Development of X-Ray absorption fine structure techniques for the study of reactions of heavy metal complexes in solution

Abstract

Extended X-ray absorption fine structure spectroscopy (EXAFS) has been used to characterise polyoxometalate (POM) species and study their reactions on the minute time-scale. Lindqvist-type tungstates have been characterised using quick extended X-ray absorption fine structure spectroscopy (QEXAFS). Differentiation between [LMW5O18]3- species with different heterometals has been demonstrated. The formation of [W6O19]2- and [(Ph2PO2)(ZrW5O18)2]6- have been studied. Intermediates in the formation reaction for [W6O19]2- may include a cluster with 3 tungsten atoms and a cluster with 5 tungsten atoms.

Keggin-type molybdates have also been characterised using QEXAFS. EXAFS data has been collected up to 20.7 Å-1 and distances of 6.2 Å have been resolved. Differentiation between different capped [PMo12O40(MX)2]n- species, where the capping species is bound to the core [PMo12O40]3- by 4 bridging oxygen atoms, and reduced [PMo12O40]n- species has been demonstrated. The Mo···Mo distances in reduced POMs are longer than in unreduced POMs. Addition of metal ions to electron-rich Keggin-type POMs by reductive aggregation has been studied and shifting peaks in Fourier transform spectra show the formation of clusters around the metal ions.

[Cu(dmp)2][PF6] was studied using X-ray absorption near edge spectroscopy (XANES), X-ray absorption fine structure spectroscopy (XAFS), resonant inelastic X-ray spectroscopy (RIXS) and X-ray emission spectroscopy (XES). Distances of 4.4 Å have been resolved using XAFS spectroscopy. RIXS has been used to demonstrate the 4 eV difference between the K? peaks for CuI and CuII. The CuII state was generated electrochemically and differentiation between CuI and CuII has been possible using K? XES.

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Identifiers

ORCID for John Evans: orcid.org/0000-0003-3290-7785

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