Synthesis, crystal structure and thermal behavior of two hydrated forms of lanthanide phthalates Ln2(O2+C6H4–CO2)3(H2O) (Ln=Ce, Nd) and Nd2(O2C–C6H4–CO2)3(H2O)3

New hydrated lanthanide phthalates have been hydrothermally prepared with cerium and neodymium in different reaction media involving water or mixed water–ethanol solvent. The monohydrated Ln2(1,2-bdc)3(H2O) (Ln=Ce or Nd) and dihydrated Nd2(1,2-bdc)3(H2O)2 forms have been characterized by single-crystal analysis. Their structures consist of infinite inorganic chains of lanthanide-centered polyhedra linked to each other through the phthalate ligands in order to generate mixed organic–inorganic layered structure. The two hydrated structures differ by the number of terminal water species attached to the lanthanide cations, which induce symmetry change from a triclinic (Nd2(1,2-bdc)3(H2O)2) to an orthorhombic (Nd2(1,2-bdc)3(H2O)2) cell for neodymium whereas the cerium-based phase only exists in the monohydrated form, with two distinct symmetries (orthorhombic or triclinic). Structural comparisons with the other members of the lanthanide phthalate series with identical chemical formula are also discussed. Thermal X-ray diffraction experiment indicates that the transformation from dihydrate form into the monohydrated form does not occur during a heating process.