4-Amino-5-(2-hydroxybenzylideneamino)benzene-1,2-dicarbonitrile

A new tetradentate unsymmetrical Schiff base, C15H10N4O, has been synthesized from 4,5-dicyano-o-phenylenediamine and o-vanillin in refluxing ethanol. The dihedral angle between the two benzene rings is 39.0 (1)°. There are intramolecular O—H⋯N and weak intermolecular N—H⋯O and N—H⋯N interactions.


Comment
During the past decades, Schiff bases have been intensively investigated not only because of their strong coordination capability but also due to their diverse biological activities, such as antibacterial, antitumor, etc. Boskovic et al., 2003;Oshiob et al., 2005). The halide groups in schiff base ligands could effectively optimize the properties of the coordination complexes.

Experimental
(I) was prepared according to the method reported in the literature (Kannappan et al., 2005). 4,5-dicyano-o-phenylenediamine (2.16 g, 0.02 mol) was added to a stirred ethanol solution of O-vanillin (3.04 g, 0.02 mol (10 ml). The reaction mixture was stirred about 3 h and then the mixture was allowed to stand at room temperature for about two days. Yellow cystals suitable for X-ray diffraction analysis were then collected with a yield of 60%.

Refinement
The H atoms of the amino group were located from difference density maps and were refined with distance restraints of d(N-H) = 0.93 (2) Å. H atoms bound to C and O atoms were visible in difference maps and were placed using the HFIX commands in SHELXL97. All H atoms were allowed for as riding atoms (C-H 0.97 Å, O-H 0.86 Å) with the constraint U iso (H) = 1.5U eq (methyl carrier), 1.5U eq (O) and 1.2U eq (carrier) for all other H atoms. Fig. 1. A view of the structure of (I), showing the atmoic numbering scheme and 30% probability displacement ellipsoids.

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 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.