Poly[dibromidobis[μ-1-(pyridin-4-ylmethyl)-1H-1,2,4-triazole-κ2 N:N′]cadmium]

The title coordination polymer, [CdBr2(C8H8N4)2]n, arose from a layer-separated diffusion synthesis at room temperature. The title compound is isotypic with the I and Cl analogues. The Cd atom, located on an inversion center, is coordinated by two bromide ions and four N atoms (two from triazole rings and two from pyridyl rings) in a distorted trans-CdBr2N4 octahedral arrangement. The bridging 1-(4-pyridylmethyl)-1H-1,2,4-triazole ligands are twisted [dihedral angle between the triazole and pyridine rings = 72.56 (13)°], affording a two-dimensional 44 sheet structure in the crystal.

The title coordination polymer, [CdBr 2 (C 8 H 8 N 4 ) 2 ] n , arose from a layer-separated diffusion synthesis at room temperature. The title compound is isotypic with the I and Cl analogues. The Cd atom, located on an inversion center, is coordinated by two bromide ions and four N atoms (two from triazole rings and two from pyridyl rings) in a distorted trans-CdBr 2 N 4 octahedral arrangement. The bridging 1-(4-pyridylmethyl)-1H-1,2,4-triazole ligands are twisted [dihedral angle between the triazole and pyridine rings = 72.56 (13) ], affording a two-dimensional 4 4 sheet structure in the crystal.

Related literature
For structures of Cd(II) polymers with related ligands, see: Liu et al. (2005); Huang et al. (2006). For the structures of isotypic analogues with I and Cl, see: Wang et al. (2008Wang et al. ( , 2010. For the structure of the isotypic complex with Cu(II) and Cl, see: Li et al. (2009).

Comment
Recently, our group has focused on the design and synthesis of some flexible unsymmetric ligands (Liu et al., 2005;Huang et al., 2006), one of which being the heterocyclic ligand pyta, N-(4-pyridylmethyl)-1,2,4-triazole. In order to explore the architectural styles and other features of this kind of ligands, we selected cadmium dibromide as a representative subject for stereoregular coordination. Among our attempts, a new polymer [CdBr 2 (pyta) 2 ] n was obtained as crystals suitable for single-crystal X-ray analysis.
The crystal structure of the title compound is isomorphous to other complexes we have reported with I or Cl in place of Br (Wang et al., 2008(Wang et al., , 2010 or with Cu(II) and Cl (Li et al., 2009). The crystallographic analysis reveals that the title compound crystallizes in the monoclinic space group P2 1 /c. The asymmetric unit contains one cadmium atom, one bromide donor and one pyta bridging molecule, as shown in Fig. 1. The Cd(II) ion is placed on an inversion center, with an octahedral [CdBr 2 N 4 ] environment, where the axial positions are occupied by two bromide ions and the equatorial positions occupied by two trans triazole N atoms and two trans pyridyl N atoms, each of which respectively belonging to four symmetry-related pyta ligands (Fig. 1). The bond angles about the Cd octahedron range from 85.88 (8) to 94.12 (8)° and deviate slightly from those of a perfect octahedron. Due to the existence of the -CH 2 -spacer between the triazole and the pyridyl ring, sufficient flexibility makes possible for pyta to be twisted in order to meet the requirement of coordination geometry of the metal center. The dihedral angle between the triazole and pyridyl rings in the ligand is 72.56 (13)°.
As conveniently shown in Fig. 2, the title compound forms an infinite two-dimensional rhombohedral sheet containing 36-membered sandglass rings. The sp 3 hybridization of C3 forces the pyta ligand to be non-linear, generating the nonlinear grid sides and thereby the sandglass grids. Every complementary four [Cd 4 (pyta) 4 ] grids are connected together by sharing the cadmium apices to give the 4 4 two-dimensional structure with a side length of 11.01 Å, and a diagonal measurement of about 14.31 × 16.73 Å 2 .

Experimental
A solution of pyta (0.021 g, 0.10 mmol) in MeOH (5 ml) was carefully layered on a solution of CdBr 2 (0.027 g, 0.10 mmol) in H 2 O (5 ml). Diffusion between the two phases over a period of two weeks produced colorless block crystals.