Construction of Lanthanide–Organic Frameworks from the Flexible Bifunctional Ligand 1,3-Bis(2-cyano-4-pyridyl)propane

The solvothermal reactions of the bifunctional flexible ligand 1,3-bis(2-cyano-4-pyridyl)propane with lanthanide salts via an in situ ligand transformation reaction afforded four novel isostructural lanthanide metal–organic frameworks, formulated as {(NH4)[Ln(bcpp)2]·2H2O}n (Ln = Eu (1), Sm (2), Nd (3), and Pr (4), H2bcpp = 1,3-bis(2-carboxyl-4-pyridyl)propane). Polymers 1–4 were characterised by elemental analyses, IR spectroscopy, and single-crystal and powder X-ray diffraction. The results reveal that the four polymers are isostructural. In the molecular structures of 1–4, the bifunctional flexible ligand bcpp2– presents two kinds of conformations, trans–gauche and trans–trans, and forms a complicated 3D architecture by sharing LnIII ions. Topology analysis shows that polymers 1–4 all have a binodal (3,5)-connected (4·6·8)(4·65·83·10) topology with alternately left- and right-handed helical chains. Moreover, polymers 1–4 show similar thermal behaviour and 1 exhibits an intense characteristic red europium emission.