INTRODUCING CRYSTAL STRUCTURE DETERMINATION USING SPREADSHEETS. Max R Taylor, Department of Chemistry, The Flinders University of South Australia, GPO Box 2100, Adelaide SA 5001, Australia.

A package which allows structure factor calculation and 2-D Fourier summation has been developed in EXCEL 5.0 for hands-on undergraduate use. The package may be used to illustrate structure solution on a PC by the heavy-atom method using Patterson and electron density maps and refinement by using difference maps. The maps are calculated (as you watch) on the worksheet grid and can be adjusted to scale for orthogonal projections. The maps may, of course, be printed if contouring is required. Using the "what if" feature of spreadsheets is particularly instructive, because one can immediately see the effect on the R-factor and the relevant part of the difference map, of shifting an atomic position.

After 2 or 3 lectures on principles, students are able to follow the process of structure solution from observed structure factors to atomic coordinates provided that they have a rudimentary knowledge of the use of spreadsheets. The structure of potassium bicarbonate is an ideal example to use as it has the required heavy atom and a small number of other atoms, including a hydrogen atom that can be located. A projection down the short a axis shows most of the structural features. If x coordinates are provided then bond lengths and angles can be calculated. Structural features such as metal ion stereochemistry, bicarbonate ion geometry and hydrogen bonding can be studied. The package is easily adapted to use other examples.