N,N′-Bis(3-methoxybenzylidene)ethane-1,2-diamine

The molecule of the title bidentate Schiff base ligand, C18H20N2O2, has twofold crystallographic rotation symmetry, giving one half-molecule per asymmetric unit. It adopts a twisted E configuration with respect to the azomethine C=N bond. The imino group is coplanar with the aromatic ring. The dihedral angle between the two benzene rings is 69.52 (5)°. The methoxy group is coplanar with the benzene ring, as indicated by the C—O—C—C torsion angle of −179.56 (8)°. In the unit cell, molecules are linked together by intermolecular C—H⋯O hydrogen bonds, forming chains along the a axis; these chains are further stacked down the b axis by both intermolecular C—H⋯O and C—H⋯π interactions.

The molecule of the title bidentate Schiff base ligand, C 18 H 20 N 2 O 2 , has twofold crystallographic rotation symmetry, giving one half-molecule per asymmetric unit. It adopts a twisted E configuration with respect to the azomethine C N bond. The imino group is coplanar with the aromatic ring. The dihedral angle between the two benzene rings is 69.52 (5) . The methoxy group is coplanar with the benzene ring, as indicated by the C-O-C-C torsion angle of À179.56 (8) .
In the unit cell, molecules are linked together by intermolecular C-HÁ Á ÁO hydrogen bonds, forming chains along the a axis; these chains are further stacked down the b axis by both intermolecular C-HÁ Á ÁO and C-HÁ Á Á interactions.

N,N'-Bis(3-methoxybenzylidene)ethane-1,2-diamine
Schiff bases are one of most prevalent mixed-donor ligands found in the field of coordination chemistry. There has been growing interest in Schiff base ligands, mainly because of their wide applications in the fields of biochemistry, synthesis, and catalysis (Kia et al., 2007a,b;Pal et al., 2005;Hou et al., 2001). Many Schiff base complexes have been structurally characterized, but in comparison only a relatively small number of free Schiff bases have been described (Calligaris & Randaccio, 1987). As an extension of our work (Fun et al., 2008a(Fun et al., , 2008b(Fun et al., , 2008c(Fun et al., , 2008d on the structural characterization of Schiff base compounds, the title compound (I), (Fig. 1), is reported here.
(I) has twofold crystallographic rotation symmetry to give 1/2 molecule per asymmetric unit and it adopts a twisted E configuration with respect to the azomethine C=N bond. Bond lengths and angles are within normal ranges. The imino group is coplanar with the aromatic ring. The dihedral angle between two phenyl rings is 69.52 (5)°. The methoxy group is coplanar with the benzene ring as indicated by the C9-O1-C2-C1 torsion of -179.56 (8)°. In the unit cell, (Fig. 2), neighbouring molecules are linked together by intermolecular C-H···O hydrogen bonds to form chains along the a-axis and these chains are further stacked down the b-axis by both intermolecular C-H···O and C-H···π interactions (Table 1).

Experimental
The overall synthetic method has been described earlier (Fun et al., 2008a), except that ethylenediamine (1 mmol, 60 mg) and 3-methoxybenzaldehyde (2 mmol, 137 mg) were used as starting materials. Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.

Refinement
H atoms bound to C7 and C8 were located from the difference Fourier map and freely refined. The rest of the hydrogen atoms were positioned geometrically with C-H = 0.93-0.96 Å and refined in riding mode with U iso (H) = 1.2 or 1.5 U eq (C).
A rotating-group model was used for the methyl group. Fig. 1. The molecular structure of (I) with atom labels and 50% probability ellipsoids for non-H atoms [symmetry code for A: -x + 1, Y, 0.5 -Z].

Special details
Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.  (4)