Manganese(II)-Porphyrin and Cumyl Hydroperoxide: An Efficient Catalyst for Aryl-Pentazole C-N Bond Cleavage.

The selective cleavage of C-N bonds in N-containing compounds holds significant research value in organic synthesis, particularly for the synthesis of promising polynitrogen species. For instance, the discovery of the cyclo-pentazolate (cyclo-N5-) anion in 2017 as a result of cleavage of the C-N bond has sparked interest within the field of high energy density materials. However, previous methods using ferrous glycinate and m-chloroperoxybenzoic acid generated the cyclo-N5- anion in a low yield of 19.5% after 24 hours, and the mechanism remained unclear. In this study, we developed an efficient catalytic system comprising Mn (II) tetraphenylporphyrin and cumyl hydroperoxide. This system enables the cyclo-N5- anion to be produced from 3,5-dimethyl-4-hydroxyphenylpentazole in 35.4% yield in 4 hours. Characterization of Mn(IV)-oxo porphyrins, •CH3, and •C8H8ON5 radicals provides evidence for the mechanism whereby the cyclo-N5- anion forms. Our study underscores the competitive potential of radical-initiated selective C-N bonds cleavage in N-arylazoles and opens avenues for further exploration in this field.

2D Microporous Polymers/Reduced Graphene Oxide with Built-In Lithiophilic Sites for Uniform Lithium Deposition in Lithium Metal Anode.

Lithium (Li) metal is an attractive anode material for use in high-energy lithium-sulfur and lithium-air batteries. However, its practical application is severely impeded by excessive dendrite growth, huge volume changes, and severe side reactions. Herein, a novel Li metal anode composed of lithiophilic two dimensional (2D) conjugated microporous polymer (Li-CMP) and reduced graphene oxide (rGO) sandwiches (Li-CMP@rGO) for Li metal batteries (LiMBs) is reported. In the Li-CMP@rGO anode, the conductive rGO facilitates the charge transfer while the functionalized-CMP provides Li nucleation sites within the micropores, thereby preventing dendrite growth. As a result, the Li-CMP@rGO anode can be cycled smoothly at 6 mA cm-2 of current density with a platting capacity of 2 mAh cm-2 for 1000 h. A Coulombic efficiency of 98.4% is achieved over 350 cycles with a low overpotential of 28 mV. In a full cell with LiFePO4 cathode, the Li-CMP@rGO anode also exhibited good cycling stability compared to CMP@rGO and CMP/Super-P. As expected, the simulation results reveal that Li-CMP@rGO has a strong affinity for Li ions compared to CMP@rGO. The strategies adopted in this work can open new avenues for designing hybrid porous host materials for developing safe and stable Li metal anodes.

Enhanced stability and kinetic performance of sandwich Si anode constructed by carbon nanotube and silicon carbide for lithium-ion battery.

Owing to highly theoretical capacity of 3579 mAh/g for lithium-ion storage at ambient temperature, silicon (Si) becomes a promising anode material of high-performance lithium-ion batteries (LIBs). However, the large volume change (∼300 %) during lithiation/delithiation and low conductivity of Si are challenging the commercial developments of LIBs with Si anode. Herein, a sandwich structure anode that Si nanoparticles sandwiched between carbon nanotube (CNT) and silicon carbide (SiC) has been successfully constructed by acetylene chemical vapor deposition and magnesiothermic reduction reaction technology. The SiC acts as a stiff layer to inhibit the volumetric stress from Si and the inner graphited CNT plays as the matrix to cushion the volumetric stress and as the conductor to transfer electrons. Moreover, the combination of SiC and CNT can relax the surface stress of carbonaceous interface to synergistically prevent the integrated structure from the degradation to avoid the solid electrolyte interface (SEI) reorganization. In addition, the SiC (111) surface has a strong ability to adsorb fluoroethylene carbonate molecule to further stabilize the SEI. Consequently, the CNT/SiNPs/SiC anode can stably supply the capacity of 1127.2 mAh/g at 0.5 A/g with a 95.6 % capacity retention rate after 200 cycles and an excellent rate capability of 745.5 mAh/g at 4.0 A/g and 85.5 % capacity retention rate after 1000 cycles. The present study could give a guide to develop the functional Si anode through designing a multi-interface with heterostructures.

