Design And Synthesis Of Polyoxometalate-based Metal-organic Composite Materials With Bichelate-bridging Ligands

Polyoxometalate(POM)-based metal-organic composite materials are one importantresearch subject in the field of inorganic chemistry and coordination chemistry, owing totheir various structural features and potential applications in catalysis, adsorption, molecularrecognition, optical, electronic, and magnetic materials. Such composite materials usuallycontain three main secondary building blocks, that is, the POM units, metal ions, andorganic ligands. During the design and synthesis of new POM-based metal-organic hybridcompounds, the first and the most important key factors is the design and choice of organicligands. Especially the neutral N-donor ligands have been widely explored in the last twodecades. Based on our review of neutral N-donor ligands employed in the POM-basedmetal-organic hybrid compounds, it is found that the advantages of bridging and chelateligands, respectively. Thus, we imagine that if the chelate and bridging functional groupscan combine together to form new chelate-bridging ligands, thus, such ligands may be usedto explore new type of POM-based metal-organic hybrid compound system with novelstructural features and functionalities. Therefore, the aim of this thesis is the design and theresearch of new chelate-bridging ligands, which is combined with TM ions and POM unitsto synthesize new type of POM-based metal-organic hybrid system, explore the potentialstructure-component relationships, and investigate the relevant properties.According to the description above, We have designed and synthesized four newcomposite materials based on copper(I) ion, a neutral N-donor bichelate-bridging ligand (Lpor Lo) and a Lindqvist-type polyoxometalate under different synthetic conditions, namely[CuILp]2[W6O19]·H2O (1),[CuILp]3[W6O19]Cl (2),[CuILp]2[W6O19]·2H2O (3)[CuILo]3[NbW5O19]·H2O (4)Lp=α,α’-bis-[3-(2-pyridyl)pyrazol-1-yl]-1,4-dimethylbenzeneLo=α,α’-bis-[3-(2-pyridyl)pyrazol-1-yl]-1,2-dimethylbenzene.And do a series of structurally characterization, such as elemental analyses, IR spectra, TGanalyses, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction analyses.In compounds1-4, the Lindqvist-type polyoxometalates are synthesized by the followingmethods: in suit synthesis and pre-synthesis. For Nb-substitute Lindqvist-typepolyoxometalate [NbW5O19]3-, the change of electric charge number has a certain effect inthe final structure of composite materials. The research results show that Compounds1,2 and4contain three different but topologically similar meso-helical chainlike coordinationmoieties. Compound3contains both left-and right-handed chiral “mobius strip” units.These cationic meso-helical chains and “mobius strip” units in compounds1-4are furthercombined with Lindqvist-type polyoxoanions to form3-D supramolecular assembliesthrough extensive electrostatic forces and/or π…π interactions. The Lindqvist-typepolyoxoanions reside in the voids. Finally, we investigate the photo-luminescent propertiesof1-4,which are mainly attributed to the Lp/oligand-centered emission. In addition, we alsodiscussed the influence of the Lindqvist-type polyoxoanions in the process of constructingmetal-organic coordination polymers, and propose a new synthetic strategy to construct newPOM-based metal-organic composite system with chelate-bridging ligands.