ReportCrystal Growth

Aqueous formation and manipulation of the iron-oxo Keggin ion

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Science  26 Feb 2015:
DOI: 10.1126/science.aaa4620

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There is emerging evidence that growth of synthetic and natural phases occurs by aggregation of pre-nucleation clusters, rather than classical atom-by-atom growth. Ferrihydrite, an iron oxyhydroxide mineral, is the common form of Fe3+ in soils, and is also in the ferritin protein. Here we isolate a 10 Å discrete iron-oxo cluster (known as the Keggin ion, Fe13) that has the same structural features as ferrihydrite. The stabilization and manipulation of this highly reactive polyanion in water is controlled exclusively by its counterions. Upon dissolution of Fe13 in water with precipitation of its protecting Bi3+-counterions, it rapidly aggregates to ~22 Å spherical ferrihydrite nanoparticles. Fe13 may therefore also be a pre-nucleation cluster for ferrihydrite formation in natural systems, including by microbial and cellular processes.

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