catena-Poly[[(pyridine-κN)copper(II)]-μ3-pyridine-2,6-dicarboxylato-κ3 O 2:O 2′,N,O 6:O 6′]

In the title compound, [Cu(C7H3NO4)(C5H5N)]n, the CuII atom is in a slightly distorted octahedral coordination environment. Each CuII atom is bound to two N atoms and one O atom of the pyridinedicarboxylate (PDA) ligand in a tridentate manner, one N atom of the pyridine molecule and two bridging carboxylate O atoms of adjacent PDA ligands, leading to a linear one-dimensional chain running along the c axis. These chains are further assembled via weak C—H⋯O and π–π interactions into a three-dimensional supramolecular network structure. The centroid–centroid distance between the π–π interacting pyridine rings is 3.9104 (13) Å. The two N atoms are trans to each other with respect to Cu.

In the title compound, [Cu(C 7 H 3 NO 4 )(C 5 H 5 N)] n , the Cu II atom is in a slightly distorted octahedral coordination environment. Each Cu II atom is bound to two N atoms and one O atom of the pyridinedicarboxylate (PDA) ligand in a tridentate manner, one N atom of the pyridine molecule and two bridging carboxylate O atoms of adjacent PDA ligands, leading to a linear one-dimensional chain running along the c axis. These chains are further assembled via weak C-HÁ Á ÁO andinteractions into a three-dimensional supramolecular network structure. The centroid-centroid distance between theinteracting pyridine rings is 3.9104 (13) Å . The two N atoms are trans to each other with respect to Cu.

Experimental
Crystal data [Cu(C 7   M. Trivedi, D. S. Pandey and N. P. Rath

Comment
The rapidly expanding field of the crystal engineering (the design of crystalline materials) of polymeric coordination networks stems has recently attracted great interest because of their potential applications as zeolite-like materials for molecular selection, ion exchange, and catalysis, as well as in the variety of architectures and topologies (Kitagawa et al., 2004;Kirillov et al., 2008). The main strategy popularly used in this area is a building-block approach (Hoskins & Robson, 1990;Eddaoudi et al., 2001). 2,6-Pyridinedicarboxylic acid (H 2 PDA) is an efficient ligand. Polymeric structure of PDA complexes with transition and lanthanide metals have been reported, in which PDA not only chelates but also bridges to form diversified structures with three coordination sites (Zhao et al., 2003;Choi et al., 2003;Ghosh et al., 2004;Xie et al., 2004). We report the synthesis, and crystal structures of one compound, [Cu(µ-2,6-PDA)(py)] n , (1).
Molecular structure of (1) shows a slightly distorted octahedral coordination geometry. The equatorial sites are occupied by an NO 2 donor from the carboxylate groups at the pyridine-2,6-position of PDA (N2, O1, O1 i ) and one N atom from pyridine (N1). Two O atoms from two other neighboring PDA ligands occupy the axial sites (O2, O2 i ) at a distance of 2.761 Å ( (Uçar et al., 2007;Manna et al., 2007;Gao et al., 2006). The pyridine is essentially planar with no deviation from planarity for pyridyl N1-atom. The C-C-C angles about the pyridyl ring are 118.2 (3) to 128.5 (2)°, indicating sp 2 hybridization. Å. The PDA ligand and pyridine are trans to each other (N2-Cu1-N1 = 180°). However, one-dimensional polymeric chains are connected in the solid state through weak C-H···O and π-π interactions. Weak C-H···O interactions that connects polymeric chains into two-dimensional network (Fig. 3). Contact distances for C-H···O interactions are 2.43-2.76 Å ( Table   1). The weak π-π interactions are present in (1). Further, the importance of π-π stacking interactions between aromatic rings has widely been recognized in the intercalation of drugs with DNA especially in biological systems, which lie in the range 3.4-3.5 Å. The complex (1) exhibits intermolecular face-to-face π-π interactions [π-pyridyl/π-pyridyl ct/ct distance 3.9104 (13) Å; Fig. 4].

Refinement
All H atoms were added in their calculated positions (C-H = 0.95 Å) and were treated using appropriate riding models, with U iso (H) = 1.2U eq (C). Fig. 1. A view of the structure of (1), showing the atom-numbering scheme and the Cu coordination octahedra; displacement ellipsoids are drawn at the 50% probability level.

Special details
Experimental. All H atoms were added in their calculated positions and were treated using appropriate riding models.
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 mat-