Syntheses, structures, and luminescence properties of a new family of three-dimensional open-framework lanthanide coordination polymers

Deprotonation of 2,6-naphthalenedicarboxylic acid (H2NDC) with pyridine followed by its copolymerization with Ln(III) nitrates (where Ln = Eu, Tb, Ce) in DMF at room temperature gave a family of 3-D open-framework lanthanide coordination polymers, formulated as {[Ln2(NDC)3(DMF)4]·mH2O}n (where Ln = Eu, Tb, Ce, 1–3; m=3, 4, 2 for 1–3, respectively, DMF = N,N′-dimethylformamide, and H2NDC = 2,6-naphthalenedicarboxylic acid) on the basis of elemental analysis and single-crystal X-ray diffraction. Compounds 1–3 were isostructural and crystallized in triclinic space group P(-1). In these structures, lanthanide ion dimers were interlinked together by NDC ligands with three different carboxylate coordination modes, to yield scaffolds with 3-D interconnecting tunnels where enclathrated water molecules reside. The results of IR and TG were consistent with the structural determination results. Fluorescence measurements show that 1 and 2 emit strong red and green light, respectively, upon irradiation with UV–vis light source. However, these open frameworks collapsed upon desolvation as evidenced by XRPD investigations, which renders their potential use as fluorescent sensors impossible.