Influence of 3-{5-[4-(diethylamino)benzylidene]-rhodanine}propionic acid on the conformation of 5-(4-chlorobenzylidene)-2-(4-methylpiperazin-1-yl)-3H- imidazol-4(5H)-one

The arylidene-imidazolone derivatives are a group of compounds of great interest in medicinal chemistry due to their various pharmacological actions. In order to study the possible conformations of an arylidene-imidazolone derivative, two new crystal structures were determined by X-ray diffraction, namely (Z)-5-(4-chlorobenzylidene)-2-(4-methylpiperazin-1-yl)-3H-imidazol-5(4H)-one, C15H17ClN4O, (6), and its salt 4-[5-(4-chlorobenzylidene)-5-oxo-4,5- dihydro-3H-imidazol-2-yl]-1-methylpiperazin-1-ium3-{5-[4-(diethylamino)benzylidene]-4-oxo-2-thioxothiazolidin-3-yl} propionate, C15H18ClN4O+center dot C17H19N2O3S2-, (7). Both compounds crystallize in the space group P (1) over bar. The basic form (6) crystallizes with two molecules in the asymmetric unit. In the acid form of (6), the N atom of the piperazine ring is protonated by proton transfer from the carboxyl group of the rhodanine acid derivative. The greatest difference in the conformations of (6) and its protonated form, (6c), is observed in the location of the arylidene-imidazolone substituent at the N atom. In the case of (6c), the position of this substituent is close to axial, while for (6), the corresponding position is intermediate between equatorial and axial. The crystal packing is dominated by a network of N-H center dot center dot center dot O hydrogen bonds. Furthermore, the crystal structures are stabilized by numerous intermolecular contacts of types C-H center dot center dot center dot N and C-H center dot center dot center dot Cl in (6), and C-H center dot center dot center dot O and C-H center dot center dot center dot S in (7). The geometry with respect to the location of the substituents at the N atoms of the piperazine ring was compared with other crystal structures possessing an N-methylpiperazine moiety.