Fourfold versus Sixfold Coordination of the Silicon Atoms in Phosphosilicates: Syntheses, Structures and Consequences for Materials Properties

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The proposed project focuses on the syntheses, structural characterisation and selected properties of phosphosilicates. These contain SiO4- and PO4-tetrahedra as well as octahedrally coordinated silicon atoms. So far these materials were formed under high temperatures or high pressure. Recently, we found a novel synthesis route to generate phosphosilicates with SiO6-octahedra. The characteristics are: -anhydrous syntheses in organic solvents -at room temperature and ambient pressure. On the one hand the research will deal with the dependency of the SiO6-formation on different reagents and reaction conditions. On the other hand phosphosilicates with specific structural features and compositions will be generated via novel precursors. The products are expected to be oligomeric or polymeric. They will be characterized with respect to elemental composition, structure and arrangement of the building blocks, which will require extensive use of NMR spectroscopy. In order to gain structural models which are as realistic as possible a theoretical group (P. Kroll, Arlington, Texas) will be involved who perform quantum mechanical calculations, the results of which will be compared and verified by spectroscopic and thermo¬chemical measurements. At the same time material properties will be tested. These include thermal and chemical stability as well as optical characteristics. The knowledge of syntheses, structures and properties will help to develop future potential applications of the phosphosilicate materials.