Ein Cobalt(IV)‐Oxido‐Komplex: Stabilisierung durch Lewis‐Säure‐Wechselwirkung mit Sc<sup>3+</sup>

Pfaff, Florian Felix; Kundu, Subrata; Risch, Marcel; Pandian, S.; Heims, Florian; Pryjomska-Ray, Iweta; Haack, Peter; Metzinger, Ramona; Bill, Eckhard; Dau, Holger; Comba, Peter; Ray, Kallol

doi:10.1002/ange.201005869

Cited by 43 publications

(16 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…63,[67][68][69] Using XRD, a bond length of 1.85 Å was obtained for Na0.35CoO2·yH2O. 71,72 In conclusion, the EXAFS analysis supports the formation of Co IV ions at higher potentials. 71,72 In conclusion, the EXAFS analysis supports the formation of Co IV ions at higher potentials.…”

Section: Structural Changes In the Cocat Redox Transitions Assessed Bmentioning

confidence: 66%

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Risch

Ringleb

Kohlhoff

et al. 2015

Energy Environ. Sci.

Self Cite

306

431

View full text Add to dashboard Cite

Water oxidation by amorphous oxides is of high interest in artificial photosynthesis and other routes towards non-fossil fuels, but the mode of catalysis in these materials is insufficiently understood. We tracked mechanistically relevant oxidation-state and structural changes of an amorphous Co-based catalyst film by in-situ experiments combining directly synchrotron-based X-ray absorption spectroscopy (XAS) with electrocatalysis. Unlike a classical solid-state material, the bulk material is found to undergo chemical changes. Two redox transitions at midpoints potentials of about 1.0 V (Co II 0.4Co III 0.6  all-Co III ) and 1.2 V (all-Co III  Co III 0.8Co IV 0.2) vs. NHE at pH 7 are coupled to structural changes. These redox transitions can be induced by variation of either electric potential or pH; they are broader than predicted by a simple Nernstian model, suggesting interacting bridged cobalt ions. Tracking reaction kinetics by UV-Vis-absorption and time-resolved mass spectroscopy reveal that accumulated oxidizing equivalents facilitate dioxygen formation. On these grounds, a new framework model of catalysis in the amorphous, hydrated and volume-active oxide is proposed: Within the oxide film, cobalt ions at the margins of Co-oxo fragments undergo Co II Co III Co IV oxidationstate changes coupled to structural modification and deprotonation of Co-oxo bridges. By encounter of two (or more) Co IV ions, an active site is formed at which the O-O bondformation step can take place. The Tafel slope is determined by both the interaction between cobalt ions (width of the redox transition) and their encounter probability. Our results represent a first step toward development of new concepts that address the solid-molecular Janus nature of the amorphous oxide. Insights and concepts described herein for the Co-based catalyst film may be of general relevance also for other amorphous oxides with water-oxidation activity. EXPERIMENTAL XAS measurements -in-situ experimentCoCat-coated electrodes were prepared by electrodeposition in a separate electrochemical setup before start of the in-situ XAS measurements from a solution of 0.5 mM Co 2+ ions in 0.1 M KPi at pH 7 (deposition of about 50 nmol cm -1 of Co ions, see ESI for further details). The in-situ XAS measurements were performed at the SuperXAS beamline of the Swiss Light Source (SLS) in Villigen, Switzerland. The excitation energy was selected by a double-crystal monochromator (Si-111, detuning to 50 % intensity, scan range of 7650-8400 eV) and used to irradiate the backside of the ITO/PET electrode at an angle of 45°. The spot size of the X-ray beam on the sample was 5 mm × 1 mm. Due to employment of a large spot size (defocussed beam) and a rapid-scanning mode, the influence of radiation-induced modifications was negligible, as verified in control experiments. The cobalt K-edge fluorescence was monitored perpendicular to the incident beam by a scintillation detector (19.6 cm 2 active area, 51BMI/2E1-YAP-Neg, Scionix), which was shielded by a 25 μm iron foil agai...

show abstract

Section: Structural Changes In the Cocat Redox Transitions Assessed Bmentioning

confidence: 66%

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Risch

Ringleb

Kohlhoff

et al. 2015

Energy Environ. Sci.

