catena-Poly[[diaquacopper(II)]-μ-7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylato]

In the crystal structure of the title compound, [Cu(C8H8O5)(H2O)2]n, the Cu(II) cation is in a Jahn–Teller distorted six-coordination by two O atoms from water molecules, by the bridging O atom from the bicyclo moiety, by two carboxylate O atoms from two different carboxylate groups and by one carboxylate O atom from a symmetry-related bridging ligand.The polymeric structure is made up from double-strands propagating parallel to the c axis that are held together via intermolecular O—H⋯O hydrogen bonds.

In the crystal structure of the title compound, [Cu(C 8 H 8 O 5 )-(H 2 O) 2 ] n , the Cu(II) cation is in a Jahn-Teller distorted sixcoordination by two O atoms from water molecules, by the bridging O atom from the bicyclo moiety, by two carboxylate O atoms from two different carboxylate groups and by one carboxylate O atom from a symmetry-related bridging ligand.The polymeric structure is made up from doublestrands propagating parallel to the c axis that are held together via intermolecular O-HÁ Á ÁO hydrogen bonds.

Related literature
For related literature, see: Yin et al. (2003).

catena-Poly[[diaquacopper(II)]-µ-7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylato]
Yun-Yun Wang, Rui-Ding Hu and Yan-Jun Wang S1. Comment 7-Oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride (norcantharidin), a traditional Chinese drug, has great anti-cancer activity. It has been widely used as an anticancer drug to treat hepatoma, lung cancer, esophagus cancer and gastric cancer for a long time. Copper is an essential microelement in human body and it exists in the form of copper proteins in animal bodies. Copper coordination compounds have strong bioactivity and various structures, therefore people pay more attention to them and have synthesized some complexes that have pronounced anticancer activity, bactericidal activity, anti-proliferative effect in recent years (Yin et al., 2003). In order to prepare compounds with pronounced anti-cancer activity, we synthesized Cu II complex of norcantharidin, whose anti-cancer activity test is being carried out.
In the title compound, each Cu II ion is six-coordinated by two oxygen atoms from water, one bridge oxygen, two carboxylate oxygen atoms in two different carboxylate groups and one carboxylate oxygen atom in another asymmetric unit. O4, O5, O2W and O1W lie in the equatorial plane with the torsion angle -1.004 (62)°. Carboxylate oxygen atom O2 and O3 from another bridge ligand unit are in the axial positions. The bond angle of O2-Cu1-O3 is 171.256 (73)°, so it forms a distorted octahedral. Owing to the binding of the bridge oxygen atom with Cu, two six-membered rings (Cu1-O5-C4-C5-C8-O4 and Cu1-O2-C7-C6-C1-O5) are created. In addition, a seven-membered ring (Cu1-O4 -C8-C5-C6-C7-O2) is formed because of the coordination of carboxylate oxygen atoms O2 and O4. What's more, intermolecular hydrogen bonds of the complex make the compound more stable.

S2. Experimental
A mixture of norcantharidin and CuCl 2. 2H 2 O was dissolved in 20 mL absolute ethyl alcohol and stirred for 4 h at room temperature and then refluxed for 2 h at 333 K. The blue solution was filtered and after 2 weeks block green single crystals were obtained.

S3. Refinement
The H atoms bonded to C atoms were positioned geometrically and refined using a riding model [aliphatic C-H = 0.97 (2)   A view of the molecule of (I) showing the atom-labelling scheme with displacement ellipsoids drawn at the 30% probability.

catena-Poly[[diaquacopper(II)]-µ-7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylato]
Crystal data [Cu(C 8  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.38 e Å −3 Absolute structure: Flack (1983), 857 Freidel pairs Absolute structure parameter: 0.001 (16) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq