http://www.mdpi.com/journal/materials/special_issues/polyoxometalate-comp/ Dear Colleagues, Inorganic oxides are ubiquitous compounds that possess a remarkable compositional range and structural diversity. An important subclass of the oxides is the polyoxometalates, molecular early transition metal oxide cluster anions. Since their discovery in the mid-nineteenth century, thousands of polyoxometalate compounds have been described, incorporating nearly every element of the periodic table. This chemical and structural versatility is reflected in a range of physical properties, giving rise to applications in magnetics, sorption, electron transfer and medicine. More recently, with the discovery of polyoxometalates of increasing nuclearities and dimensions, the applications to the rational design of nanocomposites have received considerable attention. Today many properties and possible applications are being found for POMs since they can be seen as potential semiconducting molecule metal oxides and have remarkably diverse structural, electronic, magnetic and chemical properties and, as such, they provide a rich tool-box for bottom-up assembly of functional systems using ‘soft’ chemical approaches. The enormous potential of these robust building blocks to define a new type of molecular nanoscience using chemical assembly paradigms is extremely exciting. This volume collects the recent investigations and insights of some of the leading scientists in the field. The choice of topics illustrates the scope of the research and its applications and an overview of recent advances. We hope that the volume communicates some of the excitement and novel science that continue to evolve from the study of these “venerable” compounds to the cutting edge applications in molecular nanoscience. Prof. Dr. Jon Zubieta and Prof. Dr. Lee Cronin FRSE Guest Editors Submission All papers should be submitted to materials@mdpi.com. To be published continuously until the deadline and papers will be listed together at the special website. Submitted papers should not have been published previously, nor be under consideration for publication elsewhere. All papers are refereed through a peer-review process. A guide for authors is available on the Instructions for Authors page. Materials is an international peer-reviewed quarterly journal published by MDPI. Review manuscripts: Before writing their manuscripts, potential authors of review articles should forward the title and a short abstract to materials@mdpi.com. We will then provide feedback on the suitability of the topic. Article Processing Charges (APC) Article Processing Charges (APC) will be waived for well prepared manuscripts of invited papers. For the first two volumes of this new journal the APC are of 300 CHF (or 550 CHF per paper for those papers that require extensive additional formatting and/or English corrections). http://www.mdpi.com/1996-1944/3/3/1888/ Chemical pulps are produced by chemical delignification of lignocelluloses such as wood or annual non-woody plants. After pulping (e.g., kraft pulping), the remaining lignin is removed by bleaching to produce a high quality, bright paper. The goal of bleaching is to remove lignin from the pulp without a negative effect on the cellulose; for this reason, delignification should be performed in a highly selective manner. New environmentally-friendly alternatives to conventional chlorine-based bleaching technologies (e.g., oxygen, ozone, or peroxide bleaching) have been suggested or implemented. In an attempt to find inorganic agents that mimic the action of highly selective lignin-degrading enzymes and that can be applicable in industrial conditions, the researchers have