6,6′-[(1E,1′E)-Oxybis(4,1-phenylene)bis(azanylylidene)bis(methanylylidene)]bis(2-methylphenol): supramolecular assemblies in two dimensions mediated by weak C—H⋯N, C—H⋯O and C—H⋯π interactions

The title compound is a flexible Schiff base, as illustrated by its dihedral angles. The sp 2-hybridized character of the azanylylidene groups is confirmed by their bond lengths and bond angles. In the crystal, molecules of the title compound are assembled into two-dimensional networks connected by weak C—H⋯O, C—H⋯N and C—H⋯π intermolecular interactions.


Chemical context
The oxybis Schiff base compound is an important group in chemistry. Bis-carbazones are formed by connecting via a ring or C-C bond to carbazone moieties having four coordinated sites. These tetradentate ligands can be used to entrap metal ions to form square-planer complexes (Alsop et al., 2005;Blower et al., 2003;Jasinski et al., 2003). The length of the C-C bond in the backbone of the compounds affects the stability of the complexes. The higher the number of C-C bonds (obtained via alkylation or arylation) allows the cavity within the ligand to fit the metal ion with a proper orientation (Blower et al., 2003). These tetradentate compounds and transition metal complexes have potential anticancer and antibacterial activity (Lobana et al., 2009). The bis compounds chelate to transition metal ions via coordination sites to form complexes that may also exhibit fluorescent properties that could be used as biosensors and chemosensors (Liu et al., 2011;Jiang & Guo, 2004). ISSN 2056-9890 In view of the above mentioned properties and of our research interest in the synthesis of oxybis Schiff base compounds, we present in this study the crystal structure and supramolecular features of the flexible Schiff base ligand 6,6 0 -{(1E,1 0 E)-[oxybis(4,1-phenylene)bis(azanylylidene)bis(methanylylidene)]bis(2-methylphenol}.

Synthesis and crystallization
To a sample of 2-hydroxy-3-methylbenzaldehyde (0.68 g, 5.00 mmol) dissolved in 20.0 ml methanol was added 0.20 ml glacial acetic acid and the mixture was refluxed for 30 min. A solution of 4,4 0 -oxydianiline (0.50 g, 2.50 mmol) in 20.0 ml methanol was then added dropwise with stirring to the aldehyde solution. The resulting yellow solution was refluxed for 4 h (Fig. 4). A yellow-coloured precipitate formed. The precipitate was filtered and washed with 5.0 ml ethanol and 5.0 ml n-hexane. The recovered product was dissolved in acetone for recrystallization. Yellow single crystals suitable for X-ray diffraction were obtained by slow evaporation of acetone. A view along (111) showing weak C-HÁ Á Á (green dotted lines) supramolecular interactions in the title compound. Table 1 Hydrogen-bond geometry (Å , ).
Cg1 is the centroid of the C14-C19 ring.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The phenolic hydrogen atoms were located in difference-Fourier maps and refined freely. All other H atoms attached calculated geometrically and refined using a riding model with C-H = 0.95-0.98 Å and U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl).

Special details
Experimental. The following wavelength and cell were deduced by SADABS from the direction cosines etc. They are given here for emergency use only: CELL 0.71062 10.322 11.055 11.397 108.521 96.732 110.436 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.