Synthesis of magnesium-nitrogen salts of polynitrogen anions

Xia K., Zheng X., Yuan J., Liu C., Gao H., Wu Q., Sun J.

Polynitrogen compounds especially pentazolate anion complexes recently have attracted substantial attention due to their promising potential as high-energy-density materials. Here, using a machine-learning-accelerated crystal structure search method and first-principles calculations, we predict a new hybrid compound by inserting a large fraction of nitrogen into alkaline-earth metals. It is a new stoichiometric type MN10 (M = Be, Mg), which possesses a metal-centering octahedral pentazolate framework with the space group Fdd2. This type of ionic-like molecular crystal is found to be energetically more favorable than the mixtures of M3N2 or MN4 compounds and pure nitrogen and is possibly synthesized at relatively low pressures (around 12 GPa for MgN10). The ab initio molecular dynamics simulations show that they are metastable and can be quenched to ambient conditions once synthesized at high pressure. Moreover, decomposition of this polymeric MN10 structure can release a large amount of energy and shows h...

Bykov M., Khandarkhaeva S., Fedotenko T., Sedmak P., Dubrovinskaia N., Dubrovinsky L.

Iron tetranitride, FeN4, was synthesized from the elements in a laser-heated diamond anvil cell at 180 (5) GPa and 2700 (200) K. Its crystal structure was determined based on single-crystal X-ray diffraction data collected from a submicron-sized grain at the synchrotron beamline ID11 of ESRF. The compound crystallizes in the triclinic space groupP\overline{1}. In the asymmetric unit, the Fe atom occupies an inversion centre (Wyckoff position 1d), while two N atoms occupy general positions (2i). The structure is made up from edge-sharing [FeN6] octahedra forming chains along [100] and being interconnected through N—N bridges. N atoms formcatena-poly[tetraz-1-ene-1,4-diyl] anions [–N=N—N—N–]∞2−running along [001]. In comparison with the previously reported structure of FeN4at 135 GPa [Bykovet al.(2018).Nat. Commun.9, 2756], the crystal structure of FeN4at 180 GPa is similar but the structural model is significantly improved in terms of the precision of the bond lengths and angles.

Bykov M., Bykova E., Aprilis G., Glazyrin K., Koemets E., Chuvashova I., Kupenko I., McCammon C., Mezouar M., Prakapenka V., Liermann H.-., Tasnádi F., Ponomareva A.V., Abrikosov I.A., Dubrovinskaia N., et. al.

Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N–N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure. Here, through a direct reaction between Fe and N2 in a laser-heated diamond anvil cell, we synthesize three ironnitrogen compounds Fe3N2, FeN2 and FeN4. Their crystal structures are revealed by single-crystal synchrotron X-ray diffraction. Fe3N2, synthesized at 50 GPa, is isostructural to chromium carbide Cr3C2. FeN2 has a marcasite structure type and features covalently bonded dinitrogen units in its crystal structure. FeN4, synthesized at 106 GPa, features polymeric nitrogen chains of [N42−]n units. Based on results of structural studies and theoretical analysis, [N42−]n units in this compound reveal catena-poly[tetraz-1-ene-1,4-diyl] anions.Owing to the energetic nature of N–N bonds, poly-nitrogen compounds are considered promising high energy density materials. Here, the authors synthesize three iron–nitrogen compounds at high pressure, including FeN4, which features polymeric nitrogen chains of [N42−]n units.

Bykov M., Bykova E., Koemets E., Fedotenko T., Aprilis G., Glazyrin K., Liermann H., Ponomareva A.V., Tidholm J., Tasnádi F., Abrikosov I.A., Dubrovinskaia N., Dubrovinsky L.

A nitrogen-rich compound, ReN8 ⋅x N2 , was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN8 framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, ReN8 ⋅x N2 is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [-N=N-]∞ that constitute the framework have not been previously observed in any compound. Ab initio calculations on ReN8 ⋅x N2 provide strong support for the experimental results and conclusions.

Laniel D., Weck G., Gaiffe G., Garbarino G., Loubeyre P.

