Aqueous formation and manipulation of the iron-oxo Keggin ion

摘要

There is emerging evidence that growth of synthetic and natural phases occurs by the aggregation of prenucleation clusters, rather than classical atom-by-atom growth. Ferrihydrite, an iron oxyhydroxide mineral, is the common form of Fe~(3+) in soils and is also in the ferritin protein. We isolated a 10 angstrom discrete iron-oxo cluster (known as the Keggin ion, Fe_(13)) 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 Fe_(13) in water with precipitation of its protecting Bi~(3+) -counterions, it rapidly aggregates to ～22 angstrom spherical ferrihydrite nanoparticles. Fe_(13) may therefore also be a prenucleation cluster for ferrihydrite formation in natural systems, including by microbial and cellular processes.