Crystal structures and conformational features of new forms of tinidazole.

The crystal structures of two new tinidazole {1-[2-(ethane-sulfon-yl)eth-yl]-2-methyl-5-nitro-1H-imidazole, TNZ, C8H13N3O4S} forms, triclinic and hemihydrate, have been determined and compared to that of the known monoclinic form. The triclinic and hemihydrate structures each contain two independent mol-ecules with similar conformations, whereas the monoclinic form adopts a distinct geometry. The conformational differences arise mainly from variations in the N-C-C-S torsion angle. A conformational study confirmed two preferred types of mol-ecular conformations characteristic of tinidazole polymorphs. Inter-action-energy analysis indicates that, despite differences in the crystal packing of the monoclinic and triclinic polymorphs, dispersion forces play a major role in consolidation of their structures.