Crystal structures of 3-methoxy-4-{[5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl]methoxy}benzonitrile and N-(4-{[5-(4-chlorophenyl)-1,3,4-oxadiazol-2-yl]methoxy}phenyl)acetamide

The title heterocyclic 1,3,4-oxadiazole derivatives differ from each other in the groups attached to the carbon atoms: a methoxyphenyl ring and a benzonitrile group in (I) and a chlorophenyl ring and an acetamide group in (II).


Chemical context
Oxadiazole is a versatile heterocyclic nucleus, which has attracted a wide attention of the medicinal chemists for the development of new drugs. Compounds containing a heterocyclic ring system are of great importance both medicinally and industrially (Pace & Pierro, 2009). This stable and neutral hetero aromatic nucleus is associated with potent pharmacological activity that can be attributed to the presence of the toxophoric -N C-O-linkage (Rigo & Couturier, 1985). Furthermore, 1,3,4-oxadiazole heterocycles are very good bioisosteres of amides and esters, which can contribute substantially in increasing pharmacological activity by participating in hydrogen-bonding interactions with the receptors (Guimaraes et al., 2005). In view of the above importance of the title compounds, we have undertaken single-crystal X-ray diffraction studies for the both compounds and the results are presented here. ISSN 2056-9890

Structural commentary
The molecular structures of (I) and (II) are illustrated in Figs. 1 and 2, respectively. In (I), the 4-methoxyphenyl and oxadiazole (r.m.s. deviation 0.007 Å ) rings are almost coplanar with a dihedral angle of 1.4 (1) . The methoxy atoms O4 and C16 are also coplanar with the rings, deviating by 0.080 (1) and 0.020 (1) Å from the mean plane of the phenyl ring, respectively. In (II), the chlorophenyl ring is almost coplanar with the oxadiazole ring, the angle between their mean planes being 4.0 (1) . The whole molecule is almost planar: the r.m.s. deviation is 0.098 Å and the largest deviation from the mean plane of 0.230 (2) Å is observed for atom C17. Such planarity is not observed in (I) since the methoxyphenyl ring and the benzonitrile moiety are oriented at a dihedral angle of 66.8 (1) . This difference can be seen in Fig. 3, which shows a superposition of the two molecular structures through the oxadiazole ring (C7/N1/N2/C8/O1) obtained using Qmol (Gans & Shalloway, 2001).

Figure 1
A view of the molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. The dashed line represent the intramolecular C-HÁ Á ÁO interaction (Table 1).

Figure 5
The crystal packing of compound (I) viewed down the b axis. The C-HÁ Á ÁN hydrogen bonds (see Table 1) are shown as dashed lines. For clarity H atoms not involved in these hydrogen bonds have been omitted.

Figure 4
The inversion dimer formed in compound (I) via C-HÁ Á ÁO interactions (dashed lines). For clarity H atoms not involved in these hydrogen bonds have been omitted.
HÁ Á ÁO dimers form a closed cavity shape arrangement consisting of 26 atoms in the unit cell (Fig. 6). In addition, offsetinteractions are observed between the centroids of inversion-related oxadiazole and 4-methoxyphenyl rings with a centroid-centroid distance of 3.700 (3) Å and a slippage of 1.037 Å .

Figure 6
The crystal packing of the title compound (I) viewed along the a axis. The C-HÁ Á ÁN hydrogen bonds and C-HÁ Á ÁO interactions (see Table 1) are shown as dashed lines. For clarity H atoms not involved in these hydrogen bonds have been omitted.

sup-1
Acta Cryst. For both structures, data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2018 (Sheldrick, 2015) and PLATON (Spek, 2009). 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.