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Introduction to single crystal X-ray analysis VII. Refinement of disordered structure

Winter 2015 Volume 31, No. 1
16-25
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Kimiko Hasegawa

A single crystal of target material is necessary to conduct single crystal X-ray structure analysis, but in an ideal single crystal, atoms and molecules have an ordered, three-dimensional repetitive structure. That is, the ideal single crystal is one in which all molecules comprising the single crystal have the same steric structure, and the geometrical arrangement of molecules within a unit cell is the same viewing from any direction. However, it is frequently the case that actual single crystals are not ideal, and there may be irregularities such as more than one molecules in an asymmetric unit, multiple crystal domains (twinning), or the disordered structure which is the topic here (disorder).

This paper starts by describing what disordered structure is, and then introduces how to determine disordered structure, and methods of refinement using the SHELX-97 structure refinement program. The author will be happy if, when the reader encounters a situation which must be analyzed as disordered structure, he or she can take their time and handle the problem, rather than giving up simply because it is a disordered structure.