Rare earth(III) compounds with (R)-(+)-2-pyrrolidone-5-carboxylates (PCA): preparation and spectroscopic studies

Compounds between (R)-(+)-2-pyrrolidone-5-carboxylate (PCA) and rare earths are interesting due to the possible presence of a polarized luminescence character attributed to the chiral center. The salts were obtained by reaction between basic carbonates of rare earths with the ligand. CHN microanalysis, EDTA titration and thermogravimetry suggest the following general formula Ln(PCA)3·2H2O (Ln=La, Ce, Nd, Sm, Eu, Tb, and Ho). The infrared (IR) spectra of the compounds when compared with the free ligand show the νCO ring band at 1647 cm-1 is shifted to 1587 cm-1 and νasCO ring band at 1719 cm-1 shifted to 1676 cm-1. The νsCO bands due to the carboxylate anion appeared at 1427 cm-1. These results show that the ligand is bidentate indicating an eight-coordination number. The photophysical properties were analyzed from the emission and absorption spectra. The compounds with Eu(III) and Tb(III) are luminescent, upon UV excitation, and present low symmetry around the rare earth ion