The structure of cubic MOF [{Ca(H_2O)_6}{CaGd(oxydiacetate)3}2]·4H_2O. A comparison between structural models obtained from Rietveld refinement of conventional and synchrotron X-ray powder diffraction data and standard refinement of single-crystal X-ray diffraction data

摘要

The structure of the metal-organic framework (MOF) compound [{Ca(H_2O)_6}{CaGd (oxydiacetate)_3)_2]·4H_2O was determined by single-crystal X-ray diffraction and refined using conventional single-crystal X-ray diffraction data. In addition, the structure was refined using powder diffraction data collected from two sources, a conventional X-ray diffractometer in Bragg-Brentano geometry and a 12-detector high resolution synchrotron-based diffractometer in transmission geometry. Data from the latter were processed in three different ways to account for crystalline decay or radiation damage. One dataset was obtained by averaging the multiple detector patterns, another dataset was obtained by cutting the non-overlapping portions of each detector to consider only the first few minutes of data collection and a dose-corrected dataset Was obtained by fitting the independent peaks in every dataset and extrapolating the intensity and peak position to the initial time of data collection or to zero-absorbed dose. The compared structural models obtained show that special processing of powder diffraction data produced a much accurate model, close to the single-crystal-based model for this particular compound with heavy atoms in high symmetry positions that do not contribute to a significant number of diffraction intensities.