Successful Application of the Derived Crystal Packing (DCP) Model in Resolving the Crystal Structure of a Metastable Polymorph of (±) Modafinil^†

Polymorphic forms I and III of (±) modafinil have been studied. In contrast to the structure of form I which could be solved by using conventional single crystal X-ray diffraction, the crystal structure of form III could not be elucidated due to the shape and the size of the single crystals resulting from the high supersaturation under which this phase is obtained. To bypass the problem, the derived crystal packing (DCP) model has been successfully applied by recombining the slice (002)A extracted from form I. The calculated XRPD pattern of form III fits well with the experimental data. The extensive similarities between the two crystal structures are carefully detailed.