Journal of Chemical Physics, volume 147, issue 23, pages 234701

Novel rubidium poly-nitrogen materials at high pressure

Publication typeJournal Article
Publication date2017-12-15
Quartile SCImago
Q1
Quartile WOS
Q1
SJR1.101
CiteScore7.4
Impact factor3.1
ISSN00219606, 10897690
Physical and Theoretical Chemistry
General Physics and Astronomy
Abstract

First-principles crystal structure search is performed to predict novel rubidium poly-nitrogen materials at high pressure by varying the stoichiometry, i.e., relative quantities of the constituent rubidium and nitrogen atoms. Three compounds of high nitrogen content, RbN5, RbN2, and Rb4N6, are discovered. Rubidium pentazolate (RbN5) becomes thermodynamically stable at pressures above 30 GPa. The charge transfer from Rb to N atoms enables aromaticity in cyclo-N5− while increasing the ionic bonding in the crystal. Rubidium pentazolate can be synthesized by compressing rubidium azide (RbN3) and nitrogen (N2) precursors above 9.42 GPa, and its experimental discovery is aided by calculating the Raman spectrum and identifying the features attributed to N5− modes. The two other interesting compounds, RbN2 containing infinitely long single-bonded nitrogen chains and Rb4N6 consisting of single-bonded N6 hexazine rings, become thermodynamically stable at pressures exceeding 60 GPa. In addition to the compounds with high nitrogen content, Rb3N3, a new compound with 1:1 RbN stoichiometry containing bent N3 azides is found to exist at high pressures.

Novel Potassium Polynitrides at High Pressures
Steele B.A., Oleynik I.I.
Q2
American Chemical Society (ACS)
Journal of Physical Chemistry A 2017 citations by CoLab: 66  |  Abstract
Polynitrogen compounds have attracted great interest due to their potential applications as high energy density materials. Most recently, a rich variety of alkali polynitrogens (R_{x}N_{y}; R=Li, Na, and Cs) have been predicted to be stable at high pressures and one of them, CsN_{5} has been recently synthesized. In this work, various potassium polynitrides are investigated using first-principles crystal structure search methods. Several novel molecular crystals consisting of N_{4} chains, N_{5} rings, and N_{6} rings stable at high pressures are discovered. In addition, an unusual nitrogen-rich metallic crystal with stoichiometry K_{2}N_{16} consisting of a planar two-dimensional extended network of nitrogen atoms arranged in fused eighteen atom rings is found to be stable above 70 GPa. An appreciable electron transfer from K to N atoms is responsible for the appearance of unexpected chemical bonding in these crystals. The thermodynamic stability and high pressure phase diagram is constructed. The electronic and vibrational properties of the layered polynitrogen K_{2}N_{16} compound are investigated, and the pressure-dependent IR-spectrum is obtained to assist in experimental discovery of this new high-nitrogen content material.
A series of energetic metal pentazolate hydrates
Xu Y., Wang Q., Shen C., Lin Q., Wang P., Lu M.
Q1
Springer Nature
Nature 2017 citations by CoLab: 372  |  Abstract
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.
A Symmetric Co(N5 )2 (H2 O)4 ⋅4 H2 O High-Nitrogen Compound Formed by Cobalt(II) Cation Trapping of a Cyclo-N5 − Anion
Zhang C., Yang C., Hu B., Yu C., Zheng Z., Sun C.
Q1
Wiley
Angewandte Chemie - International Edition 2017 citations by CoLab: 124  |  Abstract
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.
Pentazole and Ammonium Pentazolate: Crystalline Hydro-Nitrogens at High Pressure
Steele B.A., Oleynik I.I.
