Crystal structure of catena-poly[bis[μ3-2-(2-nitrophenyl)acetato-κ3 O:O:O′]disilver(I)]

The title compound, [Ag2(C8H6NO4)2]n, is a silver complex of 2-(2-nitrophenyl)acetic acid. The molecules are not conventional crystallographic inversion dimers but consist of two independent ligands and two AgI ions, each with a distorted T-shaped coordination environment. The dihedral angles between acetate groups and the benzene rings are 51.1 (2) and 57.9 (2)°. The nitro groups are oriented at dihedral angles of 23.6 (5) and 32.3 (3)° with respect to the parent benzene rings. The dimers form polymeric chains along the a-axis direction. The Ag⋯Ag separation within a dimer is 2.8200 (5) and between symmetry-related dimers is 3.6182 (5) Å. The polymeric chains are interlinked by C—H⋯O hydrogen-bond interactions.

In (I), the two ligands of (2-nitrophenyl)acetatic acid have been coordinated to to two silver ions making a dimer. The structural behaviour of both ligands is different. In one ligand the acetato moiety A (O1/C1/C2/O2) and benzene ring B

S2. Synthesis and crystallization
The sodium salt of (2-nitrophenyl)acetic acid was prepared in water with one molar ratio of (2-nitrophenyl)acetic acid and Na(HCO 3 ). In this solution one mole of silver nitrate AgNO 3 (1.08 g) dissolved in water was added and stirred for 5 minutes. Curd white precipitate formed was dissolved by adding few drops of liquid ammonia and kept for crystallization in dark. Needle like colourless crystals were obtained after two weeks.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. The H-atoms were positioned geometrically (C-H = 0.93-0.97 Å) and refined riding on the carbon atoms with isotropic displacement parameters U iso (H) = 1.2U eq (C).

Figure 1
Molecular structure of the title compound. Anisotropic displacement ellipsoids are drawn at the 50% probability level. Hatoms are shown by small circles of arbitrary radii.

Figure 2
Crystal packing which shows that molecules form polymeric network due to interlinkage of dimers.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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