Porous Lanthanide Metal-Organic Frameworks Using Pyridine-2,4-dicarboxylic Acid as a Linker: Structure, Gas...

Two types of new lanthanide coordination networks, [Ln₃(pdc)₄(Hpdc)(H₂O)₃]·8H₂O [H₂pdc = pyridine-2,4-dicarboxylic acid; Ln = Ce (1), Pr (2), Sm (3), Eu (4); type A) and [Tb₅(pdc)₄(Hpdc)]·3H₂O (type B), have been synthesized using a hydrothermal synthetic method. The former type A compound has an unfamiliar architecture, even basically comprised of primitive cubic (pcu) topology, and demonstrate porous gas adsorption behavior, giving several hundreds of square meters per gram surface areas after evacuation of the water molecules, while the latter type B compound does not show any porous properties. Most interestingly, the solvothermal synthetic method using N,N-dimethylformamide (DMF) as a solvent gives compounds that crystallize in a structure analogous to that of type A for Ln = La-Ho, probably formulated as [Ln₃(pdc)₄(Hpdc)·(DMF)]·nDMF. These compounds also exhibit large surface areas after evacuation of the DMF molecules and also moderate amounts of hydrogen gas uptake at 77 K. The luminescence properties were investigated for Eu and Tb analogues at elevated temperatures, at which an unusual increase in the emission intensity was observed upon the release of solvents, and discussed based on their porous structure.