Q2
American Chemical Society (ACS)
Journal of Physical Chemistry A 2017 citations by CoLab: 55  |  Abstract
Two new crystalline compounds, pentazole (N_{5}H) and ammonium pentazolate (NH_{4})(N_{5}), both featuring cyclo-{\rm N_{5}^{-}} are discovered using first principles evolutionary search of the nitrogen-rich portion of the hydro-nitrogen binary phase diagram (N_{x}H_{y}, x\geqy) at high pressures. Both crystals consist of the pentazolate N_{5}^{-} anion and ammonium NH_{4}^{+} or hydrogen H^{+} cations. These two crystals are predicted to be thermodynamically stable at pressures above 30 GPa for (NH_{4})(N_{5}) and 50 GPa for pentazole N_{5}H. The chemical transformation of ammonium azide (NH_{4})(N_{3}) mixed with di-nitrogen (N_{2}) to ammonium pentazolate (NH_{4})(N_{5}) is predicted to become energetically favorable above 12.5 GPa. To assist in identification of newly synthesized compounds in future experiments, the Raman spectra of both crystals are calculated and mode assignments are made as a function of pressure up to 75 GPa.
Synthesis and characterization of the pentazolate anion cyclo -N 5 ˉ in (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl
Zhang C., Sun C., Hu B., Yu C., Lu M.
Q1
American Association for the Advancement of Science (AAAS)
Science 2017 citations by CoLab: 416
Open Access
Open access
PDF  |  Abstract
A salty route to an all-nitrogen ring The flip side of the robust stability of N 2 is the instability of any larger molecules composed exclusively of nitrogen. These molecules nonetheless remain enticing targets for explosive and propellant applications. Zhang et al. successfully prepared the pentazolate ion, a negatively charged ring of five nitrogens, by oxidative cleavage of a C–N bond in an aryl-substituted precursor (see the Perspective by Christe). The molecule was stabilized and isolated in the solid state as a hydrated ammonium chloride salt. Spectroscopic and crystallographic characterization confirmed the ring's planar geometry. Science , this issue p. 374 ; see also p. 351
High-Pressure Synthesis of a Pentazolate Salt
Steele B.A., Stavrou E., Crowhurst J.C., Zaug J.M., Prakapenka V.B., Oleynik I.I.
Q1
American Chemical Society (ACS)
Chemistry of Materials 2016 citations by CoLab: 188  |  Abstract
The pentazolates, the last all-nitrogen members of the azole series, have been notoriously elusive for the last hundred years despite enormous efforts to make these compounds in either gas or condensed phases. Here, we report a successful synthesis of a solid state compound consisting of isolated pentazolate anions N5–, which is achieved by compressing and laser heating cesium azide (CsN3) mixed with N2 cryogenic liquid in a diamond anvil cell. The experiment was guided by theory, which predicted the transformation of the mixture at high pressures to a new compound, cesium pentazolate salt (CsN5). Electron transfer from Cs atoms to N5 rings enables both aromaticity in the pentazolates as well as ionic bonding in the CsN5 crystal. This work provides critical insight into the role of extreme conditions in exploring unusual bonding routes that ultimately lead to the formation of novel high nitrogen content species.
Detection of Cyclo-N5 − in THF Solution
Bazanov B., Geiger U., Carmieli R., Grinstein D., Welner S., Haas Y.
Q1
Wiley
Angewandte Chemie - International Edition 2016 citations by CoLab: 82  |  Abstract
Compelling evidence has been found for the formation and direct detection of the cyclopentazole anion (cyclo-N5- ) in solution. The anion was prepared from phenylpentazole in two steps: reduction by an alkali metal to form the phenylpentazole radical anion, followed by thermal dissociation to yield cyclo-N5- . The reaction solution was analyzed by HPLC coupled with negative mode mass spectrometry. A signal with m/z 70 was eluted about 2.1 min after injection of the sample. Its identification as N5 was supported by single and double labeling with 15 N, which yielded signals at m/z=71 and 72, respectively, with identical retention times in the HPLC column. MS/MS analysis of the m/z=70 signal revealed a dissociation product with m/z=42, which can be assigned to N3- . To our knowledge this is the first preparation of cyclo-N5- in the bulk. The compound is indefinitely stable at temperatures below -40 °C, and has a half-life of a few minutes at room temperature.