focused on polyoxometalates (POMs), used either as regenerable redox reagents (in anaerobic conditions) or as catalysts (in aerobic conditions) of oxidative delignification. The aim of this paper is to review the basic concepts of POM delignification in these two processes. http://www.mdpi.com/1996-1944/3/3/1888/ Tue, 16 Mar 2010 00:00:00 CET Materials 2010-03-16 3 3 Review 1888 1903 1996-1944 Polyoxometalates in Oxidative Delignification of Chemical Pulps: Effect on Lignin 2010-03-16 doi: 10.3390/ma3031888 Bujanovic Ralph Reiner Hirth Atalla http://www.mdpi.com/1996-1944/3/2/897/ The synthesis and characterization of a Keggin-type mono-rhenium(V)-substituted polyoxotungstate are described. The dimethylammonium salt [Me2NH2]4[PW11ReVO40] was obtained as analytically pure homogeneous black-purple crystals by reacting mono-lacunary Keggin polyoxotungstate with [ReIVCl6]2- in water, followed by crystallization from acetone at ca. 5 °C. Single-crystal X-ray structural analysis of [PW11ReVO40]4- revealed a monomeric structure with overall Td symmetry. Characterization of [Me2NH2]4[PW11ReVO40] was also accomplished by elemental analysis, magnetic susceptibility, TG/DTA, FTIR, UV-vis, diffuse reflectance (DR) UV-vis, and solution 31P-NMR spectroscopy. Furthermore, [PW11ReVO40]4- and the Dawson-type dirhenium(V)-oxido-bridged polyoxotungstate [O{ReV(OH)(α2-P2W17O61)}2]14- were supported onto anatase TiO2 surface by the precipitation methods using CsCl and Pt(NH3)4Cl2. With these materials, hydrogen evolution from water in the presence of EDTA⋅2Na (ethylenediamine tetraacetic acid disodium salt) under visible light irradiation (≥400 nm) was achieved. http://www.mdpi.com/1996-1944/3/2/897/ Tue, 02 Feb 2010 00:00:00 CET Materials 2010-02-02 3 2 Article 897 917 1996-1944 EDTA-Reduction of Water to Molecular Hydrogen Catalyzed by Visible-Light-Response TiO2-Based Materials Sensitized by Dawson- and Keggin-Type Rhenium(V)-Containing Polyoxotungstates 2010-02-02 doi: 10.3390/ma3020897 Chika Nozaki Kato Kazunobu Hara Masao Kato Hidekuni Amano Konomi Sato Yusuke Kataoka Wasuke Mori http://www.mdpi.com/1996-1944/3/2/764/ Mesoporous silica molecular sieves are a kind of unique catalyst support due to their large pore size and high surface area. Several methods have been developed to immobilize heteropolyacids (HPAs) inside the channels of these mesoporous silicas. The mesoporous silica-supported HPA materials have been widely used as recyclable catalysts in heterogeneous systems. They have shown high catalytic activities and shape selectivities in some reactions, compared to the parent HPAs in homogeneous systems. This review summarizes recent progress in the field of mesoporous silica-supported HPAs applied in the heterogeneous catalysis area and preparation of nanostructured metal oxides using HPAs as precursors and mesoporous silicas as hard templates. http://www.mdpi.com/1996-1944/3/2/764/ Wed, 27 Jan 2010 00:00:00 CET Materials 2010-01-27 3 2 Review 764 785 1996-1944 Progress of the Application of Mesoporous Silica-Supported Heteropolyacids in Heterogeneous Catalysis and Preparation of Nanostructured Metal Oxides 2010-01-27 doi: 10.3390/ma3020764 Yuanhang Ren Bin Yue Min Gu Heyong He http://www.mdpi.com/1996-1944/3/1/741/ Green-chemistry type procedures were used to synthesize Pd0 nanostructures encapsulated by a vanadium-substituted Wells-Dawson-type polyoxometalate (Pd0@POM). The cyclic voltammogram run with the Pd0@POM-modified glassy carbon electrode shows well-defined waves, associated with Pd0 nanostructures and the VV/VIV redox couple. The Pd0@POM-modified electrode displayed remarkably reproducible cyclic voltammetry patterns. The hydrogen evolution reaction (HER) was selected as an illustrative example to test the electrocatalytic behavior of the electrode. The kinetic parameters of the HER show the high efficiency of the Pd0@POM-modified electrode. This is the first example of electrochemical characterization of a modified electrode based on a vanado-tungstic POM and Pd0 nanostructures. http://www.mdpi.com/1996-1944/3/1/741/ Tue, 26 Jan 2010 00:00:00 CET Materials 2010-01-26 3 1 Article 741 754 1996-1944 Pd0@Polyoxometalate Nanostructures as Green Electrocatalysts: Illustrative Example of Hydrogen Production 2010-01-26 doi: 10.3390/ma3010741 Rosa N. Biboum Bineta Keita Sylvain Franger Charles P. Nanseu Njiki Guangjin Zhang Jie Zhang Tianbo Liu Israel-Martyr Mbomekalle Louis Nadjo http://www.mdpi.com/1996-1944/3/1/682/ This review describes the synthesis and characterization of inorganic materials containing polyoxometalates encapsulated in oxide matrices. Examples illustrating key aspects in terms of synthesis and applications are presented according to the nature of the final hybrid material: those based on non-structured silicas, on mesostructured silicas, on macrostructured silicas and on other oxides. In each part, key points of the synthetic protocols are highlighted and structural features and properties of the resultant hybrid nanocomposites are discussed. http://www.mdpi.com/1996-1944/3/1/682/ Mon, 25 Jan 2010 00:00:00 CET Materials 2010-01-25 3 1 Review 682 703 1996-1944 Inorganic Hybrid Materials with Encapsulated Polyoxometalates 2010-01-25 doi: 10.3390/ma3010682 Véronique Dufaud Frédéric Lefebvre http://www.mdpi.com/1996-1944/3/1/503/ Reaction products of titanium(IV) sulfate in HCl-acidic aqueous solution with the dimeric species linked through three intermolecular Ti-O-Ti bonds of the two tri-titanium(IV)-substituted α-Keggin polyoxometalate (POM) subunits are described. Two novel titanium(IV)-containing α-Keggin POMs were obtained under different conditions. One product was a dimeric species through two intermolecular Ti-O-Ti bonds of the two tetra-titanium(IV)-substituted α-Keggin POM subunits, i.e., [[{Ti(H2O)3}2(μ-O)](α-PW9Ti2O38)]26- (1). The other product was a monomeric α-Keggin species containing the tetra-titanium(IV) oxide cluster and two coordinated sulfate ions, i.e., [{Ti4(μ-O)3(SO4)2(H2O)8}(α-PW9O34)]3- (2). Molecular structures of 1 and 2 were also discussed based on host (lacunary site)-guest (titanium atom) chemistry. http://www.mdpi.com/1996-1944/3/1/503/ Fri, 15 Jan 2010 00:00:00 CET Materials 2010-01-15 3 1 Article 503 518 1996-1944 Transformation of Tri-Titanium(IV)-Substituted α-Keggin Polyoxometalate (POM) into Tetra-Titanium(IV)-Substituted POMs : Reaction Products of Titanium(IV) Sulfate with the Dimeric Keggin POM Precursor under Acidic Conditions 2010-01-15 doi: 10.3390/ma3010503 Yuki Mouri Yoshitaka Sakai Yoshitaka Kobayashi Shoko Yoshida Kenji Nomiya http://www.mdpi.com/1996-1944/3/1/232/ The synthesis and structural characterization of two families of low-valent vanadium(III) {V6P4} and vanadium(III/IV) {V13P8} phosphonate complexes are reported. Magnetic characterization is reported for representative examples. http://www.mdpi.com/1996-1944/3/1/232/ Fri, 08 Jan 2010 00:00:00 CET Materials 2010-01-08 3 1 Article 232 240 1996-1944 Families of Molecular Hexa- and Trideca-Metallic Vanadium(III) Phosphonates 2010-01-08 doi: 10.3390/ma3010232 Sumit Khanra Rachel Shaw Madeleine Helliwell Floriana Tuna Christopher A. Muryn Eric J. L. McInnes Richard E. P. Winpenny http://www.mdpi.com/1996-1944/3/1/201/ A new approach for the chemical modification of the surface of paper based on the application of colloidal mixtures containing cationic starch and polyoxometalates