Syntheses, Structures and Luminescent Properties of Eu- and Tb-MOFs with 3,5-Pyridinedicarboxylate and 1,2-Benzenedicarboxylate

Two lanthanide-based MOFs (Ln-MOFs) were synthesized by reaction of Eu(III) or Tb(III) perchlorates with mixed dicarboxylates of 3,5-pdc and 1,2-bdc (3,5-H₂pdc = 3,5-pyridinedicarboxylic acid; 1,2-H₂bdc = 1,2-benzenedicarboxylic acid) by hydrothermal method. The chemical formulas of the two complexes were [Eu₂(3,5-pdc)(1,2-bdc)₂(H₂O)₄]_n (1) and {[Tb₂(3,5-pdc)(1,2-bdc)₂(H₂O)₄]·2H₂O}_n (2). IR spectra and element analyses were tested to characterize the two compounds. The crystal structures were determined by X-ray single crystal diffraction. MOF 1 was 3D porous network structure but MOF 2 was 2D layered structure. The two MOFs emitted the characteristic fluorescence of Eu(III) or Tb(III) ion with the excitations of UV-rays. Their lifetimes of excited states for Eu(III) (⁵D₀) and Tb(III) (⁵D₄) were 0.31 and 0.82 ms. The absolute quantum yields (Ф_a) of MOF1 and 2 were also tested and the Ф_a(1) (λ_ex = 320 nm) and Ф_a(2) (λ_ex = 296 nm) were 15% and 48%, respectively.