Synthesis,Structure,Magnetic And Luminescent Properties Of Polyoxometalate-based Rare Earth Derivatives

Abstract Polyoxometalates（POMs）are a class of unique inorganic nanoscale clusters with controllable shape,size and charge.In particular,lacunary POMs have shown strong affinity to other metals because of their high negative charge and oxygen-rich surface,which can be well coordinated with metal cations to form a variety of giant clusters.Benefiting from the unique 4f electron configuration of rare earth ions,POM-based rare earth derivatives not only possess new structural features,but also have application in magnetism,luminescence and catalysis.In this thesis,a series of POM-based rare earth derivatives were synthesized by controlling the stoichiometric ratio of reactants and p H value using the K₁₄[As₂W₁₉O₆₇（H₂O）]and Na₉[Sb W₉O₃₃]?19.5H₂O precursors.Moreover,the structures,magnetic and luminescence properties were studied in detail.The main contents are as follow:（1）Two novel polynuclear dysprosium（Dy）-containing polytungstoarsenates,Cs K₇Na₁₆[(As W₉O₃₃)₆Dy₆W₁₀O₂₄（H₂O）₂₃]·40H₂O（1）and Cs₂K₁₈Na₁₈[(As W₉O₃₃)₇Dy₇W₈O₂₁（H₂O）₁₇（μ₃-OH）（OH）]·78H₂O（2）,have been synthesized via the reaction of the preformed POM precursor K₁₄[As₂W₁₉O₆₇（H₂O）]and Dy³⁺ions through controlling p H.The Dy^III ions in polyanion of 1 are arranged in a linear fashion,and polyanion of 2 presents an interesting W-shaped structure.The dynamic magnetic measurements indicate that 1 and 2 exhibit slow relaxation of the magnetization.The solid-state luminescence performances demonstrate energy transfer from the photoexcitation O→M ligand to the metal charge-transfer（LMCT）bands of the POM ligands to Dy³⁺ions.（2）Two POM-based rare earth derivatives with C_3v symmetry were prepared by the,Na₉[Sb W₉O₃₃]?19.5H₂O precursor and Ln Cl₃·6H₂O in the presence of Mo O₄^2-as template agent,Na₁₈[Ln₃（CH₃COO）₄(α-Sb W₉O₃₁（OH）₂)₃（H₂O）（Mo O₄）]?n H₂O(Ln=Dy³⁺,（3）;Ho³⁺,（4）).The alternating-current susceptibility measurements show that compound 3displays single molecule magnets behavior,whereas compound 4 does not.The solid-state luminescence performances of compound 3 reveals the energy transfer from tungsten-antimonate fragment to Dy³⁺inhibits the emission attenuation of Dy³⁺to some extent.（3）Organophosphonate-bridged POM-based rare earth derivative,Cs₁₁K₂₁[(As W₉O₃₃)₆Dy₄W₈O₁₈（H₂O）₁₀（amp H）₂]·n H₂O（5）,was prepared by a one-pot reaction of the POM precursor K₁₄[As₂W₁₉O₆₇（H₂O）],Dy³⁺ions and（aminomethyl）phosphonic acid ligand.X-ray single crystal diffraction shows that the polyanion of compound 5 is composed of two identical units[(As W₉O₃₃)₃Dy₂W₄O₉（H₂O）₅]^15-connected by two organophosphonate ligands.