Bis[5-(pyridin-2-yl)pyrazine-2-carbonitrile-κ2 N 4,N 5](trifluoroacetato-κO)silver(I)

In the asymmetric unit of the title compound, [Ag(C10H6N4)2(CF3CO2)], there two mononuclear but slightly different complex units. In each, two κ2 N:N-chelating 5-(pyridin-2-yl)pyrazine-2-carbonitrile ligands surround the AgI atom, giving an N4O square-pyramidal coordination geometry with one trifluoroacetate O atom at the apex. The difference between the two lies in the Ag—N bond lengths: in one complex, three normal [range 2.272 (5)–2.552 (5) Å] and one long [2.706 (4) Å] and in the second, two normal [2.254 (5) and 2.290 (5) Å] and two long [2.647 (5) and 2.675 (5) Å] are present. Short intermolecular F⋯F contacts [2.586 (4) Å] and weak π–π stacking interactions [minimum ring centroid separation 3.836 (5) Å] between pyridyl and pyrazinyl rings connect the complex units, forming columns which extend along the b-axis direction.


Refinement
All the H atoms were discernible in the difference electron density maps. Nevertheless, the hydrogen atoms were placed in idealized positions and allowed to ride on the carrier atoms, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). The high U eq value compared to neighbors for the C22 and C44 atoms of the trifluoroacetate ligand can be ascribed to the large thermal vibration of the tail of the anion at room temperature.

Figure 1
The atom-numbering scheme for the two independent complex units in the asymmetric unit of the title complex.
Displacement ellipsoids are drawn at the 30% probability level and the intermolecular F···F interaction is shown as a dashed line. All H atoms are omitted for clarity.

Figure 2
The inter-unit F···F and π···π interactions between the mononuclear units extending along b.  The packing structure of the title complex. Dashed-lines represent F···F and N(acetonitrile)···C(pyrazine) contacts.

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.