Poly[[bis[3-(1H-tetrazol-1-yl)propanoic acid-κN 4]cadmium]-di-μ-thiocyanato-κ2 N:S;κ2 S:N]

In the title compound, [Cd(NCS)2(C4H6N4O2)2]n, the CdII cation is located on an inversion center and is coordinated by two N and two S atoms from four SCN− anions and two N atoms from two 3-(1H-tetrazol-1-yl)propanoic acid (Htzp) ligands in a distorted octahedral geometry. The SCN− anions bridge the CdII cations into a layer structure parallel to (100). A weak intramolecular C—H⋯N interaction occurs. The layers are further assembled into a three-dimensional supramolecular structure via classical O—H⋯O hydrogen bonds.

In the title compound, [Cd(NCS) 2 (C 4 H 6 N 4 O 2 ) 2 ] n , the Cd II cation is located on an inversion center and is coordinated by two N and two S atoms from four SCN À anions and two N atoms from two 3-(1H-tetrazol-1-yl)propanoic acid (Htzp) ligands in a distorted octahedral geometry. The SCN À anions bridge the Cd II cations into a layer structure parallel to (100). A weak intramolecular C-HÁ Á ÁN interaction occurs. The layers are further assembled into a three-dimensional supramolecular structure via classical O-HÁ Á ÁO hydrogen bonds.
The title coordination polymer crystallizes in the monoclinic space group P2 1 /c and the asymmetric unit contains half of the [Cd(Htzp) 2 (SCN) 2 ] molecule ( Fig. 1). Each Cd 2+ ion lies on the inversion center of an octahedral environment and is coordinated by two N atoms from two Htzp, two N and two O atoms from four different SCNions. Each Cd 2+ center is linked to four adjacent Cd 2+ centers by four SCNions, resulting in a two-dimensional layer structure with Cd···Cd distance of 6.404 Å (Fig. 2). The adjacent two-dimensional layers are further linked through intermolecular hydrogenbonding interaction between two not coordinated carboxylate group (O2-H1···O1 = 2.631 Å) to afford a threedimensional supramolecular structure (Fig. 3). In addition, weak intramolecular hydrogen bonds (C1-H1···N5 = 3.404 Å) are present in the crystal structure.

Experimental
The Htzp (0.0284 g, 0.2 mmol) and NH 4 SCN (0.0152 g, 0.2 mmol) were mixed in distilled water (5 ml) and ethanol (3 ml). Then, CdCl 2 (0.0367 g, 0.2 mmol) dissolved in distilled water (5 ml) was added slowly to the mixture. The mixture was allowed to slowly concentrate by evaporation at room temperature. Several days later, colorless block crystals suitable for X-ray diffraction were obtained with yield 63% on the basis of Htzp.

Refinement
Carboxyl H atom was located in a difference Fourier map and refined isotropically. Other H atoms were positioned geometrically and treated in a riding-model approximation, with C-H = 0.93 Å (aromatic) and 0.97 Å (CH 2 ) and with U iso (H) = 1.2U eq (C).

Figure 3
The three-dimensional supramolecular structure of the title coordination polymer. Hydrogen bonds are shown as dashed lines.

Poly[[bis[3-(1H-tetrazol-1-yl)propanoic acid-κN 4 ]cadmium]-di-µ-thiocyanato-κ 2 N:S;κ 2 S:N]
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 C1 0.30765 (