| Polyoxometalates,namely POMs,are nano-scale metal-oxygen clusters formed by high oxidation states of transition metal ions(such as V,Mo,W,etc.)with oxygens.POMs have the advantages of rich structure,high stability and easy solubility in water.The vacant sites of the lacunary POMs can be modified by other metals as active sites.The POMs doped with transition metals show unique properties and have broad application prospects in magnetism,medicine,catalysis and energy storage and other cutting-edge technologies.The traditional water-phase synthesis of metal-doped POMs is difficult to carry out systematic research due to the difficulty in structure control and easy polymerization.In this thesis,using organic extraction method,based on classic Keggin-type and Dowson-type lacunary POMs,transition metal cations are directed into the vacancies,and 11 new transition metal-doped POMs are successfully synthesized.Single crystal X-ray diffraction and high-resolution electrospray mass spectrometry have determined their compositions and structures.Compounds 1-5 are transition metal-substituted tri-lacunary Keggin-type POMs,and they are isostructurals.(TBAxHy(PW9M3O40)(CH3CN)8(CH3OH)4·n(H2O)(x=5,y=10,M=Cu(compound 1),Co(compound 2),Ni(compound 3),Mn(compound4);x=4,y=8,M=Fe(compound 5),TBA=Tetrabutylammonium cation).Magnetic studies have shown that compounds 2 and 5 exhibit antiferromagnetic coupling.Compounds 6-8 are transition metal-substituted mono-lacunary Keggin-type POMs,and they are isostructurals.(TBAxHy(PW11MO40)(CH3CN)4(CH3OH)2·n(H2O)(x=5,y=4,M=Co(compound 6),Ni(compound 7),Mn(compound 8),TBA=Tetrabutylammonium cation)Compounds 9-10 are mono-lacunary Dawson-type POMs substituted by transition metals,and they are isostructurals.(TBAxHy[(?-P2W17O67)2 M3]·n(H2O)(x=14,y=20,M=Cu(compound 9),x=12,y=22,M=Co(compound 10),TBA=Tetrabutylammonium cation)Compound 11 TBA10H4[P2W16O62Ni2]·28H2O is a hexa-lacunary Dawson-type POM substituted by transition metal.POM is a kind of"electronic sponge",which can hold electrons.POM has good electron conductivity,which could be a very good catalyst.The framework material with POM as the building block is a kind of promising heterogeneous catalyst.Paratungstate[H12W12O40]10-(W12O40)can be used as a multidentate ligand to connect with transition metals and rare earth metals to form different framework structures due to its special structural characteristics.There are few reports on the synthesis and catalysis of W12O40-copper cluster-based framework materials.In this thesis,using the hydrothermal method,by changing the p H value,heating temperature,heating time and other conditions,four cases of frame structures were successfully prepared with sodium tungstate and metal salt as raw materials.The analysis of single crystal structure shows that these structures are framework structures formed by(W12O40)as building blocks connected by transition metal cations.Compound 12(Na8(W12O40)[Cu4(CH3COO)8]·15H2O is a nanoporous 2D network structure obtained by replacing the coordination water of the"paddle wheel"copper dimer Cu2(OAc)4(H2O)2 with W12O40.Compound 12 can catalyze the phenylacetylene coupling reaction with a reaction conversion rate of 100%,and the catalytic mechanism has been studied,indicating that the ultra-high catalytic activity originates from the POM-Cu(?)synergistic catalytic mechanism.Three isomorphic three-dimensional(3D)framework structures[{M(H2O)x}y(H4W12O42)]·n(H2O)(x=4,y=6,M=Co(compound 13),x=6,y=6,M=Mn(compound 14),x=4,y=4,M=Mn(compound 15))were obtained by changing the reaction time,temperature,p H value and other conditions.The thesis herein provides a new synthesis method and experimental basis for the synthesis of POMs,and also develops the functions of POMs. |
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