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Accurate unrestrained DDM refinement of crystal structures from highly distorted and low‐resolution powder diffraction data
Author(s) -
Solovyov Leonid A.
Publication year - 2016
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520616011690
Subject(s) - materials science , powder diffraction , resolution (logic) , crystallography , diffraction , computer science , optics , physics , chemistry , artificial intelligence
The structure of benzene:ethane co‐crystal at 90 K is refined with anisotropic displacement parameters without geometric restraints from high‐resolution synchrotron X‐ray powder diffraction (XRPD) data using the derivative difference method (DDM) with properly chosen weighting schemes. The average C—C bond precision achieved is 0.005 Å and the H‐atom positions in ethane are refined independently. A new DDM weighting scheme is introduced that compensates for big distortions of experimental data. The results are compared with density functional theory (DFT) calculations reported by Maynard‐Casely et al. [(2016). IUCrJ , 3 , 192–199] where a rigid‐body Rietveld refinement was also applied to the same dataset due to severe distortions of the powder pattern attributable to experimental peculiarities. For the crystal structure of 2‐aminopyridinium fumarate–fumaric acid formerly refined applying 77 geometric restraints by Dong et al. [(2013). Acta Cryst. C 69 , 896–900], an unrestrained DDM refinement using the same XRPD pattern surprisingly gave two times narrower dispersion of interatomic distances.