Polynitrogen compounds have been actively pursued driven by their potential as ultra-high-performing propellants or explosives. Despite remarkable breakthroughs over the past two decades, the two figures of merit for a compelling material, namely a large fraction of nitrogen by weight and a bulk stability under ambient conditions, have not yet been achieved. We report the synthesis of a lithium pentazolate solid by compressing and laser-heating lithium embedded in molecular N2 around 45 GPa along with its recovery under ambient conditions. The observation by Raman spectroscopy of vibrational modes unique to the cyclo-N5- anion is the signature of the formation of LiN5. Mass spectroscopy experiments confirm the presence of the pentazolate anion in the recovered compound. A monoclinic lattice is obtained from X-ray diffraction measurements and the volume of the LiN5 compound under pressure is in good agreement with the theoretical calculations.

Zhang W., Wang K., Li J., Lin Z., Song S., Huang S., Liu Y., Nie F., Zhang Q.

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.

Xu Y., Wang Q., Shen C., Lin Q., Wang P., Lu M.

Metal complexes of the pentazole anion exhibit multiple coordination modes, through ionic, covalent and hydrogen-bonding interactions, and good thermal stability with onset decomposition temperatures greater than 100 °C. Polynitrogen compounds can decompose to N2 with an extraordinarily large energy release, which makes them promising candidate materials for explosives but difficult to produce in a stable form. Compounds containing five-membered all-nitrogen rings have attracted particular interest in the search for a stable polynitrogen molecule. Yuangang Xu et al. report five metal complexes containing the pentazole anion, cyclo--N5−, four of which exhibit good thermal stability and a range of different bonding interactions for stabilization. Given their energetic properties and stability, and the adaptability of the cyclo-N5− species in terms of its bonding interactions, these complexes might lead to the development of a new class of high-energy-density materials and of other unusual polynitrogen complexes. 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 propellants1,2,3, 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 phases4,5,6, 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 1900s7 and characterized in the 1950s8,9. Salts containing the azide anion (N3−)10,11,12 or pentazenium cation (N5+)13 are also known, with compounds containing the pentazole anion, cyclo-N5−, a more recent addition14,15,16. Very recently, a bulk material containing this species was reported17 and then used to prepare the first example of a solid-state metal–N5 complex18. 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 materials19 or enable the development of such materials containing only nitrogen20,21,22,23. 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 metallocenes24 and other unusual polynitrogen complexes.

Yu S., Huang B., Zeng Q., Oganov A.R., Zhang L., Frapper G.

Stable structures and stoichiometries of binary Mg–N compounds are explored at pressures from ambient up to 300 GPa using ab initio evolutionary simulations. In addition to Mg3N2, we identified five nitrogen-rich compositions (MgN4, MgN3, MgN2, Mg2N3, and Mg5N7) and three magnesium-rich ones (Mg5N3, Mg4N3 and Mg5N4), which have stability fields on the phase diagram. These compounds have peculiar structural features, such as N2 dumbbells, bent N3 units, planar SO3-like N(N)3 units, N6 six-membered rings, 1D polythiazyl S2N2-like nitrogen chains, and 2D polymeric nitrogen nets. The dimensionality of the nitrogen network decreases as magnesium content increases; magnesium atoms act as a scissor by transferring valence electrons to the antibonding states of nitrogen sublattice. In this context, pressure acts as a bonding glue in the nitrogen sublattice, enabling the emergence of polynitrogen molecule-like species and nets. In general, Zintl–Klemm concept and molecular orbital analysis proved useful for ration...

Mezouar M., Giampaoli R., Garbarino G., Kantor I., Dewaele A., Weck G., Boccato S., Svitlyk V., Rosa A.D., Torchio R., Mathon O., Hignette O., Bauchau S.

ABSTRACT A review of some important technical challenges related to in situ diamond anvil cell laser heating experimentation at synchrotron X-ray sources is presented. The problem of potential chemical reactions between the sample and the pressure medium or the carbon from the diamond anvils is illustrated in the case of elemental tantalum. Preliminary results of a comparison between reflective and refractive optics for high temperature measurements in the laser-heated diamond anvil cell are briefly discussed. Finally, the importance of the size and relative alignment of X-ray and laser beams for quantitative X-ray measurements is presented.

