Use of intensity quotients and differences in absolute structure refinement

Simon Parsons, Howard Flack, Wagner Trixie

Research output: Contribution to journalArticlepeer-review

Abstract

Several methods for absolute structure refinement were tested using single-crystal X-ray diffraction data collected using Cu K radiation for 23 crystals with no element heavier than oxygen: conventional refinement using an inversion twin model, estimation using intensity quotients in SHELXL-2012, estimation using Bayesian methods in PLATON, estimation using restraints consisting of numerical intensity differences in CRYSTALS and estimation using differences and quotients in TOPAS-Academic where both quantities were coded in terms of other structural parameters and implemented as restraints. The conventional refinement approach yielded accurate values of the Flack parameter, but with standard uncertainties ranging from 0.15 to 0.77. The other methods also yielded accurate values of the Flack parameter, but with much higher precision. Absolute structure was established in all cases, even for a hydrocarbon. The procedures in which restraints are coded explicitly in terms of other structural parameters enable the Flack parameter to correlate with these other parameters, so that it is determined along with those parameters during refinement.
Original languageEnglish
Pages (from-to)249–259
Number of pages11
JournalActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials
Volume69
Issue numberPart 3
DOIs
Publication statusPublished - Jun 2013

Keywords

  • absolute structure
  • crystallography
  • chirality
  • absolute configuration
  • Refinement

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