Pengcheng Wang

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 (Mu2009=u2009Mn, 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 100u2009°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.

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.

Stabilization of the Pentazolate Anion in Three Anhydrous and Metal-Free Energetic Salts

According to previous reports, metal cations or water molecules are necessary for the stabilization of pentazolate anion (cyclo-N5- ) at ambient temperature and pressure. Seeking a new method to stabilize N5- is a big challenge. In this work, three anhydrous, metal-free energetic salts based on cyclo-N5- 3,9-diamino-6,7-dihydro-5u2009H-bis([1,2,4]triazolo)[4,3-e:3,4-g][1,2,4,5] tetrazepine-2,10-diium, N-carbamoylguanidinium, and oxalohydrazinium (oxahy+ ) pentazolate were synthesized and isolated. All salts were characterized by elemental analysis, IR spectroscopy, 1 H, 13 C, and (in some cases) 15 N NMR spectroscopy, thermal analysis (TGA and DSC), and single-crystal XRD analysis. Computational studies associated with heats of formation and detonation performance were performed by using Gaussianu200509 and Explo5 programs, respectively. The sensitivity of the salts towards impact and friction was determined, and overall the real N5 explosives showed promising energetic properties.

Syntheses, Crystal Structures and Properties of a Series of 3D Metal-Inorganic Frameworks Containing Pentazolate Anion

Pentazolate anion (cyclo-N5- ), and/or N3- , NO3- were used as the ligands to obtain a series of nitrogen-rich energetic three-dimensional (3D) frameworks [Cu(N5 )(N3 )]n , [Ag(N5 )]n , [Ba(N5 )(NO3 )(H2 O)3 ]n , and [NaBa3 (N5 )6 (NO3 )(H2 O)3 ]n by self-assembly. These frameworks were characterized by single-crystal X-ray diffraction, SEM, IR and Raman spectroscopy, elemental analysis, and thermal analysis. All the frameworks exhibited regular supramolecular structures and excellent stabilities at room temperature which can be attributed to the strong coordination bonds between cyclo-N5- anions and metal ions. The successful stabilization of the cyclo-N5- in more 3D multi-ligand metal-N5- frameworks after Na-N5- frameworks has been demonstrated. This breakthrough offers new opportunities for the future of metal-pentazolate frameworks and polynitrogen chemistry.

Self-assembled energetic coordination polymers based on multidentate pentazole cyclo -N 5 –

Coordination to form polymer is emerging as a new technology for modifying or enhancing the properties of the existed energetic substances in energetic materials area. In this work, guanidine cation CN3H6+ (Gu) and 3-amino-1,2,4- triazole C2H4N4 (ATz) were crystallized into NaN5 and two novel energetic coordination polymers (CPs), (NaN5)5[(CH6- N3)N5](N5)3– (1) and (NaN5)2(C2H4N4) (2) were prepared respectively via a self-assembly process. The crystal structure reveals the co-existence of the chelating pentazole anion and organic component in the solid state. In polymer 1, Na+ and N5– were coordinated to form a cage structure in which guanidine cation [C(NH2)3]+ was trapped; for polymer 2, a mixedligand system was observed; N5– and ATz coordinate separately with Na+ and form two independent but interweaved nets. In this way, coordination polymer has been successfully utilized to modify specific properties of energetic materials through crystallization. Benefiting from the coordination and weak interactions, the decomposition temperatures of both polymers increase from 111°C (1D structure [Na(H2O)(N5)] ∙2H2O) to 118.4 and 126.5°C respectively. Moreover, no crystallized H2O was generated in products to afford the anhydrous compounds of pentazole salts with high heats of formation (>800 kJ mol–1). Compared to traditional energetic materials, the advantage in heats of formation is still obvious for the cyclo-N5– based CPs, which highlights cyclo-N5– as a promising energetic precursor for high energy density materials (HEDMs).摘要在含能材料领域, 通过协同作用形成聚合物已成为改善或增强现有含能物质性能的一种新技术. 本文将胍阳离子CH3H6+(GU)和氨基-1,2,4-三唑C2H4N4(ATZ)与NaN5一起结晶, 通过自组装过程分别制备了两种新型含能配位聚合物(CPs), (NaN5)5[(CH3H6)N5](N5)3 (1)和(NaN5)2(C2H4N4) (2). 晶体结构表明, 在固体状态下, 螯合的五唑阴离子实现了与其他有机成分共存. 聚合物1, Na+和N5−形成笼状, 并将胍阳离子[C(NH2)3]+围在里面; 而聚合物2是一个混合配体体系, N5−和ATZ与Na+分别形成两个独立但相互交织的网. 这些都说明了通过结晶形成配位聚合物, 来改变含能材料的特定性能是可行的. 受益于配位和弱相互作用, 两种聚合物的热分解温度分别从111°C (一维结构[Na(H2O)(N5)]·2H2O)提高到了118.4和126.5°C. 此外, 他们成功地除去了产物中的结晶水, 成为具有高生成热特点的五唑无水盐(> 800 kJ mol−1). 聚合物1和2比传统能量材料高得多的生成热, 表明N5−作为高能量密度材料(HEDMs)的前驱体, 具有很好的前景.