Zhang C., Yang C., Hu B., Yu C., Zheng Z., Sun C.

The reactions of (N5 )6 (H3 O)3 (NH4 )4 Cl with Co(NO3 )2 ⋅6 H2 O at room temperature yielded Co(N5 )2 (H2 O)4 ⋅4 H2 O as an air-stable orange metal complex. The structure, as determined by single-crystal X-ray diffraction, has two planar cyclo-N5- rings and four bound water molecules symmetrically positioned around the central metal ion. Thermal analysis demonstrated the explosive properties of the material.

Wei S., Li D., Liu Z., Li X., Tian F., Duan D., Liu B., Cui T.

The P1̄-MgN3 and P1̄-MgN4 are predicted to become energetically stable under pressure, suggesting that it may be prepared by high-pressure synthesis. P1̄-MgN3 and P1̄-MgN4 are expected to release an enormously large amount of energy (2.83 and 2.01 kJ g−1). The present study encourages experimental exploration of these promising materials in the future.

Kapos V.

Remote-sensing data identify functional trait variation in tropical forests

Christe K.O.

A cyclo -N 5 − anion has been synthesized as a stable salt and characterized

Zhang J., Oganov A.R., Li X., Niu H.

We report hafnium nitrides under pressure using first-principles evolutionary calculations. Metallic $P{6}_{3}/mmc$-HfN (calculated Vickers hardness 23.8 GPa) is found to be more energetically favorable than NaCl-type HfN at zero and high pressure. Moreover, NaCl-type HfN actually undergoes a phase transition to $P{6}_{3}/mmc$-HfN below 670 K at ambient pressure. ${\mathrm{HfN}}_{10}$, which simultaneously has infinite armchairlike polymeric N chains and ${\mathrm{N}}_{2}$ molecules in its crystal structure, is discovered to be stable at moderate pressure above 23 GPa and can be preserved as a metastable phase at ambient pressure. At ambient conditions (298 K, 0 GPa), the gravimetric energy densities and the volumetric energy densities of ${\mathrm{HfN}}_{10}$ are 2.8 kJ/g and 14.1 kJ/${\mathrm{cm}}^{3}$, respectively.

Lindsay C.M., Fajardo M.E.

It is well known that the performance of modern energetic materials based on organic chemistry has plateaued, with only ∼ 40% improvements realized over the past half century. This fact has stimulated research on alternative chemical energy storage schemes in various U.S. government funded “High Energy Density Materials” (HEDM) programs since the 1950’s. These efforts have examined a wide range of phenomena such as free radical stabilization, metallic hydrogen, metastable helium, polynitrogens, extended molecular solids, nanothermites, and others. In spite of the substantial research investments, significant improvements in energetic material performance have not been forthcoming. This paper discusses the lessons learned in the various HEDM programs, the different degrees of freedom in which to store energy in materials, and the fundamental limitations and orders of magnitude of the energies involved. The discussion focuses almost exclusively on the topic of energy density and only mentions in passing other equally important properties of explosives and propellants such as gas generation and reaction rate.

Ni S., Jiang J., Wang W., Wu X., Zhuo Z., Wang Z.

The novel α-2D-BeN2 monolayer shows exceptional potential as a multifunctional semiconductor for ORR/OER catalysis as well as for potassium-ion batteries.

Yang Y., Song J., Zhang H., Li Z., Liu S., Wang Y., Su X.

Pressure-induced nitrogen-rich compounds hold significant application prospects in high-energy-density materials. Utilizing first-principles calculations and swarm-intelligence structure search methods, we have identified ten new types of Gd-N compounds with different configurations, such as one-dimensional N-chains composed of N6 rings or N8 rings, and two-dimensional N-layers constructed of N14 rings, N18 rings, or N18 + N6 rings. Moreover, the predicted Gd-N compounds exhibit different magnetic properties, and a magnetic phase diagram is constructed in the pressure range of 0 to 200 GPa. Remarkably, the volumetric energy density (11.58–17.79 kJ/cm3) of Gd polynitrides with high nitrogen content, including P-1(I)-GdN6, P-1(II)-GdN6, R-3-GdN8, C2mm-GdN9, and P1-GdN10, surpassed that of TNT (7.05 kJ/cm3), making them promising candidates for energetic materials. The discovery of diverse chain-like and layered structures in the GdNx compounds highlights the role of gadolinium in inducing the diversity and complexity of nitrogen arrangements.

