Syntheses, Properties And Applications Of Prenucleation Clusters

Zirconium oxides and hafnium oxides have been widely applied in heat-insulating materials,electronic information technology,fuel cell and biomimetic materials due to their unique properties such as high hardness,high temperature resistance,good thermal stability and chemical stability.Polyoxozirconates and polyoxohafnates are molecular models or intermediates in the formation of zirconium oxides and hafnium oxides,as well as nanoscale building blocks in the assembly of functional metal-organic frameworks.They are the prenucleation clusters involved in the synthesis of zirconium oxides and hafnium oxides nanocrystals,for which the sol-gel method is the most fundamental strategy.Hence their isolation and crystal structure characterization are important for studying the crystallization mechanism of zirconium oxides and hafnium oxides on the molecular level.On the other hand,alkali halide widely exist in nature.The isolation and crystal structure of alkali halide nanoclusters will greatly benefit the studies on nucleation mechanism in water.Considering all above,during the sol-gel processes we have successfully captured a series of polyoxozirconates and polyoxohafnates,the prenucleation clusters of zirconium oxides and hafnium oxides,which are stabilized by sulfate and various carboxylate groups;we also captured an alkali halide nucleation cluster.Besides,we characterized structures and spectral properties.We also investigated their other properties such as ionic conductivities in detail.The contents of this thesis are divided into three parts as follows:In Chapter ?,the literature on the syntheses of zirconium oxides/hafnium oxides and metal-oxide clusters is reviewed.The structures and the properties of polyoxozirconates and polyoxohafnates are summaried.Besides,the significance and research progress of alkali halide clusters are reviewed.Finally,the scientific significance of this paper is highlighted.In Chapter II,we report the structure,synthesis and properties of a novel pinwheel-shaped 17-nuclear zirconium/hafnium oxo cluster.Both {Zr6} and {Zr17}were isolated as crystals during the hydrothermal treatment of ZrOCl2/HfOCl2 solutions with added SO42-and formic acid.Their roles in the formation of zirconium oxides and hafnium oxides nanocrystals from the hydrolysis and condensation of Zr4+/Hf4+ hydroxides are experimentally studied and discussed.Their spectroscopic properties and super ionic conductivities were characterized.In Chapter ?,we report a cubic alkali halide nanocluster[Cs8X27]19-(X = Cl,Br)isolated from water,the nucleation clusters which feature four unit cells of the bulk structure of CsX.They were obtained by the electrostatic attraction and face-directed recognition with[M4(OH)8(OH2)i6]8+(M = Zr? or Hf?)as the counter cations to form intercluster compounds.Their structures were determined by single crystal X-ray diffraction.Their spectroscopic properties,super ionic conductivities and solution chemistry were studied.