CO Coordination Research Articles

Modulation of Charge Redistribution in Heterogeneous CoSe-Ni0.95Se Coupling with Ti3C2Tx MXene for Hydrazine-Assisted Water Splitting.

Integrating abundant dual sites of hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER) into one catalyst is extremely urgent toward energy-saving H2 production. Herein, CoSe-Ni0.95Se heterostructure coupling with Ti3C2Tx MXene (CoSe-Ni0.95Se/MXene) is fabricated on nickel foam (NF) to enhance the catalytic performance. The heterogeneous CoSe-Ni0.95Se and MXene coupling effect can change the coordination of Ni and Co, resulting in adjusted interfacial electronic field and enhanced electron transfer from Ni0.95Se to CoSe especially near MXene surface. Also, the appearance of MXene can anchor more active sites, thereby abundant nucleophilic CoSe and electrophilic Ni0.95Se are formed induced by the charge redistribution, which can tailor d-band center, moderate *H adsorption free energy (∆GH *) and facilitate adsorption/desorption for hydrazine intermediates, contributing to much enhanced HER and HzOR performance. For example, the low potentials of -160.8 and 116.1mV at 400 mA cm-2 are seen for HER and HzOR with long-term stability of 7 days. When assembled as overall hydrazine splitting (OHzS), a small cell voltage of 0.35V to drive 100 mA cm-2 is obtained. Such concept of integrating abundant nucleophilic and electrophilic dual sites and regulating their d-band centers can offer in-depth understandings to design efficient bifunctional HER and HzOR electrocatalysts.

Synthesis and characterization of mixed ligands based Co(II)-based coordination polymers and study their photochemically antibiotic degradation

Two Co(II)-based coordination polymers （CPs）, denoted as [Co4(NPDA)4(bmb)2·3H2O]n (1) and [Co(CHDA)(bmb)]n (2) (bmb = 4, 4́-bis(2-methylimidazol-3-ium-1-yl) biphenyl; H2NPDA = 1,4-naphthalenedicarboxylic acid; H2CHDA = 1,4-cyclohexanedicarboxylic acid), were obtained from mixtures of Co(NO3)2·6H2O and H2NPDA and bmb for 1 or H2CHDA and bmb for 2 with good yields (67 % and 53 %). Single crystal XRD shows a quadruply acetate-bridged Co(II)···Co(II) center for 1 with distorted triangular bipyramid surrounding of Co atom, while 2 shows a cis-configured octahedral N2O4 coordination for Co. Thermal gravimetric analysis confirms the water content of 1 and shows remarkable thermal stabilities, with a decomposition for 1 at around 400 °C and 450 °C for 2. 1 and 2 were used as catalysts for the photochemical degradation of the antibiotics secnidazole (SIZ), nitrofurazone (NFZ), sulfasalazine (SLA), and furazolidone (FZD). Using 1 at a dosage of 10 mg/L allowed a degradation efficiency of 92.3 % for 30 ppm NFZ at 6.5 pH. A proposed photodegradation mechanism was investigated through radical trapping experiments.

Boosting the ORR/OER Activity of Cobalt-Based Nano-Catalysts by Co 3d Orbital Regulation.

The transition metal oxides/sulfides are considered promising catalysts due to their abundant resources, facile synthesis, and reasonable electrocatalytic activity. Herein, a significantly improved intrinsic catalytic activity is achieved for constructing a Co-based nanocrystal (Co-S@NC) with the coordination of Co─S, Co─S─C, and Co─Nx─C. The calculational and experimental results demonstrate that the diversified chemical environment of Co-cations induces the transition of 3d orbitals to a high spin-state that exhibits the coexistence of Co2+ with fully occupied dπ orbitals and Co3+ with unpaired electrons in dπ orbitals. The diverse dπ orbitals occupation contributes to an elevated d-band center of Co ions, which accelerates oxygen reduction reaction and oxygen evolution reaction electrocatalytic kinetics of the Co-S@NC nanocrystal. Therefore, the Li-O2 batteries with Co-S@NC as cathode catalyst exhibit 300 cycles at the current density of 500 mA g-1 with a cut-off capacity of 1000 mAh g-1. Moreover, the ultrahigh discharge specific capacity of 34 587 mAh g-1 is obtained at a current density of 1000 mA g-1, corresponding to the energy density 949 Wh kg-1 of a prototype Li-O2 battery. The study on 3d orbital regulation of nanocrystals provides an innovative strategy for bifunctional electrocatalysts toward the practical application of metal-air batteries.

