Acta Crystallographica Section B

Structural Science, Crystal Engineering and Materials

Volume 69, Part 5 (October 2013)

research papers

Acta Cryst. (2013). B69, 496-508    [ doi:10.1107/S205251921301782X ]

C6H4S2AsCl: description and interpretation of an incommensurately modulated molecular crystal structure

R. C. Bakus II, D. A. Atwood, S. Parkin, C. P. Brock and V. Petricek

Abstract: Crystals of 2-chloro-benzo-1,3,2-dithiarsole have a strongly modulated structure that can be solved and refined with relative ease in a P\overline 1, Z' = 17 approximate supercell but that is better described as incommensurate. Two conventional refinements (different superstructure approximations that differ in the placement of their crystallographic inversion centers) and a (3 + 1)-dimensional superspace refinement are all nearly equally successful, at least as measured by the usual agreement factors; the data integration, however, shows that the incommensurate description is preferable. The overall packing is determined by the stacking of the aromatic rings and probably by the segregation of As and Cl atoms to give short As...Cl contacts. A refinement of the average (Z' = 1) structure shows that there are two basic orientations of the C6S2 plane, but that those orientations must be correlated in several directions to avoid impossibly short intermolecular contacts. Along the modulation vector q the orientation of the C6S2 plane varies smoothly, but q is not a direction in which the molecules are in contact. Along the directions in which the molecules are in contact the orientation of the C6S2 plane alternates; there are also positional shifts. The single modulation q relieves packing problems in several different directions well enough that crystals that diffract well can be grown.

B-IncStrDB reference: 8082ERT5uS

Keywords: incommensurately modulated structure; packing.

hkldisplay filedownload file

Structure factor file (CIF format) (1191.9 kbytes)
[ doi:10.1107/S205251921301782X/sn5121ApproxIsup2.hkl ]
Contains datablock k04275

hkldisplay filedownload file

Structure factor file (CIF format) (1192.0 kbytes)
[ doi:10.1107/S205251921301782X/sn5121ApproxIIsup3.hkl ]
Contains datablock vp17orig

hkldisplay filedownload file

Structure factor file (CIF format) (91.0 kbytes)
[ doi:10.1107/S205251921301782X/sn5121Basicsup4.hkl ]
Contains datablock basic

hkldisplay filedownload file

Structure factor file (CIF format) (737.2 kbytes)
[ doi:10.1107/S205251921301782X/sn5121Incommensup5.hkl ]
Contains datablock Incommen


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