Pentazolate Salt Research Articles

Pentazolate Anion: A Rare and Preferred Five‐Membered Ligand for Constructing Pentasil‐Zeolite Topology Architectures

AbstractAs the fourth full‐nitrogen structure, the pentazolate anion (cyclo‐N5−) was highly coveted for decades. In 2017, the first air‐stable non‐metal pentazolate salt, (N5)6(H3O)3(NH4)4Cl, was obtained, representing a milestone in this field. As the latest member of the azole family, cyclo‐N5− is comprised of five nitrogen atoms. Although significant attention has been paid to the potential of cyclo‐N5− as an energetic material, its poor thermostability hinders any practical application. However, the unique ring structure and multiple coordination capability of cyclo‐N5− provide a platform for the fabrication of various structures, among which pentasil‐zeolite topologies are the most intriguing. In addition, the introduction of structure‐directing auxiliaries enables the self‐assembly of diverse topological architectures, potentially imparting cyclo‐N5− with the potential to impact wide‐ranging areas of coordination chemistry and topology. In this minireview, different pentasil‐zeolite topologies based on metal‐pentazolate frameworks are evaluated. To date, three zeolitic and zeolite‐like topologies have been reported, namely the melanophlogite (MEP), chibaite (MTN), and unj topologies. The MEP topology consists of two nanocages, Na20N60 and Na24N60, whereas the MTN topology contains Na20N60 and Na28N80 nanocages. Furthermore, the unj topology features multiple homochiral channels consisting of two helical chains. Various possible strategies for obtaining additional pentasil‐zeolite topologies are also discussed.

Pentazolate Anion: A Rare and Preferred Five-Membered Ligand for Constructing Pentasil-Zeolite Topology Architectures.

As the fourth full-nitrogen structure, the pentazolate anion (cyclo-N5 - ) was highly coveted for decades. In 2017, the first air-stable non-metal pentazolate salt, (N5 )6 (H3 O)3 (NH4 )4 Cl, was obtained, representing a milestone in this field. As the latest member of the azole family, cyclo-N5 - is comprised of five nitrogen atoms. Although significant attention has been paid to the potential of cyclo-N5 - as an energetic material, its poor thermostability hinders any practical application. However, the unique ring structure and multiple coordination capability of cyclo-N5 - provide a platform for the fabrication of various structures, among which pentasil-zeolite topologies are the most intriguing. In addition, the introduction of structure-directing auxiliaries enables the self-assembly of diverse topological architectures, potentially imparting cyclo-N5 - with the potential to impact wide-ranging areas of coordination chemistry and topology. In this minireview, different pentasil-zeolite topologies based on metal-pentazolate frameworks are evaluated. To date, three zeolitic and zeolite-like topologies have been reported, namely the melanophlogite (MEP), chibaite (MTN), and unj topologies. The MEP topology consists of two nanocages, Na20 N60 and Na24 N60 , whereas the MTN topology contains Na20 N60 and Na28 N80 nanocages. Furthermore, the unj topology features multiple homochiral channels consisting of two helical chains. Various possible strategies for obtaining additional pentasil-zeolite topologies are also discussed.

Syntheses, crystal structures, and energetic properties of four cyclo-pentazolate salts [NHn(CH3)4-n]+N5− (n = 0∼3)

The formation of non-metallic pentazolate salts from the combination of simple nitrogen-rich cations with cyclo-N5− is expected to be applied in propellants and explosives. In this work, a series of structurally similar cations ([NH3CH3]+, [NH2(CH3)2]+, [NH(CH3)3]+, and [N(CH3)4]+) were used to synthesize four cyclo-N5− containing energetic salts, and the contribution of crystal stacking mode, hydrogen bonding, C–H···π and π-stacking interactions in the stabilization of cyclo-N5− salts has been investigated by geometrical and Hirshfeld surface analyses as well as theoretical calculations. All salts have been thoroughly characterized by single-crystal X-ray diffraction, infrared (IR), multinuclear NMR (1H and 13C) spectroscopy, and elemental analysis. The decomposition temperatures of all salts are higher than 75 °C, as measured by thermogravimetric (TG). These compounds all show low sensitivities (IS ≥ 35 J, FS > 360 N) measured by standard BAM methods. Their heats of formation and detonation performances were calculated using the Born–Haber energy cycle and K-J method (“Pilem” program), respectively. This study has great significance for future design and synthesis of cyclo-N5− containing energetic materials.

