W0262

Structure Determination of Zeolitic Materials Using Neutron and X-ray Powder Diffraction. Brian H. Toby, NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg MD 20899-8562.

Zeolites and related microporous materials are worthy of study because they have many important commercial applications and because they have unusual and esthetically pleasing structures. Zeolitic materials have many common applications: as catalysts, they are used to produce gasoline and pharmaceuticals; as adsorbents, they are employed to separate gases for medical and industrial applications; as ion-exchange media, they are used for environmental remediation. In your home, they are found in household detergents to remove the calcium ions that make water "hard" and between double-pane windows to absorb water.

Alas, zeolitic materials can be obtained as single crystals for only a small fraction of the compositions of interest. Further, these materials typically have large asymmetric units and often scatter poorly, limiting the number of reflections that can be observed by powder diffraction. Despite this, we have had success obtaining accurate structural models for these materials, by fitting these models to neutron powder diffraction data, in combination with x-ray single-crystal data or x-ray powder diffraction data.

An overview of recent collaborative work will be presented. In these studies, structural knowledge, often in combination with modeling or spectroscopic results, have been valuable for understanding the properties these materials exhibit.