Imagination Materializes with Serendipity: Third Polymorph of N-Amino 1,8-Naphthalimide

Synthon polymorphs are less encountered in the literature. It is challenging to prepare synthon polymorphs same synthon organized in different manners. We describe here the third polymorph of N-amino 1,8-naphthalimide that has R ² ₂ (10) synthon of symmetry-related molecules assembled as a chain similar to a reported polymorph, which had symmetry-independent molecules; this made the difference in the self-assembled structure of the two polymorphs. The assemblies of three polymorphs of the compound, as well as the DFT-optimized energies of the dimeric assemblies of the two polymorphs, were also determined and compared. The new polymorph was obtained through the decomposition of 1-(2,4-dichlorophenyl)-3-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)thiourea (DTU) in dimethylformamide solution that was kept at 80°C. When the solution was cooled, crystals of the concomitant polymorphs of two closely related forms were obtained, providing a new methodology for preparing the polymorph. Besides these, the structure of DTU was analysed to show the prerequisites for the alignments of the stacked naphthalimide rings in the starting compound to easily transform to the alignments of the stacking rings observed in the concomitant polymorphs.