Can cage-like cations function as antagonistic ions towards pentazolate anions?

In this work, we synthesized and studied two cyclo-N5− salts based on the cage-like cations. The results suggest that selecting cage-like cations as antagonistic ions to cyclo-N5− anions may be a better choice compared to the chain-like cations with similar structures.

Constructing layered structure amidine-based pentazolate salts with low sensitivity

A series of layered structure, low sensitivity cyclo-N5− salts based on amidine were synthesized.

A desirable coplanar energetic pentazolate salt driven by hydrogen bonds

A coplanar and insensitive energetic pentazolate salt was effectively synthesized from a twisted molecule by protonation and hydrogen bonding assembly.

A supramolecular self-assembly material based on cucurbituril and cationic TPE as ultra-sensitive probe of energetic pentazolate salts

The successful synthesis of the pentazolate anion (cyclo-N5−) has been a great breakthrough in the field of energetic materials. However, the detection methods for these energetic materials based on the pentazolate anion are quite rare. Herein, two fluorescent probes for cyclo-N5− anion were designed. Sensor 1 (TPE2N) was synthesized with a tetraphenylethylene functionalized by two cationic groups which can generate strong electrostatic interactions with pentazolate anion and result in specific fluorescent changes. Sensor 2 was designed based on sensor 1 and supramolecular cucurbit[7]uril (CB[7]). The unique structural features of CB[7] provide sites for the interaction between the cations and N5− anion in its cavity, which would generate a platform for the detection and enhance the recognition performance. Isothermal titration calorimetry (ITC) experiment and fluorescence titration experiment indicate the binding molar ratio between sensor 1 with CB[7] is 1:2. Both sensors display typical aggregation-induced emission (AIE) features and good water-solubility. The sensors demonstrate excellent sensitivity to pentazole hydrazine salt with high enhancement constant (sensor 1: 1.34 × 106; sensor 2: 3.78 × 106) and low limit of detection (LOD: sensor 1 = 4.33 μM; sensor 2 = 1.54 μM). The formation of an AIE-based supramolecular sensor effectively improves the sensitivity to N5− anion. In addition, the probes also have good selectivity of N5− anion salts. The research would shed some light on the design of novel fluorescent sensors to detect pentazolate-based molecules and provides an example of supramolecular chemistry combined with fluorescent probes.

Synthesis, characterization, and comparison of explosive hexaamminecobalt(III) and nitropentamminecobalt(III) cyclopentazolate (cyclo‐N5−) salts

AbstractMetal pentazolate hydrates have attracted attention because of the unique stabilization mechanisms of cyclo‐N5− anions during crystal stacking. However, coordinated H2O molecules influence the stability of cyclo‐N5− anion‐containing salts, and the structure‐property relationship of high‐valent cobalt pentazolate salts has not been previously reported. Werner‐type cobalt(III) cations that trap cyclo‐N5− anions, a novel class of cyclo‐N5−‐based materials, were prepared and characterized by infrared spectroscopy, elemental analysis, electrospray ionization mass spectrometry, and thermogravimetry with differential scanning calorimetry. The [Co(NH3)5(NO2)]2+ cation was also introduced via metathesis reactions to compare the intermolecular interactions in its intriguing structures. Single‐crystal X‐ray diffraction revealed extensive hydrogen bonding networks in hexaamminecobalt(III) and nitropentamminecobalt(III) cyclo‐N5− salts between cyclo‐N5− anions and NH3 ligands or nitro groups. In addition, [Co(NH3)6(N5)3] (1) and [Co(NH3)5(NO2)](N5)2 (2) exhibited relatively high nitrogen contents of 79.2 % and 67.9 %, respectively, and the impact sensitivities of 1 (IS=5 J) and 2 (IS=4 J) are comparable to that of lead azide.

