Synthesis and characterization of iron clusters with an icosahedral [Fe@Fe₁₂]¹⁶⁺ Core

Iron-metal clusters are crucial in a variety of critical biological and material systems, including metalloenzymes, catalysts, and magnetic storage devices. However, a synthetic high-nuclear iron cluster has been absent due to the extreme difficulty in stabilizing species with direct iron-iron bonding. In this work, we have synthesized, crystallized, and characterized a (Tp*)₄W₄S₁₂(Fe@Fe₁₂) cluster (Tp* = tris(3,5-dimethyl-1-pyrazolyl)borate(1-)), which features a rare trideca-nuclear, icosahedral [Fe@Fe₁₂] cluster core with direct multicenter iron-iron bonding between the interstitial iron (Fe_i) and peripheral irons (Fe_p), as well as Fe_p···Fe_p ferromagnetic coupling. Quantum chemistry studies reveal that the stability of the cluster arises from the 18-electron shell-closing of the [Fe@Fe₁₂]¹⁶⁺ core, assisted by its bonding interactions with the peripheral tridentate [(Tp*)WS₃]^4- ligands which possess both S→Fe donation and spin-polarized Fe-W σ bonds. The ground-state electron spin is theoretically predicted to be S = 32/2 for the cluster. The existence of low oxidation-state (OS ∼ +1.23) iron in this compound may find interesting applications in magnetic storage, spintronics, redox chemistry, and cluster catalysis.