Construction of a series of lanthanide metal-organic frameworks: synthesis, structure, luminescence and white light emission

A series of new lanthanide metal-organic frameworks (Ln-MOFs) [Ln(2)(L)(3)(H2O)(4)]center dot 2H(2)O (1) (Ln = Eu, Tb, Gd), and [Gd-2(H2O)(4)(L)(C2O4)(2)]center dot 3H(2)O (2) were synthesized based on 4-hydroxypyridine-2,6-dicarboxylic acid (H2L) under hydrothermal conditions. 1 exhibits isomorphous 2D wave-like networks constructed by paddle-wheel [Ln(L)(3)] units and LnO(4)(H2O)(4) polyhedra. 2 shows a (4,4)-connected 3D framework with a Schlafli symbol of 6(6). Oxalic acid in the resulting framework of 2 is formed in situ under hydrothermal conditions. Luminescence studies indicate that 1-Eu and 1-Tb show characteristic red and green emissions of the corresponding Ln(3+) ions, respectively, while 1-Gd and 2 exhibit blue emission arising from the H2L ligand. Then, by adjusting the co-doping ratio of three different Ln(3+) ions into the same framework as that of 1, a novel doped Ln-MOF, [(Eu0.0073Tb0.0007Gd0.992)(2)(H2O)(4)(L)(3)]center dot 2H(2)O (3), is successfully designed and synthesized, which shows white light emission upon excitation at 340 nm and its emission can also be switched between different colors. In addition, 1-Gd shows weak ferromagnetic interactions.