Poly[[tetra­aqua­bis[μ(4)-2,2′-(p-phenyl­ene­di­oxy)diacetato][μ(2)-2,2′-(p-phenyl­ene­di­oxy)diacetato]dierbium(III)] hexa­hydrate]

The asymmetric unit of the title compound, [Er(2)(C(10)H(8)O(6))(3)(H(2)O)(4)]·6H(2)O, comprises one Er(3+) ion, one and a half 2,2′-(p-phenyl­enedi­oxy)diacetate (hqda) ligands, two coordinated water mol­ecules and three uncoordinated water mol­ecules. The Er(3+) ion is nine-coordinated by seven O atoms from hqda ligands and two O atoms from water mol­ecules. In the title compound, there are two types of crystallographically independent ligands: one with an inversion center in the middle of the ligand is chelating on both ends of the ligand towards each one Er center; the other hqda ligands are bridging-chelating on one side, and bridging on the other end of the ligand. Two adjacent Er(3+) ions are thus chelated and bridged by –COO groups from hqda ligands in three coordination modes (briding–chelating, bridging and chelating). These building blocks are linked by OOC—CH(2)O—C(6)H(4)—OCH(2)—COO spacers, forming two-dimensional neutral layers. Adjacent layers are linked by O—H⋯O hydrogen-bonding inter­actions, forming a three-dimensional supermolecular network.