muhammad qasim

• Polyoxometalates (POMs) are discrete, anionic metal-oxo clusters which draw much attention due to their fascinating structural and compositional diversity combined with manifold properties in the areas of catalysis, magnetism, material science and medicine. The main focus of this thesis is on the incorporation of lanthanide-peroxo fragments in POMs, as such materials (i) are of interest for redox catalysis and (ii) have never been explored systematically. This thesis comprises six chapters: Chapter 1 provides an introduction of POM chemistry as well as peroxo-containing coordination complexes of d- and f-block metals. Chapter 2 contains (i) the synthetic procedures of various lacunary POM precursors and (ii) a brief description of the instrumental techniques used for the characterization of the novel compounds reported here. Chapter 3 reports the synthesis and structural characterization of the first examples of cerium(IV)-peroxo POMs such as the trimeric 6-cerium(IV)-9-peroxo-30-tungsto-3-germanate [CeIV6(O2)9(α-GeW10O37)3]24- (1). Polyanion 1 was characterized in the solid state by single-crystal X-ray diffraction, FT-IR spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy, and in solution by 183W NMR and Raman spectroscopy, as well as theoretical DFT calculations. Both POMs were shown to act as selective homogeneous catalysts for the oxidation of methionine to the corresponding sulfoxide and sulfone, respectively. This study demonstrated that 1 acts as stable peroxo carriers that can be discharged and recharged multiple times. An even larger cerium(IV)-peroxo derivative with a tetrameric structure could also be prepared, namely the 12-cerium(IV)-14-peroxo-36-tungsto-4-germanate [CeIV12(O2)14Cl3CeIII(GeW9O34)4]24- (2). In Chapter 4, the synthesis and structural characterization of the sandwich-type cerium(III)-containing 22-tungsto-2-tellurate(VI) [Ce(β2-TeVIW11O39)2]9- (3) is described. In Chapter 5 the synthesis and structur