A novel cadmiuin(II) coordination polymer, poly[[[bis(4,4′bipyridine) cadmium(II)]-μ3-4,4′-dicarboxybiphenyl-3,3′-dicarboxylato] 0.35-hydrate], {[Cd(C16H8O8)(C 10H8N2)2]middot;-0.35H 2O}n, was obtained by reaction of Cd(CH 3COO)2·3H2O, 4,4′-bipyridine (4,4′-bpy) and biphenyl-3,3′,4,4′-tetracarboxylic acid (H 4L) under hydrothermal conditions. Each CdII atom lies at the centre of a distorted octahedron, coordinated by four O atoms from three H2L2- ligands and N atoms from two monodentate 4,4′-bpy ligands. Each H2L2- ligand coordinates to three CdII atoms through two carboxylate groups, one acting as a bridging bidentate ligand and the other in a chelating bidentate fashion. Two Cd atoms, two H2L2- anions and four 4,4′-bpy ligands form a ring dimer node, which links into an extended broad zonal one-dimensional chain along the c axis. © 2005 International Union of Crystallography.