Oxygen Atoms Research Articles

Lattice dynamics and vibrational properties of scheelite-type alkali-metal perrhenates

The present work provides insight into the structural, vibrational, and elastic properties of scheelite-type alkali-metal perrhenates AReO4(A= Na, K, Rb, and Cs) via first-principles calculations. Sodium, potassium, and rubidium perrhenates are isostructural and crystallize in a tetragonal structure, whereas cesium perrhenate crystallizes in an orthorhombic structure. All the phonon frequencies and their corresponding mode assignments were estimated through the linear response method within density-functional-perturbation theory. The phonon density of states highlights the participation of the oxygen anions and both the A-type and rhenium (Re) cations in the low-frequency range. In contrast, the oxygen and Re atoms make relatively high and moderate contributions to the remaining phonon frequency spectrum. Considerable splitting of the longitudinal and traverse optic modes was observed. Elastic constants and phonon dispersion calculations confirmed the mechanical and dynamic stability of the studied AReO4compounds. A redshift was observed with the frequency of the phonons following the sequence Na→Cs. The low value calculated for the bulk modulus (ranging from 28.36 GPa to 14.15 GPa) and shear modulus indicates the perrhenates have a low resistance to deformation. The values of these moduli decrease in the order of Na→Cs, which correlates with an increase in an ionic radius of the cation. The response to pressure was found to be anisotropic. This characteristic and the ductile nature of the alkali-metal perrhenates were confirmed through elastic analysis.

Attosecond impulsive stimulated X-ray Raman scattering in liquid water.

We report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket in water molecules. The process comprises two steps: a transition to core-excited states near the oxygen atoms accompanied by transition to valence-excited states. Thus, the wavepacket is impulsively created at a specific atomic site within a few hundred attoseconds through a nonlinear interaction between the water and the x-ray pulse. We observe this nonlinear signature in an intensity-dependent Stokes Raman sideband at 526 eV. Our measurements are supported by our state-of-the-art calculations based on the polarization response of water dimers in bulk solvation and propagation of attosecond x-ray pulses at liquid density.

The structural and electronic configuration of an amorphous silica surface, from its liquid to glassy state

Through classical molecular dynamics computational simulations, the surface of amorphous silica (vitreous silica) was generated for a system comprising 64 SiO2 molecules (192 atoms) via the classical three-body glass potential. Starting from the liquid state of silica at 3400 K, it was cooled in three different ways at intervals of 200, 400, and 2000 K, with a cooling rate of 4.4 K/ps and establishing relaxation at intermediate temperatures, yielding three groups of surfaces from 3400 to 1400 K. Subsequently, these systems underwent sudden cooling from 1400 to 300 K via the Andersen and Nosé‒Hoover thermostats, followed by relaxation at 300 K via a microcanonical ensemble (NVE constant). Each surface that underwent relaxation was analyzed through ab initio molecular dynamics for the following three physical properties, which are temperature dependent. The average electric charges of oxygen and silicon. Microstructures on the outermost part of the surface were observed and comprised nonbridging oxygen atoms, undercoordinated silicon, and N-membered rings (3 ≤ N ≤ 5). The radial distribution functions were analyzed for all surfaces. Below 2000 K, a type of freezing is observed in all the structures because of the glass transition. All analyses were performed at zero pressure.

Synthesis and characterizations of a novel trans-Pd(O,N)2 complex with an AZO-dye ligand: Crystal structure, theoretical studies and DNA binding interactions

