Dibromido{2-[(4-nitrophenyl)iminomethyl]pyridine-κ2 N,N′}zinc(II)

In the title compound, [ZnBr2(C12H9N3O2)], the ZnII ion is bonded to two Br ions and two N atoms of the diimine ligand in a distorted tetrahedral geometry. With the exception of the Br atoms, all other atoms are disordered over two sets of sites corresponding to a 180° rotation of the molecule along [02]. The refined occupancies of the components are 0.809 (2) and 0.191 (2). In addition, the crystal studied was a non-merohedral twin with a refined component ratio of 0.343 (2):0.657 (2).

In the title compound, [ZnBr 2 (C 12 H 9 N 3 O 2 )], the Zn II ion is bonded to two Br ions and two N atoms of the diimine ligand in a distorted tetrahedral geometry. With the exception of the Br atoms, all other atoms are disordered over two sets of sites corresponding to a 180 rotation of the molecule along [102]. The refined occupancies of the components are 0.809 (2) and 0.191 (2). In addition, the crystal studied was a nonmerohedral twin with a refined component ratio of 0.343 (2):0.657 (2).

Comment
In our ongoing studies on the synthesis, structural and spectroscopic characterization of transition metal complexes with diimine ligands Khalaj et al. (2010);Salehzadeh et al. (2011), we report herein the crystal structure of the title complex that was prepared by the reaction of ZnBr 2 with the bidentate ligand (4-nitrophenyl)-pyridine-2-ylmethylene-amine (Scheme I).
The molecluar structure of the title complex is shown in Fig. 1. The Zn II ion is in a distorted tetrahedral environment formed by the chelating ligand and two Br ions. A comparison of the dihedral angles between the planes of the pyridine, chelate and the benzene ring indicates that the ligand is distorted from planarity, with twist of 22.23 (24)° between the chelate (N1C5C6N2) and the benzene (C7C8C9C10C11C12) planes. The Zn-Br and Zn-N bond dimensions compare well with the values found in other tetrahedral diimine complexes of zinc bromide (Khalaj et al., 2009).

Experimental
The title complex was prepared by the reaction of ZnBr 2 (22.5 mg, 0.1 mmol) and (4-nitrophenyl)pyridin-2-ylmethyleneamine (22.7 mg, 0.1 mmol) in 15 ml acetonitrile at room temperature. The solution was then concentrated under vacuum, and diffusion of diethyl ether vapor into the concentrated solution gave yellow crystals of the title compound in 60% yield.

Refinement
The H(C) atom positions were calculated and refined in isotropic approximation within riding model with the U iso (H) parameters equal to 1.2 U eq (C) where U eq (C) is the equivalent thermal parameter of the carbon atoms to which corresponding H atoms are bonded. When the results of the initial refinements of the structure were examined for twinning the PLATON (Spek, 2009) software indicated that the crystal was a non-merohedral twin with twin matrix -1 0 0, 0 -1 0, -1 0 1. When refined using data generated by this twin matrix the ratio of the twin components refined to 0.342 (2): 0.658. Further to refinement of the twin components, residual electron density peaks were located in difference Fourier maps which indicated the structure was disordered. All atoms, except for the Br atoms were modeled as disordered corresponding to a rotation of approximately 180° (see Fig. 1). The Br atoms related by unit cell translations along the a axis are in sites which coordinate to both the major and minor components of disorder with an occupancy ratio of 0.809 (2):0.191 (2). The geometry of the twin components were constrained to be the same using the SAME instruction in SHELXL (Sheldrick, 2008) and the anisotropic displacement parameters of each individual major and minor atom site were constrained to be equal using the EADP instruction in SHELXL. The twin law corresponds to a 180° rotation about the [-1 0 2] direction and this direction is parallel to the rotation axis relating the two disordered sites of the molecule.