Poly[[[silver(I)-μ-1,4-bis[(imidazol-1-yl)methyl]benzene-κ2 N 3:N 3′-silver(I)-μ-1,4-bis[(imidazol-1-yl)methyl]benzene-κ2 N 3:N 3′] 4,4′-diazenediyldibenzoate] dihydrate]

In the title compound, [Ag2(C14H14N4)2](C14H8N2O4)·2H2O, each of the two unique Ag+ ions is two-coordinated by two N atoms from two different 1,4-bis[(imidazol-1-yl)methyl]benzene ligands in an almost linear fashion [N—Ag—N = 170.34 (10) and 160.25 (10)°]. The 4,4′-diazenediyldibenzoate anions do not coordinate to Ag. O—H⋯O hydrogen bonds stabilize the crystal structure.


Related literature
For a related structure, see: Xu et al. (2005). For applications of coordination polymers, see: Chen et al. (2008).

Comment
Coordination polymers are of considerable interest because of their potential application in the areas of catalysis, separation, sorption, sensors, and in electronic and magnetic devices (Chen et al., 2008). So far, the rigid rod-like spacer is well known in the construction of coordination polymers. However, the coordination polymers with the flexible N-donor ligands such as 1,4-bis(imidazole-1-ylmethyl)benzene (1,4-bix) and dicatrboxylic acids such as 4,4'-diazenediyldibenzoic acid (H 2 L) have not been well explored (Xu et al., 2005). Here, 1,4-bix assembles with silver and H 2 L to yield a coordination polymer [Ag 2 (1,] . L . 2H 2 O, (I).
As shown in Fig. 1, there are two Ag(I) atoms, one 1,4-bix ligand, one L anion, and two free water molecules in the asymmetric unit. Each Ag atom ( Ag1 or Ag2) is two-coordinated by two nitrogen atoms from two different 1,4-bix ligands in a linear sphere. The Ag atoms are bridged by the 1,4-bix ligands to generate a chain structure. Notably, the L anion did not coordinate to the Ag center, but acted as a counter-anion. The O-H···O hydrogen bonds further stabilize the chain structure (Table 1).

Refinement
All H atoms on C atoms were positioned geometrically (C-H = 0.93 Å) and refined as riding, with U iso (H)=1.2U eq (C). H atoms bonded to water molecules were located in difference Fourier maps and refined isotropically with distance restraints of O-H = 0.85±0.01 and H···H = 1.35 ±0.01 Å with U iso = 1.5U eq (O). Fig. 1. The structure of the title compound, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Symmetry code: (i) x-2, 1+y, 1+z.

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.