Sodium pentazolate: A nitrogen rich high energy density material
Steele B.A., Oleynik I.I.
Q1
Elsevier
Chemical Physics Letters 2016 citations by CoLab: 121  |  Abstract
Sodium pentazolates NaN5 andNa2N5, new high energy density materials, are discovered during first principles crystal structure search for the compounds of varying amounts of elemental sodium and nitrogen. The pentazole anion N5- is stabilized in the condensed phase by sodium Na+ cations at pressures exceeding 20 GPa, and becomes metastable upon release of pressure. The sodium azide (NaN3) precursor is predicted to undergo a chemical transformation above 50 GPa into sodium pentazolates NaN5 and Na2N5. The calculated Raman spectrum of NaN5 is in agreement with the experimental Raman spectrum of a previously unidentified substance appearing upon compression and heating of NaN3.
Exotic stable cesium polynitrides at high pressure
Peng F., Han Y., Liu H., Yao Y.
Q1
Springer Nature
Scientific Reports 2015 citations by CoLab: 62
Open Access
Open access
PDF  |  Abstract
New polynitrides containing metastable forms of nitrogen are actively investigated as potential high-energy-density materials. Using a structure search method based on the CALYPSO methodology, we investigated the stable stoichiometries and structures of cesium polynitrides at high pressures. Along with the CsN3, we identified five new stoichiometric compounds (Cs3N, Cs2N, CsN, CsN2 and CsN5) with interesting structures that may be experimentally synthesizable at modest pressures (i.e., less than 50 GPa). Nitrogen species in the predicted structures have various structural forms ranging from single atom (N) to highly endothermic molecules (N2, N3, N4, N5, N6) and chains (N∞). Polymeric chains of nitrogen were found in the high-pressure C2/c phase of CsN2. This structure contains a substantially high content of single N-N bonds that exceeds the previously known nitrogen chains in pure forms and also exhibit metastability at ambient conditions. We also identified a very interesting CsN crystal that contains novel N44− anion. To our best knowledge, this is the first time a charged N4 species being reported. Results of the present study suggest that it is possible to obtain energetic polynitrogens in main-group nitrides under high pressure.
Layered polymeric nitrogen in RbN3 at high pressures
Wang X., Li J., Xu N., Zhu H., Hu Z., Chen L.
Q1
Springer Nature
Scientific Reports 2015 citations by CoLab: 41
Open Access
Open access
PDF  |  Abstract
The structural evolutionary behaviors of nitrogen in RbN3 have been studied up to 300 GPa using a particle swarm optimization structure searching method combined with density functional calculations. Three stable new phases with P-1, P6/mmm and C2/m structure at pressure of 30, 50 and 200 GPa are identified for the first time. The analysis of the crystal structures of three new predicated phases reveals that the transition of N3− ions goes from linear molecules to polymeric chains, benzene-like rings and then to polymeric layers induced by pressure. The electronic structures of three predicted phases reveal that the structural changes are accompanied and driven by the change of orbital hybridization of N atoms from sp to sp2 and finally to partial sp3. Most interestingly, the Rb atoms show obvious transition metal-like properties through the occupation of 4d orbitals in high-pressure phases. Moreover, the Rb atoms are characterized by strong hybridization between 4d orbitals of Rb and 2p orbitals of N in C2/m structure. Our studies complete the structural evolution of RbN3 under pressure and reveal for the first time that the Rb atoms in rubidium nitride possess transition element-like properties under pressure.
Novel lithium-nitrogen compounds at ambient and high pressures
Shen Y., Oganov A.R., Qian G., Zhang J., Dong H., Zhu Q., Zhou Z.
