Crystal Structures And Characterization Of Coordinational Compounds From Hybrid Polyoxometalates Based On Metal-Citrate Clusters

In crystal engineering, the metal-oxygen clusters with abundant surface oxygen atoms are common used as building blocks, usually used to construct inorganic-organic materials with novel structures and varirties of physical and chemical properties. Among them, the most common inorganic metal-oxygen cluster is polyoxometalates. But in this thesis, we select citrate acid which is conformational flexibility and full of coordination sites as a ligand to coordinate to different metal atoms, which leads to the formation of metal-citrate clusters with abundant oxygen atoms. In this thesis, we defined these clusters as hybrid polyoxometalates. At the same time, the metal-citrate clusters are linked through ligands or second metal atoms to form coordinational compounds with different structures and properties.In this thesis, we obtain9metal-citrate (clusters-based) coordination compounds under hydro thermal (solvothermal) method and wet chemistry method. And we discuss the influences of different reaction condition (such as moalr ratio, reaction temperature, solvent, pH and the addition of the second metal atoms) on the structures and nature of the compounds. Meanwhile, these compounds are characterized by single crystal X-ray diffraction, X-ray powder diffraction, FT-IR spectram, TGA and Elemental analysis, as well as, we investigate their photoluminescence properties and electrical properties of some compounds. The main products are as follows:{K[Zn(C6H5O7)(H2O)]}n (1){[Zn(H2O)2][Zn2(C6H5O7)2(H2O)4]}n·4nH2O (2){[K(H2O)2][Ni(Hcit)(H2O)2]}n (3){[Mg(H2O)4][Ni2(Hcit)2(H2O)4]}n·6nH2O (4){[Ni(H2O)2][Ni2(Hcit)2(H2O)4]}n·4nH2O (5){[Ca(H2O)2][Ni(Hcit)(H2O)2][Ni(Hcit)(H2O)]}n·2nH2O (6){[Co(H2O)6][(Al3(C6H4O7)2(OH)2(H2O)4]2}n·10nH2O (7){[Ni(H2O)6][(Al3(C6H4O7)2(OH)2(H2O)4]2}n·10nH2O (8){[Zn(H2O)6][(Al3(C6H4O7)2(OH)2(H2O)4]2}n·3nH2O (9)According to different types of metals in these compounds, this thesis is devided into three parts: In the first part, we discuss Zn-citrate compound1and Zn-citrate cluster-based compound2. In compound1, the terminal carboxylate groups of citrate ligand bridge the discrete Zn metal ions into a zigzag chain with an edge-sharing mode, then the pentagonal bipyramid KO7link them into a3D network structure. In compound2, the citrate ligands and Zn atoms consist of centrosymmetric dimers [Zn2(C6H5O7)2(H2O)4], which are linked by the octahedral Zn(2)O6into a (4,6)-connected3D framework structure with pcu topology. In comparison with the emission peak of photoluminescence for citrate ligand, blue shift and red shift has been observed in compound1and2, respectively, resulting from the different coordination modes of ligand and metal ions.Secondly, at the same time Ni-citrate hybrid dimer is obtained, we explore the influence of the addition of the second metal on the structure and nature of the hybrid dimer. Compound3-6have the same dimer [Ni2(C6H5O7)2(H2O)4]. In compound3, the dimers are woven into a3D stucture by the pentagonal bipyramid KO7. In compound4, the octahedral MgO6expand the dimers into a ID chain, full of hydrogen bondings exit in compound4. Compound5and compound2are isostructural, in which the [Ni2(C6H5O7)2(H2O)4] dimers and octahedral NiO6consist of a (4,6)-connected3D framework structure with pcu topology. In compound6, there exit two similar dimers,[Ni2(Hcit)2(H2O)4] and [Ni2(Hcit)2(H2O)2], the middle carboxylate groups of citrate ligands link them into polyanion chains, then the chains are woven by pentagonal bipyramid CaO7into a3D structure. Compound3-6are promising luminescent materials. And the compounds3-5are potential ion conductors, and the second metal ions have great imfluences on their electrical properties.In the last part, compounds7-9which are all based on Al-citrate trinuclear clusters with butterfly-mode are obtained. Compounds7-8are isostructural, compound9shows a similar structure with7and8. The Al-citrate trinuclear clusters are connected to a3D network through hydrogen bonding interactions between the coordination water of Al atoms and lattice water molecules. And the second metal-water ions are situated in3D network. It has been found out that the different second metal-water ions will have great influences on emission peaks of luminescence spectra in these materials.