Di-μ-chlorido-bis(chlorido{N′-[phenyl(pyridin-2-yl-κN)methylidene]pyridine-2-carbohydrazide-κ2 N′,O}cadmium)

The title compound, [Cd2Cl4(C18H14N4O)2], was obtained from the reaction of Cd(NO3)2·4H2O with 2-phenylpyridineketon picolinoyl hydrazone and sodium chloride. Each Cd2+ cation is coordinated by two N atoms and one O atom of the tridentate ligand and three chloride anions, forming a distorted CdNOCl3 octahedron. Each pair of adjacent metal cations is linked by two bridging chloride ligands, resulting in a dinuclear complex unit. The molecular conformation is stabilized by intramolecular N—H⋯N and C—H⋯O hydrogen bonds. In the crystal, molecules are linked by nonclassical C—H⋯O and C—H⋯Cl hydrogen bonds into a three-dimensional network. In addition, π–π stacking interactions [centroid–centroid distances = 3.777 (2) and 3.631 (2) Å] contribute to the stabilization of the crystal packing.

The title compound, [Cd 2 Cl 4 (C 18 H 14 N 4 O) 2 ], was obtained from the reaction of Cd(NO 3 ) 2 Á4H 2 O with 2-phenylpyridineketon picolinoyl hydrazone and sodium chloride. Each Cd 2+ cation is coordinated by two N atoms and one O atom of the tridentate ligand and three chloride anions, forming a distorted CdNOCl 3 octahedron. Each pair of adjacent metal cations is linked by two bridging chloride ligands, resulting in a dinuclear complex unit. The molecular conformation is stabilized by intramolecular N-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds. In the crystal, molecules are linked by nonclassical C-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds into a three-dimensional network. In addition,stacking interactions [centroid-centroid distances = 3.777 (2) and 3.631 (2) Å ] contribute to the stabilization of the crystal packing.  Table 1 Hydrogen-bond geometry (Å , ).

Comment
Schiff base complexes have attracted much attention due to their interesting structures and wide potential applications.
Recently, the relative unsymmetrical tri-and tetradentate Schiff base ligands and their hydrogenated derivatives have been introduced in coordination chemistry to assemble polymers with beautiful molecular structures. Some organic Ndonor ligands are often chosen to fabricate these complexes. In this connection, some complexes with similar tridentate ligands have been studied (Chen et al., 2005;Datta et al., 2011;Akkurt et al., 2012). Herein, we report the structure of a new cadmium complex based on a pyridine based chelating Schiff base ligand. The title compound shows chloridebridged dinuclear Cd(II) units (Fig. 1). The geometry around each Cd(II) ion is distorted octahedral, in which three positions are occupied by two N atoms and one O atom from the Schiff base ligand, two positions by two bridging chloride anions and the sixth position by one terminal chloride anion. Intramolecular non-classical hydrogen bonds of the type C-H···O and N-H···N are present (Table 1). Non-classical intermolecular hydrogen bonds of type C-H···O and C -H···Cl link complexes into a three-dimensional network (Table 1). In the crystal, π-π stacking interactions also contribute to the stabilization: Cg6···Cg9 (1 -x, 1 -y, 1 -z) = 3.777 (2) Å, Cg7···Cg9(-1/2 + x, 1/2 -y, 1/2 + z) = 3.631 (2) Å; where Cg6, Cg7 and Cg9 are the centroids of the N1/C1-C5, N4/C14-C18 and N8/C32-C36 pyridine rings, respectively.

Experimental
The potentialy tridenatate ligand 2-phenylpyridineketon picolinoyl hydrazone was obtained by condensation of an equimolar mixture of 2-phenylpyridineketon and picolinic acid hydrazide in methanol. The title compound was synthesized by the reaction of a methanolic solution of the ligand and Cd(NO 3 ) 2 ·4H 2 O in the presence of excess amount of NaCl. The ligand (1 mmol, 0.302 g) and cadmium nitrate (1 mmol, 0.308 g) were placed in the main arm of the branched tube; sodium chloride (2 mmol, 0.117 g) was added to the mixture too. Methanol was carefully added to fill the arms. The tube was sealed and the ligand-containing arm was immersed in an oil bath at 333 K while the branched arm was kept at ambient temperature. After three days, suitable single crystals had deposited in the cooler arm which were isolated, filtered off, washed with acetone and ether and air dried.

Refinement
The structure was solved by the Patterson method. All H atoms were positioned geometrically with C-H = 0.93, N-H = 0.86 Å, and refined using a riding model with U iso (H) = 1.2U eq (C, N).  The molecular structure of the title compound with displacement ellipsoids drawn at the 40% probability level.

Di-µ-chlorido-bis(chlorido{N′-[phenyl(pyridin-2-yl-κN)methylidene]pyridine-2-carbohydrazide-
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.47 e Å −3 Δρ min = −0.43 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.