MODELING CRYSTAL STRUCTURES WITH DISORDER USING THE SHELXTL 5.0 SOFTWARE PACKAGE. Izya F. Burshtein and Charles F. Campana, Siemens Energy and Automation, Inc., Analytical Instrumentation, 6300 Enterprise Lane, Madison, Wisconsin 53719-1173, USA.

In the past, the existence of disorder in crystal structures has often prevented investigators from successfully completing the refinement of such structures, even though the X-ray intensity data were of very high quality. As single-crystal X-ray diffraction is utilized to solve increasingly large numbers of important real-world structural analysis problems, the ability to recognize and solve such problems becomes even more essential. The SHELXTL 5.0 Software Package includes a number of useful tools which allow complex disorder problems to be analyzed, modeled and successfully refined.

We intend to show more than a dozen examples in which the SHELXTL package has been used to model a variety of interesting disorder problems, We will present primarily structures where the successful modeling of disorder played the key role in the correct interpretation of the diffraction data. Successful modelling and refinement of a disordered structure not only improves R-values but provides a chemically reasonable description of the structure.

We will describe some of the clues that allow disorder problems to be recognized and graphical methods which may be employed to interpret the disorder mechanism and to construct the model. Specific examples of SHELXTL refinement files illustrating new features will be provided..