A kinetic investigation of thermal decomposition of 1,1′-dihydroxy-5,5′-bitetrazole-based metal salts

Three novel Co/Cu/Pb salts of 1,1′-dihydroxy-5,5′-bitetrazole (BTO) were prepared, and their thermal behaviors, decomposition reaction kinetics, thermal safety and thermodynamic parameters were investigated as potential energetic combustion catalysts for propellant. Thermogravimetric analysis and differential scanning calorimetry had been used to identify the changes in thermal and kinetic behavior of samples. The results outlined three mass loss stages in TG curves, and the major effect of the metal was observed at second stage for decomposition of organic groups. Thermal-kinetic evaluations were carried out by a model-free and a model fitting method. The model-free method indicated that the activation energy follows the order of BTO-Pbxa0>xa0BTO-Cuxa0>xa0BTO-Co. The model fitting analysis of this stage suggested: (1) the thermal decomposition of BTO-Co was an one-dimensional bounding process, and R1, nxa0=xa01. The integral form of the reaction mechanism was F(α)xa0=xa0α. (2) The thermal decomposition of BTO-Cu kept to the mechanism of nucleation and growth, respectively, in which nxa0=xa04/3. The integral form of the reaction mechanism was F(α)xa0=xa0[−ln(1xa0−xa0α)]3/4. (3) The thermal decomposition of BTO-Pb was one-dimensional diffusion referring to the 1D, D1 decelerating reaction mechanism. The integral form of the reaction mechanism was F(α)xa0=xa0α2. The thermal safety evaluation and thermodynamic parameters were finally studied. The high value of both self-accelerating decomposition temperature (TSADT) (520–550xa0K) and enthalpy of activation (ΔH≠) (200xa0kJxa0mol−1) for the three indicated that they were all of good thermal stability.

Pentazole anion cyclo-N5−: a rising star in nitrogen chemistry and energetic materials

Nitrogen and carbon are common elements in nature. The development of nitrogen chemistry, however, is obviously left behind by that of carbon chemistry. Prof. Christ [1] attributed this reason to the stability difference between nitrogen-nitrogen bond and carbon-carbon bond. From N≡N, N=N to N–N bond, the bond dissociation energy increases significantly and the stability becomes worse rapidly, which is in contrast with stable C–C bond and unstable C≡C bond in carbon chemistry. Thus, lots of stable “polycarbon” structures have been developed based on C–C bond, such as C60, graphene and diamond, while few “polynitrogen” structures based on N–N or N=N bonds can be synthesized and stably exist. For a long time, there were only two N–N or N=N bonds based polynitrogen structures isolated successfully, N3 − anion and N5 + cation. From another point of view, since the polynitrogen compounds are meta-stabilized, they would store large amount of energy and serve as potential candidates for high energy density materials. Pentazole anion, constructed of five nitrogen atoms in a plane ring and therefore denoted as cyclo-N5 , has always been a central concern in the polynitrogen chemistry. Firstly, it was predicted to be one of the most stable species among polynitrogen structures theoretically with an activation barrier of 27 kcal mol to prevent auto-decomposition [2]. Secondly, it is the last member in azole ring containing nitrogen atoms with similar aromaticity to its isoelectronic species cyclopentadienyl anion C5H5 . However, the way to isolated cyclo-N5 was unexpectedly difficult. Since the first disclose of substituted pentazole derivatives arylpentazoles in 1915, only two important milestones were witnessed, the observation of cyclo-N5 through electrospray ionization-mass spectrometry of arylpentazoles in 1999 [3], or by compressing and laser heating of MN3 (M=Na, Cs) and N2 precursors at super high pressure in 2017 [4]. It is until recently that significant progress has been made in this area. Selective C–N bond cleavage of arylpentazole was achieved through Haas’s reductive cleavage using alkali metals [5] and our oxidative cleavage using m-chloroperbenzoic acid and ferrous bisglycinate [6,7]. It is worth mentioning that, with our strategy, the bulk synthesis of cyclo-N5 could be achieved, which is a landmark in the world and of important scientific significance for the development of nitrogen chemistry and polynitrogen energetic materials. As a new synthesized structure, further exploration is still needed on the properties of cyclo-N5. Fortunately, the cycloN5 − represents acceptable stable at common condition and will decompose over 100 °C with apparent activation energies ~110 kJ/mol, which was better than N5 + (<0 °C) but worse than N3 − (>400 °C). With cyclo-N5 in hand, we envisioned that the investigations of novel pentazole derivatives should include but not limited to the following directions. Coordination chemistry. Previous polynitrogen structures including N3 − anion and N5 + cation show poor performance in bonding with other compounds, while cyclo-N5 − is quite

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.