Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal

Abstract

A detailed description of the procedures utilized in the non-routine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder.

Polymorphism of NaVO2F2: aP21/csuperstructure with pseudosymmetry ofP21/min the subcell

“…Therefore, PLATON is not effective for evaluating the real symmetry in these special cases. Some other examples may be found in (i) diffraction spots overlapped from crystal twinning or the Renninger effect diffraction intensity (Guzei et al, 2012;Sun et al, 2012), (ii) order-disorder structures (Nichol & Clegg, 2005;Aldous & Lightfoot, 2009) and (iii) pseudo-systematic absences of weak reflections (Guzei et al, 2002;Guzei & Langenhan, 2003). Sometimes it is difficult to discriminate between 'observed' and 'non-observed' reflections, so that the determination of the correct space group is not straightforward.…”

Branched Selectivity in the Pd‐Catalysed Methoxycarbonylation of 1‐Alkenes

“…From the start of the structural study of compound 1⋅ 2 CH 2 Cl 2 , we suspected possible twinning issues. The initial reflection indexing of the first three crystals selected for the single‐crystal X‐ray diffraction experiment produced C ‐centred orthorhombic unit cells . The best diffracting specimen of the three was selected for the experiment.…”

Best practice and pitfalls in absolute structure determination

“…This is particularly important for an enantiomerically pure compound, where inversion of one domain during data reduction might be needed in order to give both major domains the correct absolute structure. [24][25][26]…”