Organic crystal engineering with 1,4-piperazine-2,5-diones. 7. Crystal packing of piperazinediones derived from 2-amino-7-nitro-4-methoxyindan-2- carboxylic acid

1,4-Piperazine-2,5-diones derived from 2-amino-7-nitro-4-methoxyindan-2- carboxylic acid were prepared in meso, racemic, and enantiomerically pure forms, crystallized from DMSO or DMF, and the supramolecular organization in the crystals determined by X-ray crystallography. These molecules were designed to bear two strongly dipolar p-nitroanisole groups, aligned in the enantiomeric stereoisomers and opposed in the meso stereoisomer. Consistent with piperazinediones of similar size and shape bearing nonpolar or weakly dipolar arene groups, these compounds engage in R₂²(8) hydrogen bonding, most often forming one-dimensional tapes. However, the preference for arene perpendicular edge-to-center interactions seen in the former is replaced by a preference for parallel edge-to-center arene interactions. While the dipoles of parallel edge-to-center associated arenes are often opposed, this is not a requirement in the solid state.