Bis[μ-4-hydroxy-N′-(4-methoxy-2-oxidobenzylidene)benzohydrazidato]bis[pyridinecopper(II)]

In the title compound, [Cu2(C15H12N2O4)2(C6H5N)2], each CuII atom is chelated by the tridentate doubly deprotonated Schiff base and a pyridine molecule in a nearly planar environment (r.m.s. deviation for all non-H atoms = 0.107 Å). The metal ions are bridged by one O atom from the symmetry-related Schiff base ligands, forming a centrosymmetric dinuclear copper(II) complex. The dimeric complex is linked to another dimer via weaker Cu—O interactions and also O—H⋯N hydrogen bonds.

In the title compound, [Cu 2 (C 15 H 12 N 2 O 4 ) 2 (C 6 H 5 N) 2 ], each Cu II atom is chelated by the tridentate doubly deprotonated Schiff base and a pyridine molecule in a nearly planar environment (r.m.s. deviation for all non-H atoms = 0.107 Å ). The metal ions are bridged by one O atom from the symmetryrelated Schiff base ligands, forming a centrosymmetric dinuclear copper(II) complex. The dimeric complex is linked to another dimer via weaker Cu-O interactions and also O-HÁ Á ÁN hydrogen bonds.

Related literature
For the crystal structure of the monohydrated Schiff base ligand, see: Mohd Lair et al. (2009a). For the structure of the pyridine adduct of the copper complex of the 4-nitro analog, see: Mohd Lair et al. (2009b). For the crystal structure of a dinuclear copper(II) salphen complex with a similar coordination, see: Yu et al. (2008).

Comment
The title compound is the pyridine adduct of the copper complex of 4-hydroxy-N'-(2-hydroxy-4methoxybenzylidene)benzohydrazide. In the asymmetric unit, which contains one half of the formula unit, the copper ion is four coordinated in an approximately planar environment, the highest deviation from the best plane passing through all non-H atoms being 0.348 (2) Å for O2. From this point of view, it is similar to the structure of the 4-nitrated analogous compound (Mohd Lair et al. 2009b). However, replacement of the electron-withdrawing nitro group by a hydroxy group resulted in bridging the copper ions by O2 atoms from the symmetry related Schiff bases at (-x+1, -y+2, -z), forming a centrosymmetric dinuclear Cu II complex. The distance of Cu1-O2 i is 2.778 (1) Å which is similar to the length of the Cu-O bridge (2.783 Å) in the dinuclear copper (II) salphen complex (Yu et al. 2008). Morever, there is a weak interaction between the copper ions and O3 atoms from the symmetry related molecules at (-x+1, -y+1, -z) with Cu1-O3 iii distance of 3.576 (2) Å, which binds the molecules in one-dimensional infinite chains. Intermolecular hydrogen bonds between the hydroxy groups and the imine N atoms of the neighboring molecules connect the complexes to each other.

Experimental
The Schiff base ligand was prepared as reported previously (Mohd Lairet al., 2009a). A mixture of the Schiff base (0.57 g, 2 mmol) and copper(II) acetate monohydrate (0.4 g, 2 mmol) in the presence of a few drops of triethylamine was refluxed in ethanol (100 ml) for 5 hours. The resulting green precipitate was then filtered, washed with ethanol and dried over silica gel. The green crystal of the title compound was obtained by slow evaporation of a pyridine solution of the compound.

Refinement
A low angle reflection, (-1 0 1), probably affected by extinction, was omitted from the dataset. C-bound hydrogen atoms were placed at calculated positions (C-H 0.95-0.98 Å), and were treated as riding on their parent atoms, with U(H) set to 1.2-1.5 times Ueq(C). The hydroxy H-atom was located in a difference Fourier map, and was refined with distance restraints of O-H 0.84±0.01 Å.

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^ > σ(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.