N,N′-Bis(4-bromobenzylidene)-2,2-dimethylpropane-1,3-diamine

The molecule of the title compound, C19H20Br2N2, is a potential bidentate Schiff base ligand. The two benzene rings are inclined at a dihedral angle of 30.85 (8)°. An interesting feature of the crystal structure is a weak intermolecular Br⋯Br [3.4752 (4) Å] interaction which is shorter than the sum of the van der Waals radii of the Br atoms and links neighbouring molecules into chains along the c axis. The crystal structure is further stabilized by intermolecular C—H⋯π interactions.

The molecule of the title compound, C 19 H 20 Br 2 N 2 , is a potential bidentate Schiff base ligand. The two benzene rings are inclined at a dihedral angle of 30.85 (8) . An interesting feature of the crystal structure is a weak intermolecular BrÁ Á ÁBr [3.4752 (4) Å ] interaction which is shorter than the sum of the van der Waals radii of the Br atoms and links neighbouring molecules into chains along the c axis. The crystal structure is further stabilized by intermolecular C-HÁ Á Á interactions.
In the title compound, Fig. 1, intramolecular C-H···N hydrogen bonds forms five-membered rings, producing S(5) ring motifs (Bernstein et al., 1995). The two benzene rings make a dihedral angle of 30.85 (8)°. The crystal structure is further stabilized by weak intermolecular C-H···π interactions [Cg1 and Cg2 are the centroids of the C1-C6 and C12-C17 benzene rings] ( Table 1). The interesting feature of the crystal structure is weak intermolecular Br···Br [3.4752 (4) Å; symmetry code: 5/2 -x, 1 -y, -1/2 + z] interaction which is shorter than the sum of the van der Waals radius of Br atoms and link neighbouring molecules into chains along the c axis (Fig. 2).

S2. Experimental
The synthetic method has been described earlier (Fun et al., 2008), except that 4-bromobenzaldehyde was used. Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.

S3. Refinement
All of the hydrogen atoms were positioned geometrically and refined using a riding model approximation with C-H = 0.95-0.99 Å and U iso (H) = 1.2 or 1.5U eq (C). In the presence of the sufficient anomalous scattering, the absoulte configuration was determined (3971 Friedel pairs).

Figure 1
The molecular structure of the title compound with atom labels and 50% probability ellipsoids for non-H atoms.
Intramolecular hydrogen bond is shown as dashed line.  The crystal packing of the title compound, viewed down the a-axis showing chains along the c-axis by Br···Br interactions.

Crystal data
C 19 H 20 Br 2 N 2 M r = 436.19 Orthorhombic, P2 1 2 1 2 1 Hall symbol: P 2ac 2ab a = 5.6687 (1)  Special details Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.