Dibromido(2,3-di-2-pyridylpyrazine-κ2 N 2,N 3)platinum(II)

The PtII ion in the title complex, [PtBr2(C14H10N4)], has a slightly distorted square-planar environment defined by the two pyridyl N atoms of the chelating 2,3-di-2-pyridylpyrazine ligand and two bromide anions. In the crystal, the pyridyl rings are considerably inclined to the least-squares plane of the PtBr2N2 unit [maximum deviation = 0.064 (2) Å] with dihedral angles of 65.2 (2) and 66.0 (2)°. The nearly planar pyrazine ring [maximum deviation = 0.020 (5) Å] is almost perpendicular to the unit plane with a dihedral angle of 89.2 (2)°. Two independent weak intermolecular C—H⋯Br hydrogen bonds, both involving the same Br atom as a hydrogen-bond acceptor, give rise to chains running along the a and b axes, forming a layer structure extending parallel to (001). The complexes are stacked in columns along the a axis. When viewed down the b axis, the successive complexes stack in the opposite direction.

The Pt II ion in the title complex, [PtBr 2 (C 14 H 10 N 4 )], has a slightly distorted square-planar environment defined by the two pyridyl N atoms of the chelating 2,3-di-2-pyridylpyrazine ligand and two bromide anions. In the crystal, the pyridyl rings are considerably inclined to the least-squares plane of the PtBr 2 N 2 unit [maximum deviation = 0.064 (2) Å ] with dihedral angles of 65.2 (2) and 66.0 (2) . The nearly planar pyrazine ring [maximum deviation = 0.020 (5) Å ] is almost perpendicular to the unit plane with a dihedral angle of 89.2 (2) . Two independent weak intermolecular C-HÁ Á ÁBr hydrogen bonds, both involving the same Br atom as a hydrogen-bond acceptor, give rise to chains running along the a and b axes, forming a layer structure extending parallel to (001). The complexes are stacked in columns along the a axis. When viewed down the b axis, the successive complexes stack in the opposite direction.

Related literature
For an isomer of the title complex, see: Ha (2011). For crystal structures of the related Pt II complexes, see: Granifo et al. (2000); Cai et al. (2009).
The N3-Pt1-N4 chelate angle of 87.7 (2)° and Br-Br repelling contribute the distortion of square, and therefore the trans axes are slightly bent [<Br1-Pt1-N4 = 174.08 (15)° and <Br2-Pt1-N3 = 178.19 (14)°]. The Pt-N and Pt-Br bond lengths are nearly equivalent, respectively (Table 1). In the crystal, the two pyridyl rings are considerably inclined to the least-squares plane of the PtBr 2 N 2 unit [maximum deviation = 0.064 (2) Å] with dihedral angles of 65.2 (2)°a nd 66.0 (2)°, respectively. The nearly planar pyrazine ring [maximum deviation = 0.020 (5) Å] is almost perpendicular to the unit plane with a dihedral angle of 89.2 (2)°. The dihedral angle between the two pyridyl rings is 80.5 (2)°. Two independent intermolecular C-H···Br hydrogen bonds, both involving the same Br atom as an H-bond acceptor, give rise to chains running along the a and b axes, forming a layer structure extending parallel to the ab plane ( Fig. 2 and Table 2).
The complexes are stacked in columns along the a axis. When viewed down the b axis, the successive complexes stack in the opposite direction. In the columns, numerous inter-and intramolecular π-π interactions between the six-membered rings are present, the shortest ring centroid-centroid distance being 3.833 (4) Å.

Experimental
The title complex was obtained as a byproduct from the reaction of K 2 PtBr 4 (0.2967 g, 0.500 mmol) with 2,3-di-2pyridylpyrazine (0.1173 g, 0.501 mmol) in H 2 O (20 ml). After stirring of the reaction mixture for 3 h at room temperature, the formed precipitate was separated by filtration, washed with H 2 O and acetone, to give the main product as a red-brown powder (0.1326 g) (Ha, 2011). The yellow byproduct (0.0299 g) was obtained from the mixture of filtrate and washing solution. Crystals suitable for X-ray analysis were obtained by slow evaporation from a CH 3 NO 2 solution of the byproduct.  Fig. 1. The structure of the title complex, with displacement ellipsoids drawn at the 50% probability level; H atoms are shown as small circles of arbitrary radius.  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 Rfactors(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.