5,5′-Bis(naphthalen-2-yl)-2,2′-bi(1,3,4-oxadiazole)

The title molecule, C24H14N4O2, lies on an inversion centre and the asymmetric unit containg one half-molecule. The naphthalene ring systems are twisted slightly with respect to the oxadiazole rings, making a dihedral angle of 1.36 (6)°. These molecules are π-stacked along the crystallographic a axis, with an interplanar distance of 3.337 (1) Å. Adjacent molecules are slipped from the ‘ideal’ cofacial π-stack in both the long and short molecular axis (the long molecular axis is defined as the line through the naphthalene C atom in the 6-position and the molecular center, the short molecular axis is in the molecular plane perpendicular to it). The slip distance along the long molecular axis (S 1) is 7.064 (1) Å, nearly a two-ring-length displacement. The side slip (S 2, along the short molecular axis) is 1.159 (8) Å.

The title molecule, C 24 H 14 N 4 O 2 , lies on an inversion centre and the asymmetric unit containg one half-molecule. The naphthalene ring systems are twisted slightly with respect to the oxadiazole rings, making a dihedral angle of 1.36 (6) . These molecules are -stacked along the crystallographic a axis, with an interplanar distance of 3.337 (1) Å . Adjacent molecules are slipped from the 'ideal' cofacial -stack in both the long and short molecular axis (the long molecular axis is defined as the line through the naphthalene C atom in the 6position and the molecular center, the short molecular axis is in the molecular plane perpendicular to it). The slip distance along the long molecular axis (S 1 ) is 7.064 (1) Å , nearly a tworing-length displacement. The side slip (S 2 , along the short molecular axis) is 1.159 (8) Å .

Comment
Aromatic heterocycles, such as 1,3,4-oxadiazole and thiophene rings, which are conjugatable to phenyl rings, are often directly connected to the phenyl ring to obtain a large π-conjugated system or to tune the electronic structure. These compounds are of interest as charge transport materials or emitting layers in electroluminescent diodes (Schulz et al., 1997, Schulz et al., 2005. Comparing to thiophene derivatives, 1,3,4-oxadiazole derivatives are more likely to form π-stacked molecular packing (Schulz et al., 2005, Qu et al., 2008, Landis et al., 2008. As shown in Fig. 1, both 1,3,4-oxadiazole rings are in a trans-conformation, which yields a linear molecular shape. These molecules are π-stacked along the crystallographic a-axis (Fig. 2). The molecules in the stacks are canted relative to the stacking axis by 26.57 (1)°. Adjacent molecules are slipped off each other in both long and short molecular axis to avoid unfavorable electrostatic interactions in the "ideal" cofacial stacks (Fig. 3).

Experimental
The tile compound was synthesized through a two-step reaction. Firstly, naphthylacyl hydrazide was reacted with oxalyl chloride in THF at room temperature for 8 h, yielding the product, oxalyl acid N',N'-di-naphthylacyl hydrazide. Secondly, the title compound was derived by intramolecular cyclization of this dihydrazide derivative with POCl 3 under reflux conditions, and the coarse product was further purified by washing with DMSO for the 1H NMR FT-IR spectroscopic characterization and elemental analysis. Yield >70%. Crystals of the title compound suitable for X-ray diffraction were obtained by a slow diffusion method (diethyl ether was diffused into chloroform solution).

Refinement
Carbon-bound H-atoms were placed in calculated positions with C-H = 0.93 Å and were included in the refinement in the riding model with U iso (H) = 1.2 U eq (C).

Figures
Fig . 1. The molecular structure of the title compound with displacement ellipoids drawn at the 50% probability level. The asymmetric unit only contains a half molecule, the second half is generated by symmetry code -x, -y+1, -z+2. The line through C8 and the molecular center is defined as the long molecular axis.   (17)