2,2′-Dimethyl-1,1′-[2,2-bis(bromomethyl)propane-1,3-diyl]dibenzimidazole hemihydrate

The title compound, C21H22Br2N4·0.5H2O, contains two benzimidazole groups which may provide two potential coordination nodes for the construction of metal–organic frameworks. The mean planes of the two imidazole groups are almost perpendicular, with a dihedral angle of 83.05 (2)°, and adjacent molecules are linked into a one-dimensional chain by π–π stacking interactions between imidazole groups of different molecules [centroid-to-centroid distances of 3.834 (2) and 3.522 (2) Å].

The title compound, C 21 H 22 Br 2 N 4 Á0.5H 2 O, contains two benzimidazole groups which may provide two potential coordination nodes for the construction of metal-organic frameworks. The mean planes of the two imidazole groups are almost perpendicular, with a dihedral angle of 83.05 (2) , and adjacent molecules are linked into a one-dimensional chain by stacking interactions between imidazole groups of different molecules [centroid-to-centroid distances of 3.834 (2) and 3.522 (2) Å ].

Related literature
For preparation of the N-donor compound, see: Bai et al. (2010). For a related structure, see: Wei et al. (2011). For constructions and applications of metal-organic frameworks, see: Kuppler et al. (2009); Wang et al. (2011). Data collection: CrystalClear (Rigaku, 2007); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Crys-talClear and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 Metal-organic frameworks have gained more and more attention not only because of their intriguing structures, but also because of their potential applications as functional materials (Kuppler et al. 2009). In general, noncovalent interactions such as π-π stacking, can be used to direct the supramolecular architectures (Wang et al. 2011). So the N-donor title compound (L) is expected to be a good choice for the construction of metal-organic frameworks, mainly because the two benzimidazol N atoms can be potentially active coordination sites (Bai et al. 2010), while the two planar groups in turn can freely twist around the quaternary C atom and the two -CH 2 -groups so as to match the requirements of various coordination geometries (Wei et al. 2011). In addition, π-=π interaction may occur between benzimidazol groups from different L molecules, to promote a supramolecular assembly. Fig. 1 shows an ellipsoid plot of the asymmetric unit of (L). The dihedral angle between the mean planes of the two imidazol rings is 83.05 (2)°. In addition, π-π stacking interactions between imidazole groups from adjacent molecules (intercentroid distances: A: 3.834 (2) and B: 3.522 (2) Å) connect them into a 1D chain structure (Fig. 2).

Experimental
The synthesis, initially aimed to produce a Cd complex, followed a previous literature procedure (Bai et al. 2010).
However, the X-ray crystallographic study confirmed that the cation did not enter into the structure and the product corresponded to the title compound. A mixture of CdCl 2 (0.0183 g, 0.1 mmol), L (0.0491 g, 0.1 mmol) and water (15 ml) was stirred for one hour, and then transferred to a 25 ml Teflon-lined stainless steel reactor. The reactor was heated to 433 K for 72 h, and cooled to room temperature in the autogenous conditions. Colourless block crystals of (L) were obtained with a yield of 65%.

Refinement
H atoms attached to carbon were placed in calculated positions and refined as riding, with U iso (H) = x U eq (C) (C-H (methyl): 0.96 Å, x = 1.5; C-H (aromatic): 0.93 Å; x = 1.2; C-H (methylene): 0.97 Å, x = 1.2). The O atom of the water solvate is disordered around an inversion centre, for what its site occupation factor is 0.5. Its H atoms could not be found in the difference map.

Figure 2
A view of the 1D chain structure formed by the π-π stacking interactions through b-axis. All the H atoms and water molecules were omitted for clarity. Intercentroid distances are A: 3.834 (2); B: 3.522 (2) Å. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.00 e Å −3 Δρ min = −0.71 e Å −3 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 Occ. (