Hexaaqua(5,7-dihydroxy-4-oxo-2-phenyl-4H-chromene-8-sulfonato)calcium(II) 5,7-dihydroxy-4-oxo-2-phenyl-4H-chromene-8-sulfonate trihydrate

In the title compound, [Ca(C15H9O7S)(H2O)6](C15H9O7S)·3H2O, the Ca centre has a distorted decahedral geometry, coordinated by six O atoms from water molecules and one sulfonate O atom. The crystal structure is stabilized by aromatic π–π interactions, with centroid–centroid distances of 3.765 (5) and 3.896 (5) Å between the phenyl ring and the benzene ring of the chromene unit of neighbouring molecules. In addition, the stacked molecules exhibit inter- and intramolecular O—H⋯O hydrogen bonds, including the uncoordinated water molecules.

In the title compound, [Ca(C 15 H 9 O 7 S)(H 2 O) 6 ](C 15 H 9 O 7 S)Á-3H 2 O, the Ca centre has a distorted decahedral geometry, coordinated by six O atoms from water molecules and one sulfonate O atom. The crystal structure is stabilized by aromaticinteractions, with centroid-centroid distances of 3.765 (5) and 3.896 (5) Å between the phenyl ring and the benzene ring of the chromene unit of neighbouring molecules. In addition, the stacked molecules exhibit inter-and intramolecular O-HÁ Á ÁO hydrogen bonds, including the uncoordinated water molecules.

Experimental
Crystal data [Ca(C 15 Table 1 Hydrogen-bond geometry (Å , ). complexes. On the other hand, the weak coordination nature of SO3makes its coordination mode very flexible and sensitive to the chemical environment (Cote & Shimizu, 2003). Here we report the crystal structure of the title compound ( Fig. 1).
Experimental 5,7-Dihydroxyflavone (chrysin, 1.0 g, 3.9 mmol) was added slowly to concentrated sulfuric acid (6 ml) with stirring. The reaction was maintained at room temperature for 12 h. Then, it was poured into NaCl saturated aqueous solution (50 ml) and a yellow precipitate appeared. After 5 h, the precipitate was filtered and washed with NaCl saturated aqueous solution until the pH value of the filtrate was 7. It was dissolved in water (50 ml), and mixed with saturated CaCl 2 solution (10 ml).
(I) was obtained after 24 h. It was recrystallized from an ethanol-water (1:1 v/v) solution. Colorless sheet-shaped crystals suitable for X-ray analysis were obtained by slow evaporation of the solvent for about 3 d at room temperature (yield 78%).

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 > 2sigma(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.