Poly[[tetraaquabis[μ4-2,2′-(p-phenylenedioxy)diacetato][μ2-2,2′-(p-phenylenedioxy)diacetato]dierbium(III)] hexahydrate]

The asymmetric unit of the title compound, [Er2(C10H8O6)3(H2O)4]·6H2O, comprises one Er3+ ion, one and a half 2,2′-(p-phenylenedioxy)diacetate (hqda) ligands, two coordinated water molecules and three uncoordinated water molecules. The Er3+ 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 Er3+ 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—CH2O—C6H4—OCH2—COO spacers, forming two-dimensional neutral layers. Adjacent layers are linked by O—H...O hydrogen-bonding interactions, forming a three-dimensional supermolecular network