Poly[bis(μ-azido-κ2 N 1:N 1)[μ-1,2-bis(imidazol-1-yl)ethane-κ2 N 3:N 3′]cadmium]

In the title three-dimensional coordination polymer, [Cd(N3)2(C8H10N4)]n, the coordination geometry around the CdII atom is distorted octahedral. The CdII atom is coordinated by two N atoms from two cis-positioned bridging 1,2-bis(imidazol-1-yl)ethane (bime) ligands and four N atoms from four azide anions. Each azide ligand acts in an end-on bridging coordination mode. The azide ligands and CdII atoms form a one-dimensional zigzag chain constructed from four-membered [Cd(N3)2]n metallacycles extending along the a axis. These inorganic chains are connected with four other chains via bridging bime ligands to form a three-dimensional coordination network.

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL. This work was supported by the Natural Science Foundation of China (grant Nos. 21171126, 20671066), and the Funds of the Key Laboratory of Organic Synthesis Chemistry, Jiangsu Province, People's Republic of China. metal-organic compounds freedom when they interact with the metal ions, the flexible ligands can adjust their conformations to the geometric requirements of the metal ions (Hoskins et al., 1997a,b).
The short anion ligand azide (N 3 -) is widely used to construct novel coordination polymers because its versatile coordination modes and the ability to mediate strong magnetic coupling (Ribas et al., 1999;Leibeling et al., 2004).
In our previous studies, we synthesized two Cd II coordination polymers with the flexible ligand 1,2-bis(imidazol-1yl)ethane (bime; Zhang et al., 2005;Zhang et al., 2008) and one Cu II coordination polymer (Zhu et al., 2010). In order to extend our work, in the present paper we report the preparation and crystal structure of a novel three-dimensional cadmium(II) coordination polymer [Cd(bime)(N 3 ) 2 ] n (I) with the flexible ligand bime and short anion ligand azide.
The structure of (I) is a novel three-dimensional network. Each Cd II atom is coordinated by six nitrogen atoms: two from two bime ligands in the cis-positions and the remaining four from four azide anions, in a distorted octahedral geometry ( Fig. 1, Table 1).
There are two symmetry independent azide ligands and they both act in end-on (EO) bridging coordination mode. The A pair of azide ligands bridge the Cd II atoms to form a [Cd 2 (N 3 ) 2 ] four-membered metallacycle. The neighboring metallacycles have a common Cd II atom and form a one-dimensional inorganic zigzag chain [Cd(N 3 ) 2 ] n (Fig. 2). The Cd1 ··· Cd1# and Cd1 ··· Cd1& separations via the EO-azide ligands are 3.6804 (7) and 3.7688 (7) Å, respectively. There is one symmetry independent bime ligand in (I). The bime ligands exhibits the anti-conformation with the torsion angle N1 -C1-C2-N3 of 179.4 (2)°. The Cd ··· Cd distances between Cd II atoms bridged via bime ligands are 11.5566 (15)

Experimental
An aqueous (20 mL) solution of Cd(NO 3 ) 2 . 4H 2 O (0.50 mmol) and NaN 3 (1.0 mmol) was added to one side of a "H-shape" tube, and a methanolic solution (20 mL) of bime (0.50 mmol) was added to the another side of the "H-shape" tube.

Refinement
H atoms were placed in idealized positions and refined as riding, with C-H distances of 0.99Å (ethyl) and 0.95Å (imidazole) with U iso (H) = 1.2U eq (C).

Poly[bis(µ-azido-κ 2 N 1 :N 1 )[µ-1,2-bis(imidazol-1-yl)ethane-κ 2 N 3 :N 3′ ]cadmium]
Crystal data 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq