5,5′-Dimethoxy-2,2′-[4,5-dimethyl-o-phenylenebis(nitrilomethylidyne)]diphenol

In the crystal structure of the title compound, C24H24N2O4, the dihedral angles between the central and the two outer benzene rings are 48.12 (8) and 21.44 (8)°. Intramolecular O—H⋯N hydrogen bonding generates S(6) rings.

In the crystal structure of the title compound, C 24 H 24 N 2 O 4 , the dihedral angles between the central and the two outer benzene rings are 48.12 (8) and 21.44 (8) . Intramolecular O-HÁ Á ÁN hydrogen bonding generates S(6) rings.  Table 1 Hydrogen-bond geometry (Å , ). The crystal structure of the title compound was determined to clarify the identity of the synthetic product and to compare the structural changes upon complexation with Cu(II) and Ni(II) ions in future works.

Related literature
In the crystal structure of the title compound the dihedral angles between the central benzene ring and the two outer benzene rings amount to 48.12 (8) and 21.44 (8)°. The bond lengths and angles are comparable to those in a related structure reported recently (Kargar et al., 2010). Intramolecular O-H···N hydrogen bonding is found that generates six-membered S(6) rings. (Bernstein et al., 1995) (Table 1).

Experimental
The title compound was synthesized by adding 4-methoxy-salicylaldehyde (4 mmol) to a solution of 4,5-dimethyl-ophenylenediamine (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.

Refinement
The position of the H atoms of the hydroxy groups were located in a difference Fourier map but finally they were refined using a riding model with U iso (H) = 1.5 U eq (O). The remaining H atoms were positioned with idealized geometry (methyl H atoms allowed to rotate but not to tip) with C-H = 0.93-0.96 Å and refined using a riding model with U iso (H) = 1.2 or 1.5 U eq (C).

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 supplementary materials sup-3 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.