Self Cite

306

431

View full text Add to dashboard Cite

show abstract

“…The equilibrial character of the complex formation reaction can be weakened, i.e., the metalloporphyrin formed becomes kinetically more inert, because the porphyrin ligands can stabilize the (even extremely) high oxidation states of metal ions on the basis of their high partial negative charge and polarizing effect: e.g. manganese(III-V) [95], iron(III-V) [96], cobalt (III-IV) [97], molybdenum(V) [98], silver(II-III) [77,99] are possible oxidation states in porphyrins. (These effects of the macrocycle can be further increased by peripheral substitutions with electron donating groups [85].)…”

Section: Equilibrium and Kinetics Of The Complex Formationmentioning

confidence: 99%

Application of the electronic spectra of porphyrins for analytical purposes: The effects of metal ions and structural distortions

Valicsek

Horváth

2013

Microchemical Journal

122

118

View full text Add to dashboard Cite

We investigated the UV-Vis absorption, singlet-1 and singlet-2 fluorescence, as well as the formation of several metalloporphyrins from equilibrial and kinetic aspects in aqueous solution. Among these complexes were numerous typical out-of-plane and several in-plane metalloporphyrins, and between the two categories, a few border-line cases. On the basis of our results, we have complemented the categorization introduced by Barnes and Dorough for the metalloporphyrins. According to our observations, also in metalloporphyrins, the distortion, i.e., the planarity or nonplanarity of the macrocycle, is basically responsible for the spectral characteristics, while the electronic structure of metal center is a secondary factor, with a considerable importance mainly in the in-plane complexes. The type of complexes can be spectrophotometrically determined on the basis of their UV-Vis absorption and fluorescence spectra. Beside the spectral and photophysical effects of metalation, also those of the structural distortions were studied, which can originate also from metalation, protonation or overcrowded peripheral substitution of the free-base porphyrins, as well as from the axial ligation of metalloporphyrins. Our observation may be useful for different spectrophotometric analytical detection and determination methods, e.g. size-selective metal detection using free-base porphyrins (or other ringed chelate ligands), as well as the determination of Lewis bases as potential axial ligands, using metalloporphyrins.

show abstract

“…It shouldb en oted that the CoÀOd istance of 1.67 f or [(TAML)Co IV (O)ÀSc] 2 + determined by EXAFS is significantly shorter than the CoÀOd istances of 1.79 a nd 1.85 d etermined for [(a-P 2 W 17 O 61 Co IV ) 2 O] 14À by X-ray diffraction [72] and [(TMG 3 tren)Co IV (O)(Sc)(OTf) 3 ]] 2 + (TMG 3 tren = tris[2-(N-tetramethylguanidyl)ethyl]amine) by EXAFS. [73] The latter speciesw as later suggested to contain aC o III (OH) unit rather than aC o IV (O) unit, [74] and furtheri nvestigation is needed to clarify the nature of the CoÀO(H) moiety. Figure 6w as takenw ith permission from reference [ 69].…”

Section: Cobalt(iv)-oxo Complexesmentioning

confidence: 99%

ChemInform Abstract: Lewis Acid Coupled Electron Transfer of Metal—Oxygen Intermediates

et al. 2016

View full text Add to dashboard Cite

show abstract

Ein Cobalt(IV)‐Oxido‐Komplex: Stabilisierung durch Lewis‐Säure‐Wechselwirkung mit Sc³⁺

Cited by 43 publications

References 46 publications

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Application of the electronic spectra of porphyrins for analytical purposes: The effects of metal ions and structural distortions

ChemInform Abstract: Lewis Acid Coupled Electron Transfer of Metal—Oxygen Intermediates

Contact Info

Product

Resources

About

Ein Cobalt(IV)‐Oxido‐Komplex: Stabilisierung durch Lewis‐Säure‐Wechselwirkung mit Sc3+

Cited by 43 publications

References 46 publications

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Application of the electronic spectra of porphyrins for analytical purposes: The effects of metal ions and structural distortions

ChemInform Abstract: Lewis Acid Coupled Electron Transfer of Metal—Oxygen Intermediates

Contact Info

Product

Resources

About

Ein Cobalt(IV)‐Oxido‐Komplex: Stabilisierung durch Lewis‐Säure‐Wechselwirkung mit Sc³⁺