Anionic lanthanide metal–organic frameworks with magnetic, fluorescence, and proton conductivity properties and selective adsorption of a cationic dye

Two novel microporous anionic lanthanide metal-organic frameworks (Ln-MOFs), namely {[(CH₃)₂NH₂][Ln(bptc)]·2H₂O}_n (Ln = Gd (1) and Dy (2), H₄bptc = biphenyl-3,3',5,5'-tetracarboxylic acid) with a new 4,8-connected topology have been synthesized and structurally characterized. Ln-MOF 1 shows a significant magnetocaloric effect with -ΔSmaxm = 26.37 J kg^-1 K^-1 at 2 K for ΔH = 7 T, and a high proton conductivity of 1.02 × 10^-4 S cm^-1 at 323 K and 90% RH. Moreover, Ln-MOF 1 shows specific selective adsorption of the cationic dye Rhodamine B. Ln-MOF 2 exhibits field-induced slow magnetic relaxation with an energy barrier (U_eff) of 48.19 K, characteristic emission of Dy³⁺, and selective adsorption of Rhodamine B. Therefore, 2 is a multifunctional Ln-MOF with magnetic, fluorescence and selective adsorption properties.