5-Chloro-2-hydroxybenzene-1,3-dicarbaldehyde

In the crystal structure of the title compound, C8H5ClO3, both formyl groups are in the plane of the chlorophenyl unit and the molecule is stabilized by intramolecular O—H⋯O hydrogen bonding. The molecules are connected via intermolecular O—H⋯O hydrogen bonding into chains and are stacked into columns with a centroid–centroid distance between adjacent aromatic rings of 3.914 (2) Å.

In the crystal structure of the title compound, C 8 H 5 ClO 3 , both formyl groups are in the plane of the chlorophenyl unit and the molecule is stabilized by intramolecular O-HÁ Á ÁO hydrogen bonding. The molecules are connected via intermolecular O-HÁ Á ÁO hydrogen bonding into chains and are stacked into columns with a centroid-centroid distance between adjacent aromatic rings of 3.914 (2) Å .

Comment
Hydroxyisophthalaldehyde and its derivatives are an important class of intermediates used in synthesizing macrocyclic compounds. In recent years, a continuing attention has been drawn to them and their metal complexes . In this paper, we report the X-ray single-crystal structure of 2,6-diformyl-4-chlorophenol prepared from 4-chloro-2,6-bis(hydroxymethyl)phenol.
The molecule of the title compound is essentially planar and all structural parameters ( Fig. 1) are in good agreement with those found in similar compounds (Chu et al., 2005;Chu & Huang, 2006). There is one weak intramolecular O-H···O hydrogen bond between the hydroxyl group at O1 and the carbonyl group O3.
In the crystal structure of the title compound the molecules are connected into chains by intermolecular O-H···O hydrogen bonding ( Fig. 2 and Table 1). The molecules are stacked into columns in the direction of the crystallographic a-axis in order that π-π stacking interactions are maximized. The dihedral angle between two adjacent rings amount to 63.5 (2)° and the centroid-centroid separation is 3.914 (2) Å (Fig. 3).

Refinement
The C-H H atoms were located in difference map and were refined with varying coordinates isotropic. The O-H H atom was placed with idealized geometry allowed to rotata but not to tip O-H = 0.82 Å) and was refined using a riding model with U iso (H) = 1.5U eq (O). Fig. 1. An ORTEP drawing of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and intramolecular hydrogen bonds is shown as dashed lines.

Special details
Experimental. The structure was solved by direct methods (Bruker, 2000) and successive difference Fourier syntheses. 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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )