Crystal structure of trans-bis{4-bromo-N-[(pyridin-2-yl)methylidene]aniline-κ2 N,N′}dichloridoruthenium(II)

The RuII atom in the title complex is surrounded by a distorted Cl2N4 coordination set. In the crystal structure, adjacent complex molecules are connected through C—H⋯Cl hydrogen-bonding interactions into a layered arrangement parallel to (100). Additional C—H⋯Br hydrogen-bonding interactions along with π–π stacking interactions complete a three-dimensional supramolecular network.

In the title complex, [RuCl 2 (C 12 H 9 BrN 2 ) 2 ] or [RuCl 2 (PM-BrA) 2 ] (PM-BrA = 4-bromo-N-(2 0 -pyridylmethylene)aniline), the Ru II cation is located on a centre of inversion and is surrounded by four N atoms of two PM-BrA ligands in the equatorial plane and by two Cl atoms in a trans axial arrangement, displaying a distorted octahedral coordination environment. Two C atoms in the benzene ring of the PM-BrA ligand are equally disordered over two sets of sites. The benzene and pyridine rings of the PM-BrA ligand are oriented at dihedral angles of 62.1 (10) and 73.7 (11) under consideration of the two orientations of the disordered benzene ring. In the crystal, the complex molecules are connected via C-HÁ Á ÁCl hydrogen-bonding interactions into a layered arrangement parallel (100). C-HÁ Á ÁBr hydrogen bonding and weak aromaticstacking interactions complete a three-dimensional supramolecular network.

Chemical context
Bidentate Schiff bases are one of the most widely used ligands in coordination chemistry. Their complexes have found utility in a wide range of applications (Rezaeivala & Keypour, 2014;Gupta & Sutar, 2008). In particular, ruthenium(II) complexes of Schiff bases have been shown to display a variety of structural features and exhibit interesting biological and catalytic reactivities (Li et al., 2015;Wang et al., 2015;Drozdzak et al., 2005). Herein, we report the synthesis and crystal structure of a ruthenium(II) complex with the bidentate Schiff base ligand of 4-bromo-N-(2 0 -pyridylmethylene)aniline (PM-BrA), [RuCl 2 (C 12 H 9 BrN 2 ) 2 ], (I).

Structural commentary
The asymmetric unit of compound (I) contains one half of the complex molecule with the Ru II cation lying on an inversion centre (Fig. 1). The coordination environment around Ru II is a distorted [Cl 2 N 4 ] octahedron, whereby the metal is chelated by two PM-BrA ligands in the equatorial plane and by two Cl ISSN 2056-9890 atoms in a trans axial arrangement. The ligand exhibits an N1Á Á ÁN2 bite distance of 2.585 (7) Å with an N1-Ru1-N2 bite angle of 76.9 (1) . The reduced bite angle of the chelating ligand is one of the main factors accounting for the distortion from the ideal octahedral geometry of the coordination polyhedron, with the the largest cis angle being 103.1 (2) . The Ru-N bond lengths are 2.073 (5) and 2.084 (5) Å , and the Ru-Cl bond length is 2.3908 (14) Å , in agreement with those observed in the structures of similar compounds (Roy et al., 2012). Two C atoms in the benzene ring of the PM-BrA ligand are equally disordered over two sets of sites. The dihedral angle between the least-square planes of the benzene and pyridine rings in the PM-BrA ligand are 62.1 (10) and 73.7 (11) under consideration of the two orientations of the disordered benzene ring.

Supramolecular features
In the crystal, weak intermolecular C-HÁ Á ÁCl hydrogenbonding interactions between the C atoms of the benzene ring and the Cl atoms connect the complex molecules into a supramolecular layered arrangement parallel to (100) (Fig. 2). As shown in Fig. 3, a C-HÁ Á ÁBr hydrogen bond between the phenyl C atoms and the Br atoms, along with weak aromatic stacking interactions [centroid-to-centroid distance = 4.107 (4) Å , dihedral angle = 0.7 (3) ] complete a threedimensional supramolecular network. Numerical values of C-HÁ Á ÁX (X = Cl, Br) interactions are compiled in Table 1.

Figure 2
Crystal packing of complex (I) in a view along [100]. C-HÁ Á ÁCl hydrogen-bonding interactions are shown as dashed lines.

Synthesis and crystallization
A solution of the ligand 4-bromo-N-(2 0 -pyridylmethylene)aniline (104.4 mg, 0.4 mmol) in dry methanol (5 ml) was placed in a test tube. A solution of RuCl 3 (41.5 mg, 0.2 mmol) in dry methanol (5 ml) was then carefully layered on the top of a methanolic solution. After slow diffusion at room temperature for three days, pale-green plate-or block-like crystals of complex (I) were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were positioned with idealized geometry and refined with U iso (H) = 1.2U eq (C) using a riding model with C-H = 0.95 Å . C atoms C11 and C12 and attached H atoms in the benzene ring are disordered over two set of sites and were refined using a split model with equal occupancy.