11H-Indeno[1,2-b]quinoxalin-11-one

In the title compound, C15H8N2O, the fused ring system is approximately planar, with a maximum deviation of 0.039 (1) Å. In the crystal, weak intermolecular C—H⋯O interactions help to establish the packing.

In the title compound, C 15 H 8 N 2 O, the fused ring system is approximately planar, with a maximum deviation of 0.039 (1) Å . In the crystal, weak intermolecular C-HÁ Á ÁO interactions help to establish the packing.

Comment
Indenoquinoxaline derivatives are important classes of nitrogen containing heterocycles and they constitute useful intermediates in organic synthesis (Gazit et al., 1996). They have been reported for their applications in dyes and have also been used as building blocks for the synthesis of organic semiconductors. More interestingly, research has revealed that these compounds exhibit diverse medicinal functions such as antimetabolism and antitubercular properties (Sehlstedt et al., 1998).
In view of the biological importance of indenoquinoxalines, we report here the crystal structure of the title compound, (I). In the crystal structure, molecules are linked by weak intermolecular C3-H3A···O1 and C9-H9A···O1 hydrogen bonds (Table 1) interactions which help to stabilize the crystal structure.

Experimental
The title compound, has been synthesized by two routes: a mixture of ninhydrin (1.78 g) and o-phenylenediamine (1.08 g) in molar ratio 1:1 were [a] stirred in distilled water for 15 minutes and [b] refluxed in THF for 1 hour in presence of HCl.
Both these mixtures were separately dried on rota-vapor at low pressure and then crystallized from chloroform-n-hexane (1:1) to give yellowish needles of (I).

Refinement
Anomalous dispersion was negligible and 1465 Friedel pairs were merged for the final refinement. All the H atoms were located in a difference Fourier map and allowed to refine freely [C-H = 0.96 (2)-1.00 (2) Å].

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(F 2 ) is used only for calculating Rfactors(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.