The transition metal-azo dye complexes have attracted attention in both fundamental and applied research due to their electronic and structural properties, particularly due to their potential to yield new compounds with diverse biological activities and anticancer agents. A novel square planar-trans-Pd(O,N)2 was synthesized with a high yield utilizing a one-pot approach employing (E)-methyl 2-((2-hydroxynaphthalen-1-yl)diazenyl)benzoate as the AZO-dye ligand. In order to analyze their structure and understand their properties. The desired complex was characterized using FT-IR, UV–Vis, NMR, and CHN-EA techniques. Subsequently, theoretical modeling of the complex was performed using MEP/MAC/NPA methodologies. Two methodologies were employed to monitor the coordination process of AZO-ligand with Pd(II): UV–Vis absorption and FT-IR spectrum analysis. The TD-DFT and DFT/IR behaviors were simultaneously assessed to compare the experimental results with theoretical predictions. Furthermore, both SC-XRD and DFT analysis demonstrated that the deprotonated phenolic diazene form of the AZO-ligand attached to the Pd(II) center by utilizing one nitrogen atom of the AZO-ligand and the ionic oxygen of the phenol. The SC-XRD analysis verified the presence of a slightly distorted square-planar geometry around the PdII center in the neutral trans-Pd(O,N)2 complex. All of the oxygen atoms in the complex participated in non-classical C-H….O hydrogen bonding, leading to the formation of novel edge-fused rings R22(24) and R22(12) synthons. These synthons create a 3D-network with a linked parallel matrix. Interestingly, Hirshfeld surface analysis (HSA) stimulation revealed many hot sites on the complex surface, confirming the formation of strong non-classical [C-H....O] interactions. From the observed docking behavior with the DNA, it can be concluded that the trans-Pd(O,N)2 showed superior binding compared to the free AZO-ligand. The results of this work are a contribution to the study of this class of metal complexes and their physicochemical properties and offer promising perspectives for the realization of new works.

Diverse Effects of SO2-Induced Pt-O-SO3 on the Catalytic Oxidation of C3H6 and C3H8.

The effects of sulfur dioxide (SO2) in the catalytic purification of short-chain hydrocarbons are still controversial, and the exact role of SO2 on adsorption and reaction pathways during the catalytic oxidation of different volatile organic compounds (VOCs) remains unclear. Herein, a three-dimensional ordered macroporous Ce0.8Zr0.2O2 supported Pt nanoparticle monolithic catalyst (Pt/OM CZO) was synthesized to investigate these effects. Our findings uncover the diverse effects of SO2: Upon SO2 treatment, the coupling between the S 3p and Pt 5d orbitals promotes the Pt-O-SO3 structure in situ formed on the catalyst surface. The propene (C3H6) molecule readily binds with the oxygen atom in Pt-O-SO3, resulting in the accumulation of acetone and carbon deposition, thereby hindering C3H6 oxidation. Conversely, a cleaved oxygen atom within the Pt-O-SO3 structure enhances propane (C3H8) adsorption and activates the C-H bond, facilitating C3H8 oxidation. These insights are pivotal for advancing the frontier of sulfur-tolerant catalysts, addressing both economic and environmental challenges.

Organocatalysts for L-Lactide polymerization: 2-alkyl- and 2-aryl-1,1,3,3-tetramethylguanidines

A series of 2-alkyl- and 2-aryl-1,1,3,3-tetramethylguanidine derivatives were synthesized, and their application in L-Lactide (LA) polymerization was studied. Bn-TMG was the best catalyst in LA polymerization ( [Bn-TMG] = 5 mM, conversion = 94 % after 4 h at 25 °C) compared to other monoguanidine derivatives. In addition, the catalytic activities of C2-dTMG exhibited higher catalytic activity than Bn-TMG, nBu-TMG (monoguanidine derivatives), and C3-dTMG (diguanidine derivative). Density functional theory calculations revealed that Bn-TMG deprotonated benzyl alcohol enhanced benzyl alcohol's initiation ability to LA, and the protonated Bn-TMG activated LA ring-opening process by interacting with the ether oxygen atom of LA. Bn-TMG presented excellent catalytic activity and controllability for LA polymerization at 25 °C.

Water in the micropores of CPO-27 metal-organic frameworks: A comprehensive study

The metal-organic framework CPO-27 exhibits free coordination sites (open metal sites) and can be prepared with a wide range of metals that influence its properties. It is therefore an intriguing structure to study sorption phenomena. We analyze the water resistance and sorption behavior of these frameworks, with particular attention to the sorption mechanism in detail and the structure of the confined water molecules. For this purpose, we use manometric water vapor sorption analysis and FTIR spectroscopy. The respective metal center orchestrates both the adsorption behavior and the arrangement of the water molecules in the micropores of the framework. The extent to which water molecules form hydrogen bonds (with each other and with framework oxygen atoms) plays a crucial role in the stability of the framework towards water. Water adsorption is governed by the coordination of water molecules to the open metal sites (except for CPO-27-Cu) and subsequent H-bonding. A stepwise adsorption of water is observed, with significant differences depending on the choice of metal.

