Characterization of the Fe<sup>V</sup>=O Complex in the Pathway of Water Oxidation

Ezhov, Roman; Ravari, Alireza Karbakhsh; Pushkar, Yulia

doi:10.1002/ange.202003278

Cited by 11 publications

(2 citation statements)

References 41 publications

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“…Other short-lived Fe(V) and Fe(IV) complexes generated photochemically from lower-valent precursors have been studied by optical and infrared transient absorption spectroscopies, − while the steady-state spectroscopic properties (EPR, vibrational, optical, X-ray, Mössbauer, etc.) of isolable Fe(IV)–Fe(VI) compounds have been exhaustively documented due to the prevalence of high-valent iron centers in metalloenzymes. − Surprisingly, however, direct spectroscopic measurements of the excited-state dynamics of ferrate(VI) have not been reported.…”

Section: Introductionmentioning

confidence: 99%

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

et al. 2022

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Ferrate(VI) has the potential to play a key role in future water supplies. Its salts have been suggested as "green" alternatives to current advanced oxidation and disinfection methods in water treatment, especially when combined with ultraviolet light to stimulate generation of highly oxidizing Fe(V) and Fe(IV) species. However, the nature of these intermediates, the mechanisms by which they form, and their roles in downstream oxidation reactions remain unclear. Here, we use a combination of optical and X-ray transient absorption spectroscopies to study the formation, interconversion, and relaxation of several excited-state and metastable high-valent iron species following excitation of aqueous potassium ferrate(VI) by ultraviolet and visible light. Branching from the initially populated ligand-to-metal charge transfer state into independent photophysical and photochemical pathways occurs within tens of picoseconds, with the quantum yield for the generation of reactive Fe(V) species determined by relative rates of the competing intersystem crossing and reverse electron transfer processes. Relaxation of the metal-centered states then occurs within 4 ns, while the formation of metastable Fe(V) species occurs in several steps with time constants of 250 ps and 300 ns. Results here improve the mechanistic understanding of the formation and fate of Fe(V) and Fe(IV), which will accelerate the development of novel advanced oxidation processes for water treatment applications.

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Section: Introductionmentioning

confidence: 99%

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

et al. 2022

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“…For abundant first-row TMs in general, generation of high oxidation states resulting in active metal–oxo (MO) units is limited by the large potentials separating the different redox couples, which could favor alternative ligand oxidative degradation and/or metal oxide formation (Figure a). In particular, Cu complexes at oxidation state III can only be obtained with strongly electron-donating ligands. − Thus, to further facilitate access to formally high oxidation states, we and others − have described the use of redox-active ligands that are oxidized in a reversible manner.…”

Section: Introductionmentioning

confidence: 99%

Redox Metal–Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

et al. 2020

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Water oxidation catalysis stands out as one of the most important reactions to design practical devices for artificial photosynthesis. The use of late 1 st row transition metal (TM) complexes provides an excellent platform for the development of inexpensive catalysts with an exquisite control on their electronic and structural features via ligand design. However, the difficult access to their high oxidation states and the general labile character of their metal-ligand bonds pose important challenges. Herein, we explore a copper complex (1 2-) featuring an extended, π-delocalized, tetraamidate macrocyclic ligand (TAML) as water oxidation catalysts, and compare its activity to analogous systems with lower π-delocalization (2 2-and 3 2-). Their characterization evidences a special metal-ligand cooperativity in accommodating the required oxidative equivalents using 1 2-that is absent in 2 2-and 3 2-. This consists in charge delocalization promoted by easy access to different electronic states at a narrow energy range, corresponding to either metal-centered or ligand-centered oxidations, which we identify as essential factor to stabilize the accumulated oxidative charges. This translates into a significant improvement in the catalytic performance of 1 2-compared to 2 2-and 3 2-, and leads to one of the most active and robust molecular complexes for water oxidation at neutral pH, with a k obs of 140 s-1 at an overpotential of only 200 mV. In contrast, 2 2-degrades under oxidative conditions, what we associate to impossibility of efficiently stabilize several oxidative equivalents via charge delocalization, resulting in highly reactive oxidized ligand. Finally, the acyclic structure of 3 2-prevent its use at neutral pH due to acidic demetallation, highlighting the importance of the macrocyclic stabilization.

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Generation of Fe^IV=O and its Contribution to Fenton‐Like Reactions on a Single‐Atom Iron−N−C Catalyst

et al. 2023

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Generating FeIV=O on single‐atom catalysts by Fenton‐like reaction has been established for water treatment; however, the FeIV=O generation pathway and oxidation behavior remain obscure. Employing an Fe−N−C catalyst with a typical Fe−N4 moiety to activate peroxymonosulfate (PMS), we demonstrate that generating FeIV=O is mediated by an Fe−N−C−PMS* complex—a well‐recognized nonradical species for induction of electron‐transfer oxidation—and we determined that adjacent Fe sites with a specific Fe1−Fe1 distance are required. After the Fe atoms with an Fe1‐Fe1 distance <4 Å are PMS‐saturated, Fe−N−C−PMS* formed on Fe sites with an Fe1‐Fe1 distance of 4–5 Å can coordinate with the adjacent FeII−N4, forming an inter‐complex with enhanced charge transfer to produce FeIV=O. FeIV=O enables the Fenton‐like system to efficiently oxidize various pollutants in a substrate‐specific, pH‐tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one‐electron oxidation potential.

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Characterization of the Fe^V=O Complex in the Pathway of Water Oxidation

Cited by 11 publications

References 41 publications

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

Redox Metal–Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

Generation of Fe^IV=O and its Contribution to Fenton‐Like Reactions on a Single‐Atom Iron−N−C Catalyst

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Characterization of the FeV=O Complex in the Pathway of Water Oxidation

Cited by 11 publications

References 41 publications

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

Redox Metal–Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

Generation of FeIV=O and its Contribution to Fenton‐Like Reactions on a Single‐Atom Iron−N−C Catalyst

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Characterization of the Fe^V=O Complex in the Pathway of Water Oxidation

Generation of Fe^IV=O and its Contribution to Fenton‐Like Reactions on a Single‐Atom Iron−N−C Catalyst