Chika Nozaki Kato

A first example of polyoxotungstate-based giant molecule. Synthesis and molecular structure of a tetrapod-shaped Ti–O–Ti bridged anhydride form of Dawson tri-titanium(IV)-substituted polyoxotungstate

The preparation and structural characterization of a giant “tetrapod”-shaped inorganic molecule, [(α-1,2,3-P2W15Ti3O60.5)4Cl]37− ,1a (abbreviated to {TiO6}12; FW ∼15700), consisting of four tri-TiIV-1,2,3-substituted α-Dawson substructures and one encapsulated Cl− ion, are described. A water-soluble, all-inorganic composition compound of the tetrameric Ti–O–Ti bridged anhydride form, NaxH33−xK4[1a]·yH2O, 1 (x = 21–26, y = 60–70), being afforded by a stoichiometric reaction in aqueous solution of tri-lacunary Dawson polyoxotungstate Na12[B-α-P2W15O56]·19H2O with 3 equiv of Ti(SO4)2·4H2O in HCl-acidic aqueous solution followed by exchanging the countercation, was obtained as analytically pure, homogeneous colorless plate crystals. Single-crystal X-ray structure analysis revealed that the polyoxoanion 1a was an inorganic, giant “tetrapod”-shaped molecule (described as a sphere with a diameter of ∼31.2 A) with approximately Td symmetry. Characterization of 1 was also accomplished by complete elemental analysis, TG/DTA, FTIR, UV-vis absorption and solution (31P and 183W) NMR spectroscopy.

Syntheses and molecular structures of monomeric and hydrogen-bonded dimeric Dawson-type trialuminum-substituted polyoxotungstates derived under acidic and basic conditions.

The syntheses and molecular structures of the two types of α-Dawson-type trialuminum-substituted polyoxometalates, [B-α-H3P2W15O59{Al(OH2)}3](6-) (1) and [B-α-H3P2W15O59{Al(OH)}2{Al(OH2)}]2(16-) (2), are described herein. The potassium and cesium salts of 1, K6[B-α-H3P2W15O59{Al(OH2)}3]·14H2O (K-1), and Cs6[B-α-H3P2W15O59{Al(OH2)}3]·13H2O (Cs-1) were formed by a stoichiometric reaction in water of trilacunary α-Dawson polyoxotungstate with aluminum nitrate under acidic conditions (pH ∼3). The potassium/sodium and tetramethylammonium/sodium salts of 2, K14Na2[B-α-H3P2W15O59{Al(OH)}2{Al(OH2)}]2·30H2O (KNa-2) and [(CH3)4N]14Na2[B-α-H3P2W15O59{Al(OH)}2{Al(OH2)}]2·39H2O (TMANa-2) were obtained under basic conditions (pH ∼9). These compounds were characterized by X-ray structure analyses, elemental analyses, thermogravimetric/differential thermal analyses, Fourier transform infrared, and solution (31)P, (27)Al, and (183)W NMR spectroscopy. The polyoxoanion 1 is a monomeric, α-Dawson-type structure, resulting in an overall C3v symmetry, while the polyoxoanion 2 is a hydrogen-bonded dimeric structure, resulting in an overall S3 symmetry in the solid state. The pH dependence of polyoxoanions 1 and 2 in aqueous solution was also investigated by (31)P NMR spectroscopy.

A Novel Photocatalytic System Constructed Using Eosin Y, Titanium Dioxide, and Keggin-Type Platinum(II)- and Aluminum(III)-Coordinated Polyoxotungstates for Hydrogen Production from Water Under Visible Light Irradiation

A novel photocatalytic system constructed using Eosin Y, α-Keggin-type diplatinum(II)-coordinated tungstophosphate Cs3[α-PW11O39{cis-Pt(NH3)2}2]·8H2O (Cs-Pt-1), α-Keggin-type mono-aluminum(III)-coordinated tungstosilicate K5[α-SiW11{Al(OH2)}O39]·7H2O (K-Al-1), and titanium dioxide achieved a steady rate of hydrogen evolution with highly effective utilization of platinum sites from aqueous triethanolamine solution during a long-term visible light irradiation.Graphical Abstract

Synthesis and X-Ray Crystal Structure of α-Keggin-Type Aluminum-Substituted Polyoxotungstate

Aluminum and its derivatives such as alloys, oxides, organometallics, and inorganic compounds have attracted considerable attention because of their extreme versatility and unique range of properties, including acidity, hardness, and electroconductivity (Cotton & Wilkinson, 1988). Since the properties and activities of an aluminum species are strongly dependent on the structures of the aluminum sites, the syntheses of aluminum compounds with structurally well-defined aluminum sites are considerably significant for the development of novel and efficient aluminum-based materials. However, the use of these well-defined aluminum sites is slightly limited by the conditions resulting from the hydrolysis of the aluminum species by water (Djurdjevic et al., 2000; Baes & Mesmer, 1976; Orvig, 1993; Akitt, 1989).

Organozirconium Complex with Keggin-Type Mono-Aluminum-Substituted Silicotungstate: Synthesis, Molecular Structure, and Catalytic Performance for Meerwein–Ponndorf–Verley Reduction

The organozirconium complex with α-Keggin-type mono-aluminum-substituted silicotungstate, [(n-C4H9)4N]6[α-SiW11Al(OH)2O38ZrCp2]2·2H2O (TBA–Si–Al–Zr) was synthesized by the reaction of Cp2Zr(OTf)2·THF (or Cp2ZrCl2) with [(n-C4H9)4N]4K0.5H0.5[α-SiW11{Al(OH2)}O39]·H2O in acetonitrile. This compound showed high catalytic activities for Meerwein–Ponndorf–Verley reduction of ketones with 2-propanol in both homogeneous and heterogeneous system.Graphical Abstract

Remarkable Influence of Structures around Rhenium (V) Centers Constructed in Polyoxotungstates for Methanol Dehydrogenation under Visible Light Irradiation

The synthesis and characterization of 1-Dawson-type mono-rhenium (V)-substituted polyoxotungstate, [1-P2W17ReO62] (1), are described. The dimethylammonium salt of 1, [Me2NH2]7[1-P2W17ReO62]·9H2O (Me2NH2-1), was obtained as analytically pure homogeneous black-blue crystals by reacting mono-lacunary 1-Dawson polyoxotungstate with [ReCl6] in CH3COOH/CH3COOLi buffer, followed by crystallization via a vapor diffusion from acetonitrile/ethanol. Characterization was also accomplished by X-ray crystallography, elemental analysis, TG/DTA, FTIR, UV-vis, and solution P NMR spectroscopy; these results showed that the polyoxoanion 1 was a monomeric -Dawson structure, in which the rhenium(V) ion was coordinated to the monovacant site of [1-LiP2W17O61], resulting in an overall C1 symmetry. The polyoxoanion 1, [O{Re(OH)(2-P2W17O61)}2] (2), and [-PW11ReO40] (3) showed the Original Research Article British Journal of Applied Science & Technology, 4(16): 2302-2319, 2014 2303 hydrogen evolution from methanol under visible light irradiation (400nm) in the presence of titanium dioxide. The activities were remarkably depended on the rhenium (V) sites in 1–3; polyoxoanion 2 possessing the dirhenium(V)-oxido-bridged site showed the highest activities among these complexes.