Structures, luminescent and magnetic properties of six lanthanide-organic frameworks: Observation of slow magnetic relaxation behavior in the Dy III compound

摘要

Six novel three-dimensional (3D) lanthanide metal-organic frameworks (LnMOFs), {[Ln_2(ispc)_3(H_2O)_3] ·mH_2O}_n (Ln = Pr (1, m = 5); Eu (2, m = 5); Gd (3, m = 4); Tb (4, m = 5); Dy (5, m = 5) and Ho (6, m = 4)), ispc = 3-(4-carboxyphenylsulfonyloxy)-4-methoxybenzoic anion) have been synthesized under hydrothermal conditions. Single crystal X-ray diffraction revealed they are isostructural and crystallize in the triclinic crystal system, space group P1. The investigations on luminescent properties and lifetimes of 2 (Eu ~(III)), 4 (Tb~(III)), and 5 (Dy~(III)) exhibit characteristic emissions of Eu~(III), Tb~(III) and Dy ~(III) ions and the corresponding luminescent lifetimes are 0.14 ms, 9.93 μs and 1.25 ms, respectively. The different luminescent intensities and lifetimes among them were further discussed. Furthermore, magnetic studies of 1-6 reveal that 3-6 exhibit ferromagnetic coupling, and 5 (Dy~(III)) exhibits remarkably slow magnetic relaxation behavior with the energy barrier ΔE/k_B = 49.2 K.