Poly[[bis[μ2-N,N′-bis(2-pyridylmethyl)oxalamide-κ4 N,O:N′,O′][μ2-N,N′-bis(2-pyridylmethyl)oxalamide-κ2 N:N′]disilver(I)] bis(trifluoromethanesulfonate)]

The asymmetric unit of the title salt, [Ag(C14H14N4O2)1.5](CF3SO3), comprises a Ag+ cation, three half-molecules of N,N′-bis(2-pyridylmethyl)oxalamide (each of which is disposed about a centre of inversion) and a trifluoromethanesulfonate anion. Distinct coordination modes are found for the bridging ligands, i.e., a μ2,κ2-bridging mode involving pyridine N atoms for one ligand, and a μ2,κ4-bridging mode, employing both pyridine N and amide O atoms for the remaining ligands. The Ag+ cations, which are in a distorted square-pyramidal coordination, and the ligands combine to form a two-dimensional array parallel to (101); these arrays are connected into a three-dimensional structure by trifluoromethanesulfonate anions via N—H⋯O, C—H⋯O, and C—F⋯O interactions.

The asymmetric unit of the title salt, [Ag(C 14 H 14 N 4 O 2 ) 1.5 ]-(CF 3 SO 3 ), comprises a Ag + cation, three half-molecules of N,N 0 -bis(2-pyridylmethyl)oxalamide (each of which is disposed about a centre of inversion) and a trifluoromethanesulfonate anion. Distinct coordination modes are found for the bridging ligands, i.e., a 2 , 2 -bridging mode involving pyridine N atoms for one ligand, and a 2 , 4 -bridging mode, employing both pyridine N and amide O atoms for the remaining ligands. The Ag + cations, which are in a distorted square-pyramidal coordination, and the ligands combine to form a twodimensional array parallel to (101); these arrays are connected into a three-dimensional structure by trifluoromethanesulfonate anions via N-HÁ Á ÁO, C-HÁ Á ÁO, and C-FÁ Á ÁO interactions.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PV2322).

Comment
For silver salts, the dependence of crystal structure upon counter anions and the presence of solvent is notorious and has ramifications for photoluminescence (Kundu et al., 2010). In connection with crystal engineering studies on the isomeric N,N'bis(n-pyridylmethyl)oxalamides (Poplaukhin & Tiekink, 2010), the 3:2 reaction between Ag(trifluoromethanesulfonate) and N,N'-bis(2-pyridylmethyl)oxalamide in an ethanol/chloroform solution was investigated, which led to the characterization of the title compound, (I).
The asymmetric unit of (I) comprises a Ag cation, three half molecules of N,N'-bis(2-pyridylmethyl)oxalamide (each of which is disposed about a centre of inversion) and a trifluoromethanesulfonate anion. Each of the ligands coordinates to a Ag atom, one employing the pyridine-N atoms exclusively while the others are µ 2 ,κ 4 -bridging, employing both pyridine-N and amide-O atoms, leading to non-planar seven-membered chelate rings, Fig. 2. It is noted that the Ag-O bond distances are significantly longer than the Ag-N bond distances, Table 1. The resulting N 3 O 2 coordination geometry is distorted square pyramidal based on the value for τ in (I) of 0.02 compared to the ideal values for τ of 0.0 and 1.0 for ideal square pyramidal and trigonal bi-pyramidal geometries, respectively (Addison et al., 1984). In this description, the Ag atoms lies 0.7272 (10) Å out of the plane defined by the O1,O2,N3 and N5 atoms (r.m.s. deviation = 0.0805 Å) in the direction of the N1 atom.
The 2-D structure observed for (I) contrasts the helical coordination polymer observed in the structure of the silver tetrafluoroborate salt containing the same ligand, isolated as a hydrate (Schauer et al., 1998). The N,N'-bis(2pyridylmethyl)oxalamide ligand acts as a bidentate donor employing both pyridine-N atoms in coordination (Schauer et al., 1998).
The crystal packing in (I) can be envisaged as chains of Ag atoms bridged by the µ 2 ,κ 4 -ligands linked by the µ 2 ,κ 2 -ligands leading to 2-D arrays parallel to (1 0 1), Fig. 3. The layers are connected by contacts involving the trifluoromethanesulfonate anions. Thus, the trifluoromethanesulfonate anions participate in N-H···O hydrogen bonds formed to one layer, and C-H···O and C-H···F interactions to the other, Fig. 4 and Table 2. In addition to the intermolecular interactions, intramolecular N-H···O hydrogen bonds are also noted, Table 2.
supplementary materials sup-2 Refinement C-bound H-atoms were placed in calculated positions (N-H = 0.88 Å and C-H 0.95-0.99 Å) and were included in the refinement in the riding model approximation with U iso (H) set to 1.2U eq (C). The maximum and minimum residual electron density peaks of 0.67 and -1.05 e Å -3 , respectively, were located 0.85 Å and 0.79 Å from the S1 and Ag atoms, respectively. Fig. 1. An asymmetric unit of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. Each of the N,N'-bis(2-pyridylmethyl)oxalamide molecules is situated about a centre of inversion.   Crystal data [Ag(C 14