Hydrothermal Syntheses, Crystal Structures, and Magnetic Properties of a Series of Unique Three-Dimensional Lanthanide−Organic Coordination Frameworks with a N-Protonated 2,6-Dihydroxypyridine-4-Carboxylate Tecton.

A series of novel three-dimensional (3-D) lanthanide−organic frameworks (LnOFs), with the general formula [Ln2(H-L)3(H2O)4]∞(Ln = DyIIIfor 1, GdIIIfor 2, TbIIIfor 3, EuIIIfor 4, and HoIIIfor 5; H-L= N-protonated 2,6-dihydroxypyridine-4-carboxylate), have been synthesized under hydrothermal conditions. X-ray structural analysis reveals that complexes 1−5are isostructural and show the unique 3-D coordination framework with a trinodal (3,4,5)-connected (4.62)(42.6)(42.84)(43.6.86)(42.65.83) net topology, in which the H-Lligands adopt different μ4- and μ3-bridging forms. Variable-temperature magnetic susceptibility studies reveal that complexes 1−3and 5show ferromagnetic behaviors. Notably, complex 1(DyIII) is the first instance leading to ferromagnetic coupling for a lanthanide ion through a spin-polarization mechanism. The alternating current (ac) signal observed for 1and 5should originate from the long-range ferromagnetic ordering, or it could reflect the splitting of the Jmultiplet for DyIIIor HoIIIunder a low symmetry crystal field, which would give rise to slow relaxation of the magnetization. Additionally, thermal stability of these crystalline materials has also been investigated by thermogravimetric analysis of mass loss. [ABSTRACT FROM AUTHOR]