Connecting Thermodynamics and Kinetics of Proton Coupled Electron Transfer at Polyoxovanadate Surfaces Using the Marcus Cross Relation

Here, we evaluate the efficacy of multiple methods for elucidating the average bond dissociation free energy (BDFE) of two surface hydroxide moieties in a reduced polyoxovanadate cluster, [V6O11(OH)(2)(TRIOLNO2)(2)](-2). Through cyclic voltammetry, individual thermochemical parameters describing proton coupled electron transfer (PCET) are obtained, without the need for synthetic isolation of intermediates. Further, we demonstrate that a method involving a series of open circuit potential measurements with varying ratios of reduced to oxidized clusters is most attractive for the direct measurement of BDFE(O-H) for polyoxovanadate clusters as this approach also determines the stoichiometry of PCET. We subsequently connect the driving force of PCET to the rate constant for the transfer of hydrogen atoms to a series of organic substrates through the Marcus cross relation. We show that this method is applicable for the prediction of reaction rates for multielectron/multiproton transfer reactions, extending the findings from previous work focused on single electron/proton reactions.

Automated summary

This study evaluates the efficacy of multiple methods for determining the average bond dissociation free energy (BDFE) of hydroxide moieties in polyoxovanadate clusters. Cyclic voltammetry is used to obtain thermochemical parameters of proton coupled electron transfer (PCET) without the need for synthetic isolation of intermediates. A method involving open circuit potential measurements is found to be most attractive for direct measurement of BDFE and determination of PCET stoichiometry. The driving force of PCET is then linked to the rate constant for hydrogen atom transfer to organic substrates through the Marcus cross relation, enabling rate predictions for multielectron/multiproton transfer reactions.