Nickolet Ncube

• Polyoxometalates (POMs) are discrete, anionic metal-oxides of early d-block metals in high oxidation states that exhibit unmatched structural variety and associated physicochemical properties leading to interest in diverse areas including catalysis, magnetism, material science and biomedicine. Chapter 1 covers the historical background, structural properties and some applications of POMs. Chapter 2 presents the state of the art of bismuth(III)-, lead(II)- and scandium(III)-containing POMs. Chapter 3 is about the analytical techniques and synthetic procedures of used POM precursors. Chapter 4 reports the synthesis and structural characterization of eight novel bismuth(III)-containing POMs. This chapter is divided into two subsections, (i) synthesis of four isostructural Keggin-type ions [Bi(α-XW11O39)2]n-, X = Si (1), Ge (2), n = 13; X = P (3), As (4), n = 11) and two Wells-Dawson-type ions [Bi(α2-X2W17O61)2]17- X = P (5), As (6), n = 17, and (ii) synthesis of the 1:1 complexes [{Bi(H2O)SiW11O39}4]20- (7) and {[Bi(H2O)SiW11O39]5-}∞ (8), the latter being an infinite one-dimensional structure in the solid state. Chapter 5 reports two novel lead(II)-substituted Keggin-type heteropolytungstates, [Pb(α-XW11O39)]6- (X = Si (9), Ge (10)). This work suggests that Pb2+ and Bi3+ mimic the structural chemistry of lanthanides in POM chemistry. Chapter 6 presents the synthesis and structural characterization of two scandium(III)-containing heteropolytungstates, [(Na(H2O))2Sc2(P2W15O56)2]16- (11) and [Sc(HPW7O28)2]13- (12). Chapter 7 summarizes the work presented in this dissertation and discusses the future prospects of this work. Chapter 8 shows some incomplete results including the synthesis of [Sc4(H2O)10(B-β-TeIVW9O33)2]4- (13), [Sc4(H2O)10(B-β-AsIIIW9O33)2]6- (14) {[(Sc(H2O)4)2(H2W12O42)]4-}∞ (15), [Bi2(W3O10)(B-α-BiW9O33)3]23- (16), [Bi2(H2O)6W2O4(B-β-BiW9O33)2] (17), [Sc2Na2(H2O)2(B-α-GeW9O34)2]12- (18) and [Sc2(B-β-GeW8O31)2]14- (19) respectively.