The Role of Bi3+ in Promoting and Stabilizing Iron Oxo Clusters in Strong Acid

摘要

Metal oxo clusters and metal oxides assemble and precipitate from water in processes that depend on pH, temperature, and concentration. Other parameters that influence the structure, composition, and nuclearity of molecular and bulk metal oxides are poorly understood, and have thus not been exploited. Herein, we show that Bi3+ drives the formation of aqueous Fe3+ clusters, usurping the role of pH. We isolated and structurally characterized a Bi/Fe cluster, Fe(3)Bio(2)(-)(CCl3COO)(8)(THF)(H2O)(2), and demonstrated its conversion into an iron Keggin ion capped by six Bi3+ irons (Bi6Fe13). The reaction pathway was documented by X-ray scattering and mass spectrometry. Opposing the expected trend, increased cluster nuclearity required a pH decrease instead of a pH increase. We attribute this anomalous behavior of Bi/Fe(aq) solutions to Bi3+, which drives hydrolysis and condensation. Likewise, Bi3+ stabilizes metal oxo clusters and metal oxides in strongly acidic conditions, which is important in applications such as water oxidation for energy storage.