Hexaaquazinc(II) bis[4-(2-hydroxybenzylideneamino)benzenesulfonate]

In the title compound, [Zn(H2O)6](C13H10NO4S)2, a distorted ZnO6 octahedron results from the coordination by the six water molecules. Only three of the water molecules are crystallographically unique, as the Zn atom lies on an inversion center. The Zn—O bond lengths are in the range 2.054 (4)–2.073 (4) Å. A network of hydrogen bonds helps to establish the crystal packing.

In the title compound, [Zn(H 2 O) 6 ](C 13 H 10 NO 4 S) 2 , a distorted ZnO 6 octahedron results from the coordination by the six water molecules. Only three of the water molecules are crystallographically unique, as the Zn atom lies on an inversion center. The Zn-O bond lengths are in the range 2.054 (4)-2.073 (4) Å . A network of hydrogen bonds helps to establish the crystal packing.   Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x þ 1; y; z; (ii) x; y; z À 1; (iii) x þ 1; y; z À 1.

S2. Experimental
One mmol of zinc acetate was added to a solution of salicylaldehyde-4-aminobenzene sulfonic acid (1 mmol) in 20 ml of 95% CH 3 CH 2 OH. The mixture was continuously stirred for 2 h at refluxing temperature, evaporating some methanol, then, upon cooling, the solid product was collected by filtration and dried in vacuo (yield 76%). Clear blocks of (I) were obtained by evaporation from a methanol solution after a week.

S3. Refinement
The water H atoms were located in a difference map and refined as riding in their as-found relative positions with U iso (H) = 1.2U eq (O)". Other H atoms were placed geometrically (C-H = 0.93-0.97 Å, O-H = 0.82 Å, N-H = 0.86 Å) and refined as riding with U iso (H) = 1.2U eq (C,N) or 1.5U eq (O).

Figure 1
The complex molecule in (I) with 50% probabiility ellipsoids (arbitrary spheres for the H atoms).  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