Reports

Iron oxides and oxyhydroxides are ubiquitous in the envi-ronment, and serve vital roles in interrelated phenomena of contaminant transport, pH control of surface and ground water, and microbial activity. (1–4) Relevant phases include hematite, magnetite, goethite and ferrihydrite. The structure of ferrihydrite, the most common iron oxyhydroxide in soil and in the core of the ferritin protein, is isostructural to the Al-mineral akdalaite. (5) The ferrihydrite structure has been highly debated, (6–9) but the general framework contains linked and fused iron-oxyhydroxide Keggin units. The Keg-gin ion or molecule is a metal-oxo structural motif in natu-ral and synthetic materials. (10) Even prior to the proposed structure of ferrihydrite, an iron Keggin cluster (henceforth referred to as Fe13) was presumed to be synthetically attain-able; analogous to the Al13-Keggin cluste