W0135

The Use of an Interactive Reciprocal Lattice Visualization Method for the Analysis of Problem Structures. Charles F. Campana, Mark R. Pressprich and Stephen A. Christian, Bruker Analytical X-Ray Instruments, Inc.; 5465 East Cheryl Pkwy., Madison, WI 53711-5373 and Ward T. Robinson, Dept. of Chemistry, Univ. of Canterbury, Christchurch, New Zealand

Along with the tremendous success of CCD-based x-ray diffractometer systems for the determination of routine crystal structures has come the expectation from many synthetic chemists that a competent service crystallographer should be able to produce a good crystal structure for every sample submitted for analysis. While this expectation is unrealistic, it challenges professional crystallographers to put more effort into the analysis of marginal specimens and to become more skilled in the application of advanced techniques to the analysis of data sets collected on twinned or multiple-crystal specimens.

In order to provide more powerful tools for the analysis of problem structures, we have developed a new interactive program, RLATT, which allows reflection arrays or entire data sets to be displayed in three dimensions. Reflections are displayed in undistorted reciprocal space (similar to precession photographs) and require no indexing. Incommensurately modulated structures, beta contamination, rotational twins and multiple crystals are easily identified. This program allows reflection properties and colors to be edited interactively for display purposes and for files to be exported for use with the standard unit cell determination and refinement algorithms. This program complements the batch-mode twin indexing techniques incorporated in the GEMINI software package.

The use of the RLATT program will be illustrated with several interesting examples recently examined in our applications laboratories.