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We report the reduction of O₂to H₂O₂viaconcerted proton–electron transfer from the terminal V(iii)–OH₂moiety of a reduced polyoxovanadate-alkoxide cluster. 

Exposing consequences of ligand sterics on H-atom uptake at surfaces with POV-alkoxide clusters. 

We present the post-synthetic modification of a polyoxovanadate-alkoxide (POV-alkoxide) cluster via the reactivity of its cationic form, [V6O7(OCH3)12]1+, with water. This result indicates that cluster oxidation increases the lability of bridging methoxide ligands, affording a ligand exchange reaction that serves to compensate for the increased charge of the cluster core. This synthetic advance affords the isolation of a series of POV-alkoxide clusters with varying degrees of μ2–O2– ligands incorporated at the surface, namely, [V6O8(OCH3)11], [V6O9(OCH3)10], and [V6O10(OCH3)9]. Characterization of the POV-alkoxide clusters is described; changes in the infrared and electronic absorption spectra are consistent with the oxidation of the cluster core. We also examine the consequences of ligand substitution on the redox properties of the series of POV-alkoxide clusters via cyclic voltammetry; decreased alkoxide ligand density translates to a cathodic shift of analogous redox events. Ligand substitution also increases comproportionation constants of the Lindqvist core, indicating electron exchange between vanadium centers is promoted in structures with greater numbers of μ2–O2– ligands. 

Anionic dopants, such as O-atom vacancies, alter the thermochemical and kinetic parameters of proton coupled electron transfer (PCET) at metal oxide surfaces; understanding their impact(s) is essential for informed material design for efficient energy conversion processes. To circumvent challenges associated with studying extended solids, we employ polyoxovanadate–alkoxide clusters as atomically precise models of reducible metal oxide surfaces. In this work, we examine net hydrogen atom (H-atom) uptake to an oxygen deficient vanadium oxide assembly, [V 6 O 6 (MeCN)(OCH 3 ) 12 ] 0 . Addition of two H-atom equivalents to [V 6 O 6 (MeCN)(OCH 3 ) 12 ] 0 results in formation of [V 6 O 5 (MeCN)(OH 2 )(OCH 3 ) 12 ] 0 . Assessment of the bond dissociation free energy of the O–H bonds of the resultant aquo moiety reveals that the presence of an O-atom defect weakens the O–H bond strength. Despite a decreased thermodynamic driving force for the reduction of [V 6 O 6 (MeCN)(OCH 3 ) 12 ] 0 , kinetic investigations show the rate of H-atom uptake at the cluster surface is ∼100× faster than its oxidized congener, [V 6 O 7 (OCH 3 ) 12 ] 0 . Electron density derived from the O-atom vacancy is shown to play an important role in influencing H-atom uptake at the cluster surface, lowering activation barriers for H-atom transfer. 

The selective uptake of lithium ions is of great interest for chemists and engineers because of the numerous uses of this element for energy storage and other applications. However, increasing demand requires improved strategies for the extraction of this element from mixtures containing high concentrations of alkaline impurities. Here, we study solution phase interactions of lithium, sodium, and potassium cations with polyoxovanadate-alkoxide clusters, [V 6 O 7 (OR) 12 ] (R = CH 3 , C 3 H 7 , C 5 H 11 ), using square wave voltammetry and cyclic voltammetry. In all cases, the most reducing event of the cluster shifts anodically as the ionic radius of the cation decreases, indicating increased stability of the reduced cluster and further suggesting that these assemblies might be useful for the selective uptake of Li + . Exploring the consequence of ligand length, we found that the short-chain cluster, [V 6 O 7 (OCH 3 ) 12 ], irreversibly binds Li + in the presence of excess potassium (K + ) and exhibits an electrochemical response in titration experiments similar to that observed upon the addition of Li + to the POV–alkoxide in the presence of non-coordinating tetrabutylammonium ions. However, in the presence of excess sodium (Na + ), the cluster showed only a modest preference for lithium, with exchange between sodium and lithium ions governed by equilibrium. Extending these studies to [V 6 O 7 (OC 5 H 11 ) 12 ], we found that the presence of the pentyl ligands allows the assembly to irreversibly bind Li + in the presence of Na + or K + . The change in mechanism caused by surface functionalization of the clusters increases the differential binding affinity for more compact cations, translating to improved selectivity for Li + uptake in these molecular assemblies.