Five sra Topological Ln(III)-MOFs Based on Novel Metal-Carboxylate/Cl Chain: Structure, Near-Infrared Luminescence and Magnetic Properties

Five isostructural three-dimensional (3D) lanthanide (Ln) frameworks [LnCl­(bpdc)­(DMF)] (Ln = La (1), Ce (2), Pr (3), Nd (4), and Sm (5), H2bpdc = 4,4′-biphenyl-dicarboxylic acid, DMF = N,N-dimethylformamide) have been solvothermally synthesized and characterized by TGA, IR, and X-ray single crystal diffraction. The frameworks contain unusual Ln-carboxylate/Cl chains, and which are extended by bpdc2‑ linkers to form 4-connected sra networks with 1D rhombic channels. The effect of lanthanide contraction induces the decreases of average Ln–O and Ln–Cl distances from La to Sm. 4 exhibits strong characteristic luminescence of Nd3+ ions in the near-infrared (NIR) region, resulting from the sensitization of bpdc2–. 3 displays weak NIR emission due to the inefficient sensitization of Pr3+ ions. The depopulation of the Stark levels and possible antiferromagnetic interactions within the Ln-carboxylate/Cl chains lead to the continuous decreases of χMT for 2–4 along the decreasing temperatures.