Highly Activated Terminal Carbon Monoxide Ligand in an Iron-Sulfur Cluster Model of FeMco with Intermediate Local Spin State at Fe.

Nitrogenases, the enzymes that convert N2 to NH3, also catalyze the reductive coupling of CO to yield hydrocarbons. CO-coordinated species of nitrogenase clusters have been isolated and used to infer mechanistic information. However, synthetic FeS clusters displaying CO ligands remain rare, which limits benchmarking. Starting from a synthetic cluster that models a cubane portion of the FeMo cofactor (FeMoco), including a bridging carbyne ligand, we report a heterometallic tungsten-iron-sulfur cluster with a single terminal CO coordination in two oxidation states with a high level of CO activation (νCO = 1851 and 1751 cm-1). The local Fe coordination environment (2S, 1C, 1CO) is identical to that in the protein making this system a suitable benchmark. Computational studies find an unusual intermediate spin electronic configuration at the Fe sites promoted by the presence the carbyne ligand. This electronic feature is partly responsible for the high degree of CO activation in the reduced cluster.

Syngas Conversion over Co4 Cluster Grafted on HZSM‐5 Zeolite: Mechanistic Insights from DFT Modeling

AbstractWe present a detailed DFT‐based mechanistic investigation of syngas conversion mechanism over Co4 cluster grafted onto HZSM‐5 zeolite, [Co4H], employing a QM/MM embedded cluster approach. Starting from the [Co4H] complex, our results show that a favorable coordination of CO over H2, followed by CO hydrogenation leads to a stable −CH2O complex, [Co4(CH2O)(H)]. Coordination of a second CO molecule to [Co4(CH2O)(H)] complex, followed by CH2−O bond activation, and subsequent removal of CO as CO2 results in the formation of crucial methylene complex [Co4(CH2)(H)], serving as a branching point for the pathways leading to methane, ethene, and ethane. On the pathway to ethene formation, coordination of a third CO molecule to [Co4(CH2)(H)] complex yields the active [Co4(CH2)(CO)(H)] complex, which is 16.0 kcal mol−1 more stable than the methyl complex [Co4(CH3)] on the pathway to methane. From the active species [Co4(CH2)(CO)(H)], we demonstrate that the pathways to both methane and ethene are competing in nature, with the −CH3 hydrogenation barrier, 35.1 kcal mol−1, is lower by only 1.3 kcal mol−1 than the competing C−O bond activation barrier on the pathway to ethene, 36.4 kcal mol−1. However, the significant stability of the active species [Co4(CH2)(CO)(H)] effectively compensates for this minor difference in barriers, ultimately favoring the formation of ethene over methane. Finally, the ethene desorption barrier is 4.1 kcal mol−1 lower than the ethene hydrogenation barrier on the pathway to ethane, indicating the ease of ethene removal from the system. Overall, our DFT study describes that the syngas conversion mechanism catalyzed by [Co4H] system produces ethene selectively via 4CO+2H2→C2H4+2CO2.

Electrochemical Synthesis and Electrocatalytic Oxygen-Evolution Performance of Two-Dimensional NiCo-BPDC Materials.

Metal-organic frameworks (MOFs) have been widely studied as electrocatalysts, and the research strategy to improve their electrocatalytic oxygen evolution reaction (OER) performance is to modify their structure. In this paper, two-dimensional bimetallic MOFs were constructed to improve electrocatalytic OER performance. Using a mild electrochemical method with Ni and Co as metal sources and 4, 4 '-biphenyl dicarboxylic acid (H2BPDC) as ligand, two-dimensional NiCo-BPDC was synthesized and then deposited on a carbon cloth electrode. The results show that NiCo-BPDC/CC possessed a low overpotential of 356 mV at a current density of 20 mA cm-2 with a small Tafel slope of 86 mV dec-1 in 1.0 M KOH solution. The two-dimensional NiCo-BPDC exhibits excellent electrocatalytic OER performance because the coordination of Ni and Co in the material and the interaction of the two-dimensional materials provide a large electrochemically active surface area and expose more metal active sites for OER, thus improving the reaction efficiency and indicating NiCo-BPDC as potential OER electrocatalyst.

