Twinning by pseudo-merohedry is a common phenomenon in small-mol­ecule crystallography. In cases where twin-component volume fractions are markedly different, structure solution is often no more difficult than for non-twinned structures of similar complexity. When twin-component volume fractions are similar, however, structure solution can be much more of a problem. This paper presents hints and tips for such cases by means of three worked examples. The first example presents the most common (and simplest) case of a two-component pseudo-ortho­rhom­bic twin. The second example describes structure solution of a reticular threefold pseudo-hexa­gonal twin that benefits from use of an unconventional space-group setting. The third example covers structure solution of a reticular fourfold pseudo-tetra­gonal twin. All three structures are ultimately shown to be monoclinic crystals that twin as a consequence of unit-cell metrics that mimic those of higher symmetry crystal systems.

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Published in Acta Crystallographica Section E, v. 77, part 5.

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

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hb7973sup1.hkl (472 kB)
Diffraction data for XUBNIR in SHELX HKLF 4 format. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup1.hkl

hb7973sup2.ins.txt (1 kB)
Input file for structure solution of XUBNIR by SHELXD. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup2.ins.txt

hb7973sup3.hkl (11269 kB)
Diffraction data for WUGLES in SHELX HKLF 4 format. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup3.hkl

hb7973sup4.ins.txt (1 kB)
Input file for P21 supercell structure solution of WUGLES by SHELXD. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup4.ins.txt

hb7973sup5.hkl (608 kB)
Diffraction data for SAXDUR indexed as triclinic-P, HKLF 4 format. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup5.hkl

hb7973sup6.hkl (534 kB)
Diffraction data for SAXDUR indexed as monoclinic-I, HKLF 4 format. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup6.hkl

hb7973sup7.ins.txt (1 kB)
Input file for I2/a supercell solution of WUGLES by SHELXD. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup7.ins.txt

hb7973sup8.hkl (1219 kB)
Diffraction data for SAXDUR indexed as monoclinic-P, HKLF 5 format. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup8.hkl

hb7973sup9.txt (1 kB)
Steps for generation of an HKLF 5 format datafile from an HKLF 4 format datafile for structure SAXDUR (pinacol monohydrate), in plain ASCII text suitable for copy/paste. DOI: https://doi.org//10.1107/S205698902100342X/hb7973sup9.txt

hb7973.pptx (1426 kB)
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