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Issue 10, 2008
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Packing similarity in polymorphs of sulfathiazole

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The packing of molecules in polymorphs IV of sulfathiazole is compared using the XPac method (CrystEngComm, 2005, 7, 324). The forms denoted III, IV, V in the pharmaceutical literature, equivalent to forms III, II and IV of the CSD, exhibit 2D packing similarity. Linking this purely geometrical analysis with H-bonding information reveals that the common building unit of IIIV is a 2D layer composed of rows of helical chains of doubly H-bonded sulfathiazole molecules. The H-bonded chains are further H-bonded in the third direction to chains of adjacent layers. However, these connections involve different combinations of H-bond donor and acceptor sites in each polymorph. One consequence of this relationship is the presence of sets of local (non-crystallographic) symmetry elements in polymorph III (Z′ = 2), while forms IV and V may be interpreted as its two Z′ = 1 parent phases. The connectivity of the doubly bonded chain of modifications IIIV is also present in form II, which additionally contains 2D H-bonded sheets, but the conformation of the chain and its further connectivity is quite different to forms IIIV. The molecular packing and hydrogen bonding of form I is unique among the investigated structures. This study shows that useful new information is obtained from a strictly geometric comparison of crystal structures. Forms III–V provide yet another example for the connection between polymorphism, packing similarity and the formation of a structure with Z′ > 1 exhibiting non-crystallographic symmetry.

Graphical abstract: Packing similarity in polymorphs of sulfathiazole

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Publication details

The article was received on 08 May 2008, accepted on 18 Jul 2008 and first published on 08 Aug 2008

Article type: Paper
DOI: 10.1039/B807898J
Citation: CrystEngComm, 2008,10, 1328-1334
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    Packing similarity in polymorphs of sulfathiazole

    T. Gelbrich, D. S. Hughes, M. B. Hursthouse and T. L. Threlfall, CrystEngComm, 2008, 10, 1328
    DOI: 10.1039/B807898J

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