2-(Thiophen-2-yl)-N-(4-{(E)-[2-(thiophen-2-yl)ethyl]iminomethyl}benzylidene)ethanamine

In the crystal of the centrosymmetric title compound, C20H20N2S2, molecules are linked by head-to-tail C—H⋯N hydrogen bonds, resulting in chains extending along the a axis. Three additional C—H⋯π intermolecular interactions give rise to a herringbone packing motif which extends along the c axis. The C—H⋯N interactions provide links between the sheets.

In the crystal of the centrosymmetric title compound, C 20 H 20 N 2 S 2 , molecules are linked by head-to-tail C-HÁ Á ÁN hydrogen bonds, resulting in chains extending along the a axis. Three additional C-HÁ Á Á intermolecular interactions give rise to a herringbone packing motif which extends along the c axis. The C-HÁ Á ÁN interactions provide links between the sheets.

Comment
The title compound belongs to a class of tetradentate ligands. To the best of our knowledge, this is the first example of a neutral thiophenyldimine-based bridging ligand. This compound is a potential tetra-coordinate ligand but on complexation the compound will probably behave as a bidentate ligand as the sulfur, on the thiophene, has weak donor capacity towards co-ordination for majority of metal ions. Besides its use as a ligand, it is interesting from the crystal engineering point of view for the analysis of the packing mode of (I).
Compound (I) crystallizes with half a molecule in the asymmetric unit, with the other half generated through symmetry located in the center of the phenyl ring ( Fig. 1). The phenyl ring together with the atoms C7-N8-C9 and the thiophene ring together with the atom C6 are planar with N8 and C5 deviating the most from the planes by 0.018 (2) Å and 0.010 (2) Å respectively. The two planes are close to parallel, the angle between them being 9.3 (1)°. Bond distances and angles in (I) are as expected from the chemical bonding.
The crystal structure of (I) is composed of head-to-tail C-H···N hydrogen bonded chains ( Table 1) that extend in the crystallographic a axis (Fig. 2). Additionally, the phenyl and thiophen rings are involved in C-H···π intermolecular interactions that result in a herringbone motif that spreads along the crystallographic c axis (Fig. 3). The C-H···N interactions are found to connect these herringbone sheets along the a axis.,

Experimental
A solution of benzene 1,4-dicarboxaldehyde (0.50 g, 3.73 mmol) in methanol (10 ml) was added dropwise to a stirred solution of 2-thiophenylethylamine (0.95 g, 7.42 mmol) in methanol (10 ml). The mixture was stirred at room temperature for ca 16 h. The precipitate was filtered off and washed with diethylether and dried under vacuum for 4 h affording a fine shiny white powder in 80% yield. M.p.: 240-242 °C. Recrystallization was done by slow diffusion of Et 2 O into a concentrated CH 2 Cl 2 solution of the white powder to give colorless crystals fo (I).

Refinement
The methine and aromatic H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic, C-H = 0.99 Å and U iso (H) = 1.2U eq (C) for CH 2 C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for CH.
supplementary materials sup-2 Figures   Fig. 1. View of (I) (50% probability displacement ellipsoids) with H atoms presented as small spheres of arbitrary radii.  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 > σ(F 2 ) is used only for calculating Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 0.62222 (7