Pentaaqua(4,6-dihydroxybenzene-1,3-disulfonato-κO 1)zinc pentahydrate

The ZnII atom in the title complex, [Zn(C6H4O8S2)(H2O)5]·5H2O, is coordinated by five water molecules and an O atom of a 4,6-dihydroxybenzene-1,3-disulfonate dianion. The coordination geometry is distorted octahedral, with the Zn—Osulfonate bond relatively long compared to the Zn—Owater bonds. The coordinated and lattice water molecules interact with each other and with the hydroxy groups and sulfonate ligand through O—H⋯O hydrogen bonds, generating a tightly held three-dimensional network.

The Zn II atom in the title complex, [Zn(C 6 H 4 O 8 S 2 )(H 2 O) 5 ]Á-5H 2 O, is coordinated by five water molecules and an O atom of a 4,6-dihydroxybenzene-1,3-disulfonate dianion. The coordination geometry is distorted octahedral, with the Zn-O sulfonate bond relatively long compared to the Zn-O water bonds. The coordinated and lattice water molecules interact with each other and with the hydroxy groups and sulfonate ligand through O-HÁ Á ÁO hydrogen bonds, generating a tightly held three-dimensional network.

Comment
In earlier studies (Xie et al., 2010), the crystal structure determination of [Zn(CH 3 CN)(H 2 O) 5 ](C 6 H 4 O 8 S 2 ).3H 2 O showed that the Zn atom is octahedrally coordinated by one acetonitrile-N atom and five water molecules. The 4,6-dihydroxybenzene-1,3-disulfonate anion did not interact directly with the metal atom, instead forming hydrogen bonds to the coordinated water molecules (Xie et al., 2010). When the synthesis was repeated in the absence of acetonitrile, the title compound was obtained in which the 4,6-dihydroxybenzene-1,3-disulfonate anion is now bonded to the zinc atom, Fig. 1.
The covalent Zn-O sulfonate bond is relatively long compared to the Zn-O water bonds, Table 1. The observed coordination geometry resembles that seen in a related pentaaquozinc/sulphonate structure (Bakirci et al., 2006).
The coordinated and lattice water molecules interact with each other and with the sulphonate ligand through O-H···O hydrogen bonds to generate a tightly-held three-dimensional network, Fig. 2 and Table 2.

Experimental
Zinc nitrate (1 mmol) and 2,4-dihydroxyl-1,5-benzenedisulfonic acid (1 mmol) were dissolved in water (10 ml). The solution was filtered and then set aside for the formation of crystals. Colourless crystals were obtained after a week.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H = 0.93 Å) and were included in the refinement in the riding model approximation, with U(H) = 1.2U eq (C). The hydroxyl H and water H atoms were located in a difference Fourier map, and were refined with the distance restraints O-H = 0.84±0.01 Å and H···H = 1.37±0.01 Å; U(H) = 1.5U eq (O).

sup-3
Acta Cryst. (2012). E68, m492-m493 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.