Optimizing the intermediates adsorbability and revealing the dynamic reconstruction of Co6Fe3S8 solid solution for bifunctional water splitting.

Co9S8 has been extensively studied as a promising catalyst for water electrolysis. Doping Co9S8 with Fe improves its oxygen evolution reaction (OER) performance by regulating the catalyst self-reconfigurability and enhancing the absorption capacity of OER intermediates. However, the poor alkaline hydrogen evolution reaction (HER) properties of Co9S8 limit its application in bifunctional water splitting. Herein, we combined Fe doping and sulfur vacancy engineering to synergistically enhance the bifunctional water-splitting performance of Co9S8. The as-synthesized Co6Fe3S8 catalyst exhibited excellent OER and HER characteristics with low overpotentials of 250 and 84 mV, respectively. It also resulted in the low Tafel slopes of 135 mV dec-1 for the OER and 114 mV dec-1 for the HER. A two-electrode electrolytic cell with Co6Fe3S8 used as both the cathode and anode produced a current density of 10 mA cm-2 at a low voltage of only 1.48 V, maintaining high stability for 100 h. The results of in/ex-situ experiments indicated that the OER process induced electrochemical reconfiguration, forming CoOOH/FeOOH active species on the catalyst surface to enhance its OER performance. Density functional theory (DFT) simulations revealed that Fe doping and the presence of unsaturated coordination metal sites in Co6Fe3S8 promoted H2O and H* adsorption for the HER. The findings of this study can help develop a strategy for designing highly efficient bifunctional water splitting electrocatalysts.

Construction of a conjugated covalent organic framework for iodine capture.

Radioactive iodine in the nuclear field is considered very dangerous nuclear waste because of its chemical toxicity, high mobility and long radioactive half-life. Herein, a conjugated two-dimensional covalent organic framework, TPB-TMPD-COF, has been designed and synthesized for iodine capture. TPB-TMPD-COF has been well characterized by several techniques and showed long order structure and a large surface area (1090 m2 g-1). Moreover, TPB-TMPD-COF shows a high iodine capture value at 4.75 g g-1 under 350 K and normal pressure conditions, benefitting from the increased density of adsorption sites. By using multiple techniques, the iodine vapor adsorbed into the pores may readily generate the electron transfer species (I3- and I5-) due to the strong interactions between imine groups and iodine molecules, which contributes to the high iodine uptake for TPB-TMPD-COF. Our study will stimulate the design and synthesis of COFs as a solid-phase adsorbent for iodine uptake.

Phenolylazoindole scaffold for facilely synthesized and bis-functional photoswitches combining controllable fluorescence and antifungal properties using theoretical methods.

Functionalization is a major challenge for the application of photoswitches. With the aim to develop novel bis-functional azo photoswitches with stationary photophysical properties, a series of phenolylazoindole derivatives were designed, synthesized, and characterized via NMR spectroscopy studies and high-resolution mass spectrometry (HRMS). Herein, UV/Vis and 1H NMR spectra revealed that the photostationary state (PSS) proportions for PSScis and PSStrans were 76-80% and 68-81%, respectively. Furthermore, the thermal half-lives (t1/2) of compounds A2-A4 and B2 ranged from 0.9 to 5.3 h, affected by the diverse substituents at the R1 and R2 positions. The results indicated that azo photoswitches based on the phenolylazoindole scaffold had stationary photophysical properties and wouldn't be excessively affected by modifying the functional groups. Compounds A4 and B2, which were modified with an aryl group, also exhibited fluorescence emission properties (the quantum yields of A4 and B2 were 2.32% and 13.34%) through the modification of the flexible conjugated structure (benzene) at the R2 position. Significantly, compound C1 was obtained via modification with a pharmacophore in order to acquire antifungal activities against three plant fungi, Rhizoctonia solani (R. solani), Botrytis cinerea (B. cinerea), and Fusarium graminearum (F. graminearum). Strikingly, the inhibitory activity of the cis-isomer of compound C1towards R. solani (53.3%) was significantly better than that of the trans-isomer (34.2%) at 50 µg mL-1. In order to further reveal the antifungal mechanism, molecular docking simulations demonstrated that compound C1 effectively integrates into the cavity of succinate dehydrogenase (SDH); the optically controlled cis-isomer showed a lower binding energy with SDH than that of the trans-isomer. This research confirmed that phenolylazoindole photoswitches can be appropriately applied as molecular regulatory devices and functional photoswitch molecules via bis-functionalization.

