Highly Water Stable Lanthanide Metal–Organic Frameworks Constructed from 2,2′-Disulfonyl-4,4′-biphenyldicarboxylic Acid: Syntheses, Structures, and Properties

A series of three-dimensional (3D) lanthanide metal–organic frameworks (LnMOFs), (Me2NH2)[LnL(H2O)] (Ln = Eu (1), Gd (2), Tb (3), Dy (4); H4L = 2,2′-disulfonyl-4,4′-biphenyldicarboxylic acid) have been successfully synthesized from H4L and Ln(NO3)3·6H2O under solvothermal conditions. Single crystal X-ray diffraction (SCXRD) shows that all LnMOFs 1–4 are isomorphous and isostructural with a hepta-coordinated Ln(III) being connected through the carboxylate groups of the L4– ligands, resulting in the formation of an one-dimensional (1D) inorganic rod-like [Ln(−COO)2)]+n chain along the c axis. The infinite 1D chains are further linked by the sulfonate and biphenyl groups, leading to formation of a uninodal 5-connected 3D network with bnn topology. The present LnMOFs are the first example of anionic 3D bnn-net constructed on Ln–O–C rods with channels being filled with (Me2NH2)+ cations. The L4– ligand shows a pentadentate coordination mode with two bound sulfonate groups. All the LnMOFs are insoluble in water and highly stable against moisture. Cation-exchange with Li+, Na+, and K+ ions can be easily performed at room temperature (RT). In addition, LnMOFs 1 and 3 display characteristic photoluminescence of Eu(III) and Tb(III) ions upon excitation at 394 and 353 nm, respectively. The investigation of magnetism demonstrates relatively weak antiferromagnetic interactions between Gd(III) ions (J = −0.0042(5) cm–1) in 2, and between Dy(III) ions (θ = −0.20(2) K) in 4. The proton conductivity of 1 is 4.14 × 10–8 S cm–1 at 95% relative humidity (RH) and 25 °C.