Synthesis and Structural Characterization of Lanthanide Containing Polyoxoanions Functionalized by Peroxo Groups, and Investigation of Their Catalytic Properties

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We propose to synthesize novel polyoxotungstates substituted by lanthanide centers for which the terminal aqua ligands have been substituted by peroxo groups. To date no such species are known at all. We will also investigate the homogeneous and heterogeneous oxidation catalysis properties of this novel subclass of polyoxometalates (POMs). We will investigate the interaction of lanthanide ions with a variety of water-soluble polytungstate precursors, followed by functionalization using aqueous hydrogen peroxide. Our initial focus will be on the functionalization of known lanthanide-POMs, e.g. the spectacular 20-cerium containing 100- tungstogermanate [Ce20Ge10W100O376(OH)4(H2O)30]56- published very recently by our group.21 This species has a total of 30 terminal aqua ligands associated with the 20 cerium centers and hence represents a good candidate for functionalization with peroxo groups. Our novel lanthanide-peroxo-POMs will be characterized as usual by single-crystal X-ray diffraction, FTIR, TGA-DSC, multinuclear NMR (e.g. 183W, 31P, 29Si) and elemental analysis. The preliminary catalytic tests (e.g. peroxide-based oxidation of olefins) will also be carried out at Jacobs University. Incorporation of lanthanides into lacunary polytungstate frameworks has already resulted in several POMs with interesting properties in the areas of luminescence, magnetism, and Lewis acid-type catalysis. Due to their larger size and coordination number, compared to 3d transition metals, lanthanide ions cannot be fully inserted into the vacant sites of the lacunary POM precursors, usually resulting in 2 or more terminal, sterically accessible and labile water ligands. This in turn allows for substitution of those water molecules by organic ligands (incl. chiral ones) or for coordination to other POM fragments leading to very large discrete, molecular architectures or extended frameworks. To date some peroxo-POMs are known and they are very good oxidation catalysts.29 On the other hand, no lanthanide-peroxo-POMs have ever been reported. We believe that such POMs should exist, as formation of side-on -peroxo bridged lanthanide based coordination complexes are well known.30