A Meso Butterfly-Like Ce(III)-Containing Antimonotungstate with Catalytic Activity for Synthesizing Isoindolinones.

A unique meso Ce(III)-containing antimonotungstate, {Na(OAc)(H2O)2[Ce4(tar)(Htar)2(Sb2W21O72)2(H2O)7]}244- (Ce4tar3; H4tar = tartaric acid), consisting of two enantiomeric parts with a butterfly-like configuration, was successfully synthesized by a one-pot in situ method and characterized. The coordination of d- or l-tar ligands induced the formation of Dawson-like {Ce2Sb2W21} with right or left configurations, thereby determining the d/l configurations of {Na(OAc)(H2O)2[Ce4(tar)(Htar)2(Sb2W21O72)2(H2O)7]}22-. Carboxyl groups link these two enantiomeric parts with Ce(III) ions from each other around the symmetric center of the P1̅ space group. The three types of tar ligands exhibit distinct coordination modes, and all coordinate with at least one W(VI) atom using one carboxylate oxygen atom and one α-OH. Ce4tar3 represents the largest case among those meso-dl-tar-functionalized polyoxometalates. Furthermore, Ce4tar3 exhibits excellent catalytic activity for synthesizing isoindolinones via the three-component reaction of 2-acetylbenzoic acids, amines, and phosphine oxides.

Alternate formation of AlOH from third row diatomic hydrides and oxides

One of the most abundant Al-containing molecules detected in the interstellar medium (ISM) is AlOH. Over the past several years, there have been various pathways proposed for the formation of AlOH in the ISM, including reactions between AlO and H2 or H2O. However, these pathways include an energetic barrier from a transition state that likely prevents the reaction from progressing efficiently in the low temperature/low pressure environment of the ISM. Recently, a barrierless pathway for formation of AlOH from AlO and AlH has been proposed for the formation of AlOH. Even so, only one of these species really needs to contain an aluminum atom. To account for this, alternative but related pathways reacting the known interstellar molecule AlO with XH and AlH with XO (X = Mg, Si, P, or S) to form AlOH are explored with high accuracy quantum chemical calculations via CCSD(T)-F12b/cc-pVTZ-F12. Each third row element has at least one pair of reactants that lead to exothermic formation of AlOH. These reactions can go on to form other aluminum oxides and aluminum oxide clusters that may, in part, lead to the formation of interstellar dust grains.

First Alliance of Pyrazole and Furoxan Leading to High-Performance Energetic Materials.

Nitrogen heterocyclic scaffolds retain their leading position as valuable building blocks in material science, particularly for the design of small-molecule energetic materials. However, the search for more balanced combinations of directly linked heterocyclic cores is far from being exhausted and aims to reach ideally balanced high-energy substances. Herein, we present the synthetic route to novel pyrazole-furoxan framework enriched with nitro groups and demonstrate a promising set of properties, viz., good thermal stability, acceptable mechanical sensitivity, and high detonation performance. In-depth crystal analysis showed that the isomers having lower-impact sensitivity values in both types of regioisomeric pairs are those with the exocyclic furoxan oxygen atom being closer to the pyrazole ring. Owing to the favorable combination of high crystal densities (1.83-1.93 g cm-3), positive oxygen balance to CO (up to +13.9%), and high enthalpies of formation (322-435 kJ mol-1), the synthesized compounds show high calculated detonation velocities (8.4-9.1 km s-1) and excellent metal accelerating abilities. The incorporation of the 3-nitrofuroxan moiety increases the thermal stability (by ca. 20 °C) and decreases the mechanical sensitivity of target hybrid materials in both types of regioisomeric pairs. Simultaneously, the detonation performance of 3-nitrofuroxans is almost identical to that of 4-nitrofuroxans, highlighting the potential of the regioisomeric tunability in the future design of energetic materials.

