performance Energetic Materials

Bis(4-nitraminofurazanyl-3-azoxy)azofurazan (1) and ten of its energetic salts were prepared and fully characterized. Computational analysis based on isochemical shielding surface and trigger bond dissociation enthalpy provide a better understanding of the thermal stabilities for nitramine-furazans. These energetic compounds exhibit good densities, high heats of formation, and excellent detonation velocity and pressure. Some representative compounds, for example, 1 (vD : 9541 m s(-1) ; P: 40.5 GPa), and 4 (vD : 9256 m s(-1) ; P: 38.0 GPa) exhibit excellent detonation performances, which are comparable with current high explosives such as RDX (vD : 8724 m s(-1) ; P: 35.2 GPa) and HMX (vD : 9059 m s(-1) ; P: 39.2 GPa).

Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na20N60 and Na24N60 Nanocages

The experimental detection and synthesis of pentazole (HN5 ) and its anion (cyclo-N5- ) have been actively pursued for the past hundred years. The synthesis of an aesthetic three-dimensional metal-pentazolate framework (denoted as MPF-1) is presented. It consists of sodium ions and cyclo-N5- anions in which the isolated cyclo-N5- anions are preternaturally stabilized in this inorganic open framework featuring two types of nanocages (Na20 N60 and Na24 N60 ) through strong metal coordination bonds. The compound MPF-1 is indefinitely stable at room temperature and exhibits high thermal stability relative to the reported cyclo-N5- salts. This finding offers a new approach to create metal-pentazolate frameworks (MPFs) and enables the future exploration of interesting pentazole chemistry and also related functional materials.

Fluorescent heterometallic MOFs: tunable framework charges and application for explosives detection

A series of three-dimensional fluorescent heterometallic MOFs based on rod- and cluster-like building blocks were readily prepared under solvothermal conditions. Among them, compounds 1–4 were constructed from rod-like building blocks {Cd–O–M}n (M = Na, K, Na–K, and Mg) and BDC2− ligands, featuring right-hand and left-hand channels with a cap topology. The framework charges of 1–4 can be tuned from negative to neutral via a strategy of changing the secondary metal centre (Na+, Na+–K+, K+ and Mg2+). It is worth noting that the rod-like building block of compound 2 contained three types of metal ion centres (Cd2+, Na+ and K+). Different from compounds 1–4, the topology of 5 changed from a cap net to a 610 net in the presence of Ca2+ as a secondary metal centre. Interestingly, the anionic framework of 5 features two types of linear trinuclear clusters as the building blocks, i.e. {Cd2CaO17} and {Cd2CaO16}, which are relatively rare in known heterometallic open frameworks. Moreover, fluorescent compound 5 with a microporous structure displayed sensing properties towards some nitro-containing compounds, suggesting its potential application as a fluorescent sensor for the sensitive detection of explosives.

Towards N-alkylimidazole-borane-based hypergolic fuels

Over the past few decades, toxic and highly volatile hydrazine derivatives have been the main fuel choices for liquid bipropellants, especially in traditional hypergolic rocket engines. The search for new hypergolic fuels as replacements for hydrazine derivatives is of great interest to researchers. In this study, a series of N-alkylimidazole borane compounds has been synthesized and characterized. Interestingly, these compounds display promising applications as potential hypergolic fuels owing to their excellent physiochemical properties including low melting points, high thermal stability, low viscosities, and unique hypergolic reactivity. Compared with popular hypergolic ionic liquids, the cost-effective and scaling-up advantages of these materials highlight their promising potential as high-performance fuels in liquid bipropellant formulations.

Accelerating the discovery of insensitive high-energy-density materials by a materials genome approach

Finding new high-energy-density materials with desired properties has been intensely-pursued in recent decades. However, the contradictory relationship between high energy and low mechanical sensitivity makes the innovation of insensitive high-energy-density materials an enormous challenge. Here, we show how a materials genome approach can be used to accelerate the discovery of new insensitive high-energy explosives by identification of “genetic” features, rapid molecular design, and screening, as well as experimental synthesis of a target molecule, 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide. This as-synthesized energetic compound exhibits a graphite-like layered crystal structure with a high measured density of 1.95 g cm−3, high thermal decomposition temperature of 284 °C, high detonation velocity of 9169 m s−1, and extremely low mechanical sensitivities (impact sensitivity, >60 J and friction sensitivity, >360 N). Besides the considered system of six-member aromatic and hetero-aromatic rings, this materials genome approach can also be applicable to the development of new high-performing energetic materials.The synthesis of explosive materials that are stable, highly dense, and have low sensitivity to external stimuli is a challenge. Here, the authors use a genomic approach to accelerate the discovery of insensitive high explosive molecules with good detonation and low sensitivity properties.

