Preparation Structural Characterization and Reactivity Investigation of 3d Transition Element- Substituted Metal-Oxo Clusters

<p>ed M-O cluster.1 They are discrete multi transition metal oxides characterized by a formidable structural variety resulting in different dimensions shape charge density surface reactivity and rich redox chemistry.[2-7] A first classification of POMs is based on the chemical composition of these species essentially represented by two types of general formula [8]: </p><p>Isopolyanions [MaOb]p- (1) </p><p>Heteropolyanions [XcMaOb]q- with c := a (2) </p><p>Where M is the main transition metal constituent of the POM O is the oxygen atom and X can be a nonmetal of the p block or a different transition metal. There are no chemical limitations for X and M by definition. The X elements are the so- called primary central or heteroatoms. In general any element except noble gases can participate as X in a POM cluster as there are no strict physical requirements for this position.[1] On the other hand M is the so called secondary peripheral or addenda atom and only some elements are typically found in such compounds. Despite the simplicity of formulae (1) and (2) above the composition of a cluster can be highly complex with various M elements taking part in the structure. POMs can be described as composed of MOn units where n indicates the coordination number (n=4 5 6 or 7) of M. usually the distorted octahedral coordination (n=6) is observed. Most of POMs are based on edge- and corner- shared MO6 octahedra where M is an early transition metal in its highest oxidation state (V+5 Nb+5 Ta+5 Mo+6).</p>