Dichlorido(pyridine-κN)[2,3,5,6-tetrakis(pyridin-2-yl)pyrazine-κ3 N 2,N 1,N 6]nickel(II)

The central NiII ion has an N4Cl2 octahedral coordination sphere defined by three N atoms of the tridentate 2,3,5,6-tetra-2-pyridylpyrazine ligand, one N atom of the pyridine ligand and two Cl− anions.

In the title complex, [NiCl 2 (C 5 H 5 N)(C 24 H 16 N 6 )], the Ni II ion is six-coordinated in a distorted octahedral coordination environment defined by three N atoms of the tridentate 2,3,5,6-tetra-2-pyridylpyrazine ligand, one N atom of the pyridine ligand and two Cl À anions, with the latter being mutually trans. The complex is disposed about a twofold rotation axis along the a axis. The complex molecules are connected in the crystal via C-HÁ Á ÁCl, C-HÁ Á ÁN and -[closest intercentroid separation = 3.7446 (14) Å between pyridyl rings].
In the title complex, the central Ni II cation is six-coordinated in a considerably distorted octahedral coordination environment defined by three N atoms of the tridentate tppz ligand, one N atom of the pyridine ligand and two Cl À anions (Fig. 1). The complex is disposed about a twofold rotation axis along the a axis; thus the asymmetric unit contains one half of the complex. The main contribution to the distortion is the tight N-Ni-N chelating angle [<N1-Ni1-N3 = 77.97 (5) ], which results in a non-linear trans arrangement of the N3-Ni1-N3 i bonds [<N3-Ni1-N3 i = 155.95 (11) ; symmetry code: (i) x À y, Ày, Àz], whereas the Cl1-Ni1-Cl1 i bonds are almost linear [<Cl1-Ni1-Cl1 i = 175.77 (4) ]. The Ni-N[pyrazine(N1) or pyridyl(N3, N5)] bond lengths are roughly equivalent, with distances of 2.008 (3) -2.1026 (19) Å . The pyrazine ring (N1-C1 i ) slightly deviates from planarity, with a maximum deviation of 0.057 (2) Å for the C2 atom from the least-squares plane of the ring. The dihedral angles between the nearly planar pyridyl rings and the least-squares plane of their carrier pyrazine ring are data reports 14.90 (4) for the coordinating pyridyl ring (N3-C7) and 54.42 (9) for the non-coordinating pyridyl ring (N4-C12), respectively. The dihedral angle between the pyrazine ring and the pyridine ligand (N5-C13 i ) is 57.8 (1) .
In the crystal, the complex displays numerous inter-and intramolecularinteractions between adjacent sixmembered rings. The most significant interaction of this kind is that between Cg1 (the centroid of the ring N3/C3-C7) and Cg1 ii [symmetry code: (ii) x, x À y, Àz + 1 6 ], with a centroid-tocentroid distance of 3.7446 (14) Å and a dihedral angle between the ring planes of 22.24 (12) . In addition, the complex exhibits inter-and intramolecular C-HÁ Á ÁN and C-HÁ Á ÁCl hydrogen bonds ( Table 1) that consolidate the threedimensional packing (Fig. 2).

Synthesis and crystallization
To a solution of NiCl 2 Á6H 2 O (0.3779 g, 1.590 mmol) in ethanol (20 ml) was added 2,3,5,6-tetra-2-pyridylpyrazine (0.6220 g, 1.601 mmol), followed by stirring for 24 h at rooom temperature. The formed precipitate was separated by filtration, washed with ethanol and acetone, and dried at 323 K, to give a brown powder (0.5045 g). Brown crystals suitable for X-ray analysis were obtained by slow evaporation from its pyridine/N,N-dimethylformamide (DMF) solution at 333 K.

Figure 1
The  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.