Interlayer expansion of layer silicates with reactive metal centers, a new synthesis approach for nanoporous materials with silicate frameworks having distinct metals sites: Synthesis and crystal structure.

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Nanoporous, crystalline solids are important materials for applications in separation processes, adsorption, form selective catalysis and also as depot materials. In addition, nanoporous materials are also used in solar heat storage devices. The classical zeolites are an important sub-group of nanoporous materials, however, coordination polymers such as metal organic frameworks or organic porous polymer networks are in the focus of interest currently. However, new synthesis routes for silicate zeolites have attracted new interest. On the one hand, template free synthesis has allowed to produce zeolites more efficiently, on the other hand, new zeolite framework types were synthesized using 'precursor chemistry', leading to very interesting, thermally resistant and catalytically active materials. As precursors, layered silicates were used which have been transformed in a topotactic condensation reaction into nanoporous framework structures. The general validity of the concept has been shown for a number of precursor materials.An extension of the approach was achieved by using silicate monomers as linkers bridging the layered precursors. The silicate linker connected surface silanols of neighbouring layers with each other in a registered arrangement. This lead to crystalline, nanoporous 3-dimensional silicates frameworks with extended porosity and functional groups at the linker site. Again, the general applicability of the concept has been shown for different linker groups and also for different precursor silicates. As technical term for the reaction "interlayer expansion" has been introduced.The current proposal is aimed at an extension of the interlayer expansion by using other elements as linker materials such as oxygen coordinated metal centers. In a first experiment, Fe has been introduced in interlayer expanded RUB-36 as silicate precursor. The new nanoporous material is thermally stable up to 500 °C, the Fe-center shows catalytic activity and does not leach out of the silicate during reaction. Preliminary results from crystal structure analysis proofed that Fe occupies ca. 50% of the linker sites and, thus, the introduction of metal centers on well defined framework sites. Other metal interlayer expansion reaction show promising results and Sn, Zn, Ti, V, and Eu on linker sites have already been obtained. In order to reproduce and optimize the synthesis, to improve crystallinity of the products, and to proof the substitution of Si by metal centers on the linker site, crystal structure analyses are required which shall be in the focus of the project. The powder materials shall be studied by Rietveld analysis of powder X-ray diffraction data to show the bulk crystallinity, and by single crystal techniques such as electron crystallography in order to obtain a most detailed view on the geometrical details of the new materials.