Search

The rational control of the electrochemical properties of polyoxovanadate-alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal-functionalized cluster was examined. The redox properties of [V5 O6 (OCH3 )12 FeCl] (1-[V5 FeCl]) and [V5 O6 (OCH3 )12 Fe]X (2-[V5 Fe]X; X=ClO4 , OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal-functionalized clusters reveals that differences in the redox profiles of 1-[V5 FeCl] and 2-[V5 Fe]X arise from changes in the number of ligands surrounding the iron center (e.g., 6-coordinate vs. 5-coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed-valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster.

We report a rare example of oxygen atom transfer (OAT) from a polyoxometalate cluster to a series of tertiary phosphanes. Addition of PR3 (PR3 = PMe3, PMe2Ph, PMePh2, PPh3) to a neutral methoxide-bridged polyoxovanadate-alkoxide (POV-alkoxide) cluster, [V6O7(OMe)12]0, results in isolation of a reduced structure with phosphine oxide datively coordinated to a site-differentiated VIII ion. A positive correlation between the steric and electronic properties of the phosphane and the reaction rate was observed. Further investigation of the steric influence of the alkoxy-bridged clusters on OAT was probed through the use of POV clusters with bridging alkoxide ligands of varying chain length ([V6O7(OR')12]; R' = Et, n Pr). These investigations expose that steric hinderance of the vanadyl moieties has significant influence on the rate of OAT. Finally, we report the reactivity of the reduced POV-alkoxide clusters with styrene oxide, resulting in the deoxygenation of the substrate to generate styrene. This result is the first example of epoxide deoxygenation using homometallic polyoxometalate clusters, demonstrating the potential for mono-vacant Lindqvist clusters to catalyze the removal of oxygen atoms from organic substrates.

A number of technologies would benefit from developing inorganic compounds and materials with specific electronic and magnetic exchange properties. Unfortunately, designing compounds with these properties is difficult because metal⋅⋅⋅metal coupling schemes are hard to predict and control. Fully characterizing communication between metals in existing compounds that exhibit interesting properties could provide valuable insight and advance those predictive capabilities. One such class of molecules are the series of Lindqvist iron‐functionalized and hexavanadium polyoxovanadate‐alkoxide clusters, which we characterized here using V K‐edge X‐ray absorption spectroscopy. Substantial changes in the pre‐edge peak intensities were observed that tracked with the V 3d‐electron count. The data also suggested substantial delocalization between the vanadium cations. Meanwhile, the FeIII cations were electronically isolated from the polyoxovanadate core. [ABSTRACT FROM AUTHOR]

Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO22+ is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An = U, Np, Pu). The thioether calixarene TC4A (4-tert-butyltetrathiacalix[4]arene) binds equatorially to [AnO2]n+ (An = U, Np) forming a conical pocket that differentiates the two trans-oxo groups. The 'ate' complexes, [A]2[UO2(TC4A)] (A = [Li(DME)2], HNEt3) and [HNEt3]2[NpO2(TC4A)], enable selective oxo chemistry. Silylation of the UVI oxo groups by bis(trimethylsilyl)pyrazine occurs first at only the unencapsulated exo oxo and only one silylation is needed to enable migration of the endo oxo out of the cone, whereupon a second silylation affords the stable UIV cis-bis(siloxide) [A]2[U(OSiMe3)2(TC4A)]. Calculations confirm that only one silylation event is needed to initiate oxo rearrangement, and that the putative cis dioxo isomer of [UO2(TC4A)]2- would be stable if it could be accessed synthetically, at only 23 kcal.mol-1 in energy above the classical trans dioxo. The aryloxide (OAr) groups of the macrocycle are essential in stabilizing this as-yet unseen uranyl geometry, with further bonding in the TC4A U-OAr groups stabilizing the U=O 'yl' bonds, explaining the stability of a calculated cis[UO2(TC4A)]2- in this ligand framework., (© 2025 Wiley‐VCH GmbH.)

The isolation of the oxygen-deficient, polyoxovanadate-alkoxide (POV-alkoxide) cluster, [ n Bu 4 N][V 6 O 6 (OMe) 12 (MeCN)], and its subsequent reactivity with oxygen (O 2 ), has demonstrated the utility of these assemblies as molecular models for heterogeneous metal oxide catalysts. However, the mechanism through which this cluster activates and reduces O 2 to generate the oxygenated species is poorly understood. Currently it is speculated that this POV-alkoxide mediates the four-electron O-O bond cleavage through an O 2 bridged dimeric intermediate, a mechanism which is not viable for O 2 reduction at solid-state metal oxide surfaces. Here, we report the successful activation and reduction of O 2 by the calix-functionalized POV-alkoxide cluster, [ n Bu 4 N][(calix)V 6 O 6 (OMe) 8 ](MeCN)] (calix = 4- tert -butylcalix[4]arene). The steric hindrance imparted to the open vanadium site by the calix motif eliminates the possibility of cooperative, bimolecular O 2 activation, allowing for a comparison of the reactivity of this system with that of the nonfunctionalized POV-alkoxide described previously. Rigorous characterization of the calix-substituted assembly, enabled by its newfound solubility in organic solvent, reveals that the incorporation of the tetradentate aryloxide ligand into the POV-alkoxide scaffold perturbs the electronic communication between the site-differentiated vanadium(III) ion and the cluster core. Collectively, our results provide insight into the physiochemical factors that are important during the O 2 reduction reaction at oxygen-deficient sites in reduced POV-alkoxide clusters.