Coordination Sphere Research Articles

Optimizing s‐p Orbital Overlap between Sodium Polysulfides and Single‐Atom Indium Catalyst for Efficient Sulfur Redox Reaction

P‐block metal carbon‐supported single‐atom catalysts (C‐SACs) have emerged as a promising candidate for high‐performance room‐temperature sodium‐sulfur (RT Na‐S) batteries, due to their high atom utilization and unique electronic structure. However, the ambiguous electronic‐level understanding of Na‐dominant s‐p hybridization between sodium polysulfides (NaPSs) and p‐block C‐SACs limits the precise control of coordination environment tuning and electro‐catalytic activity manipulation. Here, s‐p orbital overlap degree (OOD) between the s orbitals of Na in NaPSs and the p orbitals of p‐block C‐SACs is proposed as a descriptor for sulfur reduction reaction (SRR) and sulfur oxidation reaction (SOR). Compared to NG and NG‐supported InN4 (NG‐InN4) SACs, the nitrogen‐doped graphene‐supported InN5 (NG‐InN5) SACs show the largest s‐p OOD, demonstrating the weakest shuttle effect and the lowest reaction energy barriers in both SRR and SOR. Accordingly, the designed catalysts allow the Na‐S pouch batteries to retain a high capacity of 490.7 mAh g‐1 at 2 A g‐1 with a Coulombic efficiency of 96% at a low electrolyte/sulfur (E/S) ratio of 4.5 μl. This work offers an s‐p orbital overlap descriptor describing the interaction between NaPSs and p‐orbital‐dominated catalysts for high‐performance RT Na‐S batteries.

Polyoxometalates as advanced-performance anions for ∼D5h Dy(III) single-ion magnets.

We enhance single-ion magnet (SIM) magnetisation reversal barriers by engineering the second coordination sphere, substituting conventional small monoanions with a bulky polyoxometalate (POM) trianion. Importantly, our approach serves as a model for creating new high-performance multifunctional hybrid materials.

Red-Light-Induced Ligand-to-Metal Charge Transfer Catalysis by Tuning the Axial Coordination of Cobyrinate.

Photoinduced ligand-to-metal charge transfer (LMCT) is a powerful technique for the formation of reactive radical species via homolytic cleavage of the metal-ligand bond. Here, we present that the excited state LMCT of a cobyrinate complex can be accessed by tuning its axial coordination with thiolates as ligands. We demonstrate the photoreduction of cobalt via the excited state Co-S bond homolytic cleavage, as guided by the DFT calculations, which signify the relevance of thiolate axial ligands facilitating the LMCT reactivity. By exploiting this excited state LMCT of cobyrinate, we developed a catalyst-controlled activator regeneration mechanism to catalyze an efficient atom transfer radical polymerization (ATRP) under low-energy light irradiation. Tuning the coordination sphere of cobyrinate provides further control over the electronic properties of the complex while also accessing photothermal conversion in mediating ATRP catalysis.

Identifying N Coordination Types of Single‐Atom Catalysts by Spin‐Modulated Luminol Cathodic Electrochemiluminescence

The type of coordinated N atoms in the metal‐N coordination structure is of paramount importance to the catalytic property of carbon‐based metal single‐atom catalysts (SACs). Extended X‐ray absorption fine structure (EXAFS) spectroscopy is a powerful tool for analyzing the coordination environments of SACs. Despite its efficacy, the limited availability of synchrotron light sources and the complexity of data analysis have constrained its broader application in identifying metal‐N coordination types within SACs. In this work, two kind of CoN4 SACs were prepared by varying the N source. Then their electrochemiluminescence (ECL) behavior in the luminol/dissolved oxygen system during cathodic scanning were investigated. In comparison to CoN4(pyridinic N), for which the spin density displays dz2 orbital characteristics, CoN4(pyrrolic N) exhibits dxz orbital features, which was more conducive to the subsequent cleavage of the O‐O bond in O2•‐ to •OH, resulting in the generation of more active intermediates *OH and the promotion of cathodic ECL emission. This work demonstrates that the ECL technique provides a novel method for the rapid identification of Co‐N coordination types and the spin nature of the metal center in CoN4 SACs.

