The Study Of Derivatives Based On Dawson-type Polyoxometalates (I)

The aim of this thesis is the synthesis of new polyoxometalate compounds on Dawson type polyoxoanions, which are decorated or bridged by transition metal coordination complexes or rare earth ions. The study on synthetic conditions and the exploration of relationships between structures and properties are also carried out.Nine new polyoxometalate compounds have been synthesized on the basis of hydrothermal technique and/or water solution synthesis methods and structurally characterized. Magnetic properties, electrochemical properties and photoluminescence properties of partial conpounds have also studied and discussed.Compounds [Co₂(bpy)₃(H₂O)₂(ox)][P₂W₁₈O₆₂]·2(H₂bpy)·3H₂O (1) and [Ni₂(bpy)₃(H₂O)₂(ox)][P₂W₁₈O₆₂]·2(H₂bpy)·2H₂O (2) are obtained under hydrothermal condition. Both of the structures exhibit 3D host frameworks constructed from the designed oxalate-bridged binuclear superoctahedron SBUs and bpy links, and the voids of which are occupied by the Dawson anions, 4,4'-bipyridine and water molecules. Magnetic studies reveal that antiferromagnetic exchange interactions among the transition metal centers. 1-CPE displays good electrocatalytic activity toward the reduction of nitrite.K2(H₃O)[Cu^I₇(Bpy)₆(BpyEt)₂][P₂W₁₈O₆₂]2·7H₂O (3) is obtained by similar synthetic condition. It is a 3D architecture constructed by saturated Dawson polyoxoanions and transition-metal coordination complexes (contain N-ethylated 4,4'-bipyridine) [CuI7(Bpy)6(BpyEt)2]. It is the first that N-ethylated bpy in the high dimentional framework.Complexes (H₃O)[Ln3(H₂O)17(α2-As2W17O61)]·nH₂O (Ln = Ce(4), Pr(5), Nd(6), Sm(7), Eu(8) and Gd(9)) have been synthesized by conventional solution method. It is 1D chain-like structure on the basis of lacunary Dawson type tungstoarsenates connected by Ln3+ ions. The striking feature of the structures is that there are three kinds of coordination environments for lanthanide cations. Photoluminescence measurements reveal that 7 and 8 exhibit orange and red fluorescent emission at room temperature, respectively.