trans-Diaquabis(6-methoxycarbonylpyridazine-3-carboxylato-κ2 N,O)zinc(II) dihydrate

In the title centrosymmetric complex, [Zn(C7H5N2O4)2(H2O)2]·2H2O, the ZnII ion is coordinated in a trans mode by two symmetry-related bis-chelating 6-methoxycarbonylpyridazine-3-carboxylate ligands via N and O atoms, and by two aqua ligand O atoms in axial positions, in a slightly distorted octahedral environment. In the crystal structure, complex molecules are linked by intermolecular O—H⋯O hydrogen bonds between coordinated and solvent water molecules and carboxylate O atoms, forming molecular ribbons propagating along the a axis.

In the title centrosymmetric complex, [Zn(C 7 H 5 N 2 O 4 ) 2 -(H 2 O) 2 ]Á2H 2 O, the Zn II ion is coordinated in a trans mode by two symmetry-related bis-chelating 6-methoxycarbonylpyridazine-3-carboxylate ligands via N and O atoms, and by two aqua ligand O atoms in axial positions, in a slightly distorted octahedral environment. In the crystal structure, complex molecules are linked by intermolecular O-HÁ Á ÁO hydrogen bonds between coordinated and solvent water molecules and carboxylate O atoms, forming molecular ribbons propagating along the a axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH2816).

S1. Comment
In the molecluar structure of the title compound (I) (Fig.1) the Zn II ion, which is located on a center of symmetry, is coordinated in trans mode by two, symmetry related, bis chelating ligand molecules through their N,O bonding atoms.
Two water O atoms in axial positions complete the number of coordinated atoms to six. The coordination geometry is slightly distorted octahedral. Bond distances and bond angles are close to those reported for two zinc complexes with pyridazine-3-carboxylate and water ligands (Gryz et al., 2003(Gryz et al., , 2004, a complex with pyridazine-3,6-dicarboxylate and water ligands (Gryz et al., 2006) and for both modifications of pyridazine-3,6-dicarboxylic acid (Sueur et al., 1987;. The ligand molecules and the Zn II ion are almost coplanar [r.m.s. 0.0074 Å]. The carboxylic C12/O11/O12 and the carboxymethyl C18/O21/O22/C19 groups make dihedral angles with the pyridazine ring of 3.0 (2) and 6.8 (1)°, respectively. In the crystal structure complex molecules are linked by hydrogen bonds to form molecular ribbons (Fig. 2). The relevant hydrogen-bond parameters are listed in Table 1.

S2. Experimental
Hot aqueous solutions containing 2 mmol of 6-carboxymethylpyridazine-3-carboxylic acid and 1 mmol of zinc(II) acetate tetrahydrate, respectively, were mixed and boiled for two hours with constant stirring and then left to crystallize at room temperature. After few days, well formed colorless single crystals were found in the mother liquid in the mass of polycrystalline material. The crystals were washed with cold ethanol and dried in air.

S3. Refinement
H atoms bonded to C atoms were placed in calculated positions with C-H = 0.93 and 0.96 Å and included in a ridingmodel approximation with U iso (H) = 1.2U eq (C) or 1.5U eq (C) for methyl atoms. Water H atoms were located in difference Fourier maps and were refined isotropically.  The molecular structure of (I) with atom labelling scheme and 50% probability displacement ellipsoids. Symmetry code: (i) -x + 1, -y + 1, -z + 1. The symmetry related solvent water molecule is not shown.

Figure 2
Part of the crystal structure with hydrogen bonds shown as dashed lines. (6-methoxycarbonylpyridazine-3-carboxylato-κ 2 N,O)  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.