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)]center dot 2H(2)O}(n) (Ln = Eu (1), Sm (2), Nd (3), and Pr (4), H(2)bcpp = 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 bcpp(2-) presents two kinds of conformations, trans-gauche and trans-trans, and forms a complicated 3D architecture by sharing Ln(III) ions. Topology analysis shows that polymers 1-4 all have a binodal (3,5)connected (4.6.8)(4.6(5).8(3).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.