catena-Poly[{μ3-4,4′,6,6′-tetrabromo-2,2′-[butane-1,4-diylbis(nitrilomethanylylidene)]diphenolato}{μ2-4,4′,6,6′-tetrabromo-2,2′-[butane-1,4-diylbis(nitrilomethanylylidene)]diphenolato}dicopper(II)]

The asymmetric unit of the title coordination polymer consists of a dinuclear neutral complex molecule of formula [Cu2(C18H14Br4N2O2)2]n. One of the CuII ions is coordinated in a distorted square-planar geometry, whereas the other is coordinated in a distorted square-pyramidal geometry, the long apical Cu—O bond [2.885 (4) Å] of the square-pyramidal coordination being provided by a symmetry-related O atom creating a one-dimensional polymer along [010]. π–π stacking interactions [centroid–centroid distance = 3.783 (4) Å] and short interchain Br⋯Br interactions [3.6142 (12)–3.6797 (12) Å] are observed.

The asymmetric unit of the title coordination polymer consists of a dinuclear neutral complex molecule of formula [Cu 2 (C 18 H 14 Br 4 N 2 O 2 ) 2 ] n . One of the Cu II ions is coordinated in a distorted square-planar geometry, whereas the other is coordinated in a distorted square-pyramidal geometry, the long apical Cu-O bond [2.885 (4) Å ] of the square-pyramidal coordination being provided by a symmetry-related O atom creating a one-dimensional polymer along [010].stacking interactions [centroid-centroid distance = 3.783 (4) Å ] and short interchain BrÁ Á ÁBr interactions [3.6142 (12)-3.6797 (12) Å ] are observed.

Experimental
Crystal data [Cu 2 (C 18 H 14 Table 1 Hydrogen-bond geometry (Å , ). Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; 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 and PLATON (Spek, 2009 chain aliphatic spacers or rigid aromatic spacers with large bite angles in these ligands favour the bis-bidentate coordination mode and allow the ligands to accomodate metal centers in one unit of the ligand. On the other hand, Schiff bases are one of the most prevalent ligands in coordination chemistry and their complexes are some of the most important stereochemical models in transition metal-organic chemistry, with their ease of preparation and structural variations (Granovski et al., 1993;Elmali et al., 2000).
The molecular structure of the title complex ( Fig. 1) consists of dinuclear units in which the Schiff base ligands are twisted around copper(II) metal centres in a bis-bidentate coordination mode. The bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable to those reported for related structures (Kargar & Kia, 2011a,b).

Experimental
The title complex was synthesized by the reaction of an methanolic solution (50 ml) of bis(3,5-bromosalicylaldeyde)-1,4butanediimine (2 mmol) and CuCl 2 .4H 2 O (2 mmol). After stirring at reflux conditions for 2 h, the solution was filtered and the resulting dark-brown powder was crystallized from DMF, giving single crystals suitable for X-ray diffraction.

Refinement
All H atoms were positioned geometrically and constrained to refine with their parent atoms using a riding-model approximation, with C-H = 0.93-0.97 Å and U iso (H) = 1.2 U eq (C).

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); 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 where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.55 e Å −3 Δρ min = −0.45 e Å −3 Absolute structure: Flack (1983), 4178 Friedel pairs Flack parameter: 0.069 (8) 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.    (8)