Poly[[diaquabis(μ4-benzene-1,3-dicarboxylato)(μ3-benzene-1,3-dicarboxylato)dierbium(III)] monohydrate]

The title erbium coordination polymer, {[Er2(C8H4O4)3(H2O)2]·H2O} n , was obtained by the hydrothermal reaction of ErCl3 with benzene-1,3-dicarboxylic acid (1,3-BDC) in alkaline aqueous solution. Each of the two crystallographically independent ErIII ions is seven-coordinate and has a distorted pentagonal–bipyramidal geometry. One Er centre is coordinated by seven O atoms from six 1,3-BDC ligands and the other Er centre is surrounded by five O atoms from five 1,3-BDC ligands and two water molecules. The bridging ligands, which have two different coordination modes, link the metal centres to form a three-dimensional network with channels parallel to the b axis in which solvent water molecules are located. The crystal structure is stabilized by intra- and intermolecular O—H...O hydrogen-bonding interactions. One benzene ring and the solvent water molecule are independently disordered over two positions each, with occupancy ratios of 0.595 (2):0.405 (2) and 0.661 (1):0.339 (1), respectively.