1,4-Bis[(3,5-dimethoxyphenyl)ethynyl]benzene

The title compound, C26H22O4, is a derivative of 1,4-bis(phenylethynyl)benzene substituted by four methoxy groups on the terminal benzene rings. The molecule is almost planar with an r.m.s. deviation of 0.266 Å. The dihedral angles between the two terminal benzene rings and the central benzene ring are 7.96 (6) and 13.32 (7)°. In the crystal structure, molecules aggregate via C—H⋯O interactions, forming molecular tapes along the a axis, which aggregate to form a herring-bone structure.

The title compound, C 26 H 22 O 4 , is a derivative of 1,4bis(phenylethynyl)benzene substituted by four methoxy groups on the terminal benzene rings. The molecule is almost planar with an r.m.s. deviation of 0.266 Å . The dihedral angles between the two terminal benzene rings and the central benzene ring are 7.96 (6) and 13.32 (7) . In the crystal structure, molecules aggregate via C-HÁ Á ÁO interactions, forming molecular tapes along the a axis, which aggregate to form a herring-bone structure.
The molecular structure of (I) is shown in Fig. 1. The molecule is almost planar with an r.m.s deviation of 0.266 Å. The dihedral angles between the terminal benzene rings and the central benzene ring are 7.96 (6)° (C1-C6) and 13.32 (7)° (C17-C22). The methoxy groups are coplanar with the attached benzene rings.
The crystal structure is characterized by a molecular tape along the a axis formed by C-H···O interactions (Table 1 and Fig. 2). The molecular tapes aggregate to form a herring-bone-type structure, as shown in Fig.3. The crystal structure of (I) is different from that of (II). The crystal structures of (I) and (II) indicate that the methoxy groups at terminal benzene rings play an important role in the crystal packing.
The organic solution was dried over Na 2 SO 4 and concentrated. The residue was chromatographed on silica gel (CH 2 Cl 2 ) to afford the title compound (0.23 g, 49%) as a yellow powder. Yellow crystals of the compound, suitable for X-ray analysis were grown from an ethanol solution.

S3. Refinement
All H atoms were placed in geometrically calculated positions, with C-H = 0.95 (aromatic) and 0.98 Å (methyl) and U iso (H) = 1.2U eq (C) (aromatic) and 1.5U eq (C) (methyl), and refined using a riding model.  The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms and H atoms are shown as small spheres of arbitrary radii.

Figure 2
Partial packing diagram of (I), showing a molecular tape along the a axis.  The packing diagram of (I), showing herringbone-type network on the bc plane. 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.