Crystal structure and Hirshfeld surface analysis of 2-(4-nitrophenyl)-2-oxoethyl picolinate

2-(4-Nitrophenyl)-2-oxoethyl picolinate was synthesized under mild conditions. The chemical and molecular structure was confirmed by single-crystal X-ray diffraction studies. The molecules are related by inversion into centrosymmetric dimers via weak C—H⋯O intermolecular interactions, and further strengthened by weak π–π interactions. A quantification of the intermolecular contacts in the crystal were estimated using Hirshfeld surface analysis and two-dimensional fingerprint plots.

2-(4-Nitrophenyl)-2-oxoethyl picolinate, C 14 H 10 N 2 O 5 , was synthesized under mild conditions. The chemical and molecular structures were confirmed by single-crystal X-ray diffraction analysis. The molecules are linked by inversion into centrosymmetric dimers via weak intermolecular C-HÁ Á ÁO interactions, forming R 2 2 (10) ring motifs, and further strengthened by weakinteractions. Hirshfeld surface analyses, the d norm surfaces, electrostatic potential and twodimensional fingerprint (FP) plots were used to verify the contributions of the different intermolecular interactions within the supramolecular structure. The shape-index surface shows that two sides of the molecules are involved with the same contacts in neighbouring molecules and curvedness plots show flat surface patches that are characteristic of planar stacking.

Chemical context
Derivatives of phenacyl bromide have found significant application in the identification of organic acids (Rather & Reid, 1919). In organic chemistry, phenacyl benzoate is a derivative of an acid, formed by reaction between an acid and phenacyl bromide. The syntheses of phenacyl esters have many advantages in organic chemistry because they are usually solids and provide a useful means of characterizing acids and phenols. Phenacyl esters are useful for the photoremoval of protecting groups for carboxylic acids in organic synthesis and biochemistry. These compounds can be photolysed under neutral and mild conditions (Sheehan et al., 1973;Ruzicka et al., 2002;Literá k et al., 2006). They also find application in the field of synthetic chemistry, such as in the synthesis of oxazoles and imidazoles (Huang et al., 1996), as well as with benzoxazepine (Gandhi et al., 1995). In continuation of our work on the synthesis of these ester derivaties (Kumar et al., 2014), we report herein the crystal and molecular structures of 2-(4-nitrophenyl)-2-oxoethyl picolinate.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1, and bond lengths and angles are listed in Table 1. The compound is composed of two aromatic rings (4-nitrophenyl and pyridine) linked by C-C( O)-O-C( O) bonds forming a bridge. The unique molecular conformation of this compound is characterized by three torsion angles, viz. 1 (N2-C10-C9-O3), 2 (C7-C8-O1-C9) and 3 (O2-C7-C6-C1), whereby 1 [À6.1 (2) ] signifies the apparent coplanarity of the mean planes of the pyridine and adjacent carbonyl rings at the connecting bridge. The torsion angle value of 2 = À147.02 (11) between the two carbonyl groups indicates a -anticlinal conformation. Likewise, owing to a substitution on the functional group, the title compound experiences steric repulsion between the substituent and adjacent carbonyl groups, which can influence the torsion angle [ 3 = 2.4 (2)%] and resulting in a +synclinal conformation. The bond lengths and angles are normal and the molecular conformation is characterized by a dihedral angle of 31.58 (8) between the mean planes of the two aromatic rings. The nitro group lies nearly in the plane of the phenyl ring, as indicated by the torsion angle values of À4.7 (2) and À5.1 (2) for C4-C3-N1-O4 and C2-C3-N1-O5, respectively.
Cg1 and Cg2 are the centroids of the pyridine and nitrophenyl rings, respectively.

Figure 3
The packing of molecules of the title compound in the ab plane, viewed along the c axis. Cyan dashed lines indicate weak intermolecular C-HÁ Á ÁO interactions forming R 2 2 (10) ring motifs.

Figure 1
The molecular structure of the title compound, indicating the atomnumbering scheme and with displacement ellipsoids drawn at the 50% probability level.

Hirshfeld surface analysis
Hirshfeld surfaces and fingerprint plots (McKinnon et al., 2007) were generated for the title compound based on the crystallographic information file (CIF) using CrystalExplorer (Wolff et al., 2012). A view of the three-dimensional Hirshfeld surface of the title compound mapped over d norm .

Figure 5
Hirshfeld surface of the title compound mapped with shape-index and curvedness.

Figure 6
Two-dimensional fingerprint plots of the title compound, showing the percentage contributions of all interactions, and the individual types of interactions.
In Fig. 4, the dark spots near the C and O atoms result from C-HÁ Á ÁO interactions, which play a significant role in the molecular packing of the title compound. The Hirshfeld surfaces illustrated in Fig. 4 also reflect the involvement of different atoms in the intermolecular interactions through the appearance of blue and red regions around the participating atoms, which correspond to positive and negative electrostatic potential, respectively. The shape-index surface clearly shows that the two sides of the molecules are involved in the same contacts with neighbouring molecules and the curvedness plots show flat surface patches characteristic of planar stacking.

Synthesis and crystallization
The title compound was synthesized as per the procedure of Kumar et al. (2014). A mixture of 2-bromo-1-(4-nitrophenyl)ethanone (0.2 g, 0.5 mmol), potassium carbonate (0.087 g, 0.63 mmol) and nicotinic acid (0.079 g, 0.65 mmol) in dimethylformamide (5 ml) was stirred at room temperature for 5 h. After completion of the reaction, the reaction mixture was poured into ice-cold water. The solid product obtained was filtered off, washed with water and recrystallized from ethanol [m.p. 407-410 K, determined with a Stuart Scientific (UK) apparatus].

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms on C atoms were positioned geometrically (C-H = 0.95-0.99 Å ) and refined using a riding model, with U iso (H) = 1.2 or 1.5U eq (C).   program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXL2015 (Sheldrick, 2015) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2015 (Sheldrick, 2015) and PLATON (Spek, 2009). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.18 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating -R-factor-obs 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.