Synthesis mechanism of four metallic Cyclo-N5- energetic materials: A theoretical Perspective.

In the past five years, over 20 types of cyclo-N5- energetic materials (EMs) have been successfully synthesized. Metallic cyclo-N5- EMs exhibit higher density and performance compared to non-metallic cyclo-N5- EMs. However, the mechanisms for such metallic cyclo-N5- EMs remain unexplored. Herein, we performed a thorough quantum chemistry study on the mechanistic pathway for the cyclo-N5- trapped by metal cations in four cyclo-N5- EMs: [Na(H2O) (N5)] · 2H2O, [M(H2O)4(N5)2] · 4H2O (M = Mn, Fe, and Co), by density functional theory methods and transition state theory. During the synthesis process, the cyclo-N5- in the precursor hybrid aromatic compound is susceptible to electrophilic attack by metal cations. This attack disrupts the hydrogen bond interaction surrounding the cyclo-N5-, ultimately leading to the formation of either an ionic bond or a coordination bond between the metal cation and the cyclo-N5-, resulting in an electrophilic substitution reaction. In addition, solvent effects reduce the energy of the ionic bond, thereby promoting the reaction. Our findings will provide valuable insights for future route design and contribute to enhancing the synthesis yield of cyclo-N5- EMs in both theoretical and experimental aspects.

In situ preparation of double gradient anode materials based on polysiloxane for lithium-ion batteries.

Although silicon has a high volumetric energy density as an anode material for Li-ion batteries, its volumetric expansion and sluggish Li+ migration kinetics need to be urgently addressed. In this work, cage-like structure materials (HRPOSS) derived from the in situ hydrogen reduction of polyhedral oligomeric silsesquioxane (T8-type POSS) were constructed as an Si@C anode for Li-ion batteries. Benefiting from the intriguing features of the Si/N double gradient and even-distributed silicon, HRPOSS-6 exhibited faint volume changes and fast ion-electron kinetics. Moreover, the uniformly immobilized nano-silicic and concentration gradient were favorable for accelerated ion migration. Therefore, HRPOSS-6 exhibited good electrochemical performances given that its cage structure could relieve the volume expansion. HRPOSS-6 demonstrated a high reversible capacity of 1814.1 mA h g-1 and long cycling performance after 200 cycles with 635 mA h g-1 at a current density of 0.5 A g-1. Accordingly, this Si/C/N composite exhibited great potential for high energy Li-ion batteries, where the corresponding full-cell (HRPOSS-6//LiNi0.6Co0.2Mn0.2O2) showed a cycle life of 200 cycles with over 80% capacity retention at rate of 1C. This work exploits the concentration gradients of dual elements for the capacity improvement of Si anodes and offers insight into the development of high-performance Si@C anode materials for advanced Li-ion batteries.

Enhancing the Iodine Adsorption Capacity of Pyrene-Based Covalent Organic Frameworks by Regulating the Pore Environment.

Regulating of pore environment is an efficient way to improve the performance of covalent organic frameworks (COFs) for specific application requirements. Herein, the design and synthesis of two pyrene-based 2D COFs with -H or -Me substituents, TFFPy-PPD-COF and TFFPy-TMPD-COF are reported. Both of them show long order structure and high porosity, in which TFFPy-PPD-COF displays a larger pore volume and bigger BET surface area (2587 m2 g-1 , 1.17 cm3 g-1 ). Interestingly, TFPPy-TMPD-COF exhibits a much higher vapor iodine capacity (4.8 g g-1 ) than TFPPy-PPD-COF (2.9 g g-1 ), in contrast to their pore volume size. By using multiple techniques, the better performance of TFPPy-TMPD-COF in iodine capture is ascribed to the altered pore environment by introducing methyl groups, which contributes to the formation of polyiodide anions and enhances the interactions between the frameworks and iodine. These results will be helpful for understanding the effect of pore environment in COFs for iodine uptake and constructing novel structure with high iodine capture performance.

Novel salicylic acid derivatives connecting to five-membered cycle through an acyl hydrazone bond as multi-stimuli responsive fluorescent smart materials with photoswitching properties.

