3-[(2-Formylthiophen-3-yl)(hydroxy)methyl]thiophene-2-carbaldehyde

In the title compound, C11H8O3S2, the dihedral angle between the mean planes of the two thiophene rings is 65.10 (10)°. Intramolecular C—H⋯O interactions form S(6) and S(7) ring motifs. In the crystal, chains along the a axis are formed by C—H⋯O interactions. Adjacent chains are connected into a three-dimensional network by C—H⋯O and O—H⋯O interactions.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: MW2040).

Comment
Thiophene aldehydes and their homologues are an important class of organic compounds. Some of them can be used as precursors for syntheses of azomethines (also named Schiff) (Guarín et al., 2007;Basu et al., 2011) thiacarbaporphyrins (Jain et al., 2010), and dicyanovinyl-derivatives (Raposo et al., 2003(Raposo et al., , 2004 for optical applications. We are interested in the structures and properties of Schiff base ligands and their metal complexes (Su, Wu, Li, et al. 2007a, 2007bSu, Gao, et al. 2007c;Su et al. 2009). Herein, a new thiophene dialdehyde, of which the aldehyde group can easily react with all kinds of arylamines to form Schiff-bases, was synthesized and the crystal structure of the title compound, (I) (Fig. 1), is reported.

Experimental
Compound (I) was synthesized from thiophene-3-carbaldehyde, n-BuLi, 3-bromothiophene and ethyl formate via a one-pot reaction (manuscript in preparation). It was crystallized slowly from ethanol at 298 K.

Refinement
The C-bound H atoms were positioned geometrically with C-H = 0.93 (aromatic and carbonyl carbons) and 0.98 (methine) Å, and allowed to ride on their parent atoms in the riding model approximation with U iso (H) = 1.2 U eq (C). The atom H1 was located in a difference map and included as a riding contribution with O-H adjusted to 0.82 Å and with UU iso (H) Fig. 1. View of the molecule of (I) showing the atom labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

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 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 > 2sigma(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.