Crystal structures of two hydrogen-bonded compounds of chloranilic acid-ethyl-eneurea (1/1) and chloranilic acid-hydantoin (1/2).

The structures of the hydrogen-bonded 1:1 co-crystal of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with ethyl-eneurea (systematic name: imidazolidin-2-one), CHClO·CHNO, (I), and the 1:2 co-crystal of chloranilic acid with hydantoin (systematic name: imidazolidine-2,4-dione), CHClO·2CHNO, (II), have been determined at 180 K. In the crystals of both compounds, the base mol-ecules are in the lactam form and no acid-base inter-action involving H-atom transfer is observed. The asymmetric unit of (I) consists of two independent half-mol-ecules of chloranilic acid, with each of the acid mol-ecules lying about an inversion centre, and one ethyl-eneurea mol-ecule. The asymmetric unit of (II) consists of one half-mol-ecule of chloranilic acid, which lies about an inversion centre, and one hydantoin mol-ecule. In the crystal of (I), the acid and base mol-ecules are linked O-H⋯O and N-H⋯O hydrogen bonds, forming an undulating sheet structure parallel to the plane. In (II), the base mol-ecules form an inversion dimer 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 (01). The acid mol-ecule and the base mol-ecule are linked an O-H⋯O hydrogen bond.