Crystal structure of 2-oxopyrrolidin-3-yl 4-(2-phenyldiazen-1-yl)benzoate

The crystal preparation and structure of a cyclic derivative of γ-aminobutyric acid, GABA, is reported.

In the title compound, C 17 H 15 N 3 O 3 , the plane of the pyrrolidone ring is inclined at an angle of 59.791 (2) to that of the azobenzene segment, which adopts a configuration close to planar. In the crystal, molecules are oriented pairwise by (2-oxopyrrolidin-3-yl)oxy moieties at an angle of 76.257 (3) , linked by hydrogen bonds and -stacking interactions, forming zigzag supramolecular chains parallel to [010] further linked via additional C-HÁ Á Á interactions.

Chemical context
Cyclic derivatives of -aminobutyric acid, GABA, are still constituting a very promising avenue for developing new drugmolecules for improving neuronal, vascular and general cognitive functions (Malykh et al., 2010). In this context, the goal of the present study was to obtain crystals and to characterize the molecular structure of a new representative of the cyclic-GABA family (racetams), 2-oxopyrrolidin-3-yl 4-(2-phenyldiazen-1-yl)benzoate.

Structural commentary
The molecular structure of the title compound ( Fig. 1) comprises the expected 4-phenylazobenzoyl and (2-oxopyrrolidin-3-yl)oxy segments linked by the carboxyester bond -C1( O2)-O1. The phenylazobenzoyl segment comprises two aromatic rings, one of which is linked at its para-position to the carbonyl C8 atom, and exhibits the more stable trans configuration to the azo group formed by N1-N2 atoms with a distance of 1.251 (5) Å . No residual peaks are observed around the N N double bond as for pure azobenzene where such peaks are observed due to a dynamic pedal-like motion orientational disorder (Harada et al., 2004). The angle between the two phenyl rings is 4.29 (13) and is consistent with a slight deviation of the system from the ideal planarity. Geometry parameters of the 3-oxy-substituted 2-pyrrolidone ISSN 2056-9890 segment are close to known data (Clark et al., 2006), with a typical deviation from planarity for the non-aromatic system as shown by the torsion angles C15-C14-C17-C16 of 22.2 (4) and C17-C14-C15-N3 of À16.3 (4) . The Cremer & Pople puckering parameters of the five-membered ring are Q = 0.222 (4) Å and ' = 279.4 (11) conforming to an envelope on C17 (Boeyens, 1978;Cremer & Pople, 1975).

Supramolecular features
The packing of the title molecules in the crystal (Fig. 2) is mainly determined by the presence of (2-oxopyrrolidin-3yl)oxy moieties interacting with each other pairwise, by forming hydrogen bonds between secondary amine and carbonyl groups (Table 1), similarly to other 3-oxy-substituted 2-pyrrolidone derivatives (Clark et al., 2006). This interaction together with ainteraction between the two different phenyl rings from the azobenzene moieties of adjacent molecules [distance between centroids of 3.934 (2) Å ] define a chain of corrugated molecules running along the b-axis direction (Fig. 2). The interactions between these chains proceed through C-HÁ Á Á contacts involving the C8-C13 ring and the terminal atom C11 (Table 1)

Database survey
A search in the Cambridge Structural Database (Version 5.39 with one update, Groom et al., 2016) returned 101 entries for unsubstituted azobenzene, including the dynamic disorder study of Harada & Ogawa (2004); five entries for O-paraphenylazobenzoyl monoesters (Fitjer et al., 1984;Fujino et al., 2007;Nakatsuji et al., 2007, Park et al., 2015; and only two entries for 3-oxy-substituted 2-pyrrolidone (Clark et al., 2006). A partial view of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines (see Table 1). Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radius.
the 0-100% gradient of solvent mixtures A and B [where A: water-acetonitrile (95%-5%) and acetic acid (0.1%); B: acetonitrile (100%) and acetic acid (0.1%)] at the following conditions: a capillary voltage of ESI source of 3000 V; a vaporizer temperature of 433 K, a nebulization pressure of 60 psig, a dry gas temperature of 573 K, and a gas flow of 5 L min À1 . The crystals of the purified product were obtained by the vapor-diffusion method. A solution of 0.05 g of 3-oxy(4phenylazobenzoyl)-2-pyrrolidone in 1 mL of chloroform, in a small open container, was placed in a sealed larger container filled with hexane, above the level of the solvent, to give orange needle-shaped crystals.

Special details
Experimental. X-ray crystallographic data for I were collected from a single crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Venture diffractometer equipped with a Photon 100 CMOS Detector, a Helios MX optics and a Kappa goniometer. The crystal-to-detector distance was 4.0 cm, and the data collection was carried out in 1024 x 1024 pixel mode. 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. Refined as a 2-component inversion twin.