Green primary energetic materials based on N-(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)nitramide

In this study, a series of high-energy-density materials (1·2H2O–9) based on N-(3-nitro-1-(trinitromethyl)-1,2,4-triazol-5-yl)nitramide were synthesized and structurally characterized using 1H NMR, 13C NMR, IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The crystal results demonstrated that potassium 3-nitro-5-(nitroimino)-1-(trinitromethyl)-1,2,4-triazolate hydrate (2·H2O) exhibits an infinite two-dimensional (2D) metal–organic framework (MOF) containing the coordination group NO2 and metal cation K+. Additionally, this 2D MOF exhibited a high oxygen content (46.41%) and a positive oxygen balance (14.77%). Heats of formation and the detonation properties of the newly prepared compounds were calculated using the Gaussian 09 and EXPLO 5 programs, respectively. Energetic evaluation indicated that these compounds demonstrate good detonation performances, all of which outperform traditional primary explosives mercury fulminate, lead azide, 2-diazo-4,6-dinitrophenol, and in some cases, even exceed the performance of high explosive RDX. Therefore, the high detonation parameters of the compounds enable these potential primary explosives to trigger the whole detonation easily. Furthermore, several attractive properties, such as an excellent density (2.00 g cm−3), an impact sensitivity of 2 J, a friction sensitivity of 32 N, and a low amount of toxic detonation products, make 2·H2O an eco-friendly primary explosive.

Synthesis of 1-(2H-tetrazol-5-yl)-5-nitraminotetrazole and its derivatives from 5-aminotetrazole and cyanogen azide: a promising strategy towards the development of C–N linked bistetrazolate energetic materials

A series of C–N linked bistetrazolate nitramino compounds, i.e., 1-(2H-tetrazol-5-yl)-5-nitraminotetrazole (2) and its energetic salts (3–8), were successfully prepared from readily available 5-aminotetrazole. All new energetic compounds were fully characterized by IR and NMR spectra and elemental analysis, and six of them (1, 3–7) were further determined by single-crystal X-ray diffraction analysis. The nitrogen contents of these energetic bistetrazolate compounds, ranging from 59.3% (3) to 74.8% (7), are much higher than those of the commonly used high explosives such as RDX (N: 37.8%), HMX (N: 37.8%) and CL-20 (N: 38.3%). And theoretical calculations by using the Gaussian 09 program package demonstrate that compounds 1–8 have high positive heats of formation, of which the heats of formation of ammonium salt 4 (3.60 kJ g−1), aminonitroguanidinium 5 (3.11 kJ g−1) and dihydrazinium salt 7 (3.25 kJ g−1) are approximately eight times higher than those of RDX (0.39 kJ g−1) and HMX (0.39 kJ g−1), and four times higher than that of CL-20 (0.83 kJ g−1). The high nitrogen contents and high heats of formation have endowed these energetic compounds with prominent detonation performance. It is noteworthy that compound 7 exhibits an excellent calculated detonation velocity of 9822 m s−1 superior to that of CL-20 (9730 m s−1), while the impact and friction sensitivities of 7 (IS = 8 J, FS = 192 N) are comparable to those of HMX (IS = 7 J, FS = 112 N). The good detonation properties with moderate sensitivities demonstrate that compound 7 is a promising candidate for application as a high-performance energetic material.

Synthesis and Properties of Triaminocyclopropenium Cation Based Ionic Liquids as Hypergolic Fluids

A novel family of hydrophobic triaminocyclopropenium cation based ionic liquids have been synthesized, and their structures and physicochemical properties characterized by NMR and IR spectroscopy, elemental analysis, differential scanning calorimetry, and hypergolic tests. The experimental results showed that all of these ionic liquids exhibited the expected hypergolic reactivity with the oxidizer white fuming nitric acid. Among them, the hypergolic ionic liquid based on the cyanoimidazolylborohydride anion showed excellent integrated properties, including high decomposition temperature (194 °C), high density (0.95 g cm-3 ), moderate viscosity (44 MPa s), ultrafast ignition delay time (6 ms), and high specific impulse (301.9 s); this demonstrates its potential as an environmentally friendly alternative to toxic hydrazine derivatives.

Construction of hydrothermally stable beryllium phosphite open-frameworks with high proton conductivity

Two new beryllium phosphite anionic open-frameworks based on Be3P4O12H4 cluster building blocks, formulated as (Him)2·Be3(HPO3)4, were synthesized under solvothermal conditions, where im is imidazole. Interestingly, the use of different alcohols, i.e., isopropanol and n-propanol, as solvents afforded two new anionic open-frameworks with the same chemical composition, but different structures. Compound 1 crystallized in the monoclinic C2/c space group, whereas compound 2 crystallized in the triclinic P space group. Both compounds displayed intersected channels with 8-, 8-, 8-, and 12-membered windows along different directions. Considering Be3P4O12H4 clusters as four-connected nodes, both compounds showed a pcu topology. Notably, the frameworks of both open-frameworks remained stable after soaking in boiling water for one month. Furthermore, compound 1 exhibited a high proton conductivity of 2.03 × 10−3 S cm−1 at 363 K and 98% relative humidity, indicating its potential as a hydrothermally stable proton-conducting material.