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Quantum chemical modeling of tri-Mn-substituted W-based Keggin polyoxoanions

Kremleva, A., Aparicio Sanchez, Pablo, Genest, A. and Rosch, N. 2017. Quantum chemical modeling of tri-Mn-substituted W-based Keggin polyoxoanions. Electrochimica Acta 231 , pp. 659-669.

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Abstract

Using Density Functional Theory (DFT) calculations, we studied the electrochemistry of polyoxome- talates (POMs), specifically the redox properties of Mn in tri-Mn-substituted W-based Keggin ions. For direct comparison with recent cyclic voltammetry results [J. Friedl et al. Electrochim. Acta, 141 (2014) 357], we estimated the reversible half-wave potentials of proton- and cation-coupled electron transfer for Mn(IV/III) and Mn(III/II), respectively. The calculated reversible potentials agree well with experiment, reproducing the trend with pH for Mn(IV/III). For adequate DFT energies, it is crucial to apply a reliable description of the electrolyte environment of the POM, accounting also for their rather high charges, up to �7 e. To this end, we included the Li+ counterions, required for charge neutralization, directly in the quantum chemical models which were embedded in a polarizable continuum. We explored various arrangements of the Li+ ions around the POMs and their effect on both structural parameters and electrochemical properties of the POMs. Hybrid functionals (TPSSh, B3LYP, PBE0) overestimate the experimental reduction potentials: the larger the exact-exchange contribution, the larger the resulting reduction potential. The best agreement with experiment is achieved with the PBE approach, likely due to fortuitous error cancellation. The results of the present work indicate that a more sophisticated (atomistic) representation of the electrolyte environment will be beneficial for predicting redox potentials in better agreement with experiment.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Uncontrolled Keywords: Polyoxometalates; Keggin ion; Redox potentials; DFT modeling; Electrolyte environment
Publisher: Elsevier
ISSN: 0013-4686
Date of First Compliant Deposit: 5 October 2017
Date of Acceptance: 10 February 2017
Last Modified: 30 Apr 2018 01:48
URI: http://orca-mwe.cf.ac.uk/id/eprint/100107

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