Inspired by the multielectron redox chemistry achieved using conventional organic-based redox-active ligands, we have characterized a series of iron-functionalized polyoxovanadate–alkoxide clusters in which the metal oxide scaffold functions as a three-dimensional, electron-deficient metalloligand. Four heterometallic clusters were prepared through sequential reduction, demonstrating that the metal oxide scaffold is capable of storing up to four electrons. These reduced products were characterized by cyclic voltammetry, IR, electronic absorption, and 1H NMR spectroscopies. Moreover, Mössbauer and X-ray absorption spectroscopies suggest that the redox events involve primarily the vanadium ions, while the iron atoms remained in the 3+ oxidation state throughout the redox series. In this sense, the vanadium portion of the cluster mimics a conventional organic-based redox-active ligand bound to an iron(III) ion. Magnetic coupling within the hexanuclear cluster was characterized using SQUID magnetometry. Overall, the results suggest extensive electronic delocalization between the metal centers of the cluster core. These results demonstrate the ability of electronically flexible, reducible metal oxide supports to function as redox-active reservoirs for transition-metal centers.

Herein we report the synthesis of a series of iron-functionalized, mixed-valent, polyoxovanadate alkoxide clusters, [V5O6(OCH3)12Fe]X (X = Cl, Br, SO3CF3) comprised of a hexanuclear Lindqvist (M6O19n–) core. By substituting a V═O moiety from the well-defined hexavanadate clusters [VIVnVV6–nO7(OR)12]4–n (R = Me, Et) with a metal cation, we have developed a novel template for investigation of the organometallic properties of these systems. Characterization of the clusters was performed by 1H NMR, Fourier transform infrared, and electron absorption spectroscopies and electrospray ionization mass spectrometry. The IR and UV–vis spectra suggest substantial electronic delocalization, similar to the previously reported cluster, V6O7(OCH3)12.