Structural and electrochemical analysis of FeCp* complexes supported by a borate-bridged dicarbene ligand

We report three new FeCp* complexes (Cp* = pentamethylcyclopentadienyl) containing a bulky and electron rich borate-bridged ligand [Ph2B(tBuNHC)2]- (NHC = N-heterocyclic carbene). These (Ph2B(tBuNHC)2)FeCp* complexes are in three different spin states and are characterized using a combination of single crystal X-ray diffraction, cyclic voltammetry, NMR/IR spectroscopy, and topographic steric mapping. The combination of bulky tBu groups and Cp* enable the isolation of coordinatively unsaturated intermediate-spin FeII (S = 1) and FeIII (S = 3/2) complexes, while CO coordination to FeII furnishes a low spin (S = 0) adduct.

A rotational isomerization of diiron complexes of ferrole type involved in the catalytic hydroboration of aldehydes under mild conditions

In this work, two new diiron(I) complexes of ferrole or ferracyclopentadiene type, [Fe2(CO)6{RC2(CH2)4C2R}] (R = H, 1; CH2CH3, 2) were synthesized by reacting the [Fe2(CO)9] with diynes (1,7-octadiyne and 3,9-dodecanediyne). The ferrole-type complexes were fully characterized, wherein the absolute structure of 2 was determined by single-crystal X-ray diffraction analysis. Interestingly, a rotational isomerization of the diiron(I) complexes (1 and 2) between the sawhorse conformer and the non-sawhorse conformer is verified, originated from the switch of CO coordination. Additionally, the sawhorse conformer with the terminal CO is dominant in solution due to the tricarbonyl iron units undergo a drastic geometrical turnstile rotation, whereas the non-sawhorse conformer with a semi-bridging CO is rigid in a solid state. Particularly, the isomerism of the diiron(I) complexes of ferrole type leads to a unique catalytic activity for hydroboration of aldehydes with pinacolborane (HBpin). Notably, twelve aldehydes (3a-3l) were exampled to be converted quantitatively into the corresponding organoboronates (4a-4l) mediated by complex 2 under mild conditions. Mechanistically, the 1H NMR and FTIR spectroscopic results proved that the ferrole-type complex 2 bound with the aldehyde to activate the carbonyl of the substrate rather than to cleave the H-B bond of pinacolborane. Collectively, a plausible mechanism for the catalytic hydroboration is proposed, with the rotational isomerization of the diiron(I) complexes involved in.

Construction of high-capacitance carbonate-rich bimetallic layered (hydr)oxides onto ZIF-67–derived Co/CoO-N-carbon hybrid cubes for high-performance symmetric supercapacitors

Herein, we fabricated carbonate-rich bimetallic layered hydr(oxides) (CoMnOx), which are primarily used as active materials for supercapacitors, using a simple hydrothermal method. CoMnOx was deposited onto cobalt oxide (CoO), which was produced by pyrolyzing ZIF-67 at 800 °C under N2 atmosphere. The Co/CoO cubes synthesized using carbonized ZIF-67 (ZIFC) were covered with CoMnOx shells with high reduction efficiency and abundant Co active sites and surface O species. The effects of the carbonate species present between the CoMnOx layers and at the surface of the hybrid CoMnOx@ZIFC materials were evaluated using PXRD and XPS. The peaks at the binding energies of 290 and 400 eV in the C 1s and N 1s XPS profiles of CoMnOx@ZIFC, respectively, indicate the presence of carbonate species and coordination of CoO and Co with the N-rich carbon materials, respectively. The FE-SEM images of CoMnOx@ZIFC revealed the partial decomposition of the cubic structure of ZIFC, which agreed with previously reported data. Moreover, the elemental composition of CoMnOx@ZIFC was confirmed using EDS mapping and point analysis. The CoMnOx@ZIFC electrodes exhibited a remarkable specific capacitance/capacitor of 963 F g−1/588 C g−1 at 1 A g−1 and excellent cycling stability over 1000 cycles, which was superior to those of previously reported MOF-derived carbonate-based materials in alkaline electrolytes. The CoMnOx@ZIFC||CoMnOx@ZIFC symmetric supercapacitor exhibited an energy density of 60.75 W h kg−1 with a power density of 5947 W kg−1 and an exceptional cycling stability (>99.5 %) after 3000 cycles.

