Bis[4-(2-benzylidenepropylideneamino)phenyl] ether

The title compound, C32H28N2O, is a flexible Schiff base displaying a trans configuration across the C=N double bond. It was prepared in high yield by condensation of α-methylcinnamaldehyde and bis(4-aminophenyl) ether in methanol at room temperature. The sample, with pseudo-orthorhombic cell parameters, exhibited merohedral twinning by rotation 180° around a*, with a refined twin domain fraction of 0.722 (1). The elongated shape of the elementary cell corresponds to the shape and direction of the molecules. The dihedral angle between the O-linked aromatic rings is 57.86 (8)°.

The title compound, C 32 H 28 N 2 O, is a flexible Schiff base displaying a trans configuration across the C N double bond.It was prepared in high yield by condensation of -methylcinnamaldehyde and bis(4-aminophenyl) ether in methanol at room temperature.The sample, with pseudo-orthorhombic cell parameters, exhibited merohedral twinning by rotation 180 around a*, with a refined twin domain fraction of 0.722 (1).The elongated shape of the elementary cell corresponds to the shape and direction of the molecules.The dihedral angle between the O-linked aromatic rings is 57.86 (8) .

Experimental
Crystal data Flexible Schiff-base ligands have received a lot of attention in the field of supramolecular coordination chemistry (Laye, 2007;Huang et al., 2005;Chu & Huang, 2007).Because of easy syntheses of these compounds by condensation between aldehydes (or ketones) and amines, many of them were designed and sued to prepare transition metal complexes in recent years.Here, we report the synthesis and crystal structure of a new flexible Schiff-base compound (I).The molecule of (I) is shown in Fig. 1.Bond lengths and angles are comparable with those observed in similar compounds (Hu et al., 2008;Xu et al., 2008).The C(7)=N(1) and C( 23)=N(2) bond lengths of 1.266 (3) and 1.270 (3) Å, respectively, conform to the usual value for a C=N double bond.Each half of the molecule displays a trans configuration across the C=N double bond.The prolongated shape of the molecule is reflected by very long b axis about 55 Å.The molecules are isolated (Fig. 2), with no intermolecular contacts.From crystallographic point of view merohedric twinning by rotation 180° around a* and pseudo-orthorhombic cell parameters should be noted.The twinning has occurred regularly in all tested samples.

S2. Experimental
The title compound was synthesized using a method analogous to the literature procedure of Khalaji and Ng (2008).
Crystals appropriate for data collection were obtained by slow evaporation from a methanol-chloroform mixture (1:5 v/v) at room temperature (yield; 88%).

S3. Refinement
All H atoms were found in difference Fourier maps, but they were constrained to ideal positions.The isotropic atomic displacement parameters of hydrogen atoms were set to 1.2U eq of the parent atom.The sample had a pseudoorthorhombic cell parameters and exhibited a merohedric twinning by rotation 180° around a* (with twinning matrix 1 0 0 / 0 -1 0 / 0 0 -1 applied to indices expressed like row vectors).The volume fraction of the second domain was refined to 0.278 (1).

Figure 1
The molecule of (I) viewed along a with atom-labeling scheme.Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
The packing of (I) viewed along c.

Special details
Refinement.The refinement was carried out against all reflections.The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively.The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement.The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one.Therefore the values of S are usually larger than the ones from the SHELX program.