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

Abstract

Metal oxoc lusters and metal oxides assemble and precipitate from water in processes that depend on pH, temperature,a nd 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 showt hat Bi 3+ drives the formation of aqueous Fe 3+ clusters,usurping the role of pH. We isolated and structurally characterized aBi/Fecluster,Fe 3 BiO 2 -(CCl 3 COO) 8 (THF)(H 2 O) 2 ,a nd demonstrated its conversion into an iron Keggin ion capped by six Bi 3+ irons (Bi 6 Fe 13 ). The reaction pathway was documented by X-ray scattering and mass spectrometry.O pposing the expected trend, increased cluster nuclearity required ap Hd ecrease instead of ap H increase.W ea ttribute this anomalous behavior of Bi/Fe(aq) solutions to Bi 3+ ,w hich drives hydrolysis and condensation. Likewise,Bi 3+ stabilizes metal oxo clusters and metal oxides in strongly acidic conditions,w hich is important in applications such as water oxidation for energy storage.

Capturing Lacunary Iron–Oxo Keggin Clusters and Insight Into the Keggin‐Fe13 Cluster Rotational Isomerization

“…In an effort to answer this question, Nyman and co‐workers, based on the comparison of the pair distance distribution function of Bi 6 Fe 13 L 12 dissolved in ethanol with that of two simulated dimers (the dimer of dodecaniobate α‐Keggin ions linked by a single alkali, and the dimer derived from the ferrihydrite structure), deduced that the conversion of Keggin‐Fe 13 clusters to ferrihydrite probably involves lacunary Keggin‐Fe 13 clusters . Although this deduction well explains the isomerization among different Keggin‐Fe 13 clusters, due to the lack of evidence regarding the lacunary Keggin‐Fe 13 cluster, especially its structural information, this deduction has not been experimentally verified.…”

“…In the nonclassic growth mode, the formation of the ferrihydrite is regarded as the aggregation of prenucleation clusters, rather than atom‐by‐atom growth . With capturing of the Keggin‐Fe 13 clusters in water, especially the experimental evidence of Keggin‐Fe 13 clusters as precursor of the ferrihydrite formation, the nonclassic growth mode has been widely adopted in the literature . Although the single phase model of the ferrihydrite clearly demonstrates that ferrihydrite consists of δ ‐Fe 13 Keggin units, it remains unclear why the Keggin‐Fe 13 cluster can undergo rotational isomerization (Figure ) …”

Iron Aquo Complex as an Efficient and Selective Homogeneous Photocatalyst for Organic Synthetic Reactions

“…This is the first report showing the potential of such simple, cheap iron ions as homogeneous photocatalyst for practical organic synthesis. The recent progress made in finding of molecular level iron ions in aqueous solutions, will make photocatalytic organic synthesis using iron catalysis more attractive and feasible.…”

Functionalization of Keggin Fe13-Oxo Clusters

“…Keggin Fe 13 -oxo clusters are basic structural motifs for iron oxides and hydroxides, such as ferrihydrite and magnetite. − They are also regarded as a prenucleation unit of ferrihydrite and magnetite. − In an effort to capture such Keggin Fe 13 -oxo clusters, not only were α-Keggin Fe 13 -oxo clusters and magnetite-type [Fe 17 ], [Fe 30 ], and [Fe 34 ] clusters obtained but also two strategies for capturing Keggin Fe 13 -oxo clusters in aqueous solution were developed, i.e., using a Bi 3+ ion to stabilize α-Keggin Fe 13 -oxo clusters , and using lanthanide (Ln 3+ ) ions to capture α-Keggin Fe 13 -oxo clusters . In the latter case, even ε-Keggin Fe 13 -oxo and lacunary Keggin Fe 13 -oxo clusters can be captured .…”