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SYNTHESIS AND CHARACTERIZATION OF CARBOXYLATE COMPLEXES OF LANTHANIDE (III) IONS**

Abstract

Lanthanide (III) complexes possess luminescence properties that make them useful in various applications such as luminescent sensors, time resolved fluoroimmunoassays, and in biological imaging. The luminescence intensity of these metal ions can be enhanced by chelating the metal ions to organic antenna chromophores that are capable of absorbing intensely in the UV region and transfer the energy to the metal ion by what is known as “antenna effect”. In this study, aromatic di- and mono-carboxylate ligands possessing large conjugated systems were used to synthesize the lanthanide ion complexes because these acids absorb strongly in the UV region and pass the energy to the lanthanide ion. The synthesis of the complexes was carried out by reactions of MCl3 ∙ 6H2O (M = Sm, Nd, Tb, Er) with 2, 2’-biquinoline-4-4’-dicarboxylic acid di-potassium salt (K2[C20H12N2O4]) and 2,6 Diphenylisonictonic sodium salt (Na[C18H12O2N]) in water or methanol. The metal chloride and ligand salt in molar ratio of 2:3 for K2[C20H12N2O4] and 1:3 for Na[C18H12O2N] were separately dissolved in the appropriate solvent and then mixed while stirring at room temperature. The reaction resulted in an immediate formation of yellowish-white and brownish powders in high yields respectively. The products were dried at 60oC under vacuum and characterized by FTIR-, UV-Vis-, fluorescence-spectroscopy and elemental analysis. Both elemental analysis and FTIR-spectral results suggest the formation of M2[C20H10N2O4]3.4H2O an eight coordinate and M[C18H12O2N]3.3H2O a nine coordinate complexes. Most of the products formed are slightly soluble in DMSO and CH3CN but insoluble in water and other organic solvents.

Acknowledgements

We thank Dr. John Bacsa, Emory X-ray Crystallography Facility for the X-ray structural analysis and acknowledge the use of the Rigaku Synery diffractometer supported by the National Science Foundation under grant CHE-1626172. We also acknowledge Berry College and the Richards Undergraduate Research Grant.

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