Lanthanide-oxalate coordination polymers formed by reductive coupling of carbon dioxide to oxalate:: [Ln2(3,5-pdc)2(C2O4)(H2O)4]•2H2O (Ln = Eu, Sm, Ho, Dy; pdc = pyridinedicarboxylate)

Hydrothermal reactions of Ln(NO3)(3.)5H(2)O (Ln = Eu (1), Sm (2), Ho (3), Dy (4)) with 3,5-pyridinedicarboxylic acid (3,5-pdcH(2)) in the presence of 4,4'-bipyridine led to the formation of the 3-D Ln(III)-coordination polymers with a formula unit of [Ln(2)(3,5-pdc)(2)(C2O4)(H2O)(4)]-2H(2)O. These polymers contain a bridging oxalate ligand (C2O42-). On the basis of GC-MS study of the mother liquor remaining after the reaction, we proposed that the C2O42- formation proceeds in three steps: (1). Ln(III)-mediated decarboxylation of 3,5-pdcH2 to give CO2, (2) the reduction of CO2 to CO2.- by the Ln(II) species, and (3) the reductive coupling of the two CO2.- radicals to the oxalate (C2O42-) ion. All polymers were structurally characterized by X-ray diffraction.