Polyoxometalate-Based Cobalt–Phosphate Molecular Catalysts for Visible Light-Driven Water Oxidation

Abstract

A series of all-inorganic, abundant-metal-based, high-nuclearity cobalt-phosphate (Co-Pi) molecular catalysts [{Co4(OH)3(PO4)}4(SiW9O34)4](32-) (1), [{Co4(OH)3(PO4)}4(GeW9O34)4](32-) (2), [{Co4(OH)3(PO4)}4(PW9O34)4](28-) (3), and [{Co4(OH)3(PO4)}4(AsW9O34)4](28-) (4) were synthesized and shown to be highly effective at photocatalytic water oxidation. The {Co16(PO4)4} cluster contains a Co4O4 cubane which is structurally analogous to the [Mn3CaO4] core of the oxygen-evolving complex (OEC) in photosystem II (PSII). Compounds 1-4 were shown to be the first POM-based Co-Pi-cluster molecular catalysts for visible light-driven water oxidation, thus serving as a functional model of the OEC in PSII. The systematic synthesis of four isostructural analogues allowed for investigating the influence of different heteroatoms in the POM ligands on the photocatalytic activities of these Co-Pi cluster WOCs. Further, the POM-based photocatalysts readily recrystallized from the photocatalytic reaction systems with the polyoxoanion structures unchanged, which together with the laser flash photolysis, dynamic light-scattering, (31)P NMR, UV-vis absorption, POM extraction, and ICP-MS analysis results collectively confirmed that compounds 1-4 maintain their structural integrity under the photocatalytic conditions. This study provides not only a valuable molecular model of the "Co-Pi" catalysts with a well-defined structure but also an unprecedented opportunity to fine-tune high-nuclearity POM clusters for visible light-driven water splitting.

Tuning the growth of metal-organic framework nanocrystals by using polyoxometalates as coordination modulators

“…Polyoxometalates (POMs) are a class of inorganic clusters of the early transition elements and have numerous intriguing properties [24][25][26]. Generally, POMs act as anionic templates/structure directing agents to build POM-based MOF bulk composites through the host-guest supramolecular interactions (such as weak coordination interactions, electrostatic interaction, and hydrogen bonding) [20,27].…”

Synthesis and photocatalytic hydrogen evolution activity of three Keggin-type polyoxometalates with different central atoms

“…Recently, our group had reported some POMs photocatalyst for both water oxidation [8] and hydrogen evolution [9]. Keggin-type POMs are the most widely recognized and thoroughly studied POMs, which have been reported to be photosensitive at near-visible and UV regions [10].…”

Photochemical Water Oxidation Using {PMo12O40@Mo72Fe30}n Based Soft Oxometalate

“…14,31,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Low stability issues of organic ligand based catalysts are circumvented in such POM based catalysts that also have higher stability. Another advantage of using POM based catalysts is that they can be used to form composite with di®erent electro active surfaces.…”