Simple/commercially‐available Lewis acid in anionic ring‐opening polymerization: powerful compounds with multiple applications in macromolecular engineering

Simple and commercially‐available Lewis acids (LA) are commonly used catalysts in anionic ring‐opening polymerization (AROP) reactions. In particular, for the AROP of epoxides, the addition of a Lewis acid allows the transition from a so‐called end‐chain mechanism to a monomer‐activated mechanism. The presence of the LA simultaneously leads to a decrease in the reactivity of active centers through the formation of a three‐species ate complex and to the activation of the monomer by LA coordination to the oxygen atom of the oxirane ring. These two effects result in both an increase in propagation kinetics and a decrease in transfer reactions, which has enabled the synthesis of high molecular weight polyethers. However, the impact of Lewis acids goes far beyond these classic effects. They have indeed enabled the polymerization of new functional monomers as well as the synthesis of heterotelechelic macromolecules. Also widely used as catalysts in copolymerization reactions (statistical, sequential, or alternating) Lewis acids can strongly influence the composition and sequence of monomer units in macromolecules. Finally, Lewis acids can also significantly influence the architecture of the obtained macromolecules. This review aims to list the various contributions of Lewis acids to macromolecular engineering and illustrate them with well‐chosen examples.

8-Hy-droxy-quinolinium tri-chlorido-(pyridine-2,6-di-carb-oxy-lic acid-κ3 O,N,O')copper(II) dihydrate.

The title compound, (C9H8NO)[CuCl3(C7H5NO4)]·2H2O, was prepared by reacting CuII acetate dihydrate, solid 8-hy-droxy-quinoline (8-HQ), and solid pyridine-2,6-di-carb-oxy-lic acid (H2pydc), in a 1:1:1 molar ratio, in an aqueous solution of dilute hydro-chloric acid. The CuII atom exhibits a distorted CuO2NCl3 octa-hedral geometry, coordinating two oxygen atoms and one nitro-gen atom from the tridentate H2pydc ligand and three chloride atoms; the nitro-gen atom and one chloride atom occupy the axial positions with Cu-N and Cu-Cl bond lengths of 2.011 (2) Å and 2.2067 (9) Å, respectively. In the equatorial plane, the oxygen and chloride atoms are arranged in a cis configuration, with Cu-O bond lengths of 2.366 (2) and 2.424 (2) Å, and Cu-Cl bond lengths of 2.4190 (10) and 2.3688 (11) Å. The asymmetric unit contains 8-HQ+ as a counter-ion and two uncoordinated water mol-ecules. The crystal structure features strong O-H⋯O and O-H⋯Cl hydrogen bonds as well as weak inter-actions including C-H⋯O, C-H⋯Cl, Cu-Cl⋯π, and π-π, which result in a three-dimensional network. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing involving the main residues are from H⋯Cl/Cl⋯H inter-actions, contributing 40.3% for the anion. Weak H⋯H contacts contribute 13.2% for the cation and 28.6% for the anion.

Quantification of Anisotropy in Exchange and Dispersion Interactions: A Simple Model for Physics-Based Force Fields.

In some compounds, exchange repulsion is orientation dependent. However, in contrast to quantum chemical methods that treat exchange explicitly, empirical models assume exchange to be spherically symmetric, yielding an average description only. Here we quantify the anisotropy of exchange and dispersion energy for hydrogen halides and water by probing these compounds with a helium atom using the symmetry-adapted perturbation theory (SAPT). The exchange interaction is reduced by up to 33% due to the σ-hole in hydrogen iodide, depending on the location of the probe. We demonstrate how this anisotropy can be modeled in empirical force fields either using an angle-dependent potential or by introducing virtual sites, reducing the error in the empirical model by a factor of 5 compared to isotropic atoms. Lone-pairs on water, positioned close to perpendicular to the plane of the molecule, on a line with the oxygen atom, and, surprisingly, σ-holes on water both modulate the exchange interaction strongly. Both lone-pairs and σ-holes can be modeled by virtual sites, leading to an 80% reduced error.

