Role of halogen-halogen contacts in the crystal structures of three new solvates of the drug oxyclozanide.

Halogen-halogen contacts are electrostatic in nature and exhibit directionality similar to hydrogen bonds. Oxyclozanide [systematic name: 2,3,5-trichloro-N-(3,5-dichloro-2-hydroxyphenyl)-6-hydroxybenzamide] is a drug used for the treatment of fascioliasis in domestic animals. The molecule carries five chlorine substituents and represents an ideal candidate for the study of halogen bonds in the crystal. Three new crystalline solvates of oxyclozanide, namely, oxyclozanide benzene hemisolvate, CHClNO·0.5CH, (I), oxyclozanide xylene hemisolvate, CHClNO·0.5CH, (II), and oxyclozanide toluene hemisolvate, CHClNO·0.5CH, (III), were structurally characterized. In this context, the crystal structure of oxyclozanide chlorobenzene hemisolvate, CHClNO·0.5CHCl, (IV), was redetermined based on intensity data collected at 100 K. In all four solvates, the cocrystallized solvent molecules are located on crystallographic inversion centres. Solvates (I)-(IV) exhibit similar one-dimensional hydrogen-bonded chains generated by O-H...O, O-H...Cl and Cl...Cl interactions. The extension of these one-dimensional chains into two-dimensional layers is promoted by Cl...Cl and C-H...π contacts. Solvates (III) and (IV) are isostructural and differ from (I) and (II) with respect to subtle details concerning the intermolecular contacts.