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C 6 H 4 S 2 AsCl: description and interpretation of an incommensurately modulated molecular crystal structure
Author(s) -
Bakus II Ronald C.,
Atwood David A.,
Parkin Sean,
Brock Carolyn P.,
Petricek Vaclav
Publication year - 2013
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
eISSN - 2052-5206
pISSN - 2052-5192
DOI - 10.1107/s205251921301782x
Subject(s) - supercell , stacking , superstructure , superspace , crystallography , orientation (vector space) , anisotropy , materials science , molecule , crystal structure , plane (geometry) , physics , condensed matter physics , molecular physics , geometry , chemistry , optics , mathematics , thermodynamics , quantum mechanics , nuclear magnetic resonance , thunderstorm , supersymmetry , meteorology
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 , 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 C 6 S 2 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 C 6 S 2 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 C 6 S 2 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.