First evidencing of guest‐induced spin transition for dinuclear Fe(III) complex supported by calix[4]arene Schiff base ligand

For the first time the partial low spin (LS) ‐ high spin (HS) state transition back, caused by trapped guest molecule release from the macrocyclic cavity of calix[4]arene ligand, decorated with salicylideneamine coordinating binding sites, was evidenced for new dinuclear [FeIII2] diamond core cluster, displaying mixed cis‐/trans‐N2O4 coordination environment for metal centers. Such unique spin state transition behavior, triggered by the changing of calix[4]arene backbone conformation, giving rise to a new paradigm of fine‐tuning spin‐dependent functionality in materials design, was unambiguously established by the 57Fe Mössbauer spectroscopy in combination with the single crystal X‐ray diffraction, IR, TGA‐DSC analysis.

Identifying N Coordination Types of Single-Atom Catalysts by Spin-Modulated Luminol Cathodic Electrochemiluminescence.

The type of coordinated N atoms in the metal-N coordination structure is of paramount importance to the catalytic property of carbon-based metal single-atom catalysts (SACs). Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful tool for analyzing the coordination environments of SACs. Despite its efficacy, the limited availability of synchrotron light sources and the complexity of data analysis have constrained its broader application in identifying metal-N coordination types within SACs. In this work, two kind of CoN4 SACs were prepared by varying the N source. Then their electrochemiluminescence (ECL) behavior in the luminol/dissolved oxygen system during cathodic scanning were investigated. In comparison to CoN4(pyridinic N), for which the spin density displays dz2 orbital characteristics, CoN4(pyrrolic N) exhibits dxz orbital features, which was more conducive to the subsequent cleavage of the O-O bond in O2•- to •OH, resulting in the generation of more active intermediates *OH and the promotion of cathodic ECL emission. This work demonstrates that the ECL technique provides a novel method for the rapid identification of Co-N coordination types and the spin nature of the metal center in CoN4 SACs.

Neutral Terbium(III) Tris(complex) with 4,4,5,5,6,6,6-Heptafluoro-1-(1-methyl-1H-pyrazol-4-yl)hexane-1,3-dione: Synthesis, Structure, and Spectral Luminescence Properties

The reaction of 1,3-diketone containing 1-methyl-1H-pyrazol-4-yl and perfluoropropyl fragments with TbCl3·6H2O in the presence of NaOH in ethanol is studied. The molecular and crystal structures of the complex are studied by single-crystal X-ray diffraction (XRD). Compound [Tb(L)3(EtOH)2] crystallizes in the triclinic crystal system with the space group. The geometry of the coordination polyhedron {LnO8} corresponds to a square antiprism. Intermolecular interactions N…H–O, C–H…O, and C–H…F leading to the formation of supramolecular chains are observed in crystals of the complex. The UV-irradiated complex exhibits green luminescence caused by transitions 5D4 → 7Fj (j = 2–6) characteristic of the Tb3+ ion. The main photophysical luminescence parameters are determined, and the scheme of energy transfer in the complex is proposed. The synthesized compound can be of interest as an independent luminophore or as the initial substance for the synthesis of heteroligand complexes by the substitution of ethanol molecules in the internal coordination sphere.

Balancing Activity and Selectivity in Two-electron Oxygen Reduction through First Coordination Shell Engineering in Cobalt Single Atom Catalysts.

The electrochemical two-electron oxygen reduction reaction (2e- ORR) offers a potentially cost-effective and eco-friendly route for the production of hydrogen peroxide (H2O2). However, the competing 4e- ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective H2O2 production under low voltage conditions remains challenging. Herein, guided by first-principles density functional theory (DFT) calculations, we show that modulation the first coordination sphere in Co single atom catalysts (Co-N-C catalysts with Co-NxO4-x sites), specifically the replacement of Co-N bonds with Co-O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards H2O2 (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N-doped carbon-supported catalysts with Co-NxO4-x active sites, we were able to validate the DFT findings and explore the trade-off between catalytic activity and selectivity for 2e- ORR. A catalyst with trans-Co-N2O2 sites exhibited excellent catalytic activity and H2O2 selectivity, affording a H2O2 production rate of 12.86 [[EQUATION]]and an half-cell energy-efficiency of 0.07 [[EQUATION]] during a 100-h H2O2 production test in a flow-cell.

