(2Z,4E)-1-(5-Fluoro-2-hydroxyphenyl)-5-(4-fluorophenyl)-3-hydroxypenta-2,4-dien-1-one

In the title molecule, C17H12F2O3, the dihedral angle between the benzene rings is 8.6 (2)°. In the crystal, two pairs of O—H⋯O hydrogen bonds connect the molecules into inversion dimers. In addition, weak C—H⋯F hydrogen bonds link the dimers into a two-dimensional network parallel to (10-4). The carbonyl O atom is an acceptor for two weak intramolecular hydrogen bonds.


Experimental
The reaction scheme is shown in Fig. 1. A reaction mixture of (E)-3-(4-fluorophenyl) acryloyl chloride (0.37 g, 2.0 mmol) and 1-(5-fluoro-2-hydroxyphenyl)ethanone (0.31 g, 2.0 mmol) in pyridine (10 ml) was stirred for 1 h at 323K (Baker et al., 1933). The mixture was then neutralized with dilute hydrochloric acid, and extracted with ethyl acetate (3×15 ml). The organic phase was concentrated under vacuum to obtain a slurry residue to which was added pyridine (10 ml) and potassium hydroxide (0.21 g, 1.5 mmol). The solution was stirred for 3 h at 323K. The mixture was then neutralized with dilute hydrochloric acid, and extracted with ethyl acetate (3×15 ml). The organic phase was dried over anhydrous MgSO 4 and concentrated under vacuum to obtain a slurry residue. The residue was purified by chromatography using petroleum ether and ethyl acetate (v:v=5:1) as eluent to give a light yellow solid (Mahal & Venkataraman, 1934). Single crystals were obtained by crystallization of a petroleum ether and ethyl acetate (v:v=1:4) solution of the title compound.

Refinement
All H atoms were placed in geometrically idealized positions and treated as riding on their parent atoms, with C-H = 0.93 (aromatic) or 0.98 (CH), O-H = 0.82 Å and isotropic displacement parameters for were set at U iso (H) = x U eq (carried atom), with x = 1.5 for hydroxy, and x = 1.2 for methyne.

Figure 1
The reaction scheme.

Figure 2
The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level and H atoms drawn as small spheres of arbitrary radii.

Figure 3
An inversion dimers of (I). Hydrogen bonds are shown as dashed lines.  Part of the crystal structure with hydrogen bonds shown as dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.