Syntheses, structures and photoluminescence of a series of lanthanide-organic frameworks involving in situ ligand formation

A series of lanthanide-organic frameworks with aromatic pyridinecarboxylate ligand, generally formulated as [Ln(PYDC)(C₂O₄)_0.5(H₂O)₂]·H₂O (LnPr(1), Nd(2), Eu(3), Gd(4), Tb(5), Er(6); H₂PYDC3,4-pyridinedicarboxylic acid) have been successfully synthesized and characterized. Their isostructures are built up from one-dimensional (1D) infinite chains cross-linked via the tri-connected PYDC ligands, leading to the two-dimensional (2D) layer structure. The adjacent layers are further extended into three-dimensional (3D) supramolecular frameworks through hydrogen bonding and π-π stacking interactions. Interestingly, the oxalate bridging ligand is believed to form via in situ ligand synthesis through decarboxylation of the organic precursor, H₂PYDC. Complexes 3 and 5 exhibit strong fluorescent emissions in the visible region at room temperature.