(E,E)-N,N′-Bis[4-(methylsulfonyl)benzylidene]ethane-1,2-diamine

In the crystal structure of the title Schiff base compound, C18H20N2O4S2, the molecule lies across a crystallographic inversion centre. The torsion angle of the N—C—C—N fragment is 180°, as the inversion centre bisects the central C—C bond. The crystal packing is stabilized by C—H⋯O hydrogen bonds and aromatic π–π stacking interactions with a centroid–centroid distance of 3.913 (2) Å.

In the crystal structure of the title Schiff base compound, C 18 H 20 N 2 O 4 S 2 , the molecule lies across a crystallographic inversion centre. The torsion angle of the N-C-C-N fragment is 180 , as the inversion centre bisects the central C-C bond. The crystal packing is stabilized by C-HÁ Á ÁO hydrogen bonds and aromaticstacking interactions with a centroid-centroid distance of 3.913 (2) Å .

Related literature
For bond-length data, see: Allen et al. (1987); For the crystal structure of a similar Schiff base compound, see: Sun et al. (2004). For the crystal structure of a precursor molecule used in the synthesis of the title compound, see: Qian & Cui (2009 Table 1 Hydrogen-bond geometry (Å , ).

Comment
The title compound, (I), acts as an important precursor for the synthesis of Schiff base complexes. As an extension of our work on the structural characterization of Schiff base compounds, the crystal structure is reported here.
The asymmetric unit contains one-half of the molecule of (I), the other half being inversion-related by symmetry operation (-x, -y, 2-z) (Fig.1). All the bond lengths are within normal ranges (Allen et al., 1987) and comparable to the values observed in other similar compounds (Qian & Cui, 2009;Sun et al., 2004). The crystal packing is stabilized by C-H···O hydrogen bonds and aromatic π-π stacking interactions with a centroid-centroid distance of 3.913 (2) Å ( Figure 2, Table 1). The torsion angle of the N-C-C-N fragment is 180 °, as the inversion centre bisects the central C-C bond.
After keeping the solution in air for 10 d, yellow block-shaped crystals of (I) were formed at the bottom of the vessel on slow evaporation of the solvent.

Refinement
All H atoms were placed in geometrical positions and constrained to ride on their parent atoms with C-H distances in the range 0.93-0.96 Å, They were treated as riding atoms, with U iso (H) = kU eq (C), where k = 1.5 for methyl and 1.2 for all other H atoms. Fig. 1. The structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 35% probability level. The molecule is completed by symmetry operation (-x, -y, 2-z) across the central C-C bond.

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.
supplementary materials sup-3 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.