catena-Poly[(dichloridozinc)-μ-bis(pyridin-3-yl)methanone-κ2 N:N′]

In the title polymer, [ZnCl2(C11H8N2O)]n, the ZnII atom lies on a twofold rotation axis and has a distorted tetrahedral ZnCl2N2 geometry involving two chloride donors and two N-atom donors from μ2-bridging bis(pyridin-3-yl)methanone ligands, which also have twofold symmetry. A zigzag chain structure is formed, extending along (001). Each chain is surrounded by three others which are interconnected through weak C=O⋯πpyridyl [O⋯centroid = 2.999 (3) Å] and πpyridyl–πpyridyl interactions [minimum ring centroid separation = 4.014 (2) Å], giving a three-dimensional framework.


Comment
The carbonyl (C═O) group in pyridyl ketone derivatives produces versatile angular building blocks for use as ligands for the generation of various coordination supramolecular architectures (Huang et al., 2003). With two pendant pyridyl rings and the rotatable C-C σ bonds, bis(3-pyridyl)methanone functions as an excellent µ 2 -bridging linker to assemble various transition metal salts into diverse coordination motifs, such as one-dimensional helical and zigzag chains , two-dimensional nets , as well as honeycomb-like three-dimensional frameworks (Chen et al., 2009).
Reported here is the structure of a new complex of bis(3-pyridyl)methanone with ZnCl 2 , the title compound [ZnCl 2 (C 5 NH 4 ) 2 ] n . In this complex, the Zn 2+ lies on a crystallographic twofold rotation axis and adopts a distorted tetra- with two chloride donors and two N donors from separate µ 2 -bridging bis(3-pyridyl)methanone ligands, in which the C═O group also lies on a twofold rotation axis (Fig. 1). This results in a zigzag chain structure extending along (001) (Fig. 2).

Experimental
The bis(3-pyridinyl)methanone ligand was obtained using the literature reaction procedure . Reaction of this compound (19.1 mg, 0.1 mmol) with ZnCl 2 (14.0 mg, 0.1 mmol) in methanol gave a colorless solution which after filtration, was allowed to stand in air for two weeks, gave colourless block-like crystals (yield 20.8 mg; 65%).

Refinement
All H atoms were located in the difference electron density maps but were placed in idealized positions and allowed to ride on the carrier atoms, with C-H = 0.93 Å and with U iso (H) = 1.2U eq (C).

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.