Crystal structure and Hirshfeld surface analysis of 2-oxo-2-phenylethyl 3-nitroso-2-phenylimidazo[1,2-a]pyridine-8-carboxylate

In the crystal, molecules are linked by C—H⋯O hydrogen bonds, generating (5) and (28) ring motifs. In addition, weak C—H⋯π and π-stacking interactions are observed.


Hirshfeld surface analysis
Hirshfeld surface analysis was used to quantify the intermolecular contacts of the title compound, using Crystal Explorer (Turner et al., 2017). The Hirshfeld surface was generated with a standard (high) surface resolution and with the three-dimensional d norm surface plotted over a fixed colour scale of À0.1706 (red) to 1.2371 (blue) a.u. (Fig. 3a). The shape-index map of the title molecule was generated in the range À1 to 1 Å (Fig. 3b), revealing the presence of red and blue triangles that are indicative of the presence ofstacking interactions. The curvedness map of the title complex  Table 1 Hydrogen-bond geometry (Å , ).
Cg4 is the centroid of the C17-C22 phenyl ring.

Figure 1
The molecular structure of (I), with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Intramolecular hydrogen bonds are indicated by dashed lines.
was generated in the range À4.0 to 4.0 Å (Fig. 3c) Fig. 5b-h, respectively. The most important intermolecular interaction is HÁ Á ÁH, contributing 36.2% to the overall crystal packing (Fig. 5b). HÁ Á ÁC/CÁ Á ÁH contacts, with a 20.5% contribution to the Hirshfeld surface, indicate the presence of the weak C-HÁ Á Á interaction (Table 1). Two pairs of characteristic wings in the fingerprint plot with pairs of tips at d e + d i $2.74 Å are present (Fig. 5c). HÁ Á ÁO/OÁ Á ÁH contacts arising from intermolecular C-HÁ Á ÁO hydrogen bonding make a 20.0% contribution to the Hirshfeld surface and are represented by a pair of sharp spikes in the region d e + d i $2.34 Å (Fig. 5d). The CÁ Á ÁC contacts are a measure ofstacking interactions and contribute 4.3% of the Hirshfeld surface (Fig. 5h)    (a) d norm mapped on the Hirshfeld surface to visualize the intermolecular interactions, (b) shape-index map of the title compound and (c) curvedness map of the title compound using a range from À4 to 4 Å .

Synthesis and crystallization
To a solution of 2-oxo-2-phenylethyl 2-phenylimidazo[1,2-a]pyridine-8-carboxylate (0.71 g, 2 mmol) in acetic acid (50 ml), sodium nitrite (1.4 g, 2 mmol) was added at room temperature. The resulting precipitate was washed with water and extracted with dichloromethane (3 Â 20 ml). The combined dichloromethane extracts were dried over anhydrous sodium sulfate and filtered. The remaining solution was concentrated under reduced pressure. The residue was purified chromatographically on a neutral alumina gel column using dichloromethane as eluent. Single crystals were obtained by slow evaporation of a dichloromethane solution at room temperature (yield 80%).