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Piracetam Co-Crystals with OH-Group Functionalized Carboxylic Acids

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journal contribution
posted on 06.05.2009, 00:00 by Martin Viertelhaus, Rolf Hilfiker, Fritz Blatter, Markus Neuburger
We report the synthesis, crystal structures, and basic physicochemical properties of six co-crystals of piracetam. Co-crystals of piracetam with l-tartaric acid, with citric acid in a 1:1 and 3:2 ratio, with racemic mandelic acid, and with l-mandelic acid, as well as a piracetam−citric acid ethanol solvate were found in a focused screening approach. Sample amounts of up to several hundred milligrams of each co-crystal were obtained from either solvent-drop grinding, solution evaporation, or crystallization from solution. Crystal structure analysis revealed that the often observed amide-carboxylic acid R22(8) synthon is rarely found in the herein reported crystal structures. The mentioned motif can be used as a target for hydrogen bonds; however, in presence of a multitude of hydrogen bond donors and acceptors it cannot serve for an anticipation of co-crystals. Compared to piracetam the piracetam−l-tartaric acid co-crystal shows improved hygroscopic properties.