Fabrication of Metal Ion–BSA Chelation-Targeted Surface-Imprinted Particles for Protein Separation

The development of high-performance protein-imprinted materials for adsorption and separation to obtain high-purity, high-quality biomolecules is still one of the most important techniques to promote the rapid development of the protein drug industry. In this paper, a novel highly specific bovine serum albumin (BSA) cobalt–molybdenum double-hydroxides surface-imprinted composite particles (Co–Mo LDHs@MIPs) were constructed by the surface imprinting technique combined with metal chelation. ZIF-67 was etched by molybdate ions to obtain unique MOF-derived bimetallic hydroxide particles (Co–Mo LDHs), which were used as the carrier. The rough outer surface and bimetallic ion coordination of Co–Mo LDHs enable anchoring more template proteins. The adsorption capacity of Co–Mo LDHs@MIPs was up to 423.37 mg/g for BSA in 60 min with an imprinting factor of 2.65. In addition, Co–Mo LDHs@MIPs can selectively recognize and separate BSA from mixed proteins and fetal bovine serum and exhibit high reusability stability.

Lewis Acids and Electron-Withdrawing Ligands Accelerate CO Coordination to Dinuclear CuI Compounds.

A series of dinuclear molecular copper complexes were prepared and used to model the binding and Lewis acid stabilization of CO in heterogeneous copper CO2 reduction electrocatalysts. Experimental studies (including measurement of rate and equilibrium constants) and electronic structure calculations suggest that the key kinetic barrier for CO binding may be a σ-interaction between CuI and the incoming CO ligand. The rate of CO coordination can be increased upon the addition of Lewis acids or electron-withdrawing substituents on the ligand backbone. Conversely, Keq for CO coordination can be increased by adding electron density to the metal centers of the compound, consistent with stronger π-backbonding. Finally, the electrochemically measured kinetic results were mapped onto an electrochemical zone diagram to illustrate how these system changes enabled access to each zone.

Room temperature fabrication of cobalt mullite for the snappy adsorption of cationic and anionic dyes

Cobalt mullite adsorbent for the robust adsorption performance toward Victoria Blue (VB) and Metanil Yellow (MY) is fabricated by the sol-gel method at room temperature using dipropylamine as a structure-directing agent. The synthesized adsorbent is characterized by XRD, FT-IR, and HRTEM. From these analyses, it is found that dipropylamine binds with the alumina and cobalt oxide, which makes it into tetrahedral to octahedral form. This interaction causes the formation of cobalt mullite. It is observed that trigonal alumina and orthorhombic cobalt mullite are interlinked to form a hybrid network. The special feature of adopting this adsorbent for the adsorption of VB and MY is that it has a large amount of Brønsted acid site because of the octahedral coordination of Al and Co. The large availability of acid sites in the framework and hybridization of two different network systems favors robust adsorption. The rate of adsorption (K2 = 0.00402g/mg.min for VB and K2 = 0.004g/mg.min for MY) and adsorption capacity (Qe = 102.041mg/g for VB and Qe = 19.0406mg/g for MY) are greater for VB than MY. This may be due to the more steric factor involved in MY than VB. Thermodynamic parameter indicated that the adsorption of VB and MY is spontaneous, endothermic, and increased randomness in the adsorbent-adsorbate interface. The results from the enthalpy value (ΔH° = 65.43kJ/mol for VB and ΔH° = 44.729kJ/mol for MY) revealed that the chemisorption is involved in the adsorption process.

