2,5-Bis(4-methoxyphenyl)-1,3,4-oxadiazole

In the title compound, C16H14N2O3, the essentially planar 1,3,4-oxadiazole ring [maximum deviation = 0.0021 (11) Å] is inclined at dihedral angles of 8.06 (6) and 11.21 (6)° with respect to the two benzene rings; the dihedral angle between the latter rings is 11.66 (5)°. In the crystal, short intermolecular C⋯O interactions [2.9968 (15) Å] connect adjacent molecules into chains propagating in [203]. The crystal structure is further stabilized by weak intermolecular C—H⋯π interactions.


Comment
Heterocyclic compounds are becoming increasingly important in recent years due to their pharmacological activities (Rai et al., 2008). Nitrogen-and oxygen-containing five/six-membered heterocyclic compounds are of enormous significance in the field of medicinal chemistry (Hegde et al., 2008). Oxadiazoles play a very vital role in the preparation of various biologically active drugs with anti-inflammatory (Andersen et al., 1994) and anti-cancer (Showell et al., 1991) activities. The results of biological studies showed that oxadiazole derivatives also possess significant anti-inflammatory, analgesic and minimum ulcerogenic and lipid per-oxidation (Clitherow et al., 1996) properties.

Experimental
An equimolar mixture of 4-methoxybenzoic acid (0.01 mol) and 4-methoxybenzhydrazide was dissolved in POCl 3 (25-30 ml) by gentle warming. The solution is refluxed for about 12 h. Excess of POCl 3 is distilled off, and then the reaction mixture is poured into crushed ice. The separated solid was filtered, washed with water and dried. It was then recrystallized from ethanol. Yellow blocks of (I) were obtained from ethanol by slow evaporation.

Refinement
All H atoms were located from difference Fourier map and allowed to refine freely with range of C-H = 0.916 (14) -1.031 (14) Å.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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.