In order to exploit novel multi-stimuli responsive fluorescent materials, a series of novel fluorescent molecules of salicylic acid derivatives were designed and synthesized via introducing pyrazole or cyclopentane to the salicylic acid scaffold through a special Schiff base-acylhydrazone, and the molecular structures of representative compounds A2 and A4 were verified via single crystal X-ray diffraction. All title molecules could exhibit obvious solvatofluorochromism from cyan to indigo in several solutions with different polarity. The fluorescence titration data exhibited compound A2 and complex A2-Cu2+ with prime detection limits to Cu2+ (0.24 µM) and S2- ions (2.83 µM). The sensitive recognition of A2 to trifluoroacetic (TFA) and A2-TFA to triethylamine (TEA) were also confirmed via fluorescent titration experiments in various solutions, respectively. What's more, the 1H NMR and UV/Vis absorption spectra further explained the mechanism between molecules and ions or molecules and TFA/TEA. Besides, the photoswitching properties of the compounds A2 and A3 could be demonstrated via the irradiation of special wavelength light or heating accompanied with changes in quantum yields. In addition, these phenomena of multiple responses were explained via Density Functional Theory (DFT) based on the Gaussian calculations. Thus, this work provided a preliminary basis for the research of multi-stimuli responsive fluorescent molecules with photoswitching properties.

Thermal Decomposition Assisted Construction of Nano-Li3 N Sites Interface Layer Enabling Homogeneous Li Deposition.

Lithium (Li) metal is a highly desirable anode for all-solid-state lithium-ion batteries (ASSLBs) due to its high theoretical capacity and being well matched with solid-state electrolytes. However, the practical applications of Li metal anode are hindered by the uneven Li metal plating/stripping behavior and poor contact between electrolyte and Li anode. Herein, a convenient and efficient strategy to construct the Li3 N-based interlayer between solid poly(ethylene oxide) (PEO) electrolyte and Li anode is proposed by in situ thermal decomposition of 2,2'-azobisisobutyronitrile (AIBN) additive. The evolved Li3 N nanoparticles are capable of combining LiF, cyano derivatives and PEO electrolyte to form a buffer layer of about 0.9 µm during the cell cycle, which can buffer Li+ concentration and homogenize Li deposition. The Li||Li symmetric cells with Li3 N-based interlayer show excellent cycle stability at 0.2 mA cm-2 , which is at least 4 times longer cycle life than that of PEO electrolytes without Li3 N layer. This work provides a convenient strategy for designing interface engineering between solid-state polymer electrolyte and Li anode.

A rational design of titanium-based heterostructures as electrocatalyst for boosted conversion kinetics of polysulfides in Li-S batteries.

Lithium-sulfur batteries have great potential for next-generation electrochemical storage systems owing to their high theoretical specific energy and cost-effectiveness. However, the shuttle effect of soluble polysulfides and sluggish multi-electron sulfur redox reactions has severely impeded the implementation of lithium-sulfur batteries. Herein, we prepared a new type of Ti3C2-TiO2 heterostructure sandwich nanosheet confined within polydopamine derived N-doped porous carbon. The highly polar heterostructures sandwich nanosheet with a high specific surface area can strongly absorb polysulfides, restraining their outward diffusion into the electrolyte. Abundant boundary defects constructed by new types of heterostructures reduce the overpotential of nucleation and improve the nucleation/conversion redox kinetics of Li2S. The Ti3C2-TiO2@NC/S cathode exhibited discharge capacities of 1363, and 801 mAh g-1 at the first and 100th cycles at 0.5C, respectively, and retained an ultralow capacity fade rate of 0.076% per cycle over 500cycles at 1.0C. This study provides a potential avenue for constructing heterostructure materials for electrochemical energy storage and catalysis.

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 1.85 g cm‒3, and the sensitivities of these compounds are predicted to be lower than that of HMX. The detonation properties of a (D = 9.47 km s-1, P = 41.21 GPa) and d (D = 9.44 km s-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 the detonation performance and sensitivity.

Hydrogen Bond and π-π Stacking Interaction: Stabilization Mechanism of Two Metal Cyclo-N5 --Containing Energetic Materials.

