4,6-Dibromo-2-[(E)-(4-{[(E)-3,5-dibromo-2-hydroxybenzylidene]amino}butyl)iminomethyl]phenol

The asymmetric unit of the title compound, C18H16Br4N2O2, comprises half the molecule, which is located adjacent to an inversion centre at the mid-point of the central C—C bond of the butane-1,4-diamine segment. There are two intramolecular O—H⋯N hydrogen bonds making S(6) ring motifs. In the crystal, molecules are linked by pairs of weak C—H⋯Br interactions into chains along [101], which include R 2 2(8) ring motifs. These chains are further linked by C—H⋯O hydrogen bonds, forming a three-dimensional network.

The asymmetric unit of the title compound, C 18 H 16 Br 4 N 2 O 2 , comprises half the molecule, which is located adjacent to an inversion centre at the mid-point of the central C-C bond of the butane-1,4-diamine segment. There are two intramolecular O-HÁ Á ÁN hydrogen bonds making S(6) ring motifs. In the crystal, molecules are linked by pairs of weak C-HÁ Á ÁBr interactions into chains along [101], which include R 2 2 (8) ring motifs. These chains are further linked by C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Experimental
The asymmetric unit of the title compound, Fig. 1, comprises half of a potential tetradentate Schiff base ligand. The molecule is located about an inversion centre which is situated at the centre of the central C9-C9A bond of the 1,4butane-diamine segment. The bond lengths (Allen et al., 1987) and angles are within the normal ranges. The intramolecular O-H···N hydrogen bonds make S(6) ring motifs (Table 1 and Fig. 1; Bernstein et al., 1995).
In the crystal, molecules are linked by pairs of weak C-H···Br interactions to form chains along direction [101] which include R 2 2 (8) ring motifs (Table 1 and Fig. 2). These chains are further linked by C-H···O interactions (Table 1) to form a three-dimensional network.

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

Refinement
The OH H atom was located in a difference Fourier map and constrained to ride 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).

Figure 2
The crystal packing of the title compound viewed along the c axis, showing linking of molecules through C-H···O and weak C-H···Br interactions (dashed lines; see Table 1   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.74 e Å −3 Δρ min = −0.57 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.