Accuracy of molecular structures determined from high-resolution powder diffraction. The example ofm-fluorobenzoic acid

Abstract

The accuracy with which it is possible to determine atomic coordinates of light atoms at arbitrary positions using X-ray powder data alone is demonstrated. For this purpose use is made of synchrotron powder diffraction data obtained for an organic molecule, m-¯uorobenzoic acid, consisting of ten non-hydrogen atoms (C 7 H 5 FO 2 ). The results are compared with those of a single-crystal study on the same compound, and in particular the differences in bond lengths and bond angles are studied. The structure solution produced by direct methods is compared with the ®nal result after the Rietveld re®nement. The effect of performing the data collection at room temperature and at 100 K is also investigated. The bond lengths extracted from the powder data were found to differ from the single-crystal values by an average of 0.025 A Ê when data collected at room temperature were employed, and by 0.021 A Ê when using 100 K data. For the bond angles the corresponding values were 3.5 and 1.5 , respectively. With the low-temperature data it was possible to re®ne all atoms, including the hydrogen atoms, without restraints, whereas for the data collected at room temperature, strong restraints had to be used for the hydrogen atoms.

A synchrotron X-ray diffraction study of a small congruent LiNbO3crystal: A compatible approach to powder diffraction

“…Thus, the accuracy of atomic positions, thermal displacement parameters, population parameters, and so forth will generally be inferior to results determined from high-quality single-crystal diffraction. Despite recent progress in extracting intensities from the powder pattern, which improve the quality of the extracted intensity, the intrinsic problem of correctly partitioning the intensities remains (Pattison et al , 2000). Single-crystal diffraction data are three dimensional and thus provides more information which is preferred for accurate analysis (e.g., Harding, 1996).…”

Managing Experimental 3D Structures in the Beyond‐Rule‐of‐5 Chemical Space: The Case of Rifampicin

“…In this study, 21 entries of rifampicin were retrieved in the CSD database (version 5.41, update Aug 2020) and analyzed for their quality (Table S1). Despite advances in the field of powder diffraction resolution, we preferred to focus on structures obtained with single‐crystal techniques due to better accuracy in atom positions [17] . Therefore, we discarded powder structure, i. e. LOPZEX and LOPZEX10.…”

Ab initio structure determination of monoclinic 2,2-dihydroxymethylbutanoic acid from synchrotron radiation powder diffraction data: combined use of direct methods and the Monte Carlo method

“…Therefore, Rietveld re®nement conditions are mostly the same as those in the present study. Pattison et al (2000) reported that the average deviation in bond lengths from single-crystal values is 0.025 A Ê for room-temperature data. In the present study, the average deviation of nine bond lengths from single-crystal values of t-DMBA was 0.046 A Ê , being about twice as large as that of m-FBA, although we must take into account the fact that the referenced single-crystal values are not of m-DMBA, but of t-DMBA and that the contribution of H atoms was ignored in the Rietveld re®ne-ment.…”

“…The method can be applied not only to organic materials, but also inorganic materials, as has been shown in the structure analysis of 4.3. Accuracy of refined positional parameters Pattison et al (2000) discussed the accuracy of positional parameters, re®ned by the Rietveld method, of m-¯uoro-benzoic (C 7 H 3 FO 2 ) acid (m-FBA) at room temperature and 100 K. m-FBA consists of ten independent non-H atoms in a monoclinic unit cell and the maximum range of synchrotron radiation powder diffraction data used for Rietveld re®ne-ment was 0.51 A Ê À1 . Therefore, Rietveld re®nement conditions are mostly the same as those in the present study.…”