Redetermination of cis-diaquadiglycolatozinc(II)

The title complex, [Zn(C2H3O3)2(H2O)2], was prepared and the crystal structure determined as part of a 67Zn solid state nuclear magnetic resonance study. In the title complex, the Zn atom has a disorted octahedral coordination comprising two bidentate glycolate ligands and two water molecules. The water molecules are cis to each other; one is trans to a carboxylate O atom and the other trans to an alcohol O atom. The crystal structure has an extensive O—H⋯O hydrogen-bond network.

The title complex, [Zn(C 2 H 3 O 3 ) 2 (H 2 O) 2 ], was prepared and the crystal structure determined as part of a 67 Zn solid state nuclear magnetic resonance study. In the title complex, the Zn atom has a disorted octahedral coordination comprising two bidentate glycolate ligands and two water molecules. The water molecules are cis to each other; one is trans to a carboxylate O atom and the other trans to an alcohol O atom. The crystal structure has an extensive O-HÁ Á ÁO hydrogenbond network.

Related literature
The crystal structure of the title complex was first reported by Fischinger & Webb (1969). For bond-length data, see: Allen et al. (1987).
determined. The structure of this complex was first report by Fischinger & Webb (1969) but no fractional crystal coordinates were reported.
The molecular structure of (I) is illustrated in Fig. 1. The zinc atom has a distorted octahedral coordination sphere composed of two bidentate gylcolato ligands and two water molecules. The water molecules are cis to each other; one (O1) is trans to a carboxylate O-atom (O4), and the other, (O2), is trans to an alcohol O-atom (O6). The bond distances and angles are normal for zinc(II) complexes (Allen et al., 1987) In the crystal structure of (I) there in an extensive O-H···O hydrogen bonding network ( Table 1). The two water molecules (O1 and O2) bond to the two oxygens (O4 and O5) of a carboxylate group related by the c-glide. The two alcohol groups (O3 and O6) form hydrogen bonds with the other carboxylate group (atoms O7 and O8) translated by one unit cell along the b axis. The carbonyl oxygen O8 of this ligand also makes a two dimensional hydrogen bonded network with one of the waters (O1) around the inversion center. The other water molecule, (O2), forms an H-bond with a carbonyl oxygen (O5) related by the 2-fold screw axis.

Experimental
Glycolic acid (100 mg, 3 mmol), purchased from Sigma-Aldrich (99%), was dissolved in 5 ml of deionized water. Basic zinc carbonate (80 mg, 2 mmol) was added and the mixture stirred for 10 minutes while heating to ca. 60°C. The resulting mixture was filtered, and the filtrate left to stand at room temperature until large needle-like crystals grew by slow evaporation of the water.