Balancing Activity and Selectivity in Two‐electron Oxygen Reduction through First Coordination Shell Engineering in Cobalt Single Atom Catalysts

The electrochemical two‐electron oxygen reduction reaction (2e‐ ORR) offers a potentially cost‐effective and eco‐friendly route for the production of hydrogen peroxide (H2O2). However, the competing 4e‐ ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective H2O2 production under low voltage conditions remains challenging. Herein, guided by first‐principles density functional theory (DFT) calculations, we show that modulation the first coordination sphere in Co single atom catalysts (Co‐N‐C catalysts with Co‐NxO4‐x sites), specifically the replacement of Co‐N bonds with Co‐O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards H2O2 (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N‐doped carbon‐supported catalysts with Co‐NxO4‐x active sites, we were able to validate the DFT findings and explore the trade‐off between catalytic activity and selectivity for 2e‐ ORR. A catalyst with trans‐Co‐N2O2 sites exhibited excellent catalytic activity and H2O2 selectivity, affording a H2O2 production rate of 12.86 [[EQUATION]]and an half‐cell energy‐efficiency of 0.07 [[EQUATION]] during a 100‐h H2O2 production test in a flow‐cell.

Reducing Lithium‐Diffusion Barrier on the Wadsley–Roth Crystallographic Shear Plane via Low‐Valent Cation Doping for Ultrahigh Power Lithium‐Ion Batteries

AbstractRapid‐charging niobium–tungsten oxide Nb14W3O44 (NbWO) anodes with a Wadsley–Roth crystallographic shear (WRCS) structure possess 3D interconnected open tunnels. However, the anisotropic Li+ diffusion paths lead to a high lithium‐diffusion barrier of hooping between window sites across edge‐shared octahedrons, as the rate‐limiting step of hooping. To improve the rate capability of NbWO, doping it with low‐valent cations (with valences lower than W6+) to reduce the high lithium‐diffusion barrier is proposed. Electron energy loss spectroscopy reveals that low‐valent V5+, V4+, Tb4+, and Ce4+ tend to distribute on the crystallographic shear plane under electrostatic repulsion forces. The reduction in steric hindrance resulting from the increased long bond length ratio of doped edge‐shared octahedrons, coupled with coordination environment modification of [LiO5] on the crystallographic shear plane due to the low energy level of V5+, enhances Li+ diffusion kinetics and cyclic stability. V5+‐ and Tb4+‐doped NbWOs achieve rate capacities of 83 and 63 mAh g−1, at 200 C (1C = 0.178 Ag−1) and retain 75.42% and 86.79% of their capacities, respectively, after 3700 cycles at 20 C. Thus, the proposed doping strategy is promising for preparing WRCS‐type niobium‐based oxides for ultrafast lithium storage.

Harnessing of Cooperative Cu···H Interactions for Luminescent Low‐Coordinate Copper(I) Complexes towards Stable OLEDs

Although two‐coordinate Cu(I) complexes are highly promising low‐cost emitters for organic light‐emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we described a strategy to develop stable carbene‐Cu‐amide complexes through installing intramolecular noncovalent Cu···H interactions. The employment of 13H‐dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu···H distances in addition to the Cu–N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86% and radiative decay rate constants on the order of 106 s−1. Comparing with the analogues without Cu···H interactions, the pincer complexes have significantly improved stability. The vacuum‐deposited OLEDs show high‐performance electroluminescence with maximum external quantum efficiencies up to 29.5% and extremely small roll‐offs of only 3.5% at 10,000 cd m‐2. Remarkably, the operational lifetimes (LT90) were determined to be up to 68 h with an initial luminance of 3000 cd m‐2. This work proves a feasible design of robust low‐coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long‐standing stability problem.

How Do Variants of Residues in the First Coordination Sphere, Second Coordination Sphere, and Remote Areas Influence the Catalytic Mechanism of Non-Heme Fe(II)/2-Oxoglutarate Dependent Ethylene-Forming Enzyme?

How Do Variants of Residues in the First Coordination Sphere, Second Coordination Sphere, and Remote Areas Influence the Catalytic Mechanism of Non-Heme Fe(II)/2-Oxoglutarate Dependent Ethylene-Forming Enzyme?

Solvation Environment and Interface Dynamics of Li2B12H12 and Li2B12F12 Electrolytes Uncovered by Theory and Operando Optical and FTIR Spectroelectrochemistry.

In this work, we evaluated two closo-borate salts (Li2B12H12 and Li2B12F12) in propylene carbonate from theoretical and experimental perspectives to understand how the coordination environment influences their spectroscopic and electrochemical properties. The coordination environments of the closo-borate salts were modeled via density functional theory (DFT) and molecular dynamics (MD). Vibrational spectra calculated from the predicted coordination environments are in agreement with experimentally measured steady-state FTIR data. This theoretical investigation also suggested that Li2B12F12 would possess a higher ionic conductivity than Li2B12H12, which was corroborated experimentally. Additionally, an electrochemical cell was designed and fabricated that enabled operando optical and FTIR spectroelectrochemical (OP-IR-SEC) measurements. This allowed for the simultaneous measurement of the relative changes of species at a lithium electrode-liquid electrolyte interface and the visualization of lithium plating at the electrode surface. This technique could provide new chemical insights and potentially link optical changes at the electrode-electrolyte interface to specific chemical species in similar electrochemical systems. The Li2B12F12 electrolyte was found to have a higher thermal stability, which may find utility in applications for batteries that are subject to high-temperature conditions.