Hexaamminecobalt(III) Cation as Multiple Hydrogen Bond Donors: Synthesis, Characterization and Energetic Properties of cyclo-Pentazolate and Azide Based Complexes

A series of hexaaminocobalt(III) based energetic compounds [Co(NH3)6](N3)3 (1), [Co(NH3)6](N5)2(N3) (2), [Co(NH3)6](N5)3 (3), and their chloride and nitrate complex salts 4–6 were designed and synthesized by simple metathesis reactions. As far as we know, compound 3 is the first trivalent metal pentazolate salt. The structures of all the new energetic compounds were confirmed by single-crystal X-ray diffraction. Their physicochemical and energetic properties, such as density, thermal stability, sensitivity, and detonation properties, were also evaluated. Due to the extensive hydrogen bonding network, the detonation properties of these salts and acceptable mechanical sensitivities (IS = 3–6 J, FS = 40–80 N) hold the prospective potential as green primary explosives. This work suggests that the cyclo-pentazolate anion has good compatibility with azide and nitrate ions, and they can act together as hydrogen bond acceptors to form novel energetic materials with controllable properties through hydrogen bonds.

Prediction of novel tetravalent metal pentazolate salts with anharmonic effect

In recent decades, pentazolate salts have gained considerable attention as high energy density materials (HEDMs). Using the machine-learning accelerated structure searching method, we predicted four pentazolate salts stabilized with tetravalent metals (Ti-N and Zr-N). Specifically, the ground state MN20 (M = Ti, Zr) adopts the space-group P4/mcc under ambient conditions, transforming into the I-4 phase at higher pressure. Moreover, the I-4-MN20 becomes energetically stable at moderate pressure (46.8 GPa for TiN20, 38.7 GPa for ZrN20). Anharmonic phonon spectrum calculations demonstrate the dynamic stabilities of these MN20 phases. Among them, the P4/mcc phase can be quenched to 0 GPa. Further ab-initio molecular dynamic simulations suggest that the N5 rings within these MN20 systems can still maintain integrity at finite temperatures. Calculations of the projected crystal orbital Hamilton population and reduced density gradient revealed their covalent and noncovalent interactions, respectively. The aromaticity of the N5 ring was investigated by molecular orbital theory. Finally, we predicted that these MN20 compounds have very high energy densities and exhibit good detonation velocities and pressures, compared to the HMX explosive. These calculations enrich the family of pentazolate compounds and may also guide future experiments.

5,6-Biheterocyclic pentazolate salts as promising energetic materials: a new design strategy

Pentazole ( cyclo -N 5 − ) energetic salts have always been of high research value in the energetic materials field. However, the low density of the available cyclo -N 5 − salt seriously affects its comprehensive performance. Therefore, it is of great significance to effectively design and screen out pentazole salts with excellent properties. In this work, a cation design strategy based on a 5,6-biheterocycle is proposed. Based on the predicted density, heat of formation and detonation properties, the nitrogen-rich bicyclic heterocycle with -N-O − bond and -NO 2 or -NHNO 2 substituent as a cation is an effective method to improve the comprehensive properties of cyclo -N 5 − salts, and four salts of F2 , G2 , H2 and H7 with superior comprehensive properties to RDX were selected. Monte Carlo method was used to predict the stable crystal structure of four salts. Atoms in molecules theory (AIM) was used to expound the contribution of hydrogen bond and π-π superposition to the stability of cyclo -N 5 − . The cohesive energy density and mechanical properties show that the thermal stability of H2 (with best detonation performance; D : 9.16 km s −1 , P : 38.52 GPa) is similar to 3,6,7-triamino-7 H -[1,2,4]triazolo[4,3-b][1,2,4]triazol-2-ium pentazolate (decomposition temperature: 394.1 K, impact sensitivity: greater than 40 J). First-principles molecular dynamics simulation for H2 thermal decomposition was performed to explore the underlying mechanism of its excellent detonation performance. This work is expected to provide inspiration for the design and synthesis of cyclo -N 5 − salts.

