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

The structures of the hydrogen-bonded 1:1 co-crystal of chloranilic acid with ethyleneurea and the 1:2 co-crystal of chloranilic acid with hydantoin 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 acid and base molecules are linked by short O—H⋯O and N—H⋯O hydrogen bonds.

In compound (II), the base molecule is also in the lactam form and no acid-base interaction involving H-atom transfer is observed (Fig. 2). The chloranilic acid molecule is located on an inversion centre and the asymmetric unit consists of one hydantoin molecule and a half-molecule of chloranilic acid. The acid and base molecules are linked via an O-HÁ Á ÁO hydrogen bond (O2-H2Á Á ÁO3; Table 2), forming a centrosymmetric 1:2 aggregate of the acid and the base. The 1:2 unit is approximately planar with a dihedral angle of 5.42 (5) between the acid and base rings.
In the crystal of (II), two adjacent base molecules, which are related by an inversion centre, form a dimer via a pair of N-HÁ Á ÁO hydrogen bonds (N1-H1NÁ Á ÁO3 i ; symmetry code as 1728 Gotoh  The molecular structure of compound (II), showing the atom-numbering scheme. Displacement ellipsoids of non-H atoms are drawn at the 50% probability level and H atoms are drawn as small spheres of arbitrary radii. O-HÁ Á ÁO hydrogen bonds are shown by dashed lines. [Symmetry code: (iii) Àx + 1 2 , Ày + 5 2 , Àz + 1.]

Synthesis and crystallization
Single crystals of compound (I) were obtained by slow evaporation from an acetonitrile solution (150 ml) of chloranilic acid (330 mg) with ethyleneurea (140 mg) at room temperature. Crystals of compound (II) were obtained by slow evaporation from an acetonitrile solution (250 ml) of chloranilic acid (350 mg) with hydantoin (340 mg) at room temperature.

2,5-Dichloro-3,6-dihydroxy-1,4-benzoquinone-imidazolidin-2-one (1/1) (I)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cl1 1.06653 (5)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.44 e Å −3 Δρ min = −0.40 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 sigma(F 2 ) is used only for calculating Rfactor (gt).