Synthesis and Luminescence Properties of Lanthanide Complexes of a Novel Polyaminopolycarboxylate Ligand

Abstract

A novel polyaminopolycarboxylate ligand with many coordination sites, N,N,<TEX>$N^1,N^1,N^2,N^2$</TEX>-[( 2,4,6-tri(aminomethyl)-pyridine]hexakis(acetic acid) (TPHA), was designed and synthesized and its lanthanide complexes <TEX>$Na_6Tb_2$</TEX>(TPHA)<TEX>$Cl_6{\cdot}14H_2O$</TEX>, <TEX>$Na_6Eu_2$</TEX>(TPHA)<TEX>$Cl_6{\cdot}8H_2O$</TEX>, <TEX>$Na_6Gd_2$</TEX>(TPHA)<TEX>$Cl_6{\cdot}11H_2O$</TEX> and <TEX>$Na_6Sm_2$</TEX>(TPHA)<TEX>$Cl_6{\cdot}9H_2O$</TEX> were successfully prepared. The ligand and the complexes were characterized by elemental analysis, IR, mass, NMR and TG-DTA. The TG-DTA studies indicated that the complexes had a high thermal stability, whose initial decomposition temperature was over <TEX>$270^{\circ}C$</TEX>. The luminescence properties of the complexes in solid state were investigated and the results suggested that <TEX>$Tb^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions could be sensitized efficiently by the ligand, especially the Tb(III) complex displayed a very strong luminescence intensity (> 10000) and only displayed characteristic metal-centered luminescence. Also, the correlative comparison between the structure of ligand and luminescence properties showed how the number of the coordination atoms of ligand can be a prominent factor in the effectiveness of ligand-to-metal energy transfer.