Zhang B., Xu M., Wang Z., Hao J., Li Y.

Chen H., Bykov M., Batyrev I.G., Brüning L., Bykova E., Mahmood M.F., Chariton S., Prakapenka V.B., Fedotenko T., Glazyrin K., Mezouar M., Garbarino G., Steele A., Goncharov A.F.

Gao Y., Zhang Y., Liu S., Jin B., Guo L., Guo X., Yao Z., Wang P., Liu B.

Wang Y., Zhang H., Liu S., Zhang H., Wang P., Yi W., Yao Z., Li N., Liu X., Liu B.

Polymeric nitrogen materials are the crown of high energy density materials due to their environmental friendliness. Here, we proposed a general strategy to achieve crown-like polymeric nitrogen (cr-N) by combining high-pressure and chemical exfoliation methods. Using the first-principle structure search, we demonstrated that the cerium (Ce) atoms can effectively open the N≡N bond of N2 at a moderate pressure of 25.7 GPa, and then the layered chelate $$P{\bar 1}-{\rm CeN}_{8}$$ with the crown-like N18 ring is formed via the ligand effect of metallic Ce. Interestingly, when released to ambient conditions, $$P{\bar 1}-{\rm CeN}_{8}$$ can still maintain good stability due to robust N–N bonds; meanwhile, the interaction strength between the Ce atoms and N18 ring decreases. As a result, Ce atoms can be selectively removed by alkaline anions, and the dynamic progresses are presented, which is similar to the synthesis of MXenes via the alkali intercalation exfoliation method, and then crown-like polymeric nitrogen cr-N is formed. The cr-N is proved to be dynamically, mechanically, and thermally stable at ambient conditions. Moreover, the excellent gravimetric energy density, detonation pressure, and detonation velocity of cr-N make it a significant high-energy density material. This work opens a new general avenue to realize polymeric nitrogen via high-pressure and chemical exfoliation methods.

Pitié S., Niwa K., Frapper G.

Sen S., Bag A., Pal S.

AbstractActivation of molecular N2 and its catalytic ability to form NH3 using C17Si has been already reported. This current study reports the formation of exclusive polynitrogen clusters (N4 and N5) on the C17Si ring. The clusters are generated using N2 and N3 respectively. Physical and chemical property analyses of the clusters show that the N5 cluster exhibits greater stability than N4. The former is seen to experience reduced molecular strain compared to the latter owing to its co‐planar geometry. The thermodynamic calculations of the systems further show that the formation of the N5 cluster is spontaneous compared to N4 on the C17Si ring.

Zhang H., Zhang Y., Wang Y., Sui M., Yue L., Liu S., Li Q., Liu Z., Yao Z., Wang P., Liu B.

AbstractMetal polynitrides have raised significant interest for their applications as potential high‐energy‐density materials (HEDMs). Despite extensive research on energetic polynitrogen species, reducing synthesis pressures and realizing their recovery at ambient conditions remain challenging. Here, for the first time, the zigzag N4 chains are successfully stabilized in the new polynitride Ce2N6 and recovered to ambient pressure and temperature by introducing cerium nitride as a precursor. The stable mechanism of the recoverable N4 chain originates from the large quantity of charge captured, the favorable bonding environment, and low structural enthalpy. This study reveals the crucial role of precursors in stabilizing and recovering polynitrogen species, providing an alternative route to design and prepare novel HEDMs.

Zhang Y., Ding C., Zhang K., Pakhomova A., Chen S., Ding Y., Jiang S., Huang X., Sun J., Cui T.

Shi H., Chen L., Moutaabbid H., Feng Z., Zhang G., Wang L., Li Y., Guo H., Liu C.