on uncoated base paper is presented. Polyoxometalates with the Keggin-type structure and physical properties similar to those presented by coating pigments, namely H3PW12O40·23H2O, H4SiW12O40·24H2O, and K7PW11O39·9H2O, have been used in order to improve the quality of inkjet printing. The analysis of the different samples by FTIR-ATR spectroscopy showed the presence of the polyoxometalates (and the cationic starch) on the top surface of the paper. In addition, the determination of surface energy parameters, namely the polar component (σsp) and the dispersive component (σsd) of the surface energy, by contact angle measurements revealed that, for the new samples, the polar component level was much higher than that of the uncoated base paper. The quality of inkjet printing, evaluated by parameters such as the gamut area and the optical density, was considerably improved by these surface treatments. http://www.mdpi.com/1996-1944/3/1/201/ Thu, 07 Jan 2010 00:00:00 CET Materials 2010-01-07 3 1 Article 201 215 1996-1944 A New Approach for the Modification of Paper Surface Properties Using Polyoxometalates 2010-01-07 doi: 10.3390/ma3010201 Mikhail S. Saraiva José A. F. Gamelas António P. Mendes de Sousa Bruno M. Reis José L. Amaral Paulo J. Ferreira http://www.mdpi.com/1996-1944/3/1/150/ A mononuclear complex [MoOCl4(H2O)]− readily forms a metal−metal bonded {Mo2O4}2+ core. A high content of pyridine in the reaction mixture prevents further aggregation of dinuclear cores into larger clusters and a neutral, dinuclear complex with the [Mo2O4Cl2(Py)4] composition is isolated as a product. Solid state structures of two compounds containing this complex, [Mo2O4Cl2(Py)4]·2.25Py (1) and [Mo2O4Cl2(Py)4]·1.5PyHCl (2), were investigated by X-ray crystallography. http://www.mdpi.com/1996-1944/3/1/150/ Mon, 04 Jan 2010 00:00:00 CET Materials 2010-01-04 3 1 Article 150 157 1996-1944 Syntheses and a Solid State Structure of a Dinuclear Molybdenum(V) Complex with Pyridine 2010-01-04 doi: 10.3390/ma3010150 Barbara Modec Jon Zubieta http://www.mdpi.com/1996-1944/3/1/110/ This paper is a brief review of our recent research into novel uses for heteropoly compounds as precursors for thin films that can be used as catalysts and materials with good optical, conductive and other characteristics. In view of this, we have chosen thin film obtained with 12-tungsphosphoric acid on aluminum substrates. In all cases, a relatively new, microarc oxidation technique has been used to prepare oxide coatings on substrate surfaces. Advanced physicochemical methods, AFM and SEM-EDS, XRD, Raman and Micro-Raman, and luminescence spectroscopy, as the most powerful techniques, have been used for the characterization of new materials. Possible applications have been discussed as well. http://www.mdpi.com/1996-1944/3/1/110/ Thu, 31 Dec 2009 00:00:00 CET Materials 2009-12-31 3 1 Review 110 126 1996-1944 Characterization of Bronze Surface Layer Formed by Microarc Oxidation Process in 12-Tungstophosphoric Acid 2009-12-31 doi: 10.3390/ma3010110 Ubavka B. Mioč Stevan Stojadinović Zoran Nedić http://www.mdpi.com/1996-1944/3/1/64/ A28-electron reduced C2h-Mo-blue 34Ǻ outer ring diameter circular ring, [Mo142O429H10(H2O)49(CH3CO2)5(C2H5CO2)]30- (≡{Mo142(CH3CO2)5(C2H5CO2)}) comprising eight carboxylate-coordinated (with disorder) {Mo2} linkers and six defect pockets in two inner rings (four and three for each, respectively), reacts with La3+ in aqueous solutions at pH 3.5 to yield a 28-electron reduced elliptical Ci-Mo-blue ring of formula [Mo134O416H20(H2O)46{La(H2O)5}4{La(H2O)7}4{LaCl2(H2O)5}2]10- (≡{Mo134La10}), isolated as the Na10[Mo134O416H20(H2O)46{La(H2O)5}4{La(H2O)7}4{LaCl2(H2O)5}2]·144 H2O