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Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution


Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation1, CO2 capture and storage2 and water-oxidation catalysis3,4; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface5. Oxygen atoms in POM exchange isotopes at different rates6,7,8, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface.

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Figure 1: Measured rates of oxygen-isotope exchange.
Figure 2: Stable intermediates formed by OH addition to the Nb10 molecule.
Figure 3: A possible sequence of proton transfer and oxygen exchange between the incoming OH and the terminal oxygen G in the E intermediate.


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Support for this research was funded by the US Department of Energy Office of Basic Energy Science via grant DE-FG02-05ER15693 and National Science Foundation via EAR grant 0814242.

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J.R.R. designed and performed the calculations, W.H.C and J.R.R. interpreted the experiments in the context of the calculations, J.R.R. and W.H.C. wrote the paper.

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Correspondence to James R. Rustad.

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The authors declare no competing financial interests.

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Rustad, J., Casey, W. Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution. Nature Mater 11, 223–226 (2012).

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