Atomically Precise Lanthanide‐Iron‐Oxo Clusters Featuring the ϵ‐Keggin Ion.

Atomically precise molecular metal‐oxo clusters provide ideal models to understand metal oxide surfaces, self‐assembly, and form‐function relationships. Devising strategies for synthesis and isolation of these molecular forms remains a challenge. Here, the synthesis of four Ln‐Fe oxo clusters that feature the ϵ‐{Fe13} Keggin cluster in their core is reported. The {Fe13} metal‐oxo cluster motif is the building block of two important iron oxyhydroxyide phases in nature and technology, ferrihydrite (as the δ‐isomer) and magnetite (the ϵ‐isomer). The reported ϵ‐{Fe13} Keggin isomer as an isolated molecule provides the opportunity to study the formation of ferrihydrite and magnetite from this building unit. The four currently reported isostructural lanthanide‐iron‐oxo clusters are fully formulated [Y12Fe33(TEOA)12(Hyp)6(μ3‐OH)20(μ4‐O)28(H2O)12](ClO4)23⋅50 H2O (1, Y12Fe33), [Gd12Fe33(TEOA)12(Hyp)6(μ3‐OH)20(μ4‐O)32(H2O)12](ClO4)15⋅50 H2O (2, Gd12Fe33) and [Ln16Fe29(TEOA)12(Hyp)6(μ3‐OH)24(μ4‐O)28(H2O)16](ClO4)16(NO3)3⋅n H2O (Ln=Y for 3, Y16Fe29, n=37 and Ln=Gd for 4, Gd16Fe29n=25; Hyp=trans‐4‐Hydroxyl‐l‐proline and TEOA=triethanolamine). The next metal layer surrounding the ϵ‐{Fe13} core within these clusters exhibits a similar arrangement as the magnetite lattice, and Fe and Ln can occupy the same positions. This provides the opportunity to construct a family of compounds and optimize magnetic exchange in these molecules through composition tuning. Small‐angle X‐ray scattering (SAXS) and high‐resolution electrospray ionization mass spectrometry (HRESI‐MS) show that these clusters are stable upon dissolution in both water and organic solvents, as a first step to performing further chemistry towards building magnetic arrays or investigating ferrihydrite and magnetite assembly from pre‐nucleation clusters. [ABSTRACT FROM AUTHOR]