Chelating Properties of N6O-Donors Toward Cu(II) Ions: Speciation in Aqueous Environments and Catalytic Activity of the Dinuclear Complexes

This study focuses on the use of three isostructural N6O donor ligands, specifically known to form complexes with copper ions, to chelate Cu(II) from aqueous solutions. The corresponding Cu(II) complexes feature a dinuclear copper core mimicking the active site of natural superoxide dismutase (SOD) enzymes while also creating a coordination environment favorable for catalase (CAT) activity, being thus appealing as catalytic antioxidant systems. Given the critical role of copper dysregulation in the pathophysiology of Alzheimer’s disease (AD), these complexes may help mitigate the harmful effects of free Cu(II) ions: the goal is to transform copper’s reactive oxygen species (ROS)-generating properties into beneficial ROS-scavenging action. This study investigates the speciation, chelating efficiency, and metal selectivity of these ligands, as well as the antioxidant activity of the resulting complexes under aqueous and physiologically relevant conditions. Additionally, the ligands, equipped with functional groups for attaching targeting moieties, are conjugated with a small peptide that may act as an anti-aggregating agent of β-amyloid peptides, aiming to develop a multifunctional therapeutic strategy against Alzheimer’s disease.

Tailoring the Coordination Environment of Cu Single Atoms for Achieving Regioselective C–C Bond Activation of Amides

Tailoring the Coordination Environment of Cu Single Atoms for Achieving Regioselective C–C Bond Activation of Amides

Engineering the coordination of Cu–Ni dual-atom catalysts to enhance the electrochemical CO2 overall splitting

Designing the coordination environment of heteroatoms around metal sites and optimizing the electronic structure of diatomic metal sites remain significant challenges in achieving efficient CO2 overall splitting. Herein, we report four configurations (Cu/Ni–N4C2, Cu/Ni–N2C4, Cu/Ni–N2C3 and Cu/Ni–N2C2) constructed by precise regulation of the coordination environment around bimetallic atoms. Cu/Ni–N2C2 showed high performance in electrochemical CO2 reduction (ECR) and water oxidation evolution reaction (OER). In the electrochemical CO2 overall splitting reaction, it achieved a Faraday efficiency of CO (FECO) of 98.0% at a low cell voltage of −2.9 V, significantly higher than widely reported values. Moreover, the FECO is above 90% over −2.7 to −4.1 V of cell voltages. Cu/Ni–N2C2 achieved long-term ECR stability of 110 h at −100 mA cm−2. Mechanism studies revealed that the change of coordination environment around the diatomic pairs moves the d-band center of the Ni atom closer to the Fermi level, thereby modulating the adsorption capacity of the catalysts to the reaction intermediates *COOH and *O. This work presents valuable insights into the rational design of diatomic catalysts and elucidates the intricate structure-performance relationship in advancing electrochemical CO2 overall splitting technology and energy-conversion applications.

Enhancing CO2 electroreduction to formate on bismuth catalyst via sulfur doping

The electrochemical reduction of CO2 to formate is an effective approach to achieving carbon neutrality. However, the instability of catalyst remains a significant limitation. Doping heteroatoms is a recognized method for tuning the coordination environment to enhance both electrochemical performance and stability. Herein, we report a facile and mild hydrothermal method employing sulfur doping to tune the coordination environment of bismuth active sites. Sulfur doping modifies the coordination environment of active sites by partially substituting O atoms bonded with bismuth active sites and simultaneously creating an abundance of oxygen vacancies, which effectively stabilize the active sites. This results in notably improved stability, reaching 110 h with a significant FEHCOOH (around 100 %). The bismuth-based catalyst modified with sulfur exhibits an impressive FEHCOOH over 95 % across a wide applied potential range of −0.7 to −1.4 VRHE. The flower-like structure increases the electrochemical surface area, promoting greater exposure of bismuth active sites. This leads to a high formate production rate of 1248 mmol∙h-1∙cm-2 for the Cu-BiS catalyst, which is 1.7 times that of the Cu-Bi catalyst. This strategy provides an effective way to tune the coordination environment of active sites and stabilize them.

