4,4′,6,6′-Tetrabromo-2,2′-[(E,E)-ethane-1,2-diylbis(nitrilomethanylylidene)]diphenol

The asymmetric unit of the title compound, C16H12Br4N2O2, comprises half of a potential tetradentate Schiff base ligand. The whole molecule is generated by an inversion center located in the middle of the C—C bond of the ethylene segment. There are intramolecular O—H⋯N hydrogen bonds making S(6) ring motifs. In the crystal, no significant intermolecular interactions are observed.

The asymmetric unit of the title compound, C 16 H 12 Br 4 N 2 O 2 , comprises half of a potential tetradentate Schiff base ligand. The whole molecule is generated by an inversion center located in the middle of the C-C bond of the ethylene segment. There are intramolecular O-HÁ Á ÁN hydrogen bonds making S(6) ring motifs. In the crystal, no significant intermolecular interactions are observed.

Related literature
For standard values of bond lengths, see: Allen et al. (1987). For details of hydrogen-bond motifs, see: Bernstein et al. (1995). For the crystal structure of a similar compound, see: Kia et al. (2012).  Table 1 Hydrogen-bond geometry (Å , ).
The asymmetric unit of the title compound, Fig. 1, comprises half of a potentially tetradentate Schiff base ligand. The molecule is located about an inversion center, located in the middle of the C8-C8A bond of the ethylene segment. The bond lengths (Allen et al., 1987) and angles are within the normal ranges and are comparable to those reported for a similar compound (Kia et al., 2012). The intramolecular O-H···N hydrogen bonds (Table 1) make S(6) ring motifs (Bernstein et al., 1995).
In the crystal, there are no significant intermolecular interactions present.

Experimental
The title compound was synthesized by adding 3,5-dibromosalicylaldehyde (2 mmol) to a solution of ethylenediamine (1 mmol) in ethanol (30 ml). The mixture was refluxed with stirring for 30 min. The resultant solution was filtered. Yellow single crystals of the title compound suitable for X-ray structure determination were recrystallized from ethanol by slow evaporation of the solvents at room temperature over several days.

Refinement
The O-bound H atom was located in a difference Fourier map and constrained to refine on the parent O atom with U iso (H) = 1.5U eq (O). The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 and 0.97 Å for CH and CH 2 H-atoms, respectively, with U iso (H) = 1.2U eq (C).

Computing details
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009  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. 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.

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