(Z)-3-Diethylamino-6-({2-[(E)-4-(diethylamino)-2-hydroxybenzylideneamino]-4,5-dimethylphenyl}aminomethylidene)cyclohexa-2,4-dienone–5,5′-bis(diethylamino)-2,2′-[4,5-dimethyl-o-phenylenebis(nitrilomethylidyne)]diphenol

The asymmetric unit of the title Schiff base compound, C30H38N4O2, comprises two crystallographically independent molecules, A and B. The structure is non-merohedrally twinned with a refined BASF ratio of 0.219 (6):0.701 (6). Molecule B shows both phenol–imine and keto–amine tautomeric forms in a single structure. The dihedral angles between the central ring and the two outer rings are 5.9 (3) and 48.4 (3)° in molecule A, and 48.3 (3) and 6.9 (3)° in molecule B. Strong intramolecular O—H⋯N and N—H⋯O hydrogen bonds generate S(6) ring motifs. The crystal structure is further stabilized by intermolecular C—H⋯O, C—H⋯π and π–π interactions [centroid–centroid distances = 3.870 (4)–3.871 (4) Å].


Comment
Schiff base ligands are one of the most prevalent systems in coordination chemistry. As part of a general study of tetradenate Schiff bases (Kargar et al., 2009;Kargar et al., 2010a,b), we have determined the crystal structure of the title compound.
The asymmetric unit of the title Schiff base compound, Fig. 1, comprises two crystallographically independent molecules, A and B which is non-merohedrally twinned with a refined BASF ratio of 0.219 (6)/0.701 (6). Molecule B shows both phenol-imine and keto-amine tautomeric form in a single structure. The dihedral angles between the central phenyl ring with the two outer phenyl rings are 5.9 (3) and 48.4 (3)° in molecule A and 48.3 (3) and 6.9 (3)° in molecule B, respectively.

Experimental
The title compound was synthesized by adding 4-N-diethylamino-salicylaldehyde (4 mmol) to a solution of 4,5-dimethyl-1,2-phenylenediamine (2 mmol) in ethanol (20 ml). The mixture was refluxed with stirring for half an hour. The resultant yellow solution was filtered. Yellow single crystals of the title compound suitable for X-ray structure determination were recrystallized from ethanol by slow evaporation of the solvents at room temperature over several days. The quality of the crystal was not optimal and it was weakly diffracting. Although recrystallization was attempted repeatedly, we tried three data collections but no better data than this one was obtained.

Refinement
H atoms of the hydroxy and amino groups were located in a difference Fourier map. They first restrained to 0.90 (1)Å [OH] and 0.85 (1)Å [NH] and then constrained to refine with the parent atoms with U iso (H) = 1.5 U eq (O) and U iso (H) = 1.2 U eq (N), see Table 1. The remaining H atoms were positioned geometrically with C-H = 0.93-0.97 Å and included in a riding model approximation with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model was used for the methyl groups. Fig. 1. The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids and the atomic numbering. Intramolecular hydrogen bonds are drawn as dashed lines. The H atoms omitted for clarity except those involving in the hydrogen bonds.

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.