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Title: Towards solution and refinement of organic crystal structures by fitting to the atomic pair distribution function

In this study, a method towards the solution and refinement of organic crystal structures by fitting to the atomic pair distribution function (PDF) is developed. Approximate lattice parameters and molecular geometry must be given as input. The molecule is generally treated as a rigid body. The positions and orientations of the molecules inside the unit cell are optimized starting from random values. The PDF is obtained from carefully measured X-ray powder diffraction data. The method resembles `real-space' methods for structure solution from powder data, but works with PDF data instead of the diffraction pattern itself. As such it may be used in situations where the organic compounds are not long-range-ordered, are poorly crystalline, or nanocrystalline. The procedure was applied to solve and refine the crystal structures of quinacridone (β phase), naphthalene and allopurinol. In the case of allopurinol it was even possible to successfully solve and refine the structure in P1 with four independent molecules. As an example of a flexible molecule, the crystal structure of paracetamol was refined using restraints for bond lengths, bond angles and selected torsion angles. In all cases, the resulting structures are in excellent agreement with structures from single-crystal data.
Authors:
 [1] ;  [2] ;  [3] ;  [1]
  1. Goethe Univ., Frankfurt am Main (Germany)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States); Columbia Univ., New York, NY (United States)
Publication Date:
OSTI Identifier:
1240708
Report Number(s):
BNL--111879-2016-JA
Journal ID: ISSN 2053-2733; ACSAD7; R&D Project: PM032; KC0202010
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Acta Crystallographica. Section A, Foundations and Advances (Online)
Additional Journal Information:
Journal Name: Acta Crystallographica. Section A, Foundations and Advances (Online); Journal Volume: 72; Journal Issue: 1; Journal ID: ISSN 2053-2733
Publisher:
International Union of Crystallography
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY pair distribution function; organic crystal structures; structure refinement; structure solution