A nickel containing polyoxometalate water oxidation catalyst

Abstract

A new pentanickel silicotungstate complex, K(10)H(2)[Ni(5)(OH)(6)(OH(2))(3)(Si(2)W(18)O(66))]·34H(2)O (KH-), has been synthesized and characterized by X-ray crystallography and several other methods. Dynamic light scattering, kinetics and other experiments confirm that in the presence of [Ru(bpy)(3)](2+) (the photosensitizer for light-driven water oxidations) and [Ru(bpy)(3)](3+) (the oxidant in the dark water oxidations) exists in an equilibrium between solution (soluble) and a [Ru(bpy)(3)](n+)- complex (minimally soluble) form. This new pentanickel polyoxometalate catalyzes efficient water oxidation in both the dark and on irradiation with 455 nm LED light with 1.0 mM [Ru(bpy)(3)](2+) photosensitizer and 5.0 mM Na(2)S(2)O(8), sacrificial electron acceptor. Four lines of evidence indicate that in this solution [symbol:see text] Ru(bpy)(3)](n+)- complex equilibrium remains molecular and does not decompose to nickel hydroxide particles.

Synthesis, Structure, and Characterization of In10-Containing Open-Wells–Dawson Polyoxometalate

“…The difference between the bite angles of Al4-, Ga4-, and In10-open is caused by the difference in the ionic radii of the Al (0.53 Å), Ga (0.76 Å), and In (0.94 Å) ions [45,46]. In10-open displays the widest bite angles when compared to previously reported open-WellsDawson POMs, including the Co6 (60.045°) [27], Zn6 dimer (60.308°) [23], Ni5 (58.925°) [24], and Cu5 (61.663°) [15,17] clusters. The open-Wells-Dawson POM containing a Cu5 cluster (Cu5-open) exhibits a large bite angle (61.663°) due to the long bond lengths between the copper and the edge-sharing oxygen atom, caused by Jahn-Teller distortion [15,17] Thus, all the Indium atoms can be considered to be 6-coordinated.…”

“…Thus, this class of compounds may constitute a promising platform for the development of metal-substituted-POM-based materials and catalysts. To date, many compounds that contain various metal ions in their open pocket, e.g., V 5+ [19], Mn 2+ [16,21], Fe 3+ [19], Co 2+ [14,16,20,21,25,27], Ni 2+ [16,21,24,27], Cu 2+ [15][16][17], and Zn 2+ [23] [30][31][32]. Synthetic and structural studies of group 13 ion-containing POMs provide informative and definitive molecular models of group 13 metal clusters in solution.…”

“…Recently, open-Wells-Dawson POMs have been reported as an emerging class of POMs [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. These compounds are a dimerized species of the trilacunary Keggin POMs, [XW 9 O 34 ] 10´( X = Si, Ge).…”

β,β-Isomer of Open-Wells–Dawson Polyoxometalate Containing a Tetra-Iron(III) Hydroxide Cluster: [{Fe4(H2O)(OH)5}(β,β-Si2W18O66)]9−

“…However, in aqueous media, the electrostatic repulsion induced by the highly charged guest XO 4 4´( X = Si, Ge) inhibits the assembly of the standard Wells-Dawson structure [30]. Therefore, the two trilacunary Keggin units with XO 4 4´( X = Si, Ge) [19], Mn 2+ [16,21], Fe 3+ [19], Co 2+ [14,16,20,21,25,27], Ni 2+ [16,21,24,27], Cu 2+ [15][16][17], Zn 2+ [23], Al 3+ [28], Ga 3+ [28], and lanthanoid (Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ ) [22,26]. The standard Wells-Dawson structural POM is one of the most deeply studied POMs.…”

“…Recently, the open-Wells-Dawson POMs have been an emerging class of POMs [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] [29]. However, in aqueous media, the electrostatic repulsion induced by the highly charged guest XO 4 4´( X = Si, Ge) inhibits the assembly of the standard Wells-Dawson structure [30].…”