Eu(Ⅲ) coordination properties of carboxylic acids and polyfunctional carboxylic acids investigated by Eu(Ⅲ) excitation fluorescence spectroscopy

Abstract

we investigated the coordination properties of Eu(III) ion with organic carboxylic acids using laser induced Eu(III) luminescence methods. The excitation spectra($^7F_0$ $\rightarrow$ $^5D_0$) of Eu(III) complexes to carboxylates (e.g. acetate, benzoate), dicarboxylates(e.g. phthalate, succinate), and polyfunctional carboxylates (e.g. thioglycolate, nicotinate) showed peak maxima at $579.02\,\pm\,0.04$, $579.27\,\pm\,0.03$ and $579.56\,\pm\,0.05$ nm in similar manner corresponding to the formation of $EuL_{2+}$, $EuL_{2^+}$ and $EuL_3$ species (L=carboxylate) with increasing in the ligand-to-metal ratio. The hydration numbers, which are the number of coordinated water molecules, of Eu(III) coordinated to various ligands were obtained form the lifetime measurements of luminescence decay. when one carboxylate complexed with Eu(III), $EuL^{2+}$, hydration number is $7\,\sim\,8$, when two carboxylate complexed with Eu(III), $EuL_{2^+}$, hydration number suggested $6\,\sim\,7$ and $EuL_3$ suggested $4\,\sim\,6$. The complexes formed between many carboxylate ligands, including polyfunctional carboxylate ligands, and Eu(III) gave coordination behaviours that are quite similar to either Eu(III)-acetate or Eu(III)-glutarate systems. However, those polyfunctional ligands that contain "hard" base neutral donors, such as ODA and IMDA, showed greater shift in the peak positions due to the increase in the overall charge on the ligands. By contrast no such effect was shown by the S-ODA having "soft" base donor neutral S group that are known to coordinate poorly with Eu(III) ion and thus showed spectral data that are similar to the Eu(III)-glutarate system.