A second monoclinic polymorph of (pyridine-2-carboxaldehyde oximato-κ2 N,N′)(pyridine-2-carboxaldehyde oxime-κ2 N,N′)palladium(II) chloride

The asymmetric unit of the title compound, [Pd(C6H5N2O)(C6H6N2O)]Cl, contains one half of a cationic PdII complex and a Cl− anion, with a crystallographic mirror plane parallel to the ac plane passing through the Pd and Cl atoms. In the complex, the PdII ion is four-coordinated in a distorted square-planar environment by four N atoms derived from the two chelating ligands. The hydroxy H atom lies on the mirror plane and so is equidistant from the O atoms. This indicates that the negative charge is delocalized over the two O atoms. The complex molecules are stacked in columns along the c axis and are connected by C—H⋯O hydrogen bonds, forming a three-dimensional network. The structure reported herein represents a new monoclinic polymorph of the previously reported monoclinic (C2/c) form [Torabi et al. (2007 ▶). Z. Kristallogr. New Cryst. Struct. 222, 197–198].

The asymmetric unit of the title compound, [Pd(C 6 H 5 N 2 O)-(C 6 H 6 N 2 O)]Cl, contains one half of a cationic Pd II complex and a Cl À anion, with a crystallographic mirror plane parallel to the ac plane passing through the Pd and Cl atoms. In the complex, the Pd II ion is four-coordinated in a distorted squareplanar environment by four N atoms derived from the two chelating ligands. The hydroxy H atom lies on the mirror plane and so is equidistant from the O atoms. This indicates that the negative charge is delocalized over the two O atoms. The complex molecules are stacked in columns along the c axis and are connected by C-HÁ Á ÁO hydrogen bonds, forming a threedimensional network. The structure reported herein represents a new monoclinic polymorph of the previously reported monoclinic (C2/c) form [Torabi et al. (2007). Z. Kristallogr. New Cryst. Struct. 222,[197][198].

Related literature
For the C2/c polymorph of the title compound, see: Torabi et al. (2007). For the crystal structure of the related complex [PdCl 2 (C 6 H 6 N 2 O)], see: Ha (2011).
Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97. A second monoclinic polymorph of (pyridine-2-carboxaldehyde oximato-2 N,N')(pyridine-2-car- The title compound, [Pd(C 12 H 11 N 4 O 2 )]Cl, was obtained as a by-product from the reaction of Na 2 PdCl 4 with syn-2pyridinealdoxime in H 2 O. The X-ray crystal structure of the compound was previously reported in the monoclinic space group C2/c (Torabi et al., 2007). In the latter, the molecule does not exhibit molecular symmetry. The structure presented herein is essentially the same as the published structure but represents a new monoclinic polymorph with the space group C2/m. The yellow main product of the reaction, [PdCl 2 (C 6 H 6 N 2 O)], was investigated previously (Ha, 2011).
The asymmetric unit of the title compound contains one half of a cationic Pd II complex and a Clanion ( Fig. 1). The compound is disposed about a crystallographic mirror plane parallel to the ac plane passing through the Pd and Cl atoms. In the complex, the Pd II ion is four-coordinated in a distorted square-planar environment by four N atoms of the two chelating ligands. Formally, one of the ligands is coordinated to the Pd atom in the monoanionic form, but the negative charge is delocalized over the two O atoms of the ligands; the hydroxy H atom is located in the middle of the O atoms forming a nearly planar six-membered ring. The tight N1-Pd1-N2 chelate angle of 78.91 (14)° contributes the distortion of the square planar structure. The trans N1-Pd1-N2 i (symmetry code i: x,1 -y, z) bond angle is 173.62 (12)°. The Pd1-N1(pyridine) bond length is slightly longer than the Pd1-N2(oxime) bond length ( Table 1). The ligands are nearly planar, with a maximum deviation of 0.024 (3) Å from the least-squares plane, and the dihedral angle between the ligands is 5.06 (8)°. The complex molecules are stacked in columns along the c axis and are connected by intermolecular C-H···O hydrogen bonds, forming a three-dimensional network ( Fig. 2 and Table 2). In the columns, intermolecular π-π interactions between the pyridine rings are present, the shortest ring centroid-centroid distance being 3.787 (3) Å.

Experimental
The title compound was obtained as a by-product from the reaction of Na 2 PdCl 4 (0.2942 g, 1.000 mmol) with syn-2pyridinealdoxime (0.2444 g, 2.001 mmol) in H 2 O (20 ml). After stirring of the reaction mixture for 3 h at room temperature, the formed precipitate was separated by filtration, washed with H 2 O and acetone, to give the main product as a yellow powder (0.2302 g) (Ha, 2011). The orange by-product in a small amount was obtained from the mixture of filtrate and washing solution. Crystals suitable for X-ray analysis were obtained by slow evaporation from an N,N-dimethylformamide (DMF) solution of the by-product at 60 °C.