The Eu3+ complexes formed with triethylenetetraaminehexaacetic acid (TTHA) were characterized in solution by laser-induced Eu3+ luminescence spectroscopy. Both 2:1 and 1:1 metal:ligand complexes were detected at pH 6.0 depending on the metal- ligand stoichiometry. These two species exhibit distinct excited-state lifetimes of 260 and 1210 μs, respectively. The 2:1 complex coordinates three or four water molecules at each Eu3+ ion while the 1:1 complex has no coordinated water molecules. The 7F0→5D0 excitation spectra revealed multiple isomeric forms for both the 2:1 and 1:1 complexes. Spectra and excited-state lifetimes were taken as a function of pH for a 1:1 metal:ligand solution. As the pH increases, an equilibrium shift from the 2:1 species to the 1:1 species occurs. 1H and 13C spectra of the diamagnetic La3+, Y3+ and Lu3+ complexes were recorded. The La3+ chelate of TTHA exhibits long- lived nitrogen and short-lived oxygen bonds, on the NMR time scale, while the Y3+ and Lu3+ adducts spectra are complicated due to fluctional processes.
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