Q1
Springer Nature
Scientific Reports 2015 citations by CoLab: 66
Open Access
Open access
PDF  |  Abstract
AbstractUsing ab initio evolutionary simulations, we predict the existence of five novel stable Li-N compounds at pressures from 0 to 100 GPa (Li13N, Li5N, Li3N2, LiN2 and LiN5). Structures of these compounds contain isolated N atoms, N2 dimers, polyacetylene-like N chains and N5 rings, respectively. The structure of Li13N consists of Li atoms and Li12N icosahedra (with N atom in the center of the Li12 icosahedron) – such icosahedra are not described by Wade-Jemmis electron counting rules and are unique. Electronic structure of Li-N compounds is found to dramatically depend on composition and pressure, making this system ideal for studying metal-insulator transitions. For example, the sequence of lowest-enthalpy structures of LiN3 shows peculiar electronic structure changes with increasing pressure: metal-insulator-metal-insulator. This work also resolves the previous controversies of theory and experiment on Li2N2.
High-Pressure Studies of Rubidium Azide by Raman and Infrared Spectroscopies
Li D., Li F., Li Y., Wu X., Fu G., Liu Z., Wang X., Cui Q., Zhu H.
Q1
American Chemical Society (ACS)
Journal of Physical Chemistry C 2015 citations by CoLab: 11  |  Abstract
We report the high-pressure studies of RbN3 by Raman and IR spectral measurements at room temperature with the pressure up to 28.5 and 30.2 GPa, respectively. All the fundamental vibrational modes were resolved by combination of experiment and calculation. Detailed spectroscopic analyses reveal two phase transitions at ∼6.5 and ∼16.0 GPa, respectively. Upon compression, the shearing distortion of the unit cell induced the displacive structural transition of phase α → γ. Further analyses of the mid-IR spectra indicate the evolution of N3– with the arrangement sequence of orthogonal → parallel → orthogonal during the phase transition of phase α → γ → δ. Additionally, the pressure-induced nonlinear/asymmetric existence of N═N═N and the two crystallographically nonequivalent sites of N3– were observed in phase δ.
Pressure-Induced Symmetry-Lowering Transition in Dense Nitrogen to Layered Polymeric Nitrogen (LP-N) with Colossal Raman Intensity
Tomasino D., Kim M., Smith J., Yoo C.
Q1
American Physical Society (APS)
Physical Review Letters 2014 citations by CoLab: 185
Open Access
Open access
 |  Abstract
We present the discovery of a novel nitrogen phase synthesized using laser-heated diamond anvil cells at pressures between 120--180 GPa well above the stability field of cubic gauche $(cg)\text{\ensuremath{-}}\mathrm{N}$. This new phase is characterized by its singly bonded, layered polymeric (LP) structure similar to the predicted Pba2 and two colossal Raman bands (at $\ensuremath{\sim}1000$ and $1300\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ at 150 GPa), arising from two groups of highly polarized nitrogen atoms in the bulk and surface of the layer, respectively. The present result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry-lowering 3D $cg\text{\ensuremath{-}}\mathrm{N}$ to 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N ($\ensuremath{\rho}=4.85\text{ }\text{ }\mathrm{g}/{\mathrm{cm}}^{3}$ at 120 GPa).
Pressure-induced phase transitions in rubidium azide: Studied by in-situ x-ray diffraction
Li D., Wu X., Jiang J., Wang X., Zhang J., Cui Q., Zhu H.
Q1
AIP Publishing
Applied Physics Letters 2014 citations by CoLab: 28  |  Abstract
We present the in-situ X-ray diffraction studies of RbN3 up to 42.0 GPa at room temperature to supplement the high pressure exploration of alkali azides. Two pressure-induced phase transitions of α-RbN3 → γ-RbN3 → δ-RbN3 were revealed at 6.5 and 16.0 GPa, respectively. During the phase transition of α-RbN3 → γ-RbN3, lattice symmetry decreases from a fourfold to a twofold axis accompanied by a rearrangement of azide anions. The γ-RbN3 was identified to be a monoclinic structure with C2/m space group. Upon further compression, an orthogonal arrangement of azide anions becomes energetically favorable for δ-RbN3. The compressibility of α-RbN3 is anisotropic due to the orientation of azide anions. The bulk modulus of α-RbN3 is 18.4 GPa, quite close to those of KN3 and CsN3. By comparing the phase transition pressures of alkali azides, their ionic character is found to play a key role in pressure-induced phase transitions.
