Poly[[tetraaquabis(5-carboxypyridine-2-carboxylato-κ2 N, O)bis(μ4-pyridine-2,5-dicarboxylato-κ5 N, O: O: O′: O′′)dilanthanum(III)] dihydrate].

The title compound, {[La2(C7H4NO4)2(C7H3NO4)2(H2O)4]·2H2O} n, was prepared by a hydrothermal reaction at 433 K. The asymmetric unit contains two LaIII ions. Each LaIII ion is nine-coordinated in a slightly distorted tricapped trigonal–prismatic coordination geometry, formed by two N atoms from 5-carboxypyridine-2-carboxylate (Hpydc) and pyridine-2,5-dicarboxylate (pydc) ligands, five O atoms from carboxylate groups of one Hpydc and four pydc ligands, and two water molecules. Adjacent LaIII ions are linked together through single bridging carboxylate O atoms and carboxylate groups in a syn– anti mode, forming a two-dimensional layered polymeric structure. Extensive O—H...O hydrogen bonding connects adjacent layers into an infinite three-dimensional supramolecular network structure. The crystal studied was an inversion twin. [ABSTRACT FROM AUTHOR]