The first step in the structure solution process is the determination of candidate space groups on the basis of the symmetry of the diffraction pattern, in particular through the analysis of the reflection conditions. Sometimes it may happen that the diffraction pattern is indexed in an alternative setting, in which the reflection conditions appear different. The discrepancy between the observed reflection conditions and those published in the standard setting of space groups may lead the investigator to erroneously assume his sample is less symmetric than it actually is. After discussing a case from the literature, an example is presented, in which diffractions from a pyrite sample are indexed in the (Formula presented.) setting of the space group, instead of the standard (Formula presented.) setting, where the large set of strong violations of reflection conditions with respect to those of the standard setting can be interpreted as a signature of symmetry lowering to P213. The structure being well-known, the real origin of the apparent violation of reflection conditions is easy to find. In a less straightforward case, in particular when dealing with a new, unknown structure, the investigator may be deceived along a wrong path.
ASJC Scopus subject areas
- 化学 (全般)