Enhancing the Fe 3+ Sensing Sensitivity by Energy Transfer and Phase Transformation in a Bimetallic Lanthanide Metal‐Organic Framework

Two novel lanthanide metal‐organic frameworks (LnMOFs), {[Me 2 NH 2 ] 2 [Eu 4 (L) 5 (SO 4 ) 2 ]⋅H 2 O} n (EuMOF‐ 1 ) and {[Me 2 NH 2 ][Tb(L)(SO 4 )(H 2 O)]} 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 Eu x Tb 1− 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 Fe 3+ ion, the K SV constant was increased by 36.6% from monometallic EuMOF‐ 1 to bimetallic Eu 0.6 Tb 0.4 MOF. Additionally, the exclusive sensing and its enhancing mechanism towards Fe 3+ are further discussed. This work would establish a new strategy for enhancing the sensing performance of luminescent lanthanide MOFs.