Diaquabis(2-oxo-2H-chromene-3-carboxylato)zinc(II)

In the title compound, [Zn(C10H5O4)2(H2O)2], the ZnII atom lies on a crystallographic inversion center and is six-coordinated by two O atoms from water molecules in the axial positions and four O atoms from two deprotonated coumarin-3-carboxylate ligands in the equatorial plane, forming a slightly distorted octahedral coordination geometry. O—H⋯O hydrogen-bonding interactions involving the water molecules form infinite chains parallel to [010].

In the title compound, [Zn(C 10 H 5 O 4 ) 2 (H 2 O) 2 ], the Zn II atom lies on a crystallographic inversion center and is sixcoordinated by two O atoms from water molecules in the axial positions and four O atoms from two deprotonated coumarin-3-carboxylate ligands in the equatorial plane, forming a slightly distorted octahedral coordination geometry. O-HÁ Á ÁO hydrogen-bonding interactions involving the water molecules form infinite chains parallel to [010].

Comment
In the past decades, numerous papers dealing with mononuclear zinc complexes have been published (Chu et al. 2010).
Herein, we report the synthesis and crystal structure of a new mononuclear zinc complex.
In the title compound, [Zn(C 10 H 5 O 4 ) 2 (H 2 O) 2 ], each Zn II atom lies on a crystallographic inversion center and is six-coordinated by two O atoms from water molecules in the axial positions and four O atoms from two deprotonated coumarin-3-carboxylic acid ligands in the equatorial plane, forming an octahedral coordination geometry ( Fig. 1 (Etter, 1990;Bernstein et al., 1995).

Experimental
The title complex was synthesized by carefully layering a solution of ZnSO 4 .7H 2 O (28.8 mg, 0.1 mmol) in ethanol solution (10 ml) on top of a solution of coumarin-3-carboxylic acid (19.0 mg, 0.1 mmol) and LiOH (8.4 mg, 0.2 mmol) in H 2 O (10 ml) in a test-tube. After about one month at room temperature, colorless block-shaped single crystals suitable for X-ray investigation appeared at the boundary between ethanol solution and water with a yield of 27%.

Refinement
The H atoms were placed geometrically (C-H = 0.93 Å) and treated as riding with U iso(H) = 1.2 eq (C) . H atoms of water molecule were located in difference Fourier maps and included in the subsequent refinement using restraints (O-H= 0.85 (1)Å and H···H= 1.40 (2)Å) with U iso (H) = 1.5U eq (O). In the last cycle of refinement they were treated as riding on their parent O atom.

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