Crystal structure, DFT and Hirshfeld surface analysis of 2-amino-4-(2-chlorophenyl)-7-hydroxy-4H-benzo[1,2-b]pyran-3-carbonitrile

The crystal and molecular structures of the pyran derivative 2-amino-4-(2-chlorophenyl)-7-hydroxy-4H-benzo[1,2-b]pyran-3-carbonitrile is reported. Hirshfeld surface analysis was performed on the molecule and frontier orbitals were investigated with density functional theory calculations.

The bond lengths and angles are well within the expected limits and comparable with literature values (Allen et al., 1998). The plane of the benzopyran ring forms a dihedral angle of 86.85 (6) with that of the chlorophenyl ring and confirms the fact that the two moieties are in an axial orientation. The chlorophenyl group is also planar, with a maximum deviation for atom C12 of À0.040 (1) Å . The orientation of the benzopyran and chlorophenyl rings is also confirmed by the torsion angles C3-C4-C11-C12 = 76.5 (2) and C3-C4-C11-C16 = À100.4 (2) . In the benzopyran system, the attached carbonitrile, amino and hydroxy groups lie in the same plane, with a maximum deviation for atom N2 of À0.053 (2) Å . The sum of the bond angles around atom N1 of the pyran ring is in accordance with the sp 2 -hybridization state (360 ; Beddoes et al., 1986).

Supramolecular features
The packing of the molecules in the unit cell is stabilized by strong intermolecular C-HÁ Á ÁO, O-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds (Table 1). The O2-H2Á Á ÁN2 ii interaction leads to the formation of a C(10) chain running along the a axis. The molecules are also linked by pairs of intermolecular  Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
Part of the crystal structure showing the R 2 2 (8) dimers. H atoms not involved in hydrogen bonding (dashed lines) have been omitted for clarity.

Figure 1
The molecular structure of the title compound, showing the atomnumbering scheme and displacement ellipsoids drawn at the 30% probability level. The intramolecular C4-H4Á Á ÁCl1 hydrogen bond is drawn as a dashed line.

Density functional theory (DFT) study
The optimized molecular structure and frontier molecular orbitals (FMOs) were calculated using the DFT/B3LYP/6-311G(d,p) basis set implemented in the GAUSSIAN09 program package (Frisch et al., 2009). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are called FMOs as they lie at the outermost boundaries of the electrons of the molecules. The frontier orbital gap helps to characterize the chemical reactivity and the kinetic stability of the molecule. A molecule with a small frontier orbital gap is generally associated with a high chemical reactivity and a low kinetic stability, and is also termed a soft molecule. The electron distribution of the HOMO-1, HOMO, LUMO and LUMO+1 energy levels and the energy values are shown in Fig. 5. The positive and negative phases are represented in green and red, respectively.
The HOMO of the title molecule is localized on the entire molecule except for the chlorobenzene ring, while the LUMO is located on the whole molecule. However, the HOMO-1 is localized on the entire molecule, with the LUMO+1 confined to the chlorobenzene and benzopyran rings, except for the amino substituent. The DFT study shows that the FMO energies, i.e. E HOMO and E LUMO , are À6.354 and À2.712 eV, respectively, and the HOMO-LUMO energy gap is 3.642 eV.
The title compound has a small frontier orbital gap, hence the molecule has high chemical reactivity and low kinetic stability.

Figure 4
The overall crystal packing of the title compound, viewed along the a-axis direction.
2007) were performed and created with CrystalExplorer17 (Turner et al., 2017) for the idenfication of the intermolecular interactions in the title compound. The Hirshfeld surface diagram mapped over d norm is shown in Fig. 6. The 3D d norm surfaces were plotted with a standard (high) surface resolution and are shown as blue and red regions around the atoms related with positive (hydrogen-bond donors) and negative (hydrogen-bond acceptors) electrostatic potentials, respectively.

Figure 7
The 2D fingerprint plots for the title compound.

Synthesis and crystallization
A mixture of 2-chlorobenzaldehyde (6.2 g, 0.05 mol), malononitrile (3.3 ml, 0.05 mol) and resorcinol (5.5 g, 0.05 mol) in water (150 ml) was added to a 10% aqueous K 2 CO 3 solution (10 ml) in a 250 ml round-bottomed flask. The resulting solution was refluxed for about 2 h. The progress of the reaction was monitored by thin-layer chromatography using silica gel-G plates. After product formation, the reaction mixture was kept in a refrigerator overnight. The solid mass that settled was filtered off by suction and washed well with a mixture of methanol and water, and finally dried in air. The resulting crude solid was recrystalized from methanol giving a white solid. The purified sample was recrystallized from 1,4dioxane using the slow-evaporation method (m.p. 250-255 C).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were positioned geometrically (N-H = 0.88-0.90 Å and C-H = 0.93-0.98 Å ) and allowed to ride on their parent atoms, with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) otherwise.

2-Amino-4-(2-chlorophenyl)-7-hydroxy-4H-benzo[1,2-b]pyran-3-carbonitrile
Crystal data 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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) 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.