In recent years, cyclo-N5 - has attracted extensive attention because all-nitrogen high-energy-density materials (HEDMs) have been expected to reach a TNT equivalent of over 3.0. However, for cyclo-N5 --containing HEDMs, the stabilization mechanism has remained enigmatic. In this study, two typical cyclo-N5 --containing metal hydrates, [Na(H2O)(N5)]·2H2O (Na-cyclo-N5 -) and [Mg(H2O)6(N5)2]·4H2O (Mg-cyclo-N5 -), are selected to gain insights into the factors affecting their stability by the first-principles method. Both binding/lattice energy calculations and density of states analysis show that Mg-cyclo-N5 - is more stable than Na-cyclo-N5 -. Hydrogen bonding is the main stabilization mechanism for stabilizing crystals and cyclo-N5 -. Two types of hydrogen bonds, O-H···O and O-H···N, are clarified, which construct a 3D hydrogen bond network in Mg-cyclo-N5 - and an intralayer 2D hydrogen bond network in Na-cyclo-N5 -. Moreover, nonuniform stress causes distortion of cyclo-N5 -. Comparing the two samples, the distortion degree of cyclo-N5 - is higher in Na-cyclo-N5 -, which indicates that cyclo-N5 - decomposition is easier. These findings will enhance the future prospects for the design and synthesis of cyclo-N5 --containing HEDMs.

Symmetrical cyclo-N5- hydrogen bonds: stabilization mechanism of four non-metallic cyclo-pentazolate energetic salts.

Pairing different cations (R+) to stabilize cyclo-N5- is the main synthesis path for non-metallic cyclo-pentazolate (cyclo-N5-) salts. As novel energetic materials (EMs), crystalline packing-force of cyclo-N5- salts has been a puzzle, and whether cyclo-N5- is protonated also is a controversial issue. In this paper, four non-metallic cyclo-N5- salts, PHAC, N2H5N5, NH3OHN5, and NH4N5, are quantitatively studied by coupling first-principle method and bond-strength analyzing technology. Different from the traditional CHON-EMs (molecular crystal) and azide-EMs (ionic crystal), the four salts are stabilized by 3D hydrogen bond (HB) networks. One new type of hydrogen bond, protonated HB (p-H, R-H⋯N5-), is discovered to be a key stabilizing factor for cyclo-N5-. Proton competition mechanism between R and cyclo-N5- in p-H HB showed that cyclo-N5- cannot be protonated into HN5. In general, p-H HB can be adopted to estimate the stability of novel non-metallic cyclo-N5- EMs. Such findings have great significance for future design and performance prediction of novel cyclo-N5- EMs in both theoretical and experimental aspects.

Double Ionic-Electronic Transfer Interface Layers for All-Solid-State Lithium Batteries.

Large-scale implementation of all-solid-state lithium batteries is impeded by the physical limitations of the interface between the electrode and solid electrolyte; specifically, high resistance and poor stability, as well as poor compatibility with Li+ migration. We report double ionic-electronic transfer interface layers grown at electrode-electrolyte interfaces by in situ polymerization of 2,2'-bithiophene in polyethylene oxide (PEO) electrolyte. For all-solid-state LiFePO4 ∥PT-PEO-PT∥Li cells, the formation of a conductive polythiophene (PT) layer at the cathode-electrolyte interface resulted in an at least sevenfold decrease in interface resistance, and realized a capacity retention of about 94 % after 1000 cycles along with a lower polarization voltage under a rate of 2 C. The mixed ionic-electronic conductive layers imparted superior interface stability and contact while keeping good compatibility with the Li anode.

Metallo-deuteroporphyrins derived multi-layered hollow carbon spheres electrocatalysts for highly efficient oxygen reduction reaction.

The development of low-cost, highly efficient and stable non-precious metal electrocatalyst for the oxygen reduction reaction (ORR) substituting Pt has attracted much attention. Herein, we developed a promising structural platform for the fabrication of carbon nanospheres functionalized with hollow nanostructures of M-NHCS (M = Fe, Co and Mn) based on metallo-deuteroporphyrins (MDP). Benefited from the multi-layered active sites and hollow substrate with more exposed active surface area, convenient channels for the transport of electrons, the resulting Fe-NHCS electrocatalysts exhibit enhanced electrocatalytic performance in ORR with an onset potential of 0.90 V (versus RHE), and a high selectivity in the direct 4-electron pathway. The Fe-NHCS electrocatalysts also show a good methanol tolerance superior to Pt/C catalysts and an extremely high stability with only 13.0 mV negative after 5000 cycles in alkaline media. Experiments have verified that maintaining the multi-layered Fe-N-C active sites and hollow substrate were essential to deliver the high performance for ORR. The work opens new avenues for utilizing MDP-based materials in future energy conversion applications.