Unique structure and high energy properties of lithium-nitrogen compound in the N-rich region
Niu S., Liu Y., Mao Y., Zhang W., Yang Z., Zhai C., Liu S., Wang H.
Q2
Elsevier
Materials Science and Engineering B: Solid-State Materials for Advanced Technology 2025 citations by CoLab: 0
Polymerization of Potassium Azide in Liquid Nitrogen Using Nanosecond-Pulsed Spark Plasma
Song Z., Fridman A., Dobrynin D.
Q2
MDPI
Materials 2024 citations by CoLab: 0
Open Access
Open access
PDF  |  Abstract
In this manuscript, we report on the synthesis of a polynitrogen material from a potassium azide precursor using nanosecond-pulsed spark discharge plasma in liquid nitrogen. The polynitrogen material was characterized using Raman and Fourier transform infrared (FTIR) spectroscopy and identified as K2N6, with planar N6 rings and K- ions that have P6/mmm symmetry. An analysis of the mechanism behind such a transformation shows the importance of direct plasma–chemical effects in polymerization, while the crystal structure changes are believed to be due to plasma-emitted radiation in the ultraviolet range.
Novel phase of the Na-N system in the N-rich region under high pressure
Niu S., Liu Y., Zhang W., Mao Y., Yang Z., Liu S., Wang H., Yao Z.
Q1
Elsevier
Vacuum 2024 citations by CoLab: 1  |  Abstract
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.
Higher metal nitrides: current state and prospects
Mikhailov Oleg V.
Q1
Autonomous Non-profit Organization Editorial Board of the journal Uspekhi Khimii
Russian Chemical Reviews 2024 citations by CoLab: 1
Open Access
Open access
PDF  |  Abstract
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.
Sodium chloride induced nitrogen salt with cyclo- N5 anions at high pressure
Zhang B., Xu M., Xin Y., Lin S., Hao J., Wang Y., Li Y.
Q1
American Physical Society (APS)
Physical Review Research 2024 citations by CoLab: 0
Open Access
Open access
PDF  |  Abstract
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
Systematical high-pressure study of praseodymium nitrides in N-rich region
Liu R., Liu S., Zhang Y., Wang P., Yao Z.
Q1
IOP Publishing
Chinese Physics Letters 2024 citations by CoLab: 0  |  Abstract
Abstract We investigate high-pressure phase diagrams of Pr–N compounds by proposing five stable structures (Pnma-PrN, I4/mmm-PrN2, C2/m-PrN3, P 1 ¯ -PrN4, and R3-PrN8) and two metastable structures ( P 1 ¯ -PrN6 and P 1 ¯ -PrN10). The P 1 ¯ -PrN6 with the N14-ring layer and R3-PrN8 with the N18-ring layer can be quenched to ambient conditions. For the P 1 ¯ -PrN10, the N22-ring layer structure transfers into infinite chains with the pressure quenched to ambient pressure. Remarkably, a novel polynitrogen hR8-N designed by the excision of Pr atoms from R3-PrN8 is obtained and can be quenched to ambient conditions. The N-rich structures of P 1 ¯ -PrN6, R3-PrN8, c-PrN10 and the solid pure nitrogen structure exhibit outstanding properties of energy density and explosive performance.
Review of the decomposition and energy release mechanisms of novel energetic materials
Zhong K., Zhang C.