Effect of Hydrogen Bond Interaction on the Decomposition Temperature, Aromaticity, and Bond Order of Nonmetallic Pentazolate Salts

Effect of Hydrogen Bond Interaction on the Decomposition Temperature, Aromaticity, and Bond Order of Nonmetallic Pentazolate Salts

Nitrogen-rich polycyclic pentazolate salts as promising energetic materials: theoretical investigating.

Pentazolate (cyclo-N5-) salts are nitrogen-rich compounds with great development potential as energetic materials due to their full nitrogen anion. However, the densities of available N5- salts are generally low, which seriously lowers their performances. It is necessary to screen out cyclo-N5- salts with high density. To this end, eight new non-metallic cyclo-N5- salts based on fused heterocycle were designed. -NH2, -NO2, and -O- groups were introduced into the compounds to adjust and improve the detonation performance and impact sensitivity of cyclo-N5- salts. By theoretical calculations and Hirshfeld surface analyses, the densities, heats of formation, detonation performance, sensitivities, and crystal structures of the title compounds were predicted, and the contribution of hydrogen bond as well as π-π stacking to the stability of cyclo-N5- salt was revealed. The results indicate that the densities of title compounds are higher than 1.85gcm‒3, and the sensitivities of these compounds are predicted to be lower than that of HMX. The detonation properties of a (D = 9.47kms-1, P = 41.21 GPa) and d (D = 9.44kms-1, P = 40.26 GPa) are better than those of HMX. These mean that using fused ring as a cation and introducing proper substituents are an effective method to improve cyclo-N5- salt's density and balance thedetonation performance and sensitivity.

Predicted Pressure-Induced High-Energy-Density Iron Pentazolate Salts

Metal-pentazolate compounds as candidates for novel high-energy-density materials have attracted extensive attention in recent years. However, dehydrated pentazolate salts of transition metal iron are rarely reported. We predict two new iron pentazolate salts Fdd2-FeN10 and (No.1)-FeN10 using a constrained crystal search method based on first-principles calculations. We propose that the stable Fdd2-FeN10 crystal may be synthesized from FeN and N2 above 20 GPa, and its formation enthalpy is lower than the reported iron pentazolate salt (marked as (No.2)-FeN10). Crystal (No.1)-FeN10 is composed of iron bispentazole molecules. Formation enthalpy, phonon spectrum and ab initio molecular dynamics calculations are performed to show their thermodynamic, mechanical and dynamic properties. Moreover, the high energy density (3.709 kJ/g, 6.349 kJ/g) and good explosive performance indicate their potential applications as high-energy-density materials.

A hybrid of tetrazolium and pentazolate: An energetic salt with ultrahigh nitrogen content and energy

As a full nitrogen energetic anion, pentazolate (cyclo-N5ˉ) holds great promise in the fields of propellants and explosives. Nowadays, nonmetallic pentazolate salts have received extensive attention as excellent nitrogen-rich energetic materials for their high enthalpies of formation, good oxygen balance, and eco-friendly decomposition products. In this study, a 1,4,5-triaminotetrazolium-based pentazolate salt (TATe+N5ˉ, 8) with a nitrogen content of up to 90.30% was designed and synthesized. Its crystal structure indicates that a large number of hydrogen bonds form a hydrogen-bonded network, and the crystal has a mixed stacking pattern. TATe+N5ˉ, which has a relatively high density (1.64 ​g·cm−3), high heat of formation (861.9 ​kJ·mol−1), and excellent detonation performances (detonation velocity: 9487 ​m·s−1, detonation pressure: 32.5 ​GPa), provides new insights into the stability of ultrahigh-nitrogen compounds.

Synthesis and characterization of cyclo-pentazolate salts of iron(iii) and aluminum(iii)

Two trivalent metal pentazolate salts, namely, Fe(H2O)6(N5)3·9H2O (1) and Al(H2O)6(N5)3·9H2O (2) are prepared, and the coordination environment of the cyclo-N5− anions is discussed in detail.

