catena-Poly[[bis(nitrato-κO)cadmium]bis[μ-1,4-bis(pyridin-3-ylmethoxy)benzene-κ2 N:N′]]

In the title compound, [Cd(NO3)2(C18H16N2O2)2]n, the six-coordinated CdII ion is located on an inversion center and has a distorted octahedral environment defined by four N atoms from four 1,4-bis(pyridin-3-ylmethoxy)benzene ligands and two O atoms from two nitrate anions. The ligands link the CdII ions into a ribbon-like structure running along [201]. One O atom of the nitrate anion is disordered over two positions with site-occupancy factors of 0.59 (2) and 0.41 (2).

In the title compound, [Cd(NO 3 ) 2 (C 18 H 16 N 2 O 2 ) 2 ] n , the sixcoordinated Cd II ion is located on an inversion center and has a distorted octahedral environment defined by four N atoms from four 1,4-bis(pyridin-3-ylmethoxy)benzene ligands and two O atoms from two nitrate anions. The ligands link the Cd II ions into a ribbon-like structure running along [201]. One O atom of the nitrate anion is disordered over two positions with site-occupancy factors of 0.59 (2) and 0.41 (2).

Experimental
Crystal data [Cd(NO 3

Comment
The bridging compounds with rigid and flexible pyridyl-containing bidentate or multidentate organic spacers have assembled numerous interesting topology structures by coordination with metals and intermolecular supramolecular interactions. Our group focused attention on study of flexible pyridyl-based aromatic ligands, and obtained some isolated molecules, chain, two-and three-dimensional network structures (Liu et al., 2010a, b). Herein, as a continuing work for pyridyl ligands, we report the synthesis and crystal structure of the title compound, which is a isostructural compound of our previous reports (Liu et al., 2011;Zou et al., 2011).
In the title compound, the Cd II ion lies on an inversion center and is six-coordinated in a distorted octahedral geometry defined by four N atoms of the pyridine derivatives and two O atoms of the nitrate anions ( Fig. 1, Table 1). One O atom of the nitrate anion has a badly thermal ellipsoid, which is split over two positions with site-occupancy factors of 0.59 (2) and 0.41 (2). In the crystal, ribbon-like structures along [2 0 1] are built up by the N-heterocyclic ligands linking the Cd II ions (Fig. 2).

Experimental
The 1,4-bis(pyridin-3-ylmethoxy)benzene ligand was synthesized as the reference method (Liu et al., 2010a). A mixture of 1,4-dihydroxybenzene (1.10 g, 10 mmol), 3-chloromethylpyridine hydrochloride (3.28 g, 20 mmol) and NaOH (1.60 g, 40 mmol) in acetonitrile (50 ml) was refluxed under nitrogen with stirring for 24 h. After cooling to room temperature, the solution was filtered and the residue was washed with acetonitrile for several times. The mixed filtrate was dropped into a 300 ml water solution, giving a powder crude product. A total of 2.51 g (yield 86%) pure product was obtained by recrystallizing from a mixed solution of 10 ml water and 10 ml methanol. The title compound was synthesized by the reaction of 1,4-bis(pyridin-3-ylmethoxy)benzene (0.29 g, 1.0 mmol) and Cd(NO 3 ) 2 .4H 2 O (0.31 g, 1.0 mmol) in a mixed solution of 5 ml water and 5 ml methanol. The mixture was filtered after stirring for about 1 h. The filtate was allowed to stand for 4 d under room temperature to give block-like colorless crystals suitable for X-ray analysis.

Refinement
O5 atom of nitrate is disordered over two positions and the site-occupancy factors were refined to 0.41 (2) for O5 and 0.59 (2) for O5'. The command "isor 0.005 O5 O5" was used to restrain ADP. H atoms bound to C atoms were placed in calculated positions and treated as riding on their parent atoms, with C-H = 0.93 (aromatic) and 0.97 (methylene) Å and with U iso (H) = 1.2U eq (C).