Aqua[6-carboxylato-N′-(pyridin-2-ylmethylidene)pyridine-2-carbohydrazidato]copper(II) trihydrate

In the title compound, [Cu(C13H8N4O3)(H2O)]·3H2O, the complex molecule, except for the aqua ligand, is essentially planar [r.m.s. deviation = 0.034 (2) Å]. The coordination polyhedron of the Cu2+ cation is a square-pyramid, with the aqua ligand at the apex. The compound exhibits a three-dimensional structure, which is is stabilized by O—H⋯O and O—-H⋯N hydrogen bonds and π–π interactions [centroid–centroid distance = 2.987 (3) Å].

In the title compound, [Cu(C 13

Experimental
Concentrated H 2 SO 4 (2 mL)was added slowly with stirring to a solution of pyridine-2,6-dicarboxylic acid in ethanol. The solution was left to reflux for 24 h, yielding a white precipitate of ethylpyridine-2,6-dicarboxylate. This was dissolved in ethanol, then the hydrazine hydrate was slowly added with continuous stirring and the mixture was refluxed over a period of 6 h, yielding awhite crystalline solid of pyridine-2-carbohydrazide-6-carboxyl acid.

Refinement
The position of the water H atoms were located in a difference Fourier map and were refined freely. U iso of H4A, H4B, H6A atom = 0.03U eq (C), U iso of H5A, H5B, H7B atom = 0.03U eq (C), and U iso of H6B, H7A atom = 0.06U eq (C). All the C- 1.2U eq (C).

Figure 1
The molecular structure (at 30% probability) of the title compound.  Packing diagram of the title complex, showing hydrogen bonds as dashed lines.

Crystal data
[Cu (C 13  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. 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 > 2sigma(F 2 ) is used only for calculating R-factors(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.