Crystallization of (+/-)-modafinil in gel: Access to form I, form III, and twins

摘要

Single crystals of (+/-)- modafinil have been grown in gel medium obtained from the hydrolysis and condensation of tetramethoxysilane (TMOS). Three different crystal morphologies have been highlighted, corresponding to two modifications and a twin. The first polymorphic form was found to match with the known monoclinic form 1 (P2(1)/a, Z' = 2, a = 14.502 angstrom, b = 9.678 angstrom, c = 20.844 angstrom, and beta = 110.17 degrees). The determination of the second form allowed us to validate the previously predicted form III (orthorhombic Pna2(1), Z' = 2, a = 14.510 angstrom, b = 9.710 angstrom, c = 19.569 angstrom). The analysis of the twinned bodies and the structural similarities between form I and form III allowed us to identify the twin law: a stacking fault of (001)(form) (I) leading to a form III like interface. The analysis of the structures also suggested possible multitwinning.