Anusree Sundar

• Polyoxometalates (POMs) are discrete, anionic metal-oxo clusters comprising early d-block metal ions in high oxidation states. Due to the large compositional and structural variety, POMs exhibit many interesting physicochemical properties including catalysis.POMs containing peroxo-groups are of special interest in hydrogen peroxide-assisted oxidation catalysis. In this thesis, the focus is on the synthesis of novel peroxo-containing POMs, the solid-state and solution characterization, and a study of their H2O2-based biphasic homogenous as well as heterogenous oxidation catalysis. Chapter 1 is an introduction of POMs and peroxo-POMs, whereas in Chapter 2 the motivation for the planned work is lined out. In Chapter 3, the experimental details are described, as well as the instruments used for the structural characterization and catalytic studies. In Chapter 4 some novel peroxo-Zr/Hf-containing Wells-Dawson anions are reported, which were studied for various H2O2-mediated oxidation reactions, using homogenous and supported conditions. A comparative study was also carried out on structurally-related peroxo-Zr/Hf Keggin anions. In Chapter 5 several novel peroxo-Ce-containing POMs of the Wells-Dawson type were isolated and structurally characterized in solution and in the solid state, followed by a comparative catalytic study using homogenous and supported conditions for the biphasic alcohol oxidation as well as alkene epoxidation. Chapter 6 describes the synthesis and characterization of a peroxo-Ce-containing POM of the Keggin type with the highest nuclearity amongst all peroxo-cerium POMs reported to date. Finally, Chapter 8 describes the synthesis and structural characterization of two dimethylarsinate-containing molybdenum-oxo clusters, a large, anionic mixed-valence wheel and a small neutral species. The novel compounds were mainly characterized in the solid state by FTIR,TGA, elemental analysis and XPS, and in solution by NMR and UV-Vis spectroscopy.