Photocatalytic Water Oxidation by a Mixed‐Valent Mn^III₃Mn^IVO₃ Manganese Oxo Core that Mimics the Natural Oxygen‐Evolving Center

Abstract

The functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi-redox Mn III is obtained by nanosecond laser flash photolysis; its S 0 !S 1 transition within milliseconds and multiple-hole-accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7 %.The oxygen-evolving complex of photosystem II (PSII-OEC) in green plants, algae, and cyanobacteria is the unique catalytic site where, upon illumination, H 2 O is oxidized to form O 2 .[1] The natural OEC is a tetramanganese calcium oxo cluster (Mn 4 O 5 Ca) that is harbored within the PSII complex, with a flexible and adaptive coordination environment provided by the protein residues.[2] In particular, carboxylate ligands play a major role in the assembly of the OEC cluster by bridging Mn ions and the Ca 2+ site. Dynamic binding throughout a sequence of five one-electron-step redox states (S i , where i = 0-4) underpins the efficient photoinduced water oxidation that is catalyzed by the PSII-OEC and occurs under visible-light irradiation and with an exceptional turnover frequency (TOF) of 100-400 s À1

Further Investigation of a Nickel‐Based Homogeneous Water Oxidation Catalyst with Two cis Labile Sites

“…The perfect energy source of H 2 from water splitting has attracted the continuous interesto fc hemists. Up to now,w ater oxidation catalysts (WOCs) based on noble [4][5][6][7][8][9][10][11][12] and earth-abundant metals [13][14][15][16][17][18][19][20][21][22][23][24] are reported. [3] One of the key challenges for water splitting is the development of efficient catalysts that can catalyze the water oxidation reaction with low overpotential, good stability,a nd high turnover frequency (TOF).…”

A Bioinspired Molecular Polyoxometalate Catalyst with Two Cobalt(II) Oxide Cores for Photocatalytic Water Oxidation

“…In conclusion, we report that the bioinspired polyoxometalate [(A-a-SiW 9 O 34 ) 2 Co 8 (OH) 6 (H 2 O) 2 (CO 3 ) 3 ] 16À is an active homogeneousm olecular water oxidation catalystt hat exhibits high hydrolytics tabilitya nd has av ery high turnover number (1436). The unique Co II 4 O 3 core provides ac ommendable biomimeticc ase for new structuralm odelst oc atalyzew ater oxidation based on the design concept of the oxygen evolving complex in photosystem II.…”

“…[10] Recently,m any robust,m olecular polyoxometalates (POMs) as efficient WOCs have been developed, because this kind of catalyste liminates the problem of ligand oxidative instability, while being thermally stable and allowing for structuralfine-tuning. [5-6, 7c, 11] However,a part from [{Ru 4 6 ] 50À . [8] The lack of transition metals coordinated to at erminal aquo ligand in the first two catalysts mentioned above may result in al ower turnover number (TON).The number of fast, selective, and stable molecular POMs that function as WOCs is still small up to now.…”

“…Herein, we report the synthesis, crystal structure, andp hotocatalytic water oxidation activity of ah omogeneous POM WOC, [(A-a-SiW 9 O 34 ) 2 Co 8 (OH) 6 (Figure 1), with two of these cobalt atoms coordinated to ter-minal aquo ligands. [12] Co 8 POM is readily synthesized from Na 10 [A-a-SiW 9 O 34 ], CoSO 4 ,a nd potassium carbonate in an aqueous solution of sodium acetate at room temperature (see Supporting Information for details).…”

“…[3] In order to closely mimic the structure of the cubical core, many efforts have been devoted to exploring cubical tetranuclear metal catalysts.[4] However,o nly few molecular tetranuclear metal catalysts, includingr uthenium-, [5] manganese-, [6] cobalt-, [3, 7] and nickel-based [8] 4 ] mentioned above is ag enuine molecular catalyst in photocatalytic water oxidation.[9] The result of their research is that the water oxidation activityo ft he compound class [Co 4 ]c ontains no terminal aquo ligands.I nspired by the proposed PS II-oxygen evolution complex (OEC) mechanisms, the implementation of transition metals coordinated to terminala quo, hydroxo, or oxo ligands is am ajor step toward OÀOf ormation pathways via water attack and exchange processes. [10] Recently,m any robust,m olecular polyoxometalates (POMs) as efficient WOCs have been developed, because this kind of catalyste liminates the problem of ligand oxidative instability, while being thermally stable and allowing for structuralfine-tuning.…”