Cobalt Cubane Research Articles

A heterogeneous cobalt cubane polymer co-catalyst for cooperative water oxidation.

We achieve a successful transition of Co4O4 molecules from a homogeneous to a heterogeneous system by modifying the functional groups at their termini. The resulting cocatalyst, denoted as Co4O4-poly, not only preserved the catalytic sites of Co4O4 molecules but also exhibited outstanding performance in catalyzing water oxidation.

A Facile Design for Water-Oxidation Molecular Catalysts Precise Assembling on Photoanodes.

Regulating the interfacialcharge transfer behavior between cocatalysts and semiconductors remains a critical challenge for attaining efficient photoelectrochemical water oxidation reactions. Herein, using bismuth vanadate (BiVO4 ) photoanode as a model, it introduces an Au binding bridge as holes transfer channels onto the surfaces of BiVO4 , and the cyano-functionalized cobalt cubane (Co4 O4 ) molecules are preferentially immobilized on the Au bridge due to the strong adsorption of cyano groups with Au nanoparticles. This orchestrated arrangement facilitates the seamless transfer of photogenerated holes from BiVO4 to Co4 O4 molecules, forming an orderly charge transfer pathway connecting the light-absorbing layer to reactive sites. An exciting photocurrent density of 5.06mAcm-2 at 1.23V versus the reversible hydrogen electrode (3.4 times that of BiVO4 ) is obtained by the Co4 O4 @Au(A)/BiVO4 photoanode, where the surface charge recombination is almost completely suppressed accompanied by a surface charge transfer efficiency over 95%. This work represents a promising strategy for accelerating interfacial charge transfer and achieving efficient photoelectrochemical water oxidation reaction.

Graphene Mediates Charge Transfer between Lead Chromate and a Cobalt Cubane Cocatalyst for Photocatalytic Water Oxidation.

The interfacial barrier of charge transfer from semiconductors to cocatalysts means that the photogenerated charges cannot be fully utilized, especially for the challenging water oxidation reaction. Using cobalt cubane molecules (Co4 O4 ) as water oxidation cocatalysts, we rationally assembled partially oxidized graphene (pGO), acting as a charge-transfer mediator, on the hole-accumulating {-101} facets of lead chromate (PbCrO4 ) crystal. The assembled pGO enables preferable immobilization of Co4 O4 molecules on the {-101} facets of the PbCrO4 crystal, which is favorable for the photogenerated holes transferring from PbCrO4 to Co4 O4 molecules. The surface charge-transfer efficiency of PbCrO4 was boosted by selective assembly of pGO between PbCrO4 and Co4 O4 molecules. An apparent quantum efficiency for photocatalytic water oxidation on the Co4 O4 /pGO/PbCrO4 photocatalyst exceeded 10 % at 500 nm. This strategy of rationally assembling charge-transfer mediator provides a feasible method for acceleration of charge transfer and utilization in semiconductor photocatalysis.

Graphene Mediates Charge Transfer between Lead Chromate and a Cobalt Cubane Cocatalyst for Photocatalytic Water Oxidation

AbstractThe interfacial barrier of charge transfer from semiconductors to cocatalysts means that the photogenerated charges cannot be fully utilized, especially for the challenging water oxidation reaction. Using cobalt cubane molecules (Co4O4) as water oxidation cocatalysts, we rationally assembled partially oxidized graphene (pGO), acting as a charge‐transfer mediator, on the hole‐accumulating {−101} facets of lead chromate (PbCrO4) crystal. The assembled pGO enables preferable immobilization of Co4O4 molecules on the {−101} facets of the PbCrO4 crystal, which is favorable for the photogenerated holes transferring from PbCrO4 to Co4O4 molecules. The surface charge‐transfer efficiency of PbCrO4 was boosted by selective assembly of pGO between PbCrO4 and Co4O4 molecules. An apparent quantum efficiency for photocatalytic water oxidation on the Co4O4/pGO/PbCrO4 photocatalyst exceeded 10 % at 500 nm. This strategy of rationally assembling charge‐transfer mediator provides a feasible method for acceleration of charge transfer and utilization in semiconductor photocatalysis.

