Strategies for data collection on a CCD-diffractometer

Abstract

The introduction of area detectors has led to a significant reduction of the time needed for measuring a complete set of X-ray reflections. The default parameters suggested by the manufacturer of the instrument lead to good results, but both the software and the hardware provide the possibility of varying numerous parameters in order to optimize the quality of the data set. The influence of parameters (measuring time, scan angle, crystal-to-detector distance, collimator radius, detector resolution, redundancy, crystal size and scan type) is determined and rated with regard to their importance for the quality of the data. The investigations were carried out on a Siemens (now Bruker AXS) CCD diffractometer on three small organic molecules, p-nitrobenzaldehyde diacetate [P21/n; Z = 4; a = 10.785(2) Å; b = 7.420(2) Å; c = 15.407(2) Å; β = 107.30(1)°] and p-methoxyacetophenone [P21/c; Z = 4; a = 10.158(2) Å; b = 7.917(2) Å; c = 10.287(2) Å; β = 103.72(3)°], of which the crystal structures were determined. An optimized strategy for the data collection is proposed and the attainable improvement is shown by comparing the data sets based on the default parameters and the data sets obtained with the optimized strategy for the three structures examined. However, different strategies may be needed for more strongly absorbing materials.