Bis(μ-5-carboxylatotetrazolido)bis[aqua(2,2′-bipyridyl)cadmium(II)]

In the title dinuclear CdII complex, [Cd2(C2N4O2)2(C10H8N2)2(H2O)2], each Cd atom is in a slightly distorted octahedral coordination by two N atoms and one O atom of two 1H-tetrazole-5-carboxylate (TZC) ligands, two N atoms of a 2,2′-bipyridyl ligand and one water O atom. The TZC ligand acts in a tridentate N,O-chelating N-bridging mode to two symmetry-equivalent CdII atoms. The complex reveals molecular C i symmetry. Extensive O—H⋯O hydrogen bonding plays an important role in the crystal packing.

In the title dinuclear Cd II complex, [Cd 2 (C 2 N 4 O 2 ) 2 -(C 10 H 8 N 2 ) 2 (H 2 O) 2 ], each Cd atom is in a slightly distorted octahedral coordination by two N atoms and one O atom of two 1H-tetrazole-5-carboxylate (TZC) ligands, two N atoms of a 2,2 0 -bipyridyl ligand and one water O atom. The TZC ligand acts in a tridentate N,O-chelating N-bridging mode to two symmetry-equivalent Cd II atoms. The complex reveals molecular C i symmetry. Extensive O-HÁ Á ÁO hydrogen bonding plays an important role in the crystal packing.

Comment
Coordination complexes with tetrazolate-based ligands have been the subject of intense research efforts in recent years, owing to their enormous variety of interesting structural topologies, and wide physical properties such as molecular magnetism, molecular absorption, catalysis, non-linear optics, and luminescence (Zhao, 2008;Cheng et al., 2007). The crystal structures and properties of metal complexes based on tetrazolate-5-carboxylato ligand have been reported in several papers (Wu et al., 2009;Wu et al., 2010) in recent years. Herein, we report the synthesis and crystal structure of its cadmium(II) complex.
In the title compound (I), the asymmetric unit comprises a half of the molecule ( Fig. 1) and an inversion symmetry generates a dinuclear complex. The bond lengths (Table 1) and angles around Cd1 atom suggests a slightly distorted octahedral geometry. The TZC ligand acts as a tridentate linker to chelate the Cd atom and bridges the other Cd atom in a µ 2 -N2:O1,N1 coordination mode (Fig. 1). Two Cd atoms are bridged by tetrazolate groups from two symmetry-related TZC ligands to form one six-membered ring (Cd1-N1-N2-Cd1A-N1A-N2A). There are O-H···O, C-H···N, C-H···O intermolecular hydrogen bonds ( Table 2). The molecules are held together by intermolecular hydrogen bonding interactions, forming a three-dimensional network (Fig. 2).

Experimental
A mixture of Cd(NO 3 ) 2 4H 2 O (0.5 mmol), TZC (0.5 mmol), KOH (0.5 mmol) and 2,2'-bipy (0.5 mmol) in aqueous solution (15 ml) was sealed in a 25 ml Teflon-lined stainless steel vessel under autogenous pressure and heated at 383 K for 3 days, and then slowly cooled to room temperature. Colourless crystals suitable for X-ray analyses were obtained, washed with distilled water and dried in air. Yield: 50% (based on Cd).

Refinement
The H atoms of the 2,2'-bipy were placed in geometrically idealized positions with C-H distances of 0.93 Å, and were refined isotropic using a riding model with U iso (H) = 1.2Ueq(C). The H atoms of the coordinated water molecules were assigned in the difference Fourier maps and refined isotropically. Fig. 1. The structure of (I), showing 30% probability displacement ellipsoids and the atom-labeling scheme. Symmetry code: (A) -x + 1, -y, -z + 1.