trans-Diaquabis[5-(pyridine-3-carboxamido)tetrazolido-κ2 O,N 1]zinc dihydrate

The title compound, [Zn(C7H5N6O)2(H2O)2]·2H2O, consists of one ZnII ion located on the crystallographic inversion centre, two 5-(pyridine-3-carboxamido)tetrazolide ligands, two coordinated water molecules and two free water molecules. The ZnII ion adopts a slightly distorted octahedral coordination geometry formed by the N,O-chelating ligands and two O water atoms. The pyridine N atoms are not coordinated. In the crystal, complex molecules are connected by N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, [Zn(C 7 H 5 N 6 O) 2 (H 2 O) 2 ]Á2H 2 O, consists of one Zn II ion located on the crystallographic inversion centre, two 5-(pyridine-3-carboxamido)tetrazolide ligands, two coordinated water molecules and two free water molecules. The Zn II ion adopts a slightly distorted octahedral coordination geometry formed by the N,O-chelating ligands and two O water atoms. The pyridine N atoms are not coordinated. In the crystal, complex molecules are connected by N-HÁ Á ÁO, O-HÁ Á ÁN and O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Related literature
For pharmaceutical applications of amide derivatives, see: Foster et al. (1999); Rauko et al. (2001); Rowland et al. (2001Rowland et al. ( , 2002. For our recent work on the design and synthesis of amide complexes, see: Wang et al. (2010). For the use of nicotinoylamino in building novel complexes, see: Aakerö y et al.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HG5200).

Comment
In recent years, many metal compounds derived from amides, have been prepared and characterized, and have been found to possess a wide variety of pharmic applications (Foster et al., 1999;Rauko et al., 2001;Rowland et al., 2001;Rowland et al., 2002). Amides were used to construct extended frameworks sustained both by hydrogen bonds and coordination bonds owing to the inherent coordination and hydrogenbonding donor/acceptor functionalities (Aakeröy et al., 2001;Li et al., 2008;Moncol et al., 2007;Kumar et al., 2005). In this paper, we report the crystal structure of the zinc-amide complex.
The asymmetric unit of complex, (I), contains one Zn II ion located on an inversion centre, one independent N-(tetrazol-5-yl)-nicotinamide ligand, one coordination water molecule and one free water molecule. The central Zn II ion adopts a slightly distorted octahedral coordination geometry by two ligands and two coordination water molecules. The All the Zn-N or Zn-O bond lengths are comparable to those reported previously for zinc compounds (Armstrong et al., 2003;Liu et al., 2009). The dihedral angle between tetrazole and pyridine groups is 45.988 (1)°.
In the crystal, the complex molecules are connected to a two dimensional layer by intermolecular N-H···O free (O atoms from free water molecules) hydrogen bonds (Fig. 2, Table 2). The layered strcture form a three-dimensional network via O free -H···O coord (O atoms from coordination water molecules), O free -H···N and O coord -H···N hydrogen bonds.
The muddy solution obtained was stirred at room temperature for three hours, filtered and set aside to slowly crystallize at room temperature. The block-like crystals were obtained after about three weeks.

Figure 1
View of the coordination environment of Zn 2+ in title compound at 50%. H atoms have been omitted for clarity.  A view of the two-dimensional structure formed via hydrogen bonds. 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.