Aqua(benzene-1,2-dicarboxylato-κO)bis[2-(1H-pyrazol-3-yl-κN 2)pyridine-κN]cadmium(II)

In the mononuclear title complex, [Cd(C8H4O4)(C8H7N3)2(H2O)], the CdII atom is six-coordinated in a distorted octahedral geometry by four N atoms from two bidentate chelating 2-(1H-pyrazol-3-yl)pyridine ligands, one O atom from a benzene-1,2-dicarboxylate ligand and one water molecule. The molecular structure features intramolecular O—H⋯O and N—H⋯O hydrogen bonds. In the crystal structure, the complex molecules are assembled into a two-dimensional supramolecular layer parallel to (011) via O—H⋯O and N—H⋯O hydrogen bonds and π–π stacking interactions between the pyridyl and pyrazole rings [centroid–centroid distances = 3.544 (2) and 3.722 (3) Å].


Related literature
For general background to the roles played by aromatic ring stacking and hydrogen bonding in biological reactions and in molecular recognition and self-organization, see: Borrows et al. (1995);Hunter (1994). For related structures, see: Cheng et al. (2006); Hu et al. (2008); Wan et al. (2003).

Comment
The strategies for the construction of functional systems depend on the nature of the interactions responsible for creating networks. Aromatic ring stacking and hydrogen bonds are two important types of intermolecular non-covalent interactions, which play vital roles in highly efficient and specific biological reactions and are essential for molecular recognition and self-organization (Borrows et al., 1995;Hunter, 1994). Benzene-1,2-dicarboxylic acid (1,2-H 2 bdc) exhibits rich coordination modes to metal centers owing to its rigidity and polycarboxylate groups. Therefore, its metal complexes often show two-or three-dimensional structures (Cheng et al., 2006;Wan et al., 2003). 3-(2-Pyridyl)pyrazole (L) can act as a simple bidentate chelating ligand, similar to 2,2'-bipyridine (or 1,10-phenanthroline) (Hu et al., 2008). In the present paper, we report the crystal structure of the title compound, a new Cd II complex based on the mixed ligands L and 1,2-bdc, in which interesting hydrogen-bonding and π-π stacking interactions are observed.
In the title mononuclear compound, as shown in Fig. 1, the Cd II atom is coordinated by four N atoms from two L ligands, with Cd-N bond lengths in the range of 2.241 (3)-2.525 (3) Å, one O atom from the carboxylate group of a 1,2-bdc ligand, with a Cd-O bond distance of 2.306 (3)Å and one O atom from a water molecule, with a Cd-O bond distance of 2.306 (2) Å. Thus, the coordination polyhedron around the Cd II atom can be best described as distorted octahedral.
The complex molecule involves intramolecular O-H···O and N-H···O hydrogen bonds (Table 1). Analysis of the crystal packing indicates that intermolecular O-H···O and N-H···O hydrogen bonds link two complex molecules, producing a dimeric unit. The dimeric units are arranged in a parallel fashion, which makes the aromatic stacking available to afford a two-dimensional supramolecular layer (Fig. 2). The centroid-centroid distances between the pyridyl and pyrazolyl rings are 3.544 (2)Å and 3.722 (3) Å and their corresponding dihedral angles are 3.40 (2) and 4.68 (1)°, respectively.

Experimental
The title complex was obtained by the reaction of Cd(CH 3 CO 2 ) 2 .2H 2 O, 3-(2-pyridyl)pyrazole and benzene-1,2-dicarboxylic acid in a molar ratio of 1:1:1, mixed with water (10 ml) under hydrothermal conditions at 413 K for 3 d. After cooled to room temperature at a rate of 5 K h -1 , colorless block crystals suitable for X-ray analysis were obtained in a 60% yield. Analysis, calculated for C 24 H 20 CdN 6 O 5 : C 49.29, H 3.45, N 14.37%; found: C 49.33, H 3.35, N 14.44%.

Refinement
Although all H atoms were visible in difference Fourier maps, they were placed in geometrically calculated positions and Hall symbol: -P 1 Mo Kα radiation, λ = 0.71073 Å a = 10.1546 (7) Å Cell parameters from 2320 reflections b = 10.7709 (7)