Efficient overall water-splitting enabled by tunable electronic states of vanadium-substituted P–Co3O4

Despite the fact that phosphorus (P) partly substituted Co3O4 (P–Co3O4) has been considered as an intriguing electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the modulation of electronic property using hetero atoms to improve activities of P-rich Co3O4 catalyst remains an elusive goal. Herein, we demonstrate that the vanadium (V) doping provides the most promising strategy to significantly regulate the electronic states of P–Co3O4, thus yielding an outstanding overall water-splitting performance. A small cell voltage of 1.594 V is required to deliver the current density of 10 mA/cm2, largely outperforming the RuO2||Pt/C catalyst. It is further revealed that the added V5+ with empty 3d orbital can act as electron acceptors, which weakens the coordination of Co–O band. As a result, the electrons are inclined to transfer to the V through the O ligand, rather than to Co. We then report that the V doping could modulate the local electronic configuration and atomic arrangement of bonded Co and adjacent O atoms to enhance the electrons’ delocalization capacity of Co atoms for high electrical conductivity, as well as effectively accelerate the formation of key H∗ intermediates toward fast HER kinetics. These findings represent a new strategy for regulating the electronic properties of catalysts and are expected to open new opportunities for the development of high-performance catalysts.

Cu+-Mediated CO Coordination for Promoting C–C Coupling for CO2 and CO Electroreduction

Selective electrochemical upgrading of CO2 to multicarbon (C2+) products requires a C-C coupling process, yet the underlying promoting mechanism of widely involved Cu oxidation states remains largely unclear, hindering the subtle design of efficient catalysts. Herein, we unveil the critical role of Cu+ in promoting C-C coupling via coordination with a CO intermediate during electrochemical CO2 reduction. We find that, relative to other halogen anions, iodide (I-) in HCO3- electrolytes accelerates the generation of strongly oxidative hydroxyl radicals that accounts for the formation of Cu+, which can be dynamically stabilized by I- via the formation of CuI. The in situ generated CO intermediate strongly binds to CuI sites, forming nonclassical Cu(CO)n+ complexes, leading to an approximately 3.0-fold increase of C2+ Faradaic efficiency at -0.9 VRHE relative to that of I--free Cu surfaces. Accordingly, a deliberate introduction of CuI into I--containing HCO3- electrolytes for direct CO electroreduction brings about a 4.3-fold higher C2+ selectivity. This work provides insights into the role of Cu+ in C-C coupling and the enhanced C2+ selectivity for CO2 and CO electrochemical reduction.

Fluorine‐regulated carbon nanotubes decorated with Co single atoms for multi‐site electrocatalysis toward two‐electron oxygen reduction

AbstractProducing hydrogen peroxide (H2O2) via a two‐electron oxygen reduction reaction (2 e−‐ORR) is a promising alternative to the conventional anthraquinone process, because of its exceptional low‐risk and distributed features. The low yield of H2O2 on typical electrocatalysts, usually associated with limited and vulnerable catalytically active sites on their surface, has been the major restriction for improving the practical viability of this technology. Herein, we report an ultrafast microwave‐based strategy for constructing distant coordination of Co single‐atom sites with secondary fluorene heterodopants on carbon nanotubes, which successfully converts the 2 e−‐ORR active centers from a single Co atom to multiple surrounding carbon atoms, increasing both the quantity and durability of active sites for 2 e−‐ORR. Consequently, a high H2O2 yield of up to 18.6 mol g−1 L−1 has been achieved, accompanied by a Faraday efficiency of 90%. Besides, an accumulative H2O2 concentration of 5.2 g L−1 is obtained after 20 h electrocatalysis, showing the material's high stability and feasibility for practical applications. Density functional theory simulations confirm the optimal adsorption of *OOH on these carbon sites, providing very low kinetic barriers for 2 e−‐ORR. Thus, this work provides a high‐performance electrocatalyst for 2 e−‐ORR, and more importantly strategy for promoting the performance of single‐atom catalysts.image

Electronic Effect on Phenoxide Migration at a Nickel(II) Center Supported by a Tridentate Bis(phosphinophenyl)phosphido Ligand.

