International Tables for Crystallography

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Zeolites
L. B. McCusker and Ch. Baerlocher. International Tables for Crystallography (2019). Vol. H, ch. 4.6, pp. 452-464  [ doi:10.1107/97809553602060000961 ]

Abstract

Zeolites, with their relatively rigid, negatively charged 4-connected frameworks hosting labile/removable cationic and molecular guest species, display a remarkable range of applications ranging from water softeners in laundry detergents to desiccants in double-glazed windows to catalysts in the petrochemical industry. To understand how they function and how their properties might be improved for a particular application, structural characterization is essential. However, zeolites are often polycrystalline, so powder diffraction techniques have to be applied. In this chapter, the various approaches to initial (framework) structure determination (model building by hand or with the assistance of a computer, direct methods, charge flipping and using supplementary information) are discussed. Once the framework structure has been established, even more structural information can be extracted from the powder diffraction data via the analysis of difference electron-density maps and Rietveld refinement. Some of the difficulties that can arise (symmetry ambiguity, unsatisfactory geometry, diffuse electron-density maps and locating isomorphously substituted framework atoms) and how they might be surmounted are also reviewed. The determination and refinement of the structure of the high-silica zeolite SSZ-74 are presented to illustrate many of the issues described.


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About International Tables for Crystallography

International Tables for Crystallography is the definitive resource and reference work for crystallography. The multi-volume series comprises articles and tables of data relevant to crystallographic research and to applications of crystallographic methods in all sciences concerned with the structure and properties of materials.