(1H-1,3-Benzimidazole-5,6-dicarboxylic acid)(5-carboxylato-1H-1,3-benzimidazole-6-carboxylic acid)silver(I) monohydrate

The title compound, [Ag(C9H5N2O4)(C9H6N2O4)]·H2O, contains one independent Ag atom, a neutral 1H-benzimidazole-5,6-dicarboxylic acid (bdcH), its monodeprotonated form, i.e. 5-carboxylato-1H-1,3-benzimidazole-6-carboxylic acid (bdc), and one solvent water molecule, the latter being disordered over three sites with site occupancy factors of 0.375 (× 2) and 0.25. In addition, the H atom on one carboxylic acid residue is disordered, being connected to each of the O atoms 50% of the time. The Ag atom is in a virtually linear geometry defined by two N atoms derived from the bdc and bdcH ligands. The three-dimensional supramolecular structure is stablized by extensive O—H⋯O and N—H⋯O hydrogen bonds. An intramolecular O—H⋯O hydrogen bond is also present.

The title compound, [Ag(C 9 H 5 N 2 O 4 )(C 9 H 6 N 2 O 4 )]ÁH 2 O, contains one independent Ag atom, a neutral 1H-benzimidazole-5,6-dicarboxylic acid (bdcH), its monodeprotonated form, i.e. 5-carboxylato-1H-1,3-benzimidazole-6-carboxylic acid (bdc), and one solvent water molecule, the latter being disordered over three sites with site occupancy factors of 0.375 (Â 2) and 0.25. In addition, the H atom on one carboxylic acid residue is disordered, being connected to each of the O atoms 50% of the time. The Ag atom is in a virtually linear geometry defined by two N atoms derived from the bdc and bdcH ligands. The three-dimensional supramolecular structure is stablized by extensive O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. An intramolecular O-HÁ Á ÁO hydrogen bond is also present.

H. Zhai
Comment N-Heterocyclic carboxylic acids as organic ligands attract attention not only because of versatile coordination modes but also owing to its ability to facilitate the formation of high-dimensional coordination polymers. One such example, namely, 1H-benzimidazole-5,6-dicarboxylic acid (bdcH), is a semi-rigid, multidentate ligand that can provide up to six donor atoms (two N and four O atoms) with variable coordination modes. This is therefore considered as an excellent candidate for generating 3-D architectures. Up to now, the reported complexes based on the bdc ligand are rare but have attracted recent interest (Lo et al., 2007;Gao et al., 2008;Wei et al., 2008;Yao et al., 2008;Li et al., 2009). Herein, the first Ag supramolecular compound based on the bdc ligand, namely [Ag(C 9 H 5 N 2 O 2 )(C 9 H 6 N 2 O 2 )].H 2 O, (I), is reported.
As is shown in Fig. 1, the asymmetric unit consists of bdcH and bdc ligands, one Ag atom, and one solvent water molecule.
The water molecule is disordered over three sites with site occupancy factors = 0.375 (x 2) and 0.25, see Experimental. The Ag atom has a linear coordination environment being bound to two N atoms derived from the bdc ligands.
A packing diagram showing the 3-D supramolecular structure arising from a larg e number of hydrogen bonding interactions is shown in Fig. 2. Through the agency of intermolecular hydrogen bond interactions involving the bdc and bdcH ligands, Table 1, a layer structure is generated. These are connected into a 3-D network via hydrogen bonding interactions involving the water molecules.

Experimental
A mixture of the bdc (0.0415 g, 0.20 mmol), AgNO 3 (0.0340 g, 0.20 mmol) and water (10 ml) was heated to 430 K for 72 h in a 23 ml Teflon-lined stainless-steel autoclave. After the reaction, the bomb was cooled to room temperature in a rate of 278 K per hour. Colourless prismatic crystals were collected and dried in air.

Refinement
For the bdc ligand, all H atoms were placed at calculated positions and were treated as riding on the parent atoms with C-H = 0.93 and O-H = 0.86 Å, and with U iso (H) = 1.2 or 1.5 U eq (C, O). The H atom on the carboxylic acid residue with the O3 and O4 atoms was disordered. This was modelled over two sites of equal weight.  (1H-1,3-Benzimidazole-5,6-dicarboxylic acid)(5-carboxylato-1H-1,3-benzimidazole-6-carboxylic acid)silver(I) monohydrate Crystal data [Ag(C 9