Synthesis, modification, structural characterization, and nonlinear optical properties of selected aluminophosphate composites

The research objective of the project was the development, structural characterisation, and modification of physical and chemical properties of intra-crystalline composites consisting of an inorganic microporous mo-lecular sieve and an organic guest within the pore voids of the framework. Organic compounds with a high dipole moment and known non-linear properties were selected for the incorporation in a post-synthesis treatement, and aluminophosphates with a one-dimensonal pore system were choosen as the host materials, which should promote a stabilisation and an ordered placement of the organic molecules. One can expect that both features would lead to new and enhanced properties of the composite. Therefore the investigations should reveal contributions to the host- guest interactions within zeolite-type materials. Depending on the type of compound, single-crystal or powder X-ray diffraction techniques were applied to verify the ordered placement of the guest molecules within the molecular sieves. In the beginning the main interests were devoted to the synthesis of good quality single-crystals of the four selected aluminophosphates AlPO 4 -5, AlPO 4 -8, AlPO 4 -11 und VPI-5. Finally the activities revealed reasonable dimensions for AlPO 4 -5 (1 - 2 mm) and VPI-5 (0.2 - 0.5 mm), the two remaining zeolite-type materials were only available as fine grained powders for the further investigations. As the exchange of the organic guest molecules is usually performed under evacuated conditions at elevated temperatures the thermal characterisation of the actually used aluminophosphates was an essential basis for all subsequent modifications and treatements. According to these non-ambient investigations an up to now unknown change of the AlPO 4 -5 framework symmetry during dehydration from the usual hexagonal to an orthorhombic atomic arrangement could be observed. This feature provides again a graphically example for the flexibility of zeolite frameworks conforming the space requirement of the pore filling without a loss of structural stability. In the case of VPI-5, which can contain up to 25 wt% of water, 2/3 of this non-framework content can be removed by organic guest molecules. Good exchange rates are obtained under hydrothermal conditions, if water soluble molecules with a high dipole moment, e.g. formamide-type compounds, were used. As VPI-5 exhibit a high thermal stability under evacuated conditions gas-phase transport was applied for the loading with paranitroaniline resulting in a change of the cell parameters and the occurrence of a pale yellow colour. The crystallographical characterisation of these composites is the topic of current investigations.