1,4-Bis(4-chlorophenyl)-2-hydroxybutane-1,4-dione

In the title compound, C16H12Cl2O3, the benzene rings form a dihedral angle of 2.0 (3)°. Within the central O=C—CH2C(H)OH—C=O unit, the carbonyl groups are coplanar and lie to opposite sides [O—C⋯C—O = −170.1 (6)°]. In the crystal, intermolecular O—H⋯O hydrogen bonds formed between the hydroxy groups lead to a supramolecular chain along the c axis. In addition, the crystal packing features some very weak C—H⋯π interactions.

For this reason, a number of methods for their synthesis have been developed and applied (Ellison, 1973;Ohno et al., 2001).

Experimental
The title compound was obtained as a by-product in the coupling reaction between 4-ClC 6 H 4 COCH 2 Br and benzaldehyde, a reaction which is being studied in our laboratory. Colourless single crystals of the title compound suitable for X-ray diffraction were obtained by slow evaporation of an ethanol solution over a period of 20 days.

Refinement
H atoms were positioned geometrically, with O-H = 0.82 Å and C-H = 0.95-0.99 Å, and constrained to ride on their parent atoms, with U iso (H) = 1.5 U eq (O) and U iso (H) = 1.2 U eq (C). In the absence of significant anomalous scattering effects, 1009 Friedel pairs were averaged in the final refinement. Fig. 1. The molecular structure of the title compound, showing atom labels and 50% probability displacement ellipsoids.

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 supplementary materials sup-3 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 of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.