Poly[μ6-pyridine-2,4-dicarboxylato-barium]

In the title complex, [Ba(C7H3NO4)]n, the coordination geometry around the BaII ion can be described as a distorted bicapped trigonal-prismatic BaNO7 arrangement. The pyridine-2,4-dicarboxylic acid ligands exhibit a new coordination mode. Adjacent metal centers are linked by the O atoms of the pyridine-2,4-dicarboxylic acid ligands, and then form a three-dimensional supramolecular polymeric framework.

In the title complex, [Ba(C 7 H 3 NO 4 )] n , the coordination geometry around the Ba II ion can be described as a distorted bicapped trigonal-prismatic BaNO 7 arrangement. The pyridine-2,4-dicarboxylic acid ligands exhibit a new coordination mode. Adjacent metal centers are linked by the O atoms of the pyridine-2,4-dicarboxylic acid ligands, and then form a threedimensional supramolecular polymeric framework.
Here we report a complex (I) assembled by alkaline earth metal Ba II ion with pyridine-2,4-dicarboxylic acid ligand. The formula for the complex is [Ba(C 7 H 3 NO 4 )] n , X-ray crystal analyse reveals that the pyridine-2,4-dicarboxylic acid ligands in the complex are completely deprotonated, which is the same with the complex of [Sr(C 7 H 3 NO 4 )(H 2 O) 2 ] n .
In the title complex, the asymmetric unit consists of one Ba II ion and one pyridine-2,4-dicarboxylate. The coordination geometry around Ba II ion ( Fig. 1) could be described as a distorted bicapped trigonal prism arrangement with coordination number of 8, where N1, O2B and O4D form the top plane of the trigonal prism, and the bottom plane is completed by O3A, O4E, and O1C, while O1 and O3E capped two quadrilateral faces formed by N1, O3A, O1C, O4D and O2B, O4E, O1C, O4D, respectively. All the coordinated atoms in the title complex are oxygen atoms and nitrogen atoms of pyridine-2,4-dicarboxylic acid ligands, which is different from the complex of [Sr(C 7 H 3 NO 4 )(H 2 O) 2 ] n , oxygen atoms of water molecules also take part in the coordination with metal centers. The bond length of Ba-O carboxylate bonds range from 2.706 (2) to 2.8941 (19) Å, which compare well with the mean value determined from the CSD [2.798 (7) Å for Ba-O carboxylate bond]( Table 1) , that is, two 4-position carboxylate oxygen atoms (O3 and O4) coordinate to three Ba II ions, one of the 2-position carboxylate oxygen atoms (O1) coordinates to two Ba II ions, at the same time, this oxygen atom chelate a Ba II ion with the pyridyl nitrogen (N1). The other 2-position oxygen atom (O2) coordinates to one Ba II ion. This coordination mode is not observed in previous reports (Soleimannejad et al., 2009;Huang et al., 2007;Zhang, 2005;Liang et al., 2002;Li et al., 2008;Frisch et al., 2006;Noro et al., 2002). The adjacent metal centers are linked by the oxygen and nitrogen atoms of pyridine-2,4-dicarboxylic acid ligands, and then form a three-dimensional supramolecular polymeric framework ( Fig. 3), while in the complex of Sr(C 7 H 3 NO 4 )(H 2 O) 2 ] n (Soleimannejad et al., 2009), the three-dimensional structure is constructed by non-covalent interactions consisting of O-H···O hydrogen bonds and π-π stacking interactions.

Experimental
A mixture of barium chloride dihydrate (0.0244 g, 0.1 mmol), sodium hydroxide (0.0080 g, 0.2 mmol), pyridine-2,4-dicarboxylic acid (0.0167 g, 0.1 mmol), and H 2 O (3 mL) was placed in a Parr Teflon-lined stainless stell vessel (25 ml), and then the vessel was sealed and heated at 443.15 K for 4 days. Then the vessel was cooled to 373.15 K at a rate of 5 K h -1 and slowly cooled to room temperature. Colorless, rectangular single crystals suitable for X-ray diffraction were obtained.  Fig. 1. Coordination environment of Ba II ion in the title complex. Non-hydrogen atoms are shown as 30% probability ellipsoids. Hydrogen atoms are omitted for clarity. Symmetry codes: (A) -x + 1, -y, -z + 1; (B) x -1/2, y + 1/2, z; (C) -x + 1, y, -z + 1/2; (D) -x + 1, -y + 1, -z + 1; (E) x -1/2, -y + 1/2, z -1/2.   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 Rfactors(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