Iron Complex as a Water-Oxidizing Catalyst: Free Energy Barriers, Proton-Coupled Electron Transfer, Spin Dynamics and the Role of Water Molecules on Reaction Mechanism

G, Koteswara Rao and Mallik, Bhabani Shankar (2019) Iron Complex as a Water-Oxidizing Catalyst: Free Energy Barriers, Proton-Coupled Electron Transfer, Spin Dynamics and the Role of Water Molecules on Reaction Mechanism. The Journal of Physical Chemistry C. ISSN 1932-7447 (In Press)

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Abstract

The study elucidates the mechanistic study of the catalytic water oxidation process by an iron complex of cis-dichloro-1,4,8,11–tetra azacyclotetradecane (cis-[Fe(cyclam)Cl2]Cl) in the presence of explicit water molecules with the help of metadynamics method based first principles molecular dynamics simulations, performed at 300 K and ambient pressure. We considered [FeV(cyclam)(O)2]+ and [FeV(cyclam)(OH)(O)]+2 as the active catalytic species in liquid water for the water oxidation process and calculated the free-energy landscapes of various steps involved in the mechanistic pathway. Our micro kinetics study of the oxygen-oxygen bond formation by both active catalytic species reveals that the transfer of proton to the cis–Oxo or hydroxide of the active catalytic species is the rate-determining step, and the transfer of the hydroxide to iron-oxo moiety is the less free energetic path. Overall the O-O bond formation by the active catalytic species [FeV(cyclam)(OH)(O)]+2 is more favorable. We carried out partial charge analysis of the atoms involved in the reaction. From the Lowdin and Mulliken charge analysis on the atoms, we confirm that the addition of a water molecule takes place as the nucleophile that leads to the formation of the peroxide complex. The superoxide complex is formed from the peroxide complex through the proton-coupled electron transfer (PCET) process. The electron transfer was confirmed by the analysis of the projected density of states (PDOS) and the local density of states (LDOS). We presented the energetics of crystal field splitting for the peroxide and superoxide complexes based on the PDOS. In the case of the liberation of dioxygen with an addition of the water molecule, micro kinetics analysis reveals that the release of the oxygen is a high free energetic step than the addition of water molecules. Overall, both the steps involving the oxygen-oxygen bond formation and release of oxygen molecules are possible in the case of [FeV(cyclam)(OH)(O)]+2 as the active catalytic species. These thermodynamic and kinetic aspects of the water oxidation process may help in developing new water oxidation catalysts.

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IITH Creators:
IITH CreatorsORCiD
Mallik, Bhabani Shankarhttp://orcid.org/0000-0001-9657-1497
Item Type: Article
Subjects: Chemistry
Divisions: Department of Chemistry
Depositing User: Team Library
Date Deposited: 26 Dec 2019 03:48
Last Modified: 26 Dec 2019 03:48
URI: http://raiith.iith.ac.in/id/eprint/7251
Publisher URL: http://doi.org/10.1021/acs.jpcc.9b10378
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