Combining coordination and chelation moieties to engineer a new linker for lanthanide coordination chemistry

Abstract

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 the metal–organic networks of type 1 and type 2 compounds exhibit distinct decomposition patterns, and the photoluminescent properties of 3 were also examined, revealing efficient ligand based sensitization and characteristic emission bands for Eu(III).