Decoupling "Cling-Cover-Capture" Triple Effects on Stable Zn Anode/Electrolyte Interface.

The electrochemical performance of the Zn anode in a water-based electrolyte is influenced by the Zn anode/electrolyte interface. In the present work, a distinctive interfacial chemistry is enabled by introducing synergistic "cling-cover-capture" effects of different components in aspartame (APM) molecule, which can be described in detail as clinging to the surface of Zn anode by incompletely coordinated nitrogen and oxygen atoms in the main chain, covering the surface by the benzene rings and capturing Zn2+ by the side chains. Benefiting from its triple effects, this steady anode/electrolyte interface homogenizes Zn2+ flux and excludes interfacial active water, thus effectively suppressing both dendrite growth and side reactions. Consequently, the stability and reversibility of Zn anode experience an enhancement, leading to a long cycle lifespan of 5100 h at 1 mA cm-2 and 1 mA h cm-2, and an average Coulombic efficiency of 99.73% at 1 mA cm-2 and 0.5 mA h cm-2 over 1600 cycles. The improved rate capability and cycling durability of Zn||NH4V4O10 full cells further confirm the important role of APM in stabilizing the Zn anode.

Synthesis of Quinone‐Amine‐Linked Covalent Organic Frameworks for Boosting the Photocatalytic Removal of Uranium

AbstractCompared to imine covalent organic frameworks (COFs), the superior stability of amine‐linked COFs renders them more suitable for long‐term harsh real‐world environments. Their numerous amine sites can serve as functional groups or be subjected to post‐modification to further enhance the performance of the material. However, the assortment and abundance of amine‐linked COFs via currently lacking due to restricted monomer varieties and synthetic methods. Herein, this study presents an innovative approach for synthesizing quinone‐amine‐linked COFs by directly combining 2,5‐dihydroxy‐1,4‐benzoquinone (DHBQ) with various amine monomers and introduce a novel photocatalyst, DHBQ‐TAPP‐COF, specifically tailored to efficiently reduce uranium in harsh environments. DHBQ‐TAPP‐COF features a unique donor–acceptor structure, with the DHBQ units serving as acceptors because they contain abundant oxygen atoms that facilitate metal ion coordination, thereby enhancing charge carrier separation, carrier utilization, and uranium reduction efficiency. The quinone‐amine linkages offer improved stability, extended π‐conjugation, heightened local polarity, and conductivity, which enable efficient carrier transfer within the material and thus enhance the overall performance of the uranium photocatalyst. The proposed photocatalyst can efficiently reduce U(VI) without sacrificial agents or decomposition to precipitate UO2 at a recovery rate exceeding 98%. This catalyst provides an efficient and convenient strategy for the stable and high‐performance photocatalytic reduction of uranium.

Synthesis, characterization, and crystal structure of hexa-kis-(1-methyl-1H-imidazole-κN 3)zinc(II) dinitrate.

The synthesis of the title compound, [Zn(C4H6N2)6](NO3)2, is described. This complex consists of a central zinc metal ion surrounded by six 1-methyl-imidazole ligands, charge balanced by two nitrate anions. The complex crystallizes in the space group P. In the crystal, the nitrate ions are situated within the cavities created by the [Zn(N-Melm)6]2+ cations, serving as counter-ions. The three oxygen atoms of the nitrate ion engage in weak C-H⋯O inter-actions. In addition to single-crystal X-ray diffraction analysis, the complex was characterized using elemental analysis, 1H NMR, 13C NMR, and FTIR spectroscopy.

Modular Synthesis of α-Aryl Acrylamido Carboxylic Acids by Triple C-F Bond Cleavage of (Trifluoromethyl)alkenes with Unprotected Amino Acids.

A straightforward and efficient strategy for the construction of tertiary and secondary α-aryl acrylamido carboxylic acids is reported. This N-acrylation protocol of unprotected amino acids is achieved by triple C-F bond cleavage of (trifluoromethyl)alkenes. This method features mild conditions, is operationally simple, is free of transition metals and racemization, can be used on a gram scale, and is compatible with various functional moieties. Mechanistic studies indicate that oxygen atom exchange happens among H2O, NaOH, and amino acids, and the oxygen atom of the amide moiety of the product is incorporated by the ipso-defluorooxylation of (trifluoromethyl)alkene.

