Co4-polyoxometalates in aqueous solutions. Stability, ion pairing and electron transfer: Some insights from molecular modeling

DA Tuzov and EM Zueva and TT Zinkicheva and RR Nazmutdinov, ELECTROCHIMICA ACTA, 508, 145182 (2024).

DOI: 10.1016/j.electacta.2024.145182

Some qualitatively important features of the electrochemical behavior of Co(II)-based polyoxometalates (POM) are addressed by means of density functional theory and classical molecular dynamics. According to the results obtained, a subsequent oxidation of four Co(II) centers does not result in & acy; chemical bond break, although the innersphere reorganization energy is significant. Standard electrode potentials are estimated; only the first Co (II)/Co(III) redox process seems to be feasible at usual electrochemical conditions and has a fast rate. Ion pairing in aqueous solution leads to the formation of Co4-POM/nNa+ associates (existing in both contact and solvent shared forms), which favours electron-transfer steps. The diffusion of water molecules and Na cations in two different solution regions is also investigated. Some equilibria describing initial steps of the Co4-POM degradation are modeled as well. It is shown that the polyoxometalate is the most stable in neutral aqueous solutions; the degradation becomes remarkably feasible in alkali media and a clear trend of decreasing the Co4-POM stability is observed in acid solutions. These findings are in qualitatively agreement with experiment.

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