Q1
Elsevier
Chemical Engineering Journal 2024 citations by CoLab: 6  |  Abstract
Nowadays, some new materials with high-energy as well as a certain stability are emerging as the novel energetic materials (EMs), such as all-nitrogen energetic ionic compounds (EICs), high-pressure EMs, and special-structure EMs. These novel EMs differ much from traditional EMs in their intrinsic structure, and exhibit different decomposition and energy release mechanisms, which are attracting increasing attention. However, there is still a lack of a comprehensive summary of the mechanisms. In view of this, this paper reviews for the first time the research progress of representative novel EMs in terms of the decomposition and energy release mechanisms, including the decomposition reaction path, energy barrier, reaction rate and reaction products, as well as the magnitude and speed of energy release, and compares them with traditional EMs. Finally, the existing issues and application potential in current novel EMs are proposed to guide future research directions. This paper will clarify the similarities and differences in decomposition and energy release mechanisms between novel and traditional EMs, and provide beneficial inspiration for the continuous innovation and application of EMs.
Lanthanium Nitride LaN9 Featuring Azide Units: the First Metal Nine-nitride as High-energy Density Material
Lin S., Chen J., Zhang B., Hao J., Xu M., Li Y.
Q1
Royal Society of Chemistry (RSC)
Physical Chemistry Chemical Physics 2024 citations by CoLab: 5  |  Abstract
The high-pressure phase diagrams of the La-N binary system were systematically constructed using the CALYPSO method and first-principles calculations. In addition to the pressure-induced La-N compounds reported previously, we have...
The relationships between direct substituents, aromaticity and kinetic stability of pentazole ring
Yang C., Li X., Zhou N., Chen B., Dong H., Jin J., Hu X., Huang T., Shen L., Yi J., Wang Q., Wang J., Ouyang D.
Elsevier
FirePhysChem 2023 citations by CoLab: 2
Open Access
Open access
 |  Abstract
The two directly substituted pentazoles, N5NH2 and N5COOH, were designed to theoretically study the relationships between substituents, aromaticity and kinetic stability thereof. Analysis shows their kinetic stability order described by the energy separations between the highest occupied molecule orbital (HOMO) and the lowest unoccupied molecule orbital (LUMO), viz. HOMO-LUMO gap, is line with the aromaticity orders obtained from nucleus-independent chemical shift (NICS), harmonic oscillator measure of aromaticity (HOMA), Bird aromaticity index (I) and isochemical shielding surface (ICSS), which is N5NH2 > N5COOH. But this order is contrary to the heat stability order according to Ref [1] The inconsistency between heat stability and kinetic stability reveals the fact that stability of compounds is a complex character and different according to the compound property of the study. The consistency of kinetic stability order with the aromaticity orders described by NICS, NICSSZZ, HOMA, I and ICSS indicates these widely accepted methods for aromaticity estimating are reliable for the two given compounds. As for the effect on aromaticity of pentazole ring from substituent, electron-donating substituent have stronger effect than electron-withdrawing substituent.
Polymeric nitrogen in alkaline earth metal N-rich nitrides (MN2, M = Be, Mg, Ca, Sr, and Ba): A first-principles study
Lin J., Guan P.
Q1
Elsevier
Computational Materials Science 2023 citations by CoLab: 1  |  Abstract
The distinctive chemical and physical characteristics of all-nitrogen salts have attracted significant interest. Some stable polymeric nitrogen with novel chemical bonding patterns are predicted using first-principles calculations and crystal structure prediction methods. However, the element effects of the chemical bonding pattern and structural stability are still unclear. Here, we select the cmcm-MgN2 structure, which is predicted to be free energy favorable between 5 and 40 GPa, and substitute the Mg atoms with other alkaline earth elements (beryllium, calcium, strontium, and barium) to systematically study the influence of the elements on the properties of the compound. We found that the N = N bonds are all covalent, but have metallic properties in BeN2 and BaN2, semiconductor properties in MgN2, CaN2, and SrN2 and the width of the indirect band gap increases with increasing pressure. The charge transfer between metal and N atoms is closely related to the electronegativity of metal elements. Furthermore, thermal stability is investigated based on the phonon spectrum and the imaginary phonons of unstable systems correspond to special vibrational modes of the N = N bond. The anisotropy of lattice constant compressibility is found to be a signal of structural thermal instability. Our results shed some light on the influence of elements on the physical properties of all-nitrogen salts under high pressure, thus accelerating the prediction of crystal structure.
