7-(2-Chlorophenyl)-2,6,9-trimethyldibenzo[b,h][1,6]naphthyridine

In the title compound, C25H19ClN2, the dibenzo[b,h][1,6]naphthyridine system is planar to within 0.16 (2) Å, and the chlorophenyl ring is inclined to it by 82.53 (7)°. In the crystal, molecules are linked by C—H⋯N hydrogen bonds, forming chains propagating in [100]. There are also a number of weak π–π stacking interactions present [centroid–centroid distances = 3.8531 (1) and 3.7631 (1) Å].

The crystal packing is stabilized by C-H···N hydrogen bonds forming chain like patterns propagating along [100] ( Table   1, Fig. 2). A number of weak π-π stacking interactions may also stablize the crystal packing (see Table 2 for details).

Experimental
The precursor of the title compoud, 2,6,4'-trimethyl-4-(N-phenylamino) quinoline, was prepared following the procedure of (Nandha Kumar et al.., 2007). 4-Chloro-2,6-dimethylquinoline (0.002 mol) was reacted with p-toluidine (0.002 mol) under neat conditions at 433 K for 30 mins. The product obtained was washed with water, dried, and purified by column chromatography over silica gel using an ethyl acetate:methanol (95:5) mixture to obtain the product as a white solid. A mixture of 2,6,4'-trimethyl-4-(N-phenylamino) quinoline (0.001 mol) and o-chlorobenzoic acid (0.0011 mol) was added to polyphosphoric acid (1 g of P 2 O 5 and 0.5 ml H 3 PO 4 ) and heated at 433 k for 5 h. The reaction mixture was poured into ice water, neutralized with saturated sodium bicarbonate solution to remove the excess of o-chlorobenzoic acid, extracted with ethyl acetate. It was then purified using silica gel column chromatography and the product was eluted with a petroleum ether:ethyl acetate (99:1) mixture to get the final product as a pale yellow solid. Recrystallization using ethanol gave yellow block-like crystals of the title compound suitable for X-ray diffraction analysis.

Refinement
The H-atoms of methyl group C20 were disordered over two positions and were placed in calculated positions and treated as riding atoms, each with an occupancy of 0.5. The remaining H-atoms were positioned geometrically and treated as riding on their parent atoms; N-H = 0.86 Å, C-H = 0.93, 0.96 and 0.97 Å, for CH(aromatic), methyl and methylene H-atoms, respectively, with U iso = k × U eq (parent N, or C atom), where k = 1.5 for methyl H-atoms and 1.2 for all other H-atoms.

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.