Aqua[4-(hydroxyiminomethyl)pyridine-κN 1](pyridine-2,6-dicarboxylato-κ3 O 2,N,O 6)copper(II)

In the title compound, [Cu(C7H3NO4)(C6H6N2O)(H2O)], the coordination geometry of the CuII atom can be described as distorted square pyramidal. The basal plane is defined by one N atom and two O atoms from the deprotonated pyridine-2,6-dicarboxylate ligand, and a pyridyl N atom from the 4-pyridyl aldoxime ligand. The apical position is occupied by a water molecule. O—H⋯O hydrogen bonds lead to the formation of a two-dimensional network.

In the title compound, [Cu(C 7 H 3 NO 4 )(C 6 H 6 N 2 O)(H 2 O)], the coordination geometry of the Cu II atom can be described as distorted square pyramidal. The basal plane is defined by one N atom and two O atoms from the deprotonated pyridine-2,6dicarboxylate ligand, and a pyridyl N atom from the 4-pyridyl aldoxime ligand. The apical position is occupied by a water molecule. O-HÁ Á ÁO hydrogen bonds lead to the formation of a two-dimensional network.

Comment
In the design and synthesis of polymeric complexes, various bridging and chelating ligands have been used extensively.
Coordination bonds and hydrogen bonds are the major interactions in these assemblies (Xie et al., 2004). Pyridine-2,6-dicarboxylic acid (H 2 pydc) is an efficient ligand with three coordinating sites. H 2 pydc coordinates with transition metals in different ways to form various coordination geometries. The relative positions of the coordinating atoms (O and N) determine the type of coordination that will be seen in the molecular structure. The interest in this ligand centers on the versatile yet unpredictable manner in which it coordinates to a wide variety of metals due to its rigid and planar nature (Ucar et al., 2007). This paper aims to report one of the rare coordination modes that can be exhibited by copper(II) when coordinated by H 2 pydc, 4-pyridyl aldoxime and H 2 O.
The structure of the title compound is shown in Fig. 1. The molecule is approximately planar and the increased co-planarity is due to the resonance between the pyridine rings, which leads to the formation of square-pyramidal geometry (Fig. 1).
The elongated square-pyramidal geometry of the structure (Table 1) is typical of Jahn-Teller-distorted copper(II) (Blake et al., 2002). The structure shows hydrogen-bonding interactions, which enhance the formation of two-dimensional network of the structure (Germán-Acacio et al., 2007). Bond lengths and angles are in the range expected for heteroaromatic-oximes and pryridne dicarboxylates. The hydrogen-bonding interactions are presented in Fig. 2. A l l the hydrogen-bonding donors and acceptors are involved in O-H···O hydrogen bonds (Table 2), which organize the molecules into a two-dimensional network (Fig. 3).

Experimental
An aqueous solution of Cu(CH 3 COO) 2 .6H 2 O (0.290 g, 1 mmol), KOH (0.220 g, 2 mmol) and H 2 pydc (0.360 g, 2 mmol) in a 1:2:2 molar ratio was refluxed for 2 h and the resultant reaction mixture was reduced to less than 50 ml. After one day, the grown crystals of K 2 [Cu(C 7 H 3 NO 4 ) 2 ] were filtered out and dried in air. Equimolar amounts of K 2 [Cu(C 7 H 3 NO 4 ) 2 ] and 4-pyridyl aldoxime were dissolved in water in small vials, respectively, and then mixed together. The solution was left at room temperature in a vapour diffusion setup with ethanol. Blue crystals of the title compound were obtained after 3 weeks.