Abstract
A macrobicyclic cyclen-based ligand containing a geminal bis(phosphinate) N,N'-bridge was synthesized via a Mannich-type reaction. The other two macrocycle amine groups were modified with two acetate pendants, yielding ligand H4L.
The cyclen-bis(phosphinate) intermediate, the ligand salt Na-0.5(H5L) (H3.5L)Cl . 20 H2O and Cu-II complex Li-2[Cu(L)] . 4 H2O were characterized by single-crystal X-ray diffraction. The ligand protonation constants and the stability constants of H4L complexes with Cu(II) and Zn(II) and lanthanide(III) ions were determined by potentiometry.
The ligand protonation constants and the stability constants of H4L complexes with Cu(II) and Zn(II) ions are similar to those of H(4)dota. Conversely, the stabilities of its Ln(III) complexes are similar to 7-10 orders of magnitude lower than those of H(4)dota complexes due to steric restrictions of the methylene-bis(phosphinate) side bridge.
Therefore, these findings indicate that the ligand H4L is suitable for the complexation of transition metal ions.