Triaqua(7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylato-κ3 O 2,O 3,O 7)cobalt(II) monohydrate

The title complex, [Co(C8H8O5)(H2O)3]·H2O, was synthesized by reaction of cobalt acetate with 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride (norcantharidin) in aqueous solution. In the molecule, the CoII atom is six-coordinated in a distorted octahedral environment, binding to the bridging O atom of the bicycloheptane unit, to two O atoms from monodentate carboxylate groups and to three water O atoms. The crystal structure is stabilized by several O—H⋯O hydrogen-bonding interactions involving both the coordinated and uncoordinated water molecules as donors and the carboxylate O atoms of neighbouring molecules as acceptors.

The title complex, [Co(C 8 H 8 O 5 )(H 2 O) 3 ]ÁH 2 O, was synthesized by reaction of cobalt acetate with 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride (norcantharidin) in aqueous solution. In the molecule, the Co II atom is six-coordinated in a distorted octahedral environment, binding to the bridging O atom of the bicycloheptane unit, to two O atoms from monodentate carboxylate groups and to three water O atoms. The crystal structure is stabilized by several O-HÁ Á ÁO hydrogen-bonding interactions involving both the coordinated and uncoordinated water molecules as donors and the carboxylate O atoms of neighbouring molecules as acceptors.
A manganese complex of dimethylcantharate was reported recently (Wang et al., 2010) and a similar cobalt complex of dimethylcantharate (Kaplonek et al., 1994) has also been reported.
The molecular structure of the title complex is shown in Fig. 1. The cobalt(II) atom is six-coordinated in a distorted octahedral coordination mode, binding to the bridging O atom of the bicycloheptane unit, to two O atoms from corresponding carboxylate groups and to three O atoms from water. The crystal structure is stabilized by several O-H···O hydrogenbonding interactions involving both the coordinated and uncoordinated water molecules as donors and the carboxylate O atoms of neighbouring molecules as acceptors.

Experimental
An ethanol solution containing 0.5 mmol salicylic acid was dropwisely added into 0.5 mmol aqueous cobalt acetate solution.
After stirring for one hour, an aqueous solution containing 0.5 mmol norcantharidin was dropwisely added into the mixture.
Two hours later, the solution was filtered and after 2 weeks, crystals with suitable size for single-crystal X-ray diffraction were obtained.