Na+ salt. The elliptical structure of {Mo134La10} showing 36 and 31 Å long and short axes for the outer ring diameters is attributed to four (A-D) modes of LaO9/LaO7Cl2 tricapped-trigonal-prismatic coordination (TTP) geometries. Two different LaO2(H2O)7 and one LaO2(H2O)2Cl2 TTP geometries (as A-C modes) for each of two inner rings result from the coordination of all three defect pockets of the inner ring for {Mo142(CH3CO2)5(C2H5CO2)}, and two LaO4(H2O)5 TTP geometries (as D mode) result from the displacement of two (acetate/propionate-coordinated) binuclear {Mo2} linkers with La3+ in each inner ring. The isothermal titration calorimetry (ITC) of the ring modification from circle to ellipsoid, showing the endothermic reaction of [La3+]/[{Mo142(CH3CO2)5(C2H5CO2)}] = 6/1 with DH = 22 kJ×mol-1, DS = 172 J×K-1×mol-1, DG = −28 kJ×mol-1, and K = 9.9 ´ 104 M-1 at 293 K, leads to the conclusion that the coordination of the defect pockets to La3+ precedes the replacement of the {Mo2} linkers with La3+. 139La- NMR spectrometry of the coordination of {Mo142(CH3CO2)5(C2H5CO2)} ring to La3+ is also discussed. http://www.mdpi.com/1996-1944/3/1/64/ Mon, 28 Dec 2009 00:00:00 CET Materials 2009-12-28 3 1 Article 64 75 1996-1944 Coordination of {Mo142} Ring to La3+ Provides Elliptical {Mo134La10} Ring with a Variety of Coordination Modes 2009-12-28 doi: 10.3390/ma3010064 Eri Ishikawa Yutaka Yano Toshihiro Yamase http://www.mdpi.com/1996-1944/2/4/2319/ The hydroisomerization of n-butane was carried out in a fixed-bed gas-flow reactor over Pt-promoted Cs2.5H0.5PW12O40 (denoted as Cs2.5). Two kinds of catalysts, a direct impregnation of Pt on Cs2.5 (denoted as Pt/Cs2.5), as well as a mechanical mixture of Pt/Al2O3 and Cs2.5 (denoted as Pt/Al2O3+Cs2.5), were used for the hydroisomerization. Pt/Al2O3+Cs2.5 showed a higher stationary activity than Pt/Cs2.5 because the Pt particles supported on Al2O3 were much smaller than those supported on Cs2.5. The initial activity decreased with increasing H2 pressure over Pt/Al2O3+Cs2.5. This indicates that the hydroisomerization of n-butane over Pt/Al2O3+Cs2.5 proceeded through a bifunctional mechanism, in which n-butane was hydrogenated/dehydrogenated on Pt sites and was isomerized on acid sites of Cs2.5. For the hydroisomerization of n-butane over Pt/Al2O3+Cs2.5 the hydrogenation/dehydrogenation on Pt sites is a limiting step at a low Pt loading and the isomerization on solid acid sites is a limiting step at a high Pt loading. During the reaction, hydrogen molecules were dissociated to active hydrogen atoms on Pt sites, and then the formed active hydrogen atoms moved to the solid acid sites of Cs2.5 (spillover effect) to eliminate the carbonaceous deposits and suppress the catalyst deactivation. Because Cs2.5 has suitably strong and uniformly-distributed solid acid sites, Pt/Al2O3+Cs2.5 showed a higher stationary activity than Pt/Al2O3+H-ZSM-5 and Pt/Al2O3+SO4/ZrO2 for the hydroisomerization of n-butane at a low H2 pressure. http://www.mdpi.com/1996-1944/2/4/2319/ Mon, 14 Dec 2009 00:00:00 CET Materials 2009-12-14 2 4 Article 2319 2336 1996-1944 Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid 2009-12-14 doi: 10.3390/ma2042319 Yanyong Liu Makoto Misono http://www.mdpi.com/1996-1944/2/3/869/ Efficient and simple syntheses of [(n-C4H9)4N]4[a-Mo8O26] (I) and [(n-C4H9)4N]2[Mo2O7] (II) from MoO3 and aqueous [(n-C4H9)4N]OH are described. The yield is 72% for I and 73% for II. http://www.mdpi.com/1996-1944/2/3/869/ Tue, 28 Jul 2009 00:00:00 CEST Materials 2009-07-28 2 3 Article 869 875 1996-1944 Efficient Syntheses of [(n-C4H9)4N]4[α-Mo8O26] and [(n-C4H9)4N]2[Mo2O7] 2009-07-28 doi: 10.3390/ma2030869 Shusaku Ikegami Atsushi Yagasaki