Constructing Unsaturated Ru Atom Arrays Confined in Mn Oxides to Boost Neutral Water Reduction

Recently, Ru single atoms supported on carbon nanomaterials have demonstrated ultrahigh activity for acid hydrogen evolution reaction (HER), however their neutral HER activity remains low due to the sluggish kinetics for both the water dissociation step to generate H* intermediates and subsequent H* recombination in neutral electrolytes. Here, we synthesize ordered low‐coordinated Ru atom arrays confined in Mn oxides (i.e., Li4Mn5O12) for concurrently boosting the water dissociation and H* recombination, thus achieving a 6‐fold HER activity enhancement than commercial Pt/C in neutral media. Control experiments indicate that low‐coordinated Ru atoms with strong affinity to oxygen atoms of water molecules facilitate the water dissociation to rapidly generate H*. More importantly, both electrochemical and theoretic results uncover that the array‐like structure allows the activation of two water molecules on two adjacent Ru atoms for enabling direct H*–H* recombination via the Tafel step, while isolated Ru atoms can only activate water one by one for recombining H* via the sluggish Heyrovsky step. Clearly, this work paves new avenues to boosting the electrocatalytic activity by constructing ordered metal atoms assembles with controllable coordination environments.

Mn‐Fe dual‐metal Assemblages on Carbon‐coated Al2O3 Spheres for Catalytic Ozonation Oxidation: Structure, Performance, and Reaction Mechanism

Catalysts with high catalytic activity and low production cost are important for industrial application of heterogeneous catalytic ozonation (HCO). In this study, we designed a carbon‐coated aluminum oxide carrier (C‐Al2O3) and reinforced it with Mn‐Fe bimetal assemblages to prepare a high‐performance catalyst Mn‐Fe/C‐Al2O3. The results showed that the carbon embedding significantly improved the abundance of surface oxygen functional groups, conductivity, and adsorption capacity of γ‐Al2O3, while preserving its exceptional mechanical strength as a carrier. The prepared Mn‐Fe/C‐Al2O3 catalyst exhibited satisfactory catalytic ozonation activity and stability in the degradation of p‐nitrophenol (PNP). Electron paramagnetic resonance (EPR) and quenching experiments reveal that radical (•OH and •O2–) and nonradical oxidation (1O2) dominated the PNP degradation process. Theoretical calculations corroborated that the anchored atomic Fe and Mn sites regulated the local electronic structure of the catalyst. This modulation effectively promoted the activation of O3 molecules, resulting in the generation of atomic oxygen species (AOS) and reactive oxygen species (ROS). The economic analysis on Mn‐Fe/C‐Al2O3 revealed that it was a cost‐competitive catalyst for HCO. This study not only deepens the understanding on the reaction mechanism of HCO with transition metal/carbon composite catalysts, also provides a high‐performance and cost‐competitive ozone catalyst for prospective application.

Surface loss probability of atomic oxygen on silica under atmospheric-pressure CO2

Abstract The surface loss probability γ O of atomic oxygen was measured for SiO2 in atmospheric-pressure CO2 and Ar/CO2(3.05%) mixture at 300 K. O atoms were produced via the photolysis of CO2 using a 172 nm Xe2 excimer lamp. After irradiation by Xe2 lamp, the working gas flowed through a quartz tube, causing O atoms to be lost on its inner surface. By measuring the density of O atoms at the end of the tube for different tube lengths, we obtained the value of γ O on the inner surface of the tube. The measured value was 5.5 × 10 − 4 ± 50 % , which falls within the range of referred values of γ O ( 1 × 10 − 5 to 1 × 10 − 3 ) at 4 to 1300 Pa measured using low-pressure O2 plasmas. Despite the 2 to 5 orders of magnitude pressure difference, no significant difference in γ O was obtained. The potential influence of the difference in background gas (CO2 and O2) on the value of γ O was also considered.