Crystal structures of two hydrogen-bonded compounds of chloranilic acid–ethyleneurea (1/1) and chloranilic acid–hydantoin (1/2)

Abstract

The structures of the hydrogen-bonded 1:1 co-crystal of chloranilic acid (systematic name: 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone) with ethyleneurea (systematic name: imidazolidin-2-one), C6H2Cl2O4·C3H6N2O, (I), and the 1:2 co-crystal of chloranilic acid with hydantoin (systematic name: imidazolidine-2,4-dione), C6H2Cl2O4·2C3H4N2O2, (II), have been determined at 180 K. In the crystals of both compounds, the base molecules are in the lactam form and no acid–base interaction involving H-atom transfer is observed. The asymmetric unit of (I) consists of two independent half-molecules of chloranilic acid, with each of the acid molecules lying about an inversion centre, and one ethyleneurea molecule. The asymmetric unit of (II) consists of one half-molecule of chloranilic acid, which lies about an inversion centre, and one hydantoin molecule. In the crystal of (I), the acid and base molecules are linked via O—H...O and N—H...O hydrogen bonds, forming an undulating sheet structure parallel to the ab plane. In (II), the base molecules form an inversion dimer via a pair of N—H...O hydrogen bonds, and the base dimers are further linked through another N—H...O hydrogen bond into a layer structure parallel to (\overline{1}01). The acid molecule and the base molecule are linked via an O—H...O hydrogen bond.