Sib Sankar Mal

• Polyoxometalates (POMs) are inorganic metal-oxygen clusters with an enormous structural and compositional variety. To date no transition metal derivatives of the crown-shaped 48-tungsto-8-phosphate [H7P8W48O184]33- (P8W48) or its half unit [H6P4W24O94]12- (P4W24) are known. Therefore, we decided to perform a systematic study on the interaction of different transition metal ions with P8W48 and P4W24 in aqueous, acidic medium. Chapter 1 contains an extensive introduction to the class of POMs. Chapter 2 describes the synthetic procedures for the lacunary POM precursors and the experimental techniques used for characterizing the products. Chapter 3 describes the synthesis and structural characterization of the wheel-shaped Cu20 tungstophosphate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25-. The Cu2+ containing polyanion is composed of a cyclic P8W48 template fragment with a highly symmetrical, cationic {Cu20(OH)24}16+ cluster guest. Chapter 4 describes the synthesis and structural characterization of [P8W48O184Fe16(OH)28(H2O)4]20- which is composed of a 16 metal center iron-oxide nanocluster incorporated in the cyclic P8W48 template wheel. Chapter 5 describes the synthesis and characterization of an organoruthenium derivative of the cyclic P8W48 anion: [{K(H2O)}3{Ru(-pcymene)(H2O)}4P8W49O186(H2O)2]27-. Chapter 6 describes the synthesis and characterization of [Li(H2O)K4(H2O)3{(UO2)4(O2)4(H2O)2}2(PO3OH)2P6W36O136]25- which represents a uranium–peroxo derivative of the hitherto unknown “P6W36” Wells–Dawson ion. Chapter 7 describes the facile incorporation of platinum(IV) into polyoxometalate frameworks by the preparation of [H2PtIVV9O28]5- and its characterization by 195Pt and 51V NMR spectroscopy. Chapter 8 describes collaborative projects on the electrochemical, electrocatalytic, magnetic and EPR properties of some of the above mentioned compounds. Chapter 9 describes unpublished and incomplete results.