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Mechanochemical Polyoxometalate Super-Reduction with Lithium Metal

Lookup NU author(s): Dr Magda Pascual-BorrasORCiD, Dr Elisabetta Arca, Professor Thomas PenfoldORCiD, Dr Paul Waddell, Dr John ErringtonORCiD

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

In this first systematic investigation of mechanochemical polyoxometalate (POM) reduction, (TBA)₃[PMo₁₂O₄₀] was reacted with n equivalents of lithium metal (n = 1 – 24) to generate PMo₁₂/n products which were shown to be mixtures of electron-rich PMo₁₂Li_x species. FTIR analysis revealed the lengthening/weakening of terminal Mo=O bonds with increasing levels of reduction, while EXAFS spectra indicated the onset of Mo–Mo bond formation at n ~ 8 and a significant structural change at n > 12. Successive Mo^VI reductions were monitored by XANES and XPS and, at n = 24, results were consistent with the formation of at least one Mo^IV–Mo^IV bonded {Mo^IV₃} triad together with Mo^V. Upon dissolution, the PMo₁₂Li_x species present in the solid PMo₁₂/n products undergo electron exchange and single-peak ³¹P NMR spectra were observed for n = 1 – 12. For n ≥ 16, changes in solid state and solution ³¹P NMR spectra coincided with the emergence of features in the UV-vis spectra associated with Mo^V-Mo^V and {Mo^IV₃} bonding in an ε-Keggin structure. Bonding between {Li(NCMe)}⁺ and 2-electron-reduced PMo₁₂ in the crystal structure of (TBA)₄[PMo₁₂O₄₀{Li(NCMe)}] suggested that stronger Li–O interactions in more highly reduced products could result in lithium-oxide-promoted TBA cation decomposition and POM degradation, which might explain the appearance of XPS peaks for Mo₂C at n ≥ 16. This work revealed some of the complex, unexplored chemistry of super-reduced POMs and establishes a new, solvent-free approach in the search for a better fundamental understanding of the electronic properties and reactivity of electron-rich nanoscale metal oxides.

Publication metadata

Author(s): Pascual-Borràs M, Arca E, Yoshikawa H, Penfold T, Waddell PG, Errington RJ

Publication type: Article

Publication status: Published

Journal: Journal of the American Chemical Society

Year: 2024

Volume: 146

Issue: 38

Pages: 26485-26496

Print publication date: 25/09/2024

Online publication date: 10/09/2024

Acceptance date: 01/09/2024

Date deposited: 02/09/2024

ISSN (print): 0002-7863

ISSN (electronic): 1520-5126

Publisher: American Chemical Society

URL: https://doi.org/10.1021/jacs.4c09998

DOI: 10.1021/jacs.4c09998

Data Access Statement: The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.4c09998. CCDC 2305190-2305191 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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