catena-Poly[[bis(μ-2-sulfonatobenzoato)bis[triaquagadolinium(III)]]-μ-oxalato].

The asymmetric unit of the title coordination polymer, [Gd2(C7H4O5S)2(C2O4)(H2O)6]n or [Gd(2-SB)(ox)0.5(H2O)3]2n (2-SB is 2-sulfonato­benzoate and ox is oxalate), (I), consists of one GdIII ion, one 2-SB anion, three coordinated water mol­ecules and one half of an ox ligand. The ox ligand is located on a crystallographic inversion centre. The GdIII centre shows a distorted tricapped trigonal–prismatic coordination formed by nine O atoms from two 2-SB anions, one ox ligand and three coordinated water mol­ecules. The carboxylate and sulfonate groups of the 2-SB anions adopt μ2-η1:η2 and μ1-η0:η0:η1 coordination modes to link two GdIII ions, generating a centrosymmetric binuclear [Gd2(2-SB)2(H2O)6]2− subunit. The ox ligand acts as a bridge, linking the binuclear [Gd2(2-SB)2(H2O)6]2− subunits into a one-dimensional chain structure parallel to the b axis. Furthermore, extensive O—H⋯O hydrogen bonds connect the chains into a three-dimensional supra­molecular architecture.