Enhancing the Fe3+ Sensing Sensitivity by Energy Transfer and Phase Transformation in a Bimetallic Lanthanide Metal-Organic Framework

Two novel lanthanide metal-organic frameworks (LnMOFs), {[Me2NH2](2)[Eu-4(L)(5)(SO4)(2)]center dot H2O}(n) (EuMOF-1) and {[Me2NH2][Tb(L)(SO4)(H2O)]}(n) (TbMOF-2), were successfully synthesized by using protonated pyridine-3,5-dicarboxylic acid sulfate ligand (H(3)L(+)1/2SO(4)(2-)) under identical solvthermal conditions. To our delight, structural analyses indicate that these two LnMOFs (Ln=Eu or Tb) exhibit two extremely different structures in terms of three-dimensional open framework and two-dimensional stacking layered network, which is entirely different from the usual isostructures of LnMOFs (Ln = Eu and Tb). The "Gadolinium break" effect was unprecedentedly observed, leading to phase transformation from EuMOF-1 to TbMOF-2 by gradual decrease of Eu content. A serious of bimetallic EuxTb1-x MOFs (x = 0.8, 0.6, 0.4, 0.2) materials during phase transformation process were achieved. When evaluated as luminescent quenching sensors for Fe3+ ion, the K-SV constant was increased by 36.6% from monometallic EuMOF-1 to bimetallic Eu0.6Tb0.4 MOF. Additionally, the exclusive sensing and its enhancing mechanism towards Fe3+ are further discussed. This work would establish a new strategy for enhancing the sensing performance of luminescent lanthanide MOFs.