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New Functional Polyoxometalates: from Fundamental Aspects to Application

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 June 2019) | Viewed by 10473

Special Issue Editor

Department of Marine Resource Science, Faculty of Agriculture and Marine Science, Kochi University, 200 Monobe-otsu, Nankoku 783-8502, Japan
Interests: synthesis and characterization of novel polyoxometalates; electrochemistry and analytical application of polyoxometalates; analysis for the formation mechanism of polyoxometalates

Special Issue Information

Dear Colleagues,

A huge number of polyoxometalates (POMs) have been prepared and characterized for ca. 200 years. POMs exhibit fascinating chemical properties and many of POMs have complicated structure to form beautiful molecule architecture. Therefore, POMs have been applied to versatile fields, such as catalysts, analytical chemistry and biochemistry and material chemistry. Although POMs are one family of inorganic clusters, organic molecule moiety attached POMs, ionic liquid-type POMs and other types inorganic-organic hybrid POMs have been prepared to exhibit unique chemical properties recently. The POMs chemistry is still promising research area and keeps spreading to wide range of scientific disciplines. This Special Issue focuses on the most recent advances in polyoxometalate-based material chemistry covering synthetic methods and application (perspectives) in catalysis, battery, fuel cell, magnetism, bio-medicine, sensor and other interesting areas. In addition, the detailed mechanistic and theoretical studies for chemical properties of POMs are included in this Special Issue.

Prof. Dr. Tadaharu UEDA
Guest Editor

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Keywords

  • Polyoxometalates
  • synthesis
  • characterization
  • hybrid material
  • catalysis
  • magnetism
  • electrochemistry

Published Papers (3 papers)

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Research

13 pages, 2692 KiB  
Article
Synthesis, X-ray Crystal Structure, and Photochromism of a Sandwich-Type Mono-Aluminum Complex Composed of Two Tri-Lacunary α-Dawson-Type Polyoxotungstates
by Chika Nozaki Kato, Daichi Kato, Toshifumi Kashiwagi and Shunpei Nagatani
Materials 2019, 12(15), 2383; https://doi.org/10.3390/ma12152383 - 26 Jul 2019
Cited by 1 | Viewed by 2311
Abstract
The synthesis and molecular structure of a dimeric, mono-aluminum complex composed of two tri-lacunary α-Dawson polyoxometalates, [H14Al(B-α-P2W15O56)2]7− (1), is described herein. The tetra-n-butylammonium salt of 1, [(n-C4 [...] Read more.
The synthesis and molecular structure of a dimeric, mono-aluminum complex composed of two tri-lacunary α-Dawson polyoxometalates, [H14Al(B-α-P2W15O56)2]7− (1), is described herein. The tetra-n-butylammonium salt of 1, [(n-C4H9)4N]7[H14Al(B-α-P2W15O56)2] (TBA-1) was prepared by passing an aqueous solution of K6[B-α-H3P2W15O59{Al(OH2)}3]⋅14H2O through an ion-exchange resin column (H+-form), followed by addition of tetra-n-butylammonium bromide. Analytically pure and colorless crystals of TBA-1 were obtained via vapor diffusion from acetonitrile/methanol at ~25 °C. Single-crystal X-ray structure analysis revealed that a six-coordinate aluminum ion was sandwiched between two tri-lacunary α-Dawson-type units, resulting in an overall C2h symmetry. The characterization of TBA-1 was accomplished by elemental analyses, thermogravimetric/differential thermal analyses, Fourier-transform infrared spectroscopy, and solution 31P nuclear magnetic resonance spectroscopy. The photochromic properties of TBA-1 were also characterized in methanol under light irradiation (λ = 365 nm and ≥400 nm). Full article
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11 pages, 1102 KiB  
Article
Keggin-Type Heteropoly Salts as Bifunctional Catalysts in Aerobic Baeyer-Villiger Oxidation
by Katarzyna Pamin, Jan Połtowicz, Mateusz Prończuk, Joanna Kryściak-Czerwenka, Robert Karcz and Ewa M. Serwicka
Materials 2018, 11(7), 1208; https://doi.org/10.3390/ma11071208 - 13 Jul 2018
Cited by 16 | Viewed by 3761
Abstract
The cobalt, manganese, and iron salts of tungstophosphoric or molybdophosphoric acid with growing content of metals were applied for the first time as catalysts in the Baeyer-Villiger (BV) oxidation of cyclohexanone to ε-caprolactone with molecular oxygen. The catalysts were characterized with Fourier transform [...] Read more.
The cobalt, manganese, and iron salts of tungstophosphoric or molybdophosphoric acid with growing content of metals were applied for the first time as catalysts in the Baeyer-Villiger (BV) oxidation of cyclohexanone to ε-caprolactone with molecular oxygen. The catalysts were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and ethanol decomposition reaction. Introduction of transition metals into the heteropoly structure increases the activity of resulting heteropoly salts in comparison with parent heteropolyacids. It was shown that the most active catalysts are salts of the heteropoly salts with one metal atom introduced and one proton left (HMPX) type, (where M = Co, Fe, Mn, and X = W, Mo) with the metal to proton ratio equal one. Among all of the studied catalysts, the highest catalytic activity was observed for HCoPW. The effect indicates that both the acidic and redox properties are required to achieve the best performance. The Baeyer-Villiger (BV) oxidation mechanism proposed identifies the participation of heteropoly compounds in three steps of the investigated reaction: oxidation of aldehyde to peracid (redox function), activation of carbonyl group (Lewis acidity), and decomposition of the Criegee adduct to ε-caprolactone (Brønsted acidity). Full article
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11 pages, 4263 KiB  
Article
Proton-Enhanced Dielectric Properties of Polyoxometalates in Water under Radio-Frequency Electromagnetic Waves
by Shuntaro Tsubaki, Shogo Hayakawa, Tadaharu Ueda, Tomohiko Mitani, Ei-ichi Suzuki, Satoshi Fujii and Yuji Wada
Materials 2018, 11(7), 1202; https://doi.org/10.3390/ma11071202 - 13 Jul 2018
Cited by 9 | Viewed by 3958
Abstract
Electromagnetic waves, such as microwaves, have been used to enhance various chemical reactions over polyoxometalates. The dielectric properties of catalysts are among the relevant parameters facilitating catalytic reactions under electromagnetic radiation. This study describes the dielectric properties of polyoxometalate catalysts in aqueous and [...] Read more.
Electromagnetic waves, such as microwaves, have been used to enhance various chemical reactions over polyoxometalates. The dielectric properties of catalysts are among the relevant parameters facilitating catalytic reactions under electromagnetic radiation. This study describes the dielectric properties of polyoxometalate catalysts in aqueous and organic solutions to understand the mechanism of interactions between polyoxometalates and electromagnetic waves. Specific loss factors of polyoxometalates were observed at lower frequencies (<1 GHz) by the ionic conduction of the polyoxometalate solution. The evolution of ionic conduction depended strongly on cations rather than anions. Proton-type polyoxometalates exhibited significantly higher loss factors than other cations did. The activation energy for ionic conduction in protonated silicotungstic acid (H4SiW12O40) was significantly low in water (7.6–14.1 kJ/mol); therefore, the high loss factor of protonated polyoxometalates in water was attributed to the proton relay mechanism (i.e., Grotthuss mechanism). The results suggested that the proton relay mechanism at the radio-frequency band is critical for generating selective interactions of polyoxometalates with applied electromagnetic fields. Full article
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