Bis{2-[(pyridin-4-yl-κN)sulfanyl]pyrazine}silver(I) tetrafluoridoborate

In the title mononuclear complex, [Ag(C9H7N3S)2]BF4, the AgI ion adopts a virtually linear coordination geometry [N—Ag—N = 178.06 (11)°] with the two ligands bound to the metal atom via the pyridine N atoms. The metal-coordinated pyridine rings are almost coplanar, making a dihedral angle of 1.5 (2)°, while the two pendent pyrazine rings are arranged on the same side of the N—Ag—N line. Along the a axis, the mononuclear coordination units are stacked with π–π interactions between the pyridine rings [centroid–centroid distance = 3.569 (4) Å], leading to infinite chains. The chains are interconnected through intermolecular N(pyrazine)⋯π(pyrazine) interactions forming layers parallel to the ab plane [N⋯centroid = 3.268 (5) Å]. These layers are further stacked along the c-axis direction, furnishing a three-dimensional supramolecular framework with the tetrafluoridoborate anions embedded within the interstices.

In the title mononuclear complex, [Ag(C 9 H 7 N 3 S) 2 ]BF 4 , the Ag I ion adopts a virtually linear coordination geometry  ] with the two ligands bound to the metal atom via the pyridine N atoms. The metal-coordinated pyridine rings are almost coplanar, making a dihedral angle of 1.5 (2) , while the two pendent pyrazine rings are arranged on the same side of the N-Ag-N line. Along the a axis, the mononuclear coordination units are stacked withinteractions between the pyridine rings [centroid-centroid distance = 3.569 (4) Å ], leading to infinite chains. The chains are interconnected through intermolecular N(pyrazine)Á Á Á(pyrazine) interactions forming layers parallel to the ab plane [NÁ Á Ácentroid = 3.268 (5) Å ]. These layers are further stacked along the c-axis direction, furnishing a threedimensional supramolecular framework with the tetrafluoridoborate anions embedded within the interstices.

Comment
Chalcogenobispyridines and derivates were widely used as versatile building blocks for supramolecular assembly (Baradello et al., 2004;Dunne et al., 1997). The ligand, such as the di-2-pyridyl sulfide and its N-positional isomers, endowed with the rotatable C(sp 2 )-S bond and a variable C(sp 2 )-S-C(sp 2 ) angle (about 100°), exhibits flexible ligation modes in construction of diverse coordination motifs with unusual properties (Jung et al., 2001;Jung et al., 2003). Herein, we report a new silver complex derived from the 2-(pyridin-4-ylsulfanyl)pyrazine ligand.
Experimental 4-Pyridyl-2-pyrazinyl sulfide was synthesized by reacting 2-chloropyrazine (0.6 g, 5.2 mmol) with sodium pyridine-4-thiolate (5 mmol) in 40 ml methanol. The mixture was refluxed with stirring for 10 hours under the protection of N2. After filtration and concentration in vacuo, the obtained crude product was further purified by chromatography on silica gel using ether acetate/dichloromethane (1:3) as the eluent, giving 0.444 g of yellow powder of 4-pyridyl-2-pyrazinyl sulfide in 47% yield. Reaction of 4-pyridyl-2-pyrazinyl sulfide (19 mg, 0.1 mmol) and AgBF 4 (20 mg, 0.1 mmol) in 4 ml methanol with stirring at room temperature for 3 hours. The obtained clear solution was filtrated, and the filtration was left evaporation in air. After about one week, the block-like crystals of the title complex were deposited (18.1 mg, yield 63%).

Refinement
The H atoms were placed in idealized positions and allowed to ride on the relevant carbon atoms, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). Fig. 1. The atom-numbering scheme of the title complex. Displacement ellipsoids are drawn at the 50% probability level, while the H atoms are shown as rods of arbitrary radius.

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.