%0 Journal Article
%T Hybrid Organic-Inorganic Materials Based on Polyoxometalates and Ionic Liquids and Their Application in Catalysis
%A Svetlana Ivanova
%J ISRN Chemical Engineering
%D 2014
%R 10.1155/2014/963792
%X An overview of the recent advances in the field of polyoxometalate, ionic liquid hybrids, is proposed with a special attention paid to their application in catalysis, more precisely biphasic and heterogeneous catalysis. Both components of the hybrids are separately outlined pointing to their useful properties and potential for catalysis, followed by the description of the hybrids preparation and synergy between components in a large range of organic transformations. And finally a vision on the future developments is proposed. 1. Polyoxometalates: General Aspects Polyoxometalates (POMs) are a class of anionic metal-oxygen clusters built by the connection of [MO]x polyhedra of the early transition metals in their highest oxidation states [1, 2]. Nevertheless, the strict rules for nomenclature, the polyoxometalate compounds [3], could be referred to also as hetero- or isopolyacids and hetero- or isopolyanions or polyoxoanions. The most studied polyoxo structures formers are molybdenum (VI) and tungsten (VI), structures resulting from accessibility of empty d-orbitals for metal-oxygen -bonding and favorable combination of ionic radius and charge. Polyoxo structures of the hexavalent Tc, Re, Ru, and Os, the pentavalent Cr, Mo, W, Tc, and Re, and tetravalent Ti, V, Cr Mo, and W are also known [4]. The formation of the polyoxometalate structures obeys generally on two principles: (i) each atom must occupy only one edge shared [MO]x polyhedron in which the metal is displaced toward the edge, as a result of the M¨CO -bonding and (ii) the structures with three and more terminal oxo groups are not observed (known as Lipscomb restriction) [4, 5]. Although the first polyoxometalates were reported over almost 200 years ago, continuously new structures are reported together with unusual properties and/or applications. Various reviews resume the main application domains of the polyoxometalates, for example, material science, medicine, or catalysis [6¨C9]. There are literally thousands of compounds in the polyoxometalate category which defers on their size, shape, and composition. Recently, Long et al. [10] proposed a very elegant way to classify the POM¡¯s compounds in-as-called ¡°polyoxometalate periodic table.¡± They proposed three broad groups taking into account essentially the anionic metal-oxygen cluster type.(i)Heteropolyanions: clusters including heteroatoms, such as [XM12O40]n£¿ anion, where M is generally Mo or W and X is a tetrahedral template. Inside this group, three main families could be attributed, Anderson [XM6O24n£¿], Keggin [XM12O40]n£¿, and Dawson structure
%U http://www.hindawi.com/journals/isrn.chemical.engineering/2014/963792/