catena-Poly[[[aqua(7-hydroxy-2H-1-benzopyran-2-one)sodium]-di-μ-aqua] 2-oxo-2H-1-benzopyran-7-olate monohydrate]

The asymmetric unit of the title compound, {[Na(C9H6O3)(H2O)3](C9H5O3)·H2O}n, contains two crystallographically independent Na atoms, two 7-hydroxycoumarin ligands, six coordinated water molecules, two 7-hydroxycoumarin anions and two uncoordinated water molecules. Both Na atoms exhibit a distorted octahedral coordination geometry and are coordinated by five water O atoms and the terminal O atom from a 7-hydroxycoumarin ligand. Four of the water molecules are bridging, whereas the fifth is terminal. Na—O bond distances are in the range 2.288 (2)–2.539 (2) Å. In the chains, extending parallel to [100], adjacent Na atoms are separated by 3.60613 (7) Å. The uncoordinated water molecules and 7-hydroxycoumarin phenolate anions are located between the chains and are hydrogen bonded to the chains.


Comment
It has been suggested that coumarin (1,2-benzopyrone) may be a pro-drug and its major biotransformed product 7-hydroxycoumarin, also known as umbelliferone, is an active drug (Egan et al., 1990). The 7-hydroxycoumarin is also a widely distributed natural product which shows anti-imflammatory activity (Toyama et al., 2009), and the complexes of coumarin with metal have increased bioactivities such as anti-imflammatory activity (Nath et al., 2005). We synthesized the complexe of 7-hydroxycoumarin with sodium for further bioactivities study. This paper is devoted to the crystal structure of the sodium salt of 7-hydroxycoumarin.
The molecular structure of the title compound is shown in Fig. 1. The main moiety of crystal structure is build up of cation chains -(C 18 H 24 Na 2 O 12 ) 2+ n . The polymeric chain contains two independent crystallographic Na centers. Both Na atoms is six-coordinated by five O atoms of water molecules and one O atom of a ligand. Each 7-hydroxycoumarin ligand links Na centers via its O atom of carbonyl group in a chelating manner. Oxygen atoms of two water are bridging atom between two sodium atoms. Na-O bond distances are in the range of 2.288 (2)-2.539 (2)Å. In the chain, two adjacent Na1···Na2 distance of 3.60613 (7)Å. In addition, two 7-hydroxycoumarin anions and two water molecules are hydrogen bonded to the chains.

Experimental
A stoichiometric amount of NaOH (0.25 mmol) and a quantitative amount of 7-hydroxycoumarin (0.5 mmol) were mixed and then dissolved in ethanol (20 ml). The pH value of the solution was about to 6.5. The solution mixture was stirred continuously for 2 h at room temperature and then filtered. Single crystals were obtained by evaporation after one week.

Refinement
Hydrogen atoms of the water molecules were located from a difference map and were refined isotropically. The C-bound H-atoms were positioned geometrically and refined using a riding model: C-H = 0.95Å with U iso (H) = 1.2U eq (C). The

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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.