Two 3D Isostructural Ln(III)-MOFs: Displaying the Slow Magnetic Relaxation and Luminescence Properties in Detection of Nitrobenzene and Cr₂O₇^2–

Two new three-dimensional isostructural lanthanide metal–organic frameworks (Ln­(III)-MOFs), [LnL­(H₂O)₃]·3H₂O·0.75DMF (1-Ln; Ln = Dy­(III) and Eu­(III) ions, H₃L = biphenyl-3′-nitro-3,4′,5-tricarboxylic acid, DMF = N,N′-dimethylformamide), were synthesized and characterized. The appearance of temperature-dependent out-of-phase (χ″_M) signal reveals that complex 1-Dy displays slow magnetic relaxation behavior with the energy barrier (ΔU_eff) of 57 K and a pre-exponential factor (τ₀) of 3.89 × 10^–8 s at 1200 Oe direct current field. The luminescence explorations demonstrated that 1-Eu exhibits high quenching efficiency and low detection limit for sensing nitrobenzene and Cr₂O₇^2–. Meanwhile, the fluorescence intensity of the quenched 1-Eu samples will be resumed after washing with DMF or water, indicating that 1-Eu may be used as a highly selective and recyclable luminescence sensing material for sensing nitrobenzene and Cr₂O₇^2– anion.