Structure and Solution Behavior of Rare-Earth-Metal Complexes with Tripodal N-Donor Ligands.

We report the synthesis of multiple rare-earth-metal complexes (Ln = Y, La, Ce, Sm, Lu) using tripodal N-donor ligands, which offer the key advantage of featuring only C, H, O and N elements, facilitating incineration to recover the metal. The structural properties of the Ln3+ complexes were investigated by X-ray diffraction, revealing that the ligands form complexes with a 1:1 ligand-to-metal ratio, with two of the three triflate anions coordinated to the metal centers in all cases. The coordination of the third triflate anion was found to be variable, as supported by various NMR spectroscopic investigations. Additionally, transitioning from the previously reported tris(hydrazonyl)thiophosphanyl (SP)-based ligand system to the herein reported tris(2-aminoethyl) amine (tren)-anchored ligand system enhanced flexibility, resulting in improved encapsulation of the lanthanide ions. Competition studies between the two systems revealed selective coordination of the lutetium ion with the more flexible system. Thus, enhancing the flexibility of the ligand systems used for extraction has the potential to increase their efficiency.