Structure, polymorphism and thermal properties of phenyliminoisoindolines

The crystal and molecular structures of (a) 1-imino-3-phenyliminoisoindoline (2), (b) two polymorphs (3Mono and Mic) and a hexane solvate (3Hex) of 1,3-bis(phenylimino)isoindoline (3) and (c) 3-phenyliminoisoindolitione (4) were determined via single-crystal x-ray diffraction. The two polymorphs and solvate of 3 were all obtained by crystallization from hexane. In the solid state, 2 is found as the anti isomer of the amino tautomer, and all forms of 3 exist as either the syn,anti or anti,anti isomers of the diimino tautomer. The 3Tric and 3Mono polymorphs represent a rare. example in which the phenomena of conformational polymorphism and conformational isomorphism occur for the same substance. Compound 4 crystallizes as the anti isomer of the keto form. Differential scanning calorimetry and thermogravinietric analysis were performed to characterize the thermal properties of samples of 2-4. X-ray powder diffraction studies on 2, 3 and 4 reveal that, whereas specimens of 2 are a single phase, none of the samples of 3 and 4 crystallize as single phases under the conditions of the experiments. Copyright (C) 2004 John Wiley Sons, Ltd.