Nitric oxide activation facilitated by cooperative multimetallic electron transfer within an iron-functionalized polyoxovanadate-alkoxide cluster.

A series of NO-bound, iron-functionalized polyoxovanadate-alkoxide (FePOV-alkoxide) clusters have been synthesized, providing insight into the role of multimetallic constructs in the coordination and activation of a substrate. Upon exposure of the heterometallic cluster to NO, the vanadium-oxide metalloligand is oxidized by a single electron, shuttling the reducing equivalent to the {FeNO} subunit to form a {FeNO}7 species. Four NO-bound clusters with electronic distributions ranging from [VV3VIV2]{FeNO}7 to [VIV5]{FeNO}7 have been synthesized, and characterized via 1H NMR, infrared, and electronic absorption spectroscopies. The ability of the FePOV-alkoxide cluster to store reducing equivalents in the metalloligand for substrate coordination and activation highlights the ultility of the metal-oxide scaffold as a redox reservoir.

Site-selectivity in the halogenation of titanium-functionalized polyoxovanadate-alkoxide clusters.

Herein, we report the synthesis and characterization of a dititanium-functionalized polyoxovanadate-alkoxide cluster. The incorporation of a second heterometal within the cluster core results in striking differences in reactivity of the multimetallic complex. Chlorination of the metal oxide cluster is reported, revealing the directing role of titanium in M-O bond cleavage.

Polyoxovanadate-alkoxide clusters as multi-electron charge carriers for symmetric non-aqueous redox flow batteries.

Non-aqueous redox flow batteries have emerged as promising systems for large-capacity, reversible energy storage, capable of meeting the variable demands of the electrical grid. Here, we investigate the potential for a series of Lindqvist polyoxovanadate-alkoxide (POV-alkoxide) clusters, [V6O7(OR)12] (R = CH3, C2H5), to serve as the electroactive species for a symmetric, non-aqueous redox flow battery. We demonstrate that the physical and electrochemical properties of these POV-alkoxides make them suitable for applications in redox flow batteries, as well as the ability for ligand modification at the bridging alkoxide moieties to yield significant improvements in cluster stability during charge-discharge cycling. Indeed, the metal-oxide core remains intact upon deep charge-discharge cycling, enabling extremely high coulombic efficiencies (∼97%) with minimal overpotential losses (∼0.3 V). Furthermore, the bulky POV-alkoxide demonstrates significant resistance to deleterious crossover, which will lead to improved lifetime and efficiency in a redox flow battery.

Tuning the redox profiles of polyoxovanadate-alkoxide clusters via heterometal installation: toward designer redox Reagents.

Herein, we describe a rational synthetic approach for tuning the electrochemical profiles of a series of Lindqvist polyoxovanadate-alkoxide clusters through heterometal functionalization. Synthetic procedures for group(IV) functionalization of the mixed-valent POV-alkoxide cluster, [V6O7(OCH3)12], are established, resulting in the heterometallic species, [NBu4][V5O6(OCH3)12MOCH3] (M = Ti, Zr, Hf). We demonstrate that these d0, heterometallic dopants anodically shift the potential of the electrochemical processes associated with the cluster, making the molecule more resistant to oxidation. Conversely, incorporation of electron rich heterometals yields a more readily oxidized molecule, with redox processes shifted cathodically. The predictable tuning and remarkable electrochemical profiles of this family of heterometal-functionalized polyoxometalates highlights their potential use as designer redox agents.