AbstractPressure‐modulated self‐trapped exciton (STE) emission mechanism in all‐inorganic lead‐free metal halide double perovskites characterized by large Stokes‐shifted broadband emission, has attracted much attention across various fields such as optics, optoelectronics, and biomedical sciences. Here, by employing the all‐inorganic lead‐free metal halide double perovskite Cs2TeCl6 as a paradigm, the authors elucidate that the performance of STE emission can be modulated by pressure, attributable to the pressure‐induced evolution of the electronic state (ES). Two ES transitions happen at pressures of 1.6 and 5.8 GPa, sequentially. The electronic behaviors of Cs2TeCl6 can be jointly modulated by both pressure and ES transitions. When the pressure reaches 1.6 GPa, the Huang–Rhys factor S, indicative of the strength of electron‐phonon coupling, attains an optimum value of ≈12.0, correlating with the pressure‐induced photoluminescence (PL) intensity of Cs2TeCl6 is 4.8‐fold that of its PL intensity under ambient pressure. Through analyzing the pressure‐dependent STE dynamic behavioral changes, the authors have revealed the microphysical mechanism underlying the pressure‐modulated enhancement and quenching of STE emission in Cs2TeCl6.

Niu S., Liu Y., Zhang W., Mao Y., Yang Z., Liu S., Wang H., Yao Z.

The study of the Na-N system in the N-rich region under high pressure enriches the structural types of polynitrogen structure: four novel structures (P1-NaN7, Cm-NaN7, C2-NaN8, and R 3‾-NaN8) are proposed. The layered structure of the Cm-NaN7 and R 3‾-NaN8 phase consisting of the N16 and N18 ring respectively are first proposed in the Na-N system under high pressure. The Cm-NaN7 and R 3‾-NaN8 phase not only can be stabilized to the ambient conditions, but also the Cm-NaN7 phase can decompose and release energy at 325 K, while the R 3‾-NaN8 phase can be stable to at least 1000 K. The research shows that the different decomposition barriers and charge transfer are important reasons for the difference of decomposition temperature. The Cm-NaN7 phase is semiconductor phase with a band gap of 0.06 eV, while the R 3‾-NaN8 phase is metal phase. Furthermore, the excellent energy density, detonation pressure, and detonation velocity of the Cm-NaN7 and R 3‾-NaN8 phase make them as potential candidates in the application of high energy density materials.

Mikhailov Oleg V.

The review integrates and systematizes data published in the last 15 years on the physicochemical characteristics of specific chemical compounds formed by metal elements with nitrogen atoms containing three or more nitrogen atoms per metal atom. Most often, the total number of nitrogen atoms exceeds their greatest number allowed by the formal higher oxidation state of the metal atom present in the compound. The conceptual possibility of practical application of these compounds now and in the future is also discussed.The bibliography includes 230 references.

Zhang B., Xu M., Xin Y., Lin S., Hao J., Wang Y., Li Y.

The energy landscape of sodium chloride-nitrogen mixtures has been comprehensively explored to examine the ability of the formation of unknown compounds under pressures of up to 100 GPa, using swarm-intelligence structure prediction methodology and first-principles calculations. We identified a thermodynamically stable NaN5ClN5 compound containing two cyclo-N5 species under pressures exceeding 53 GPa, representing milder conditions in comparison to those requisite for pure solid nitrogen. In NaN5ClN5, the high electron affinity of the cyclo-N5 motif allows it to oxidize the chlorine atoms, resulting in the formation of two cyclo-N5 anions. Additionally, the weak covalent interactions between Cl and nearby N atoms plays a key role in stabilization of structure. It has been demonstrated that simple NaN5 salt was a suitable precursor for the synthesis of NaN5ClN5 at high pressure. molecular dynamics simulations demonstrated the recoverability of NaN5ClN5 as a metastable phase at ambient pressure-temperature conditions. Additionally, NaN5ClN5 exhibits a higher energy density of 3.86 kJ/g and a lower mass density of 1.67 g/cm3 in comparison to metal pentazolate salts, highlighting its potential as a high energy-density material. Published by the American Physical Society 2024

Zhang B., Xin Y., Xu M., Zhang Y., Li Y., Wang Y., Chen C.