Novel nitrogen-rich Lanthanum nitrides induced by the ligand effect under pressure
Jin B., Liu Y., Yao Z., Liu S., Wang P.
Q1
Royal Society of Chemistry (RSC)
Dalton Transactions 2023 citations by CoLab: 4  |  Abstract
Unique tri-coordinated atoms with alternate sp2 and sp3 hybridizations are formed in the N18 ring of LaN8. The ligand effect of the introduced La atom on the N10 cage induces the structural evolution from I4̄3m-N10 to Imm2-LaN10.
Predicted the structural diversity and electronic properties of Pt−N compounds under high pressure
Feng Q., Xiao X., Dai W., Sun W., Ding K., Lu C.
Q2
IOP Publishing
Journal of Physics Condensed Matter 2023 citations by CoLab: 2  |  Abstract
Abstract The nitrogen-rich transition metal nitrides have attracted considerable attention due to their potential application as high energy density materials. Here, a systematic theoretical study of PtN x compounds has been performed by combining first-principles calculations and particle swarm-optimized structure search method at high pressure. The results indicate that several unconventional stoichiometries of PtN2, PtN4, PtN5, and Pt3N4 compounds are stabilized at moderate pressure of 50 GPa. Moreover, some of these structures are dynamically stable even when the pressure release to ambient pressure. The P 1 ˉ phase of PtN4 and the P 1 ˉ phase of PtN5 can release about 1.23 kJ g−1 and 1.71 kJ g−1, respectively, upon the decomposition into elemental Pt and N2. The electronic structure analysis shows that all crystal structures are indirect band gap semiconductors, except for the metallic Pt3N4 with Pc phase, and the metallic Pt3N4 is a superconductor with estimated critical temperature T c values of 3.6 K at 50 GPa. These findings not only enrich the understanding of transition metal platinum nitrides, but also provide valuable insights for the experimental exploration of multifunctional polynitrogen compounds.
Helical Organic and Inorganic Polymers
Hirata S., Shigeta Y., Xantheas S.S., Bartlett R.J.
Q1
American Chemical Society (ACS)
Journal of Physical Chemistry B 2023 citations by CoLab: 3
Aromatic hexazine [N6]4− anion featured in the complex structure of the high-pressure potassium nitrogen compound K9N56
Laniel D., Trybel F., Yin Y., Fedotenko T., Khandarkhaeva S., Aslandukov A., Aprilis G., Abrikosov A.I., Bin Masood T., Giacobbe C., Bright E.L., Glazyrin K., Hanfland M., Wright J., Hotz I., et. al.
Q1
Springer Nature
Nature Chemistry 2023 citations by CoLab: 20  |  Abstract
The recent high-pressure synthesis of pentazolates and the subsequent stabilization of the aromatic [N5]− anion at atmospheric pressure have had an immense impact on nitrogen chemistry. Other aromatic nitrogen species have also been actively sought, including the hexaazabenzene N6 ring. Although a variety of configurations and geometries have been proposed based on ab initio calculations, one that stands out as a likely candidate is the aromatic hexazine anion [N6]4−. Here we present the synthesis of this species, realized in the high-pressure potassium nitrogen compound K9N56 formed at high pressures (46 and 61 GPa) and high temperature (estimated to be above 2,000 K) by direct reaction between nitrogen and KN3 in a laser-heated diamond anvil cell. The complex structure of K9N56—composed of 520 atoms per unit cell—was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. The observed hexazine anion [N6]4− is planar and proposed to be aromatic. Aromatic polynitrogen units can display both high stability and high energy content. A hexazine anion has now been identified in a complex compound, K9N56, which is formed at high pressures and temperatures under laser-heating in a diamond anvil cell. The [N6]4− ring is planar and proposed to be aromatic.

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