Structures of Polymorphic Agomelatine and Its Cocrystals with Acetic Acid and Ethylene Glycol

Two polymorphic structures of Form II and Form III of agomelatine were determined by single and powder X-ray diffraction, respectively, in which the agomelatine molecules are linked through the intermolecular hydrogen bonding interactions to form a one-dimensional (1D) chain, and the 1D chains are further packed through interchain π···π and C−H···π interactions to generate the three-dimensional (3D) structures. Two agomelatine cocrystals with acetic acid ( 1 ) and ethylene glycol ( 2 ) were synthesized, and their structures were determined by single and powder X-ray diffraction, respectively, in which the acetic acid molecules in 1 alternately link the agomelatine molecules to form 1D right-handed and left-handed helical chains, while the alternately linking of agomelatine molecules by ethylene glycol molecules in 2 generates the homochiral right-handed helical chains. After the formation of cocrystals of 1 and 2, the melting points dramatically decrease, and the solubility is approximately twice as large as that of Form II.