Ligand Exchange Reaction in [Co4O4]-Cobalt Cubane: A Versatile Strategy Towards the Preparation of Cobalt Cubane-based Functional Small Molecules and Polymeric Materials

Herein, we report the mechanistic and application study of ligand exchange reaction in Co4O4-cobalt cubane, a well-known water oxidation catalyst (WOC). The ligand exchange reaction involves the instantaneous dissociation of attached pyridine ligand and replacement of target ligand in an appropriate solvent. The kinetic and thermodynamic parameters were quantified for the ligand exchange reaction under mild conditions. Activation parameters revealed that the ligand exchange mechanism follows dissociative (D) or interchange-dissociative (Id) pathway in case of Co4O4, as it is evident by the high activation enthalpy (ΔH‡) and the positive activation entropy (ΔS‡) values. The effects of ligand derivatization, reaction temperature and type of the solvent on the exchange kinetics and the product purity were also investigated in detail. Furthermore, our theoretical studies disclosed the most probable ligand exchange pathway in case of Co4O4. Finally, this methodology was successfully applied to the preparation of Co4O4-containning functional poly-4vinylpyridine (P4VP) and cross-linked heterogeneous polymeric catalysts. The present mechanistic study clearly demonstrates that the ligand exchange method is an efficient and versatile method for the preparation of Co4O4-based functional materials.

Ballistic ΔS = 2 intersystem crossing in a cobalt cubane following ligand-field excitation probed by extreme ultraviolet spectroscopy.

Femtosecond M2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to probe the excited-state dynamics of the cobalt cubane [CoIII4O4](OAc)4(py)4 (OAc = acetate, py = pyridine), a model for water oxidation catalysts. After ligand-field excitation, intersystem crossing (ISC) to a metal-centered quintet occurs in 38 fs. 30% of the hot quintet undergoes ballistic back-ISC directly to the singlet ground state, with the remainder relaxing to a long-lived triplet.

Cobalt Cubane Clusters Based on Schiff Base: Synthesis, Characterization, Magnetic Properties and Hirshfeld Surface Analysis

Three cobalt cubane clusters with the composition of [Co4(L)4], (1, H2L is 1-{3-[(3,5-dibromo-2-hydroxy-benzylidene)-amino]-2-hydroxy-phenyl}-ethanone (H2DBHBA); 2, H2L is 1-{3-[(5-bromo-2-hydroxy-benzylidene)-amino]-2-hydroxy-phenyl}-ethanone (H2BHBA); 3, H2L is 1-{3-[(3,5-dichloro-2-hydroxy-benzylidene)-amino]-2-hydroxy-phenyl}-ethanone (H2DCHBA)), were prepared by the reaction of cobalt nitrate hexahydrate with 2-hydroxy-benzaldehyde ramification under solvothermal conditions. All the complexes were characterized by elemental analysis, infrared spectroscopy, and X-ray single-crystal diffraction. Complexes 1–3 have tetranuclear clusters with a cubane topology in which the metal ions and the oxygen atoms from the L ligands occupying the alternate vertices of the cubane. The {Co4O4} cores display dominant anitferromagnetic interactions owing to the μ3-O bridged binding modes. Hirshfeld surface analysis revealed that H···H, and C···X (X = Br or Cl) interactions were the dominant intermolecular interactions.

Immobilization of a molecular cobalt cubane catalyst on porous BiVO4via electrochemical polymerization for efficient and stable photoelectrochemical water oxidation.

A facile and efficient strategy is described in this communication for preparing a molecular catalyst/semiconductor hybrid photoanode by immobilizing a cobalt cubane water oxidation catalyst onto a porous BiVO4 electrode via electrochemical polymerization. With the introduction of Vpa as the anchoring linkage, the poly-1/Vpa/Al2O3/BiVO4 photoanode exhibits high performance as well as stability for photoelectrochemical water oxidation.

Large Magnetic Polyoxometalates Containing the Cobalt Cubane '[CoIIICo (OH)3(H2O)6-m(PW9O34)]3-' (m = 3 or 5) as a Subunit.

A synthetic procedure is presented to construct new magnetic polyoxometalates (POMs) containing one or two subunits of ‘[CoIIICo(OH)3(H2O)6−m(PW9O34)]3−' (m = 3 or 5). The substitution of the water ligands present in these subunits by oxo or hydroxo ligands belonging to other POM fragments, gives rise to four, larger POM anions: [Co7(OH)6(H2O)6(PW9O34)2]9− (2), [Co7(OH)6(H2O)4(PW9O34)2] (2′), [Co11(OH)5(H2O)5(W6O24)(PW9O34)3]22− (3) and [{Co4(OH)3(H2O)(PW9O34)}2{K⊂(H2W12O41)2}{Co(H2O)4}2]17− (4). The crystal structures, magnetic characterization and stabilities in aqueous solutions of these POM derivatives are also presented.

