Poly[[octaaqua-μ₄-(benzene-1,2,4,5-tetra­carboxyl­ato)-dicobalt(II)] octa­hydrate]

The title polymeric coordination compound, {[Co₂(C₁₀H₂O₈)(H₂O)₈]·8H₂O}_n, was obtained by slow diffusion of a dilute aqueous solution of CoCl₂ and the sodium salt of benzene-1,2,4,5-tetracarboxylic acid (H₄btec) through an agar–agar gel bridge in a U-shaped tube. The two independent Co²⁺ ions are each situated on an inversion centre and are coordinated in a slightly distorted octa­hedral geometry by four water O atoms and two carboxyl­ate O atoms from two btec⁴⁻ ligands (-1> symmetry), forming a layer parallel to (11-1). This layer can be described as a mol­ecular two-dimensional square grid with the benzene rings at the nodes and the Co^II atoms connecting the nodes. O—H...O hydrogen-bonding interactions involving the coordinating water molecules, the carboxylate O atoms and lattice water molecules lead to the formation of a three-dimensional network.