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-ium 3-{5-[4-(di­ethyl­amino)­benzyl­idene]-4-oxo-2-thioxothia­zolidin-3-yl}propionate, C₁₅H₁₈ClN₄O⁺·C₁₇H₁₉N₂O₃S₂⁻, (7). Both com­pounds crystallize in the space group P. 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—HO hydrogen bonds. Furthermore, the crystal structures are stabilized by numerous inter­molecular contacts of types C—HN and C—HCl in (6), and C—HO and C—HS 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.