Syntheses and characterization of α-Keggin- and α2-Dawson-type diplatinum(II)-coordinated polyoxotungstates: Effects of skeletal structure, internal element, and nitrogen-containing ligand coordinated to the platinum center for hydrogen production from water under light irradiation

Abstract

The tetramethylammonium and cesium salts of diplatinum(II) complexes composed of mono-lacunary α-Keggin- and α2-Dawson-type polyoxotungstates, [(CH3)4N]4H[α-AlW11O39{cis-Pt(NH3)2}2]⋅11H2O (TMA-AlW11-Pt-NH3), [(CH3)4N]4H[α-BW11O39{cis-Pt(NH3)2}2]⋅9H2O (TMA-BW11-Pt-NH3), Cs4[α-GeW11O39{Pt(bpy)}2]⋅10H2O (bpy = 2,2′-bipyridine; Cs-GeW11-Pt-bpy), Cs3.5H0.5[α-GeW11O39{Pt(phen)}2]⋅3H2O (phen = 1,10-phenanthroline; Cs-GeW11-Pt-phen), and Cs6[α2-P2W17O61{cis-Pt(NH3)2}2]⋅13H2O (Cs-P2W17-Pt-NH3), were synthesized and characterized by X-ray crystallography, elemental analysis, TG/DTA, FTIR, and solution {1H and 31P} NMR spectroscopy. The characterization results showed that the two platinum(II) moieties, [cis-Pt(NH3)2]2+, [Pt(bpy)]2+, and [Pt(phen)]2+, were coordinated to the mono-vacant site of [XW11O39](12−n)− (Xn+ = Al3+, B3+, and Ge4+) and [α2-P2W17O61]10−. When the eight platinum(II) compounds, [(CH3)4N]3[α-PW11O39{cis-Pt(NH3)2}2]⋅10H2O (TMA-PW11-Pt-NH3), [(CH3)4N]4[α-SiW11O39{cis-Pt(NH3)2}2]·13H2O (TMA-SiW11-Pt-NH3), [(CH3)4N]4[α-GeW11O39{cis-Pt(NH3)2}2]·11H2O (TMA-GeW11-Pt-NH3), TMA-AlW11-Pt-NH3, TMA-BW11-Pt-NH3, Cs-GeW11-Pt-bpy, Cs-GeW11-Pt-phen, and Cs-P2W17-Pt-NH3 were used as photocatalysts for hydrogen evolution from aqueous triethanolamine (TEOA) solution under the light irradiation, Cs-P2W17-Pt-NH3 exhibited the highest activities among the eight diplatinum(II) compounds.