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zeolites with AST-topology causes reduction of the framework, hence structural destruction, in a notable extension. This is due to the impossibility for the organic cation occluded inside to react with ambient oxygen. As the temperature increases, reoxidation in air of the reduced framework causes episodes of weight-gain. When calcination is carried out in N2, weight losses close to 70% imply a loss of Ge due to sublimation of germanium monoxide, GeO. The nature of the organic cation occluded determines the nature and oxidation state of the final residue after calcination in N2: for tetramethylammonium the residue is GeO2 while trimethyl-terc-butylammonium, thanks to its larger C content, yields metallic Ge. Framework organoreduction is not unique to GeO2-AST zeolites but also occurs during the calcination in air of other germanium-containing zeolites with larger pore openings. [ABSTRACT FROM AUTHOR]

A synthesis of zeolite-like aluminogermanates using N,N,N-trimethyl-terc-butylammonium (TMTBA) and fluoride evolved from an initially crystallized zeolite with the AST Zeolite Framework Type and very little Al in it into an Al-free GeO2 phase with the same structure but a slightly smaller unit cell. In spite of both zeolites having the same framework type, same symmetry, a much similar unit cell size and almost the same framework composition, phase segregation occurred at intermediate crystallization times as the initial AST phase was gradually replaced by the new one. For reaction mixtures with a high Al content complete replacement of the large cell by the smaller cell phase was accomplished. The solids have been characterized by powder X-ray diffraction (XRD), Rietveld refinement from synchrotron diffraction data, multinuclear Nuclear Magnetic Resonance (NMR) of both intact and disolved solids and infrarred spectroscopy. The study reveals TMTBA can degrade under the crystallization conditions to initially yield triethylamine (tMA), whereas transmethylation between TMTBA and tMA produces tetramethylammonium (TMA), as probed by liquid NMR. The TMA cation can also structure-direct to AST zeolites but with a smaller unit cell volume and no Al in the framework. Phase segregation occurs despite the lack of structural mismatch because both crystallization events are decoupled, occurring at different moments and from largely different solutions. When both TMTBA and TMA cations are intentionally added at the start, no phase segregation but crystallization of a solid solution occurs instead. [ABSTRACT FROM AUTHOR]

HPM-2 is a new organosilicate layeredmaterial synthesized by thefluoride route using 2-ethyl-1,3,4-trimethylimidazolium. The layersare of a new structural type (denoted mtf) and are held together bystrong hydrogen bonds giving rise to a 1H magic angle spinning(MAS) nuclear magnetic resonance (NMR) at around 16 ppm and by Coulombicinteractions between silanolates and the organic cations residingin the interlayer space. Upon calcination HPM-2 transforms into thepure silica MTF zeolite by topotactic condensation, a process thatis essentially completed at 400 °C. Attempts to apply known methodsto derive new materials (swelling, delamination, interlayer expansion)are described. In the case of the interlayer expansion reaction, anonmicroporous dense phase is obtained, which is likely due to anunfavorable disposition of silanols in close couples within each layer.Silanol condensation between the newly incorporated silicon speciesoccurs across the main window producing narrower (6 member ring, 6MR)rather than wider (10MR) windows. [ABSTRACT FROM AUTHOR]