4-Imino-1,3-diazabicyclo[3.1.0]hexan-2-one

The title compound, also known as imexon, C₄H₅N ₃O, is an iminopyrrolidone that, due to its selective growth inhibitory effect against multiple myeloma, has been under investigation as an anticancer agent since the 1970s. Crystals of the title compound were grown from absolute ethanol saturated with imexon at 296 K, by slow evaporation. Under these conditions, imexon crystallizes as plates with well developed (100) faces. The crystals readily twin by a twofold rotation about the a axis. When crystallized via rapid evaporation of solvent, the resulting powder has a slightly larger unit cell. Simulation of the powder pattern using the atomic parameters and the larger powder cell agree well with measured powder patterns but indicate some preferred orientation towards the (100) plane. The anticancer molecule crystallizes as a zwitterion, with the imino N atom doubly protonated. Each molecule makes four hydrogen bonds which form continuous tapes of molecules along [010].