Bis[5-(2-pyridyl)pyrazine-2-carbonitrile]silver(I) tetrafluoridoborate

In the title mononuclear complex, [Ag(C10H6N4)2]BF4, the AgI atom adopts a square-planar N4 coordination geometry and is surrounded by two 5-(2-pyridyl)pyrazine-2-carbonitrile ligands. The tetrafluoridoborate anions link the mononuclear cations through intermolecular C—H⋯F hydrogen-bonding interactions, forming an infinite tape structure along [110]. Other weak interactions occur: π–π stacking with centroid–centroid distances of 3.820 (2) and 3.898 (1) Å between pyridyl rings and 3.610 (2) and 3.926 (2) Å between pyrazinyl rings as well as F⋯π contacts involving the tetrafluoridoborate anions and pyrazine rings [F⋯centroid = 2.999 (3) Å]; these combine with the hydrogen-bonding interactions to link the mononuclear cations into a three-dimensional supramolecular architecture.


Comment
During the past decades, coordination chemistry based on multidentate N-containing ligands has been widely developed and received intense interests (Peedikakkal et al., 2010). 2,2'-bipyridine is a popular member of the pyridine-based family and attracts a great of attentions because of the potential medicinal applications (Casini et al., 2006) and the fascinating framework structures (Li et al., 2010;Wang et al., 2009) of its divers metal complexes. Many 2,2'-bipyridine derivatives together with their various metal complexes have also been synthesized and well characterized (Berghian et al., 2005;Mathieu et al., 2001).

Experimental
The ligand 5-(2-pyridyl)-2-cyanopyrazine was obtained commercially.The ligand (0.182 g, 0.1 mmol) was dissolved in a mixture of methanol, 2 ml, and acetonitrile, 2 ml was added to AgBF 4 (0.194g, 0.1mmol), with constantly stirring. After four hours, the clear solution was filtered and kept in air for one week at room temperature to yield colorless rod-like crystals (274 mg, 72% yeild).

Refinement
The hydrogen atoms were placed in idealized positions and allowed to ride on the relevant carbon atoms, with C-H = 0.93 Å and Uĩso~(H) = 1.2Ueq(C). Fig. 1. The atom-numbering scheme of the title [Ag(C 10 H 6 N 4 ) 2 ]BF 4 . Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as sticks of arbitrary radii.   Table 2).

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