Insights into a photo-driven laccase coupling system for enhanced photocatalytic oxidation and biodegradation

Effective depolymerization of lignin into environmentally friendly aromatic chemicals under mild conditions is gaining interest. Fungal laccase is capable of catalyzing a wide range of reactions, but its low redox potential and preference for acidic pH limit its potential applications. Herein, we developed a laccase-methylene blue (LAC-MB) coupling system, combining the selectivity of enzyme catalysis with the high reactivity of photocatalysis, for the efficient degradation of lignin model compounds. Theoretical calculations indicate that the electron donor’s distance to the LAC’s active site T1 Cu is shortened from 29.7 to 7.3 Å in the LAC-MB. In this system, MB, possessing strong interaction with T1 Cu, acts as a light absorber, enabling the rapid transfer of photogenerated electrons to T1 Cu. This significantly enhances the degradation rate of guaiacol (GUA) from 28.8 % to 91.46 %. The LAC-MB can oxidize both phenolic and non-phenolic lignin model compounds under red-LED irradiation with wide pH ranging from 3.0 to 7.0 and high-efficiency. By tuning the primary coordination sphere and the access tunnel of T1 Cu, we further revealed that enhanced binding affinity and active site accessibility for the LAC-MB complex attributed to the photocatalysis’s high reactivity. Based on this, LAC variants with enhanced binding capabilities were constructed and the resulting mutant LAC-MB are characterized by higher oxygen consumption and ROS generation activated by red-LED, specifically a higher quantum yield of 1O2, demonstrating increased electron transfer and light-driven reactivity. This photo-enzyme coupling system presents a new pathway for the high-efficiency processing of lignocellulosic biomass and offers insights for designing future artificial photosynthetic systems.

Improving macromolecular structure refinement with metal-coordination restraints.

Metals are essential components for the structure and function of many proteins. However, accurate modelling of their coordination environments remains a challenge due to the complexity and diversity of metal-coordination geometries. To address this, a method is presented for extracting and analysing coordination information, including bond lengths and angles, from the Crystallography Open Database. By using these data, comprehensive descriptions of metal-containing components are generated. A stereochemical information generator for a particular component within a specific macromolecule leverages an example PDB/mmCIF file containing the component to account for the actual surrounding environment. A matching process has been developed and implemented to align the derived metal structures with idealized coordinates from a coordination geometry library. Additionally, various strategies, depending on the quality of the matches, were employed to compile distance and angle statistics for the refinement of macromolecular structures. The developed methods were implemented in a new program, MetalCoord, that classifies and utilizes the metal-coordination geometry. The effectiveness of the developed algorithms was tested using metal-containing components from the PDB. As a result, metal-containing components from the CCP4 monomer library have been updated. The updated monomer dictionaries, in concert with the derived restraints, can be used in most structural biology computations, including macromolecular crystallography, single-particle cryo-EM and even molecular mechanics.

MOF-derived S, N co-doped porous carbon matrix with single Fe atoms and CoSx nanoparticles dual-sites for enhanced oxygen reduction

Metal-air batteries, as a clean energy technology, are of great significance in alleviating the increasingly serious energy and environmental problems, but the sluggish oxygen reduction reaction (ORR) kinetics of air–cathode severely restrict their development. In this work, a zeolitic imidazole frameworks (ZIFs)-derived dual-site electrocatalyst (Fe/CoSx-SNC) composed of Fe single atom and ultrafine cobalt sulfide nanoparticle sites supported on S, N co-doped porous carbon was successfully prepared. Benefited from the advantages of large specific surface area, high porosity, high-density metal centers, and synergistic effects between the dual sites, Fe/CoSx-SNC electrocatalyst presents excellent electrocatalytic ORR activity with a half-wave potential of 0.885 V, a kinetic current density of 27.00 mA cm−2 (at 0.80 V), and good stability, which are superior to the commercial 20 % Pt/C catalyst. The density functional theory (DFT) calculations reveals that the presence of cobalt sulfide nanoparticles could effectively modulate the electron density around Fe single atom, which reduces the desorption energy barrier (rate-determining step) of *OH on Fe sites. In addition, the rechargeable zinc-air battery assembled with Fe/CoSx-SNC as air cathode oxygen catalyst exhibits a high peak power density of 156.63 mW cm−2 and over 100 h of cycling stability. This study provides a straightforward and feasible approach to precisely adjusting the coordination environment and constructing high-performance metal single-atom-based oxygen electrocatalysts, which will be beneficial to promoting the development of metal-air batteries.