2-Amino-4-(4-chlorophenyl)-4H-chromeno[8,7-b]pyridine-3-carbonitrile

The asymmetric unit of the title compound, C19H12ClN3O, contains two molecules with similar conformations. The 14 non-H atoms comprising the 4H-chromeno[8,7-b]pyridine residue are essentially coplanar (r.m.s. deviations = 0.037 and 0.042 Å for the two molecules) and the main difference between them is seen in the twist about the bond linking the main residue to the attached chlorobenzene rings [dihedral angles = 79.01 (12) and 76.22 (11)° for the two molecules]. Zigzag supramolecular chains along the a-axis direction mediated by amino–pyridine N—H⋯N hydrogen bonds feature in the crystal packing; these are connected into a three-dimensional architecture by C—H⋯π interactions and Cl⋯Cl contacts [Cl⋯Cl = 3.3896 (14) Å].


Tiekink Comment
Motivated by their biological activities and in continuation of an on-going programme on the chemistry of 4H-pyran derivatives (Al-Ghamdi et al., 2012;El-Agrody et al., 2012), the synthesis and crystal structure determination of (I) is reported.
Two independent molecules comprise the asymmetric unit of (I), Fig. 1. As illustrated in Fig. 2, where the O2containing molecule is super-imposed upon the inverse of the O1-containing molecule, the molecules are virtually superimposable with differences apparent in the relationship between the 4H-chromeno [8,7-b]pyridine residue and the attached benzene ring. For the O1-containing molecule, the r.m.s. deviation of the 14 non-hydrogen atoms comprising the fused ring system is 0.037 Å, the dihedral angle between this and the benzene ring is 79.01 (12)° and the twist between these groups is manifested in the C7-C12-C14-C15 torsion angle of -132.9 (3)°. The comparable values for the second molecule are 0.042 Å, 76.22 (11)° and 149.0 (3)°, respectively. The observed conformation is in accord with that established previously for the 2-chloro analogue (Wang et al., 2003).
The most prominent feature of the crystal packing is the formation of supramolecular zigzag chains along the a axis mediated by (amino)N-H···N(pyridyl) hydrogen bonding, Fig. 3 and Table 1. Whereas the second N1-bound H2 atom forms a weak interaction to the N5 atom, Table 1, reinforcing the chain, the second N2-bound H4 atom does not form a significant intermolecular interaction. The chains are connected into a three-dimensional architecture by C-H···π interactions along with Cl2···Cl2 i contacts [Cl2···Cl2 i = 3.3896 (14) Å for i: 2 -x, 1 -y, 2 -z], Fig. 4.

Experimental
A solution of 8-hydroxyquinoline (0.01 mol) in EtOH (30 ml) was treated with α-cyano-p-chlorocinnamonitrile (0.01 mol) and piperidine (0.5 ml). The reaction mixture was heated for 60 minutes by which time complete precipitation occurred. The solid product was collected by filtration and recrystallized from ethanol to give yellow prisms of the title compound, (I); M.pt: 522-523 K.

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.93-0.98 Å) and refined as riding with U iso (H) = 1.2U eq (C).
The N-bound-H atoms were refined freely.

Figure 1
The molecular structures of the two independent molecules comprising the asymmetric unit in (I) showing displacement ellipsoids at the 35% probability level.

Figure 2
Overlay diagram of the two independent molecules in (I) with the inverted N1-containing molecule illustrated in red. The molecules are overlaid so that the pyridyl rings are superimposed.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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. Symmetry codes: (i) x−1, y, z; (ii) −x−3/2, y−1/2, −z−1/2; (iii) −x+2, −y+1, −z+1.