A phosphide nickel(II) phenoxide pincer complex (2) reacts with CO(g) to give a pseudo-tetrahedral nickel(0) monocarbonyl complex (3) possessing a phosphinite moiety. This metal-ligand cooperative (MLC) transformation occurs with a (PPP)Ni scaffold (PPP- = P[2-PiPr2-C6H4]2-), which can accommodate both square planar and tetrahedral geometries. The 2-electron reduction of a nickel(II) species induced by CO coordination involves group transfer to generate a P-O bond. For better mechanistic understanding, a series of nickel(II) phenolate complexes (2a-2e, XC6H4O- (X = OMe, Me, H, and CF3) and pentafluorophenolate) were prepared. Kinetic experimental data reveal that a phenolate species with an electron-withdrawing group reacts faster than those with electron-donating groups. The reaction kinetic experiments were conducted in pseudo-first order conditions at room temperature monitored by UV-vis spectroscopy. A pentafluorophenolate nickel(II) complex (2e) reveals instantaneous reactions even at -40 °C to give a nickel(0) monocarbonyl species (3e) and the reverse reaction is also possible. According to kinetic experiments, the rate determining step (RDS) would be the formation of a 5-coordinate intermediate 4 with a negative entropy value (ΔS‡ < 0), and a positive ρ value based on the Hammett plot indicates that the electron-deficient phenolate leads to a faster CO association. Furthermore, scramble experiments suggest that phenolate de-coordinates from the intermediate 4, which gives a (PPP)Ni-CO species 6. The cationic nickel monocarbonyl intermediate can possess a P--Ni(II), P•-Ni(I), or even a P+-Ni(0) character. Such an inner-sphere electron transfer is suggested when a π-acidic ligand such as CO coordinates to a metal ion. Another possible reaction is homolysis of a Ni-O bond to give P--Ni(I) or P•-Ni(0), when a phenoxyl radical is liberated. Considering the P-O bond formation, closed-shell nucleophilic and open-shell radical pathways are suggested. A phenolate pathway reveals a lower energy state for 2e relative to other complexes (2c and 2d), while its radical pathway undergoes via a higher energy state. Therefore, the formation of a P-O bond may occur with the binding of a closed-shell phenolate to the electron-deficient P center.

Co and Ni single sites on the (111)n surface of γ-Al2O3 – a periodic boundary DFT study

Coordination of Co and Ni single-atom on the most active tri-coordinated Al/Metal single-site (111)n surface of γ-Al2O3 leads to stable electron configuration of d7 for Co and d8 for Ni on the surface of γ-Al2O3.

Understanding the role of Zn vacancy induced by sulfhydryl coordination for photocatalytic CO2reduction on ZnIn2S4

Zn vacancy ZnIn2S4tuned Gibbs free energy of *COOH which is the rate determining step of phototcatalytic CO2reduction from endothermic to exothermic process.

Effective electronic tuning of Pt single atomsviaheterogeneous atomic coordination of (Co,Ni)(OH)2for efficient hydrogen evolution

A Pt1/(Co,Ni)(OH)2/C single-atom electro-catalyst efficiently splits water for H2generation,viabalanced water-dissociation and H2-formation steps from the synergistic effect of surface-defective (Co,Ni)(OH)2and electronically tuned Pt sites.

Disilicon Dicarbonyl Complex: Synthesis and Protonation of CO with O-H Bond.

Reaction of solid NHB-stabilized disilyne (NHB)Si≡Si(NHB) (1, NHB = [ArN(CMe)2NAr]B, Ar = 2,6-iPr2C6H3) with 1 atm of carbon monoxide yielded the first 1,2-disilicon dicarbonyl complex (NHB)(OC)SiSi(CO)(NHB) (2). Hydrolysis and methanolysis of 2 led to the C-C coupling and protonation of two CO oxygen atoms giving disilacyclobutene derivatives 3 and 4. In contrast, reaction of 2 with iodomethane resulted in the oxidative addition to the silicon atoms with the formation of 1,2-diiodo-disilane 5 with the liberation of CO molecules. Single-crystal X-ray diffraction analysis of 2 disclosed the coordination of CO to the two silicon atoms with a unique 1,2-dicarbonyl-disilane skeleton, in which the pronounced backbonding from the lone pairs of silicon p orbitals to CO π* orbitals was elucidated by DFT calculations.