Combining Coordination and Chelation Moieties to Engineer a New Linker for Lanthanide Coordination Chemistry

Organic linkers play a crucial role in constructing lanthanide (Ln) coordination polymers (CPs), influencing structural topologies and physicochemical properties. Herein, we introduce 6-oxo-1,6-dihydro-2,5-pyridinedicarboxylic acid (2,5-H3PODC) as a new ligand for constructing lanthanide coordination polymers that integrates the structural features of terephthalic acid with the chelation capabilities of pyridinone-based functional groups. Six lanthanide-based coordination polymers were synthesized with 2,5-H3PODC, forming two types of CPs - type 1: [Ln(HPODC)(Ox)0.5(H2O)2] (where (Ox) = oxalic acid and Ln = Pr3+ (1), Nd3+ (2)) and type 2: [Ln(H2PODC)(HPODC)(H2O)] (Ln = Eu3+ (3), Gd3+ (4), Dy3+ (5), Er3+ (6). All compounds were structurally characterized by single-crystal and powder X-ray diffraction, and both compound types are 2D ladder-like networks with cem topologies where the trivalent metal centers are bridged via HPODC2- and Ox2- ligands in type 1 structures and H2PODC- and HPODC2- linkers in type 2 structures. Thermogravimetric analysis (TGA) demonstrated that compound 2 exhibits stability up to 310 °C, while compound 4 exhibits stability up to 325 °C, and the photoluminescent properties of 3 were also examined, revealing efficient ligand based sensitization and characteristic emission bands for Eu(III).