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

In the cation of the title compound, [Co(H2O)6](C13H10NO4S)2, the Co atom lies on a centre of symmetry and its coordination geometry is octahedral. The crystal structure is stabilized by water–anion O—H⋯O hydrogen bonds. An intramolecular O—H⋯N hydrogen bond occurs in the anion.

In the molecule of (I), the Co (II) centre is six-coordinate with six O donors of the water molecules. The C7-N1 bond length of 1.281 (8) Å is close to double-bond. Otherwise, the geometrical parameters for (I) are in normal range (Allen et al., 1987). The dihedral angle between the two benzene ring is 33.5°, indicating that the molecule is non-planar, which perhaps correlates with the intramolecular and intermolecular hydrogen bonds (Table 1).

S2. Experimental
1 mmol of Cobalt acetate was added to a solution of salicylaldehyde-4-aminobenzene sulfonic acid (1 mmol) in 10 ml of 95% ethanol. The mixture was stirred for 2 h at refluxing temperature. Evaporating some ethanol, clear blocks of (I) were obtained after one weeks.

S3. Refinement
The H atoms were placed geometrically [C-H = 0.93 Å, O-H = 0.82 for hydroxy group and O-H = 0.85 Å for water molecules] and refined as riding with U iso (H) = 1.2U eq (carrier).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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