Pressure-induced phase transition of a series of energetic pentazolate anion salts: a DFT study

The distortion angles of two energetic pentazolate salts (N5−)2DABTT2+ and N5−GU+.

Synthesis and characterization of the layered insensitive pentazolate salts based on two triazolium isomers

The all-nitrogen cyclo-pentazolate (c-N5ˉ) anion has attracted interest because of its promising application in high-energy materials. Now, nonmetallic pentazolate salts were prepared by assembling cyclo-N5ˉ and cations but it was shown to be challenging to balance excellent detonation performance and good stability, which results in restrictions for practical applications. However, we find the layer-by-layer crystal stacking structure can enhance the sensitivity of pentazolate salts. Herein, we designed and synthesized two targeted cyclo-pentazolate salts with layered stacking mode in their crystal structures based on two isomeric cations: 3,4,5-triamino-1,2,4-triazolium and 3-hydrazino-4-amino-1,2,4-triazolium. The results demonstrate that the aromaticity of triazole and pentazole rings arouse the π−π interaction force, promoting the formation of a layer-by-layer crystal stacking structure. Two compounds show very low sensitivity characteristics (FS>40 and IS>360) and good detonation properties (detonation velocity: 3, Dv= 8796m⋅s−1; 4, Dv=8574m⋅s−1. detonation pressure: 3, P = 26.6 GPa; 4, P = 25.1 GPa). Computational analysis based on noncovalent interaction index, localized orbital locator-π and electron density difference provide a better understanding about the effects of layer-by-layer stacking structure on the stabilities. These findings contribute to preparation of both high-energy and low sensitivity pentazolate salts.

LiN5: A novel pentazolate salt with high nitrogen content

A high energy cyclo-pentazolate (cyclo-N5−) salt with 90.98 % nitrogen content, LiN5, was synthesized by a simple metathesis reaction of AgN5 and LiCl in deionized water. It was characterized by 15N nuclear magnetic resonance, infrared and Raman spectroscopy, elemental analysis, thermogravimetry-mass (TG-MS) spectrometry, and differential scanning calorimetry. Besides, its trihydrate (LiN5·3H2O) and anhydrous zeolitic architecture (LPF, lithium-pentazolate framework) structures were confirmed by single-crystal X-ray diffraction. LiN5 achieved stability in air and under ambient conditions. It starts to decompose when heated to 133 °C (onset) under Ar2 flow. Its relatively high density (1.75 g cm−3), impact and friction sensitivity (IS = 3 J; FS = 20 N), and calculated high heat of formation (3.44 kJ g−1), combined with its theorical superior detonation velocity and pressure (D = 11362 m s−1, P = 40.9 GPa), endow LiN5 with potential as an environmentally primary explosive.

Syntheses and Characterization of two cyclo‐pentazolate salts

AbstractTwo energetic salts of cyclo‐N5−, O‐methylisoure pentazolate (1) and guanidinoacetic acid pentazolate (2), were synthesized by metathesis reaction. All the energetic cyclo‐N5− salts were characterized by single‐crystal XRD, IR spectroscopy, 1H and 13C multinuclear NMR spectroscopy, thermal analysis (DSC) and elemental analysis. They exhibit good thermal stability with decomposition temperatures of more than 100 °C and they are in excellent agreement with those reported non‐metallic salts. Salt 1 also exhibits strong π‐π interactions. The standard enthalpies of formation and detonation performances of these salts were calculated using Gaussian 09 and EXPLO5 v6.01 programs. The detonation velocities of compound 1 and 2 are both about 7400 m s−1 and these two salts exhibit low mechanical sensitivity (IS>23 J, FS>220 N). Therefore, in this work, the synthesis of the new pentazolate salts enriches the cyclo‐pentazolate salts system, which is conducive to the exploration of more heat‐resistant and higher detonation velocities pentazolate salts.