Measurement of high-quality diffraction data with a Nonius KappaCCD diffractometer: finding the optimal experimental parameters

摘要

The influence of the different experimental parameters on the quality of the diffraction data collected on tetrafluoroterephthalonitrile (TFT) with a Nonius KappaCCD instrument has been examined. Data sets measured with different scan widths (0.25degrees, 0.50degrees, 1.0degrees) and scan times (70 s/degrees and 140 s/degrees) were compared with a highly redundant data set collected with an Enraf-Nonius CAD4 point detector diffractometer. As part of this analysis it was investigated how the parameters employed during the data reduction performed with the EvalCCD and SORTAV programs affect the quality of the data. The KappaCCD data sets did not show any significant contamination from lambda/2 radiation and possess good internal consistency with low R-int values. Decreasing the scan width seems to increase the standard uncertainties, which conversely are improved by an increase in the scan time. The suitability of the KappaCCD instrument to measure data to be used in charge density studies was also examined by performing a charge density data collection with the KappaCCD instrument. The same multipole model was used in the refinement of these data and of the CAD4 data. The two refinements gave almost identical parameters and residual electron densities. The topological analysis of the resulting static electron densities shows that the bond critical points have the same characteristics. [References: 41]