Crystal structure of poly[[hexa-aqua-tris-(μ-3,6-di-oxo-cyclo-hexa-1,4-diene-1,4-diolato)dierbium(III)] octa-deca-hydrate].

The title lanthanide complex, [Er2(C6H2O4)3(H2O)6]·18H2O, is isostructural with its La, Gd, Yb and Lu analogues. The Er3+ ion, located on a threefold rotation axis, is nine-coordinated in a distorted tricapped trigonal-prismatic geometry, which is completed by six oxygen atoms from three dhbq2- ligands and three oxygen atoms from coordinated water mol-ecules. Each dhbq2- ligand acts in a μ2-bis-(bidentate) bridging mode to connect two Er3+ ions to form honeycomb (6,3) two-dimensional sheets extending in the ab plane, having an Er⋯Er separation of 8.7261 (2) Å. In the crystal, extensive O-H⋯O hydrogen-bonding inter-actions involving the coordinated water mol-ecules and the water mol-ecules of crystallization, as well as the oxygen atoms of the dhbq2- ligands, generate an overall three-dimensional supra-molecular network.