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Positron annihilation lifetime spectroscopy has been used for observation of the free voids in low silica zeolites, of LTA and FAU structure and different crystal size, before and after their heating at different temperatures below 200 A degrees C. Sizes of crystals of the zeolite samples, as well as their structures and water contents, were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetry, and particle size distribution measurements. The number of positron lifetime components as well as their values and intensities, after water removal from the zeolite structure, vary. However, changes are not uniform in all investigated zeolites. The differences are compared and discussed in the dependence of different structure types and crystal sizes of investigated zeolites.

A 3-D open-framework and a chain-structured zinc terephthalate are obtained by hydrothermal crystallization under microwave heating at 180 degrees C. The study shows that these structures have rather similar principal building units, which facilitates the structure transformation from the low-dimensional to the open-framework one during crystallization. The transformation involves the formation of new coordinative bonds between a Zn atom in a chain and two terephthalate groups from two different chains: one from the same stack and the other from the neighboring stack. Also, one water molecule coordinated to the Zn atom in the chain-like structure is lost and the zinc atom expands its coordination number to five. A considerable shift of the chains as well as bond twisting in them are necessary to occur prior to the formation of the network.

The lattice energies of the as-synthesized fluoride-containing chabazite-like aluminophosphate (AlPO4-34F) and of the corresponding metal-substituted materials [MeAPO-34F, Me = Mn(II), Co(II), Ni(II)] have been calculated in order to investigate the Al-site preference the transition metal substitution in the AlPO4-34F. The calculations show that the transition metal ions in MeAPO-34F should preferentially occupy octahedral Al3+ sites, and kinetic reasons are suggested as an explanation for the actual preference of tetrahedral sites. The lattice energies have also been calculated for the calcined AlPO4-34F material (AlPO4-34) and the rehydrated-calcined product (AlPO4-34h). The AlPO4-34 is found to be less stable than either AlPO4-34F or AlPO4-34h, which is consistent with the fact that AlPO4-34 can only be prepared starting from AlPO4-34F.