Amal Hamdy Ismail

• Polyoxometalates (POMs) represent a large class of nanosized metal-oxo anions. POMs are remarkable not only in terms of molecular and electronic structural versatility, but also due to their reactivity and relevance in fields such as photochemistry, analytical chemistry, clinical chemistry, magnetism, catalysis, biology, medicine and materials science. Lanthanide-containing POMs have been investigated less than those containing 3d-transition metals. The former have shown interesting properties in the areas of photoluminescence, catalysis, electrochemistry, and magnetism. Chapter I contains an extensive introduction to the class of POMs. Chapter II describes the synthetic procedures for some POM precursors and presents the different experimental techniques used for the characterization of the products. Chapter III comprises the lanthanide-containing polyoxotungstates results, divided into two sections, the lanthanide isopolytungstates and the lanthanide heteropolytungstates. In the first section, the polyanions [Ln2(H2O)10W22O71(OH)2]8− (Ln = La, Ce, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) {Ln2W22} and the V-shaped polyanions [Ln2(H2O)10W28O93(OH)2]14− (Ln = Sm, and Eu) {Ln2W28} were discussed. The {Ln2W22} family consists of the [H2W22O74]14− fragment and two {Ln(H2O)5}3+ supporting units while the {Ln2W28} consists of the [H2W28O95]20− unit and two {Ln(H2O)n}3+ supporting groups. The [H2W22O74]14− cluster is made up of two undecatungstate fragments while the [H2W28O95]20− cluster consists of two undecatungstate and a hexatungstate fragment. In the second section, the mono- and di-lanthanide derivatives of the tungstoarsenates(III) [Yb(H2O)2K(H2O)2As2W19O67(H2O)]10− {YbAs2W19}; [La2(H2O)6As2W19O67(H2O)]8− {La2As2W19}, the mono- and di-lanthanide derivatives of the tungstoantimonates(III) [Ln(H2O)3Sb2W21O72(OH))]10− (Ln = Yb, Lu, Y) {LnSb2W21}; [Ln2(H2O)6Sb2W20O70)]8− (Yb, Lu, Y) {Ln2Sb2W20}, and the acetate sandwich-type tungstogermanates [(Ln(GeW11O39)(H2O))2(m-CH3COO)2]12− (Ln = Eu, Gd, Lu) have been presented. Polyanions {YbAs2W19}, {La2As2W19}, {LnSb2W21} and {Ln2Sb2W20} were synthesized in simple, one-pot reactions of Ln3+ ions with the lone pair containing polyanion precursors ([As2W19O67(H2O)]14−, [B-α-AsW9O33]9−, [Sb2W22O74(OH)2]12−, [B-α-SbW9O33]9−). Chapter IV describes the mixed lanthanide/d-transition metal containing POMs, the novel open-ring shaped polyanions [Fe16O2(OH)23(H2O)9(P8W49O189)Ln4(H2O)20]11− {Ln4Fe16P8W49}(Ln = Eu and Gd) which have been synthesized by reaction of the known [H7P8W48O184]33− {P8W48} cyclic precursor with Fe3+ and Ln3+ ions in acidic aqueous medium in the presence of hydrogen peroxide. The unique novel open-ring tungstophosphate(V) unit {P8W48O188(WO3)}44− exists in the structure of the {Ln4Fe16P8W49}compounds in addition to the {Fe16O2(OH)20(H2O)12}21+ nanocluster and four {Ln(H2O)5}3+ grafted units. Chapter V comprises non-lanthanide-containing POMs, divided into two sections, tellurium and d-transition metal containing POMs. The tungstotellurates(IV) [H2Te4W20O80]22− and [NaTeW15O54]13− and the molybotellurate(IV) [H2Te24Mo44O198]34− are described in the first section. In the second section, the sandwich-type tungstogermanates [Cu3(H2O)(B-β-GeW9O33(OH))(B-β-GeW8O30(OH))]12−, [Co(H2O)2{Co3(B-β-GeW9O33(OH))(B-β-GeW8O30(OH))}2]22− and [Mn(H2O)2{Mn3(H2O)(B-β-GeW9O33(OH))(B-β-GeW8O30(OH))}2]22− are presented. All obtained compounds have been characterized in the solid state by FTIR, single-crystal XRD, TGA and elemental analyses. Furthermore, solution studies of the diamagnetic derivatives (La, Lu and Y analogues) by 183W and 89Y NMR spectroscopy were also performed, in addition to 13C NMR and 1H NMR spectroscopy for the acetate containing POMs.