Characterization of Polynuclear Complexes Synthesized by Reaction of Lanthanide Oxides with Diethylenetriaminepentaacetic Acid

抄録

Diethylenetriaminepentaacetic acid (H₅dtpa) was allowed to react individually with five lanthanide (Ln) oxides of La₂O₃, Eu₂O₃, Gd₂O₃, Ho₂O₃, and Er₂O₃ at a molar ratio (Ln:H₅dtpa) of 5.1:3.0 in water. The composition of the resulting pentanuclear complexes was estimated on the basis of elemental analysis data. Thus, the chemical reaction has been written as 5 Ln₂O₃ + 6 H₅dtpa → 2 Ln₅(dtpa)₃ + 15 H₂O. The complexes were characterized by Fourier-transform infrared and ultraviolet–visible spectroscopy, X-ray diffraction, and pH measurements. The infrared spectra showed a high probability of a bridged COO^– structure. For three absorption bands in the range of 360–460 cm^-1, the absorption maximum wavenumber was plotted as a function of the effective ionic radius (for a coordination number of 8) of the Ln(III) ions. The linear plots are probably related to Ln–O or Ln–N bonding. As expected, the 4f electrons of the Ln(III) ions did not play a role in the bonding between the central metal and its ligands. The nonparticipation of these electrons is a requirement for MRI contrast-enhancing agents.