Structural Investigation of Cobalt Oxide Clusters Derived from Molecular Cobalt Cubane, Trimer, and Dimer Oligomers in a Phosphate Electrolyte

Cobalt oxide clusters were formed from three molecular cobalt oligomers, the Co-cubane, [Co4(μ3-O)4(μ-OAc)4(py)4], Co-trimer, [Co3(μ3-O)(μ-OAc)6(py)3][PF6], and Co-dimer, [Co2(μ-OH)2(μ-OAc)(OAc)2(py)4][PF6], in phosphate buffer electrolyte after aging. Phosphate is essential for the formation of these cobalt oxide clusters. XAS characterization shows the cobalt oxide clusters are CoII/IIIOx clusters with CoII(O)4 and CoIII(O)6 subunits. The cobalt oxide clusters formed have a structure similar to that of aged “CoPi” oxygen evolution catalysts prepared by electrodeposition.

Highly Efficient Photoelectrochemical Water Splitting with an Immobilized Molecular Co4O4 Cubane Catalyst

Molecular Co4 O4 cubane water oxidation catalysts were combined with BiVO4 electrodes for photoelectrochemical (PEC) water splitting. The results show that tuning the substituent groups on cobalt cubane allows the PEC properties of the final molecular catalyst/BiVO4 hybrid photoanodes to be tailored. Upon loading a new cubane complex featuring alkoxy carboxylato bridging ligands (1 h) on BiVO4 , an AM 1.5G photocurrent density of 5 mA cm-2 at 1.23 V vs. RHE for water oxidation was obtained, the highest photocurrent for undoped BiVO4 photoanodes. A high solar-energy conversion efficiency of 1.84 % was obtained for the integrated photoanode, a sixfold enhancement over that of unmodified BiVO4 . These results and the high surface charge separation efficiency support the role of surface-modified molecular catalysts in improving PEC performance and demonstrate the potential of molecule/semiconductor hybrids for efficient artificial photosynthesis.

Highly Efficient Photoelectrochemical Water Splitting with an Immobilized Molecular Co4O4 Cubane Catalyst

AbstractMolecular Co4O4 cubane water oxidation catalysts were combined with BiVO4 electrodes for photoelectrochemical (PEC) water splitting. The results show that tuning the substituent groups on cobalt cubane allows the PEC properties of the final molecular catalyst/BiVO4 hybrid photoanodes to be tailored. Upon loading a new cubane complex featuring alkoxy carboxylato bridging ligands (1 h) on BiVO4, an AM 1.5G photocurrent density of 5 mA cm−2 at 1.23 V vs. RHE for water oxidation was obtained, the highest photocurrent for undoped BiVO4 photoanodes. A high solar‐energy conversion efficiency of 1.84 % was obtained for the integrated photoanode, a sixfold enhancement over that of unmodified BiVO4. These results and the high surface charge separation efficiency support the role of surface‐modified molecular catalysts in improving PEC performance and demonstrate the potential of molecule/semiconductor hybrids for efficient artificial photosynthesis.

Immobilising a cobalt cubane catalyst on a dye-sensitised TiO2 photoanode via electrochemical polymerisation for light-driven water oxidation

A cobalt cubane catalyst Co4O4(O2CMe)4(4-vinylpy)4 was immobilised on a dye-sensitized TiO2 electrode via electrochemical polymerization for light-driven water oxidation.

Electrochemical investigation of [Co4(μ3-O)4(μ-OAc)4(py)4] and peroxides by cyclic voltammetry.

Two oxidative redox processes of the neutral cobalt(iii) cubane, [Co4(μ3-O)4(μ-OAc)4(py)4], were investigated by cyclic voltammetry at a glassy carbon electrode in acetonitrile. In addition to the first quasi-reversible one-electron oxidation at E1/2 = 0.283 V vs. Fc0/+, a second quasi-reversible one-electron oxidation was observed at E1/2 = 1.44 V vs. Fc0/+. Oxidation at this potential does not facilitate water oxidation. In the presence of tert-butylhydroperoxide the peak current of this second oxidation increases, suggesting oxidation of the peroxide by the doubly oxidised cubane.

Photo-active Cobalt Cubane Model of an Oxygen-Evolving Catalyst

A dyad complex has been constructed as a soluble molecular model of a heterogeneous cobalt-based oxygen-evolving catalyst (Co-OEC). To this end, the Co(4)O(4) core of a cobalt-oxo cubane was covalently appended to Re(I) photosensitisers. The resulting adduct was characterised both in the solid state (by X-ray diffraction) and in solution using a variety of techniques. In particular, the covalent attachment of the Re(I) moieties to the Co(4)O(4) core promotes emission quenching of the Re(I) photocentres, with implications for the energy and electron transduction process of Co-OEC-like catalysts.