Luminescence properties of isomeric and tautomeric lanthanide pyridinedicarboxylates

The luminescence and PMR spectra of europium salts of six isomers of 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-pyridinedicarboxylic acids (PDA) had been studied. The distribution of the effective charge in the nearest surroundings of the Eu³⁺ ion in these salts was evaluated from Stark splittings of electronic transitions. The values of relative integral intensities of electronic transitions ⁵D₀–⁷F_J (J=0–4) in the luminescence spectra were reported. Compounds investigated were divided into three subgroups taking into account the details of the structure of the ligands and details of the luminescence spectra. The ligand coordination manners as well as the strength of interaction between lanthanide ion and ligands were confirmed by data of the PMR and IR spectroscopy.