(E)-3-(2,6-Dichlorobenzylidene)indolin-2-one

There are two independent molecules in the asymmetric unit of the title compound, C15H9Cl2NO. The dihedral angles between the oxindolyl and dichlorophenyl rings are essentially identical for the two independent molecules [63.4 (1) and 63.2 (1)°]. Dimers linked by amide–carbonyl N—H⋯O hydrogen bonds are formed from each symmetry-independent molecule and the respective symmetry equivalent created by inversion.

There are two independent molecules in the asymmetric unit of the title compound, C 15 H 9 Cl 2 NO. The dihedral angles between the oxindolyl and dichlorophenyl rings are essentially identical for the two independent molecules [63.4 (1) and 63.2 (1) ]. Dimers linked by amide-carbonyl N-HÁ Á ÁO hydrogen bonds are formed from each symmetry-independent molecule and the respective symmetry equivalent created by inversion.
For studying the biological properties a series of 3-substituted indolin-2-one derivatives have been synthesized in our lab and their neuroprotective activities have been tested (Balderamos et al. 2008). As a part of our research on the relationship between the biological activities and solid structures a couple of crystal structures of the derivatives have been carried out (Zhang, et al., 2008(Zhang, et al., , 2009a(Zhang, et al., , 2009b(Zhang, et al., , 2009c. The title compound consists of an oxindolyl and a dichlorophenyl unit (Fig 1).
The dihedral angles between the two aromatic rings are basically identical for the two independent molecules and measure to 63.4°(1) and 63.2°(1), respectively. The crystal structure revealed that intermolecular H-bonds (Table 1), linking two symmetry related inverted molecules, form an eight membered dimeric ring system (Fig 2).

Experimental
The title compound was synthesized by the condensation of 2,6-dichlorobenzaldehyde (1 mmol) with 2-oxindole (1 mmol) in ethanol (10 ml) in the presence of catalytic amount of piperidine (0.1 mmol) with a yield of 83%. After refluxing for 3 hr, the reaction mixture was left to stand overnight. The resulting crude solid was filtered, washed with cold ethanol (10 ml) and dried. Red single crystals of the compound suitable for X-ray structure determination obtained by recrystallization from ethanol.

Refinement
All H atom were placed in calculated positions and included in the final cycles of refinement using a riding model, with distances N-H = 0.86 Å and C-H = 0.93 Å, and displacement parameters U ĩso (H) = 1.2U eq (N,C). Fig. 1. : A view of one of the independent molecules with displacement ellipsoids drawn at the 40% probability level. H atoms are presented as open circles with arbitrary radii. Atoms of another independent molecule were labeled as N21 H21 C22 O22 through C36 Cl36.   (2)