Synthesis, Structure And Properties Of Coordinated Complex Based On Lanthanide/Monovacant Dawson Polyoxometalates

Polyoxometalates (POMs), a class of metal oxygen clusters with fascinating structural variety and interesting physicochemical properties, have been attracting a great deal of attention as a result of their potential applications in catalysis, medicine and materials science. Lanthanide (Ln) cations, in virtue of their multiple coordination numbers and oxophilicity, are suitable to be incorporated into the lacunary POMs and link polyoxometalates to form new classes of materials with useful magnetic, luminescent properties etc. In this thesis, six new compounds based on lacunary Dawson type POMs have been synthesized by conventional methods, and characterized by single crystal X-ray diffraction, elemental analyses, IR, TG and X-ray powder diffraction. The electrochemical properties, magnetic properties and photoluminescence properties have also been studied.Complexes [(CH3)4N]8[Ln(H2O)M8]2[α2-As2W17O61)Ln(H2O)2]2·nH2O (Ln= Er(1), Dy(2)) were synthesized by reaction of trivacant [α-As2W15O56]12- with Ln3+. The polyoxoanion [(α2-As2W17O61)Ln(H2O)2]7-is based on the well-known Dawson structure of the with one W atom substituted by a Ln atom. The structures of 1 and 2 are centrosymmertric dimers built from two [(α2-As2W17O61)Ln(H2O)2]7- fragments by means of two Ln-O-W link. Furthermore, the dimers are linked by [Ln(H2O)8]3+ to extend into a 3D supramolecular network structure in virtue of hydrogen bonds interaction. The magnetic measurements on 1 and 2 reveal weak antiferromagnetic interactions between the Ln ions. Interestingly, the dynamic magnetic measurements for compound 2 display a slow relaxation of magnetization, showing a frequency-dependent susceptibility.Complexes [(CH3)4N]14Na4(H3O)16[(α2-As2W17O61)2Ln]2·nH2O (Ln= Nd (3), Pr(4)) show traditional sandwich type structures based on [α2-As2W17O61]10-. Two adjancent [(α2-As2W17O61)2Ln]17- have been connected by a [Na2(H2O)6]2+ cluster. The magnetic measurements on 3 and 4 reveal weak antiferromagnetic interactions between the Ln ions.Complexes [H2N(CH2CH2)2O]10Na(H3O)6[(α2-As2W17O61)2Ln]·nH2O (Ln= Pr (5), Eu(6)) are 1D chains constructed from sandwich type [(α2-As2W17O61)2Ln]17- and sodium cations. The magnetic measurements on 5 reveal weak antiferromagnetic interactions between the Ln ions. Luminescence properties of complex 6 was studied in the power solid state at room temperature. The emission spectrum reveal that 6 exhibits the characteristic transition of Eu3+ ion.