Insights into the deposition chemistry of Li ions in nonaqueous electrolyte for stable Li anodes.

Lithium (Li) is the lightest and most electronegative metallic element and has been considered the ultimate anode choice for energy storage systems with high energy density. However, uncontrollable dendrite formation caused by high ion transfer resistance and low Li atom diffusion, and dendrite growth with large volume expansion and high electronegative activity, result in severe safety concerns and poor coulombic efficiency. In this review, the latest progress is presented from the viewpoint of dendrite evolution (from dendrite formation to growth) as the main line to understand the factors that influence the deposition chemistry. For the dendrite formation, specific attention is focused on the four distinct but interdependent factors: (a) how the dielectric constant, donor number, viscosity and salt concentration affect the movement of solvated Li+ in nonaqueous electrolyte. (b) The effect of non-polar solvents and anions with polar groups or high concentration on the Li+ desolvation step. (c) The effect of the formation of solid electrolyte interphase (SEI), along with its specific adsorption and solvated structure, and its physical structure, chemical composition and growth thickness on Li+ diffusion. (d) The effect of the diffusion coefficient of the host material on Li atom migration. After dendrite formation, the attention is focused on two detrimental factors together with dendrite growth: (e) low coulombic efficiency; (f) large volume expansion. Correspondingly, the emphasis is placed on reducing the side reactions and minimizing the volume expansion. Conclusions and perspectives on the current limitations and future research directions are recommended. It is anticipated that the dynamic dendrite evolution can provide fresh insight into similar electrochemical reaction processes of other anode chemistries in nonaqueous electrolytes, ranging from a conversion-reaction metal anode (Li, Na, Al) and an alloying anode (LiAlx, NaAlx) to an intercalation-based anode (graphite, TiS2), as well as aqueous, ionic liquid and flow redox battery systems.

Key Aspects of Lithium Metal Anodes for Lithium Metal Batteries.

Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel-based energy technologies. High-energy lithium-metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology-based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.

Synthesis and Characterization of cyclo-Pentazolate Salts of NH4+, NH3OH+, N2H5+, C(NH2)3+, and N(CH3)4.

A breakthrough in polynitrogen chemistry was recently achieved by our bulk synthesis of (N5)6(H3O)3(NH4)4Cl in which the cyclo-pentazolate anions were stabilized extensively by hydrogen bridges with the NH4+ and OH3+ cations. Significant efforts have been carried out to replace these nonenergetic cations and the Cl- anion by more energetic cations. In this paper, the metathetical syntheses of cyclo-pentazolate salts containing the simple nitrogen-rich cations NH4+, NH3OH+, N2H5+, C(NH2)3+, and N(CH3)4+ are reported. These salts were characterized by their crystal structures; vibrational, mass, and multinuclear NMR spectra; thermal stability measurements; sensitivity data; and performance calculations. It is shown that the cyclo-pentazolates are more energetic than the corresponding azides but are thermally less stable decomposing in the range of 80 °C to 105 °C. As explosives, the hydrazinium and hydroxyl ammonium salts are predicted to match the detonation pressure of RDX but exhibit significantly higher detonation velocities than RDX and HMX with comparable impact and friction sensitivities. Although the ammonium salt has a lower detonation pressure than RDX, its detonation velocity also exceeds those of RDX and HMX. As a rocket propellant, the hydrazinium and hydroxyl ammonium salts are predicted to exceed the performances of RDX and HMX. The crystal structures show that the cyclo-pentazolate anions are generally stabilized by hydrogen bonds to the cations, except for the N(CH3)4+ salt which also exhibits strong cation-π interactions. This difference in the anion stabilization is also detectable in the vibrational spectra which show for the N(CH3)4+ salt a decrease in the cyclo-N5- stretching vibrations of about 20 cm-1.