RESUMEN
Four tripodal carbamoylmethylphosphine oxide (CMPO)-based ligands are reported here and assessed with regard to lanthanide (Ln) coordination chemistry and selective extraction of lanthanide ions from aqueous solution. Inspired by previous liquid-liquid extraction studies that suggested a preference for terbium(iii), the current work further probes the extraction behavior of a tris-(2-aminoethyl)amine (TREN) capped, ethoxy substituted CMPO ligand with respect to the entire series of lanthanides. Upon confirmation of Tb3+ extraction selectivity versus the whole series, experiments were conducted to assess the effect of increasing the alkyl chain length within the ligand TREN cap, as well as changing the CMPO substituents by replacing the ethoxy groups with more hydrophobic phenyl groups to promote solubility in the organic extraction solvent. Extraction efficiencies remained low for most lanthanides upon increasing the cap size, with %E values consistently around 5%, and a complete loss of Tb3+ preference was noted with a decrease in %E from 18% to 3.5%. For the agent employing the original, smaller TREN cap but with phenyl substituents on the CMPO units, an increase in extraction toward the middle of the row was again observed, albeit modest, with relatively high %E values for both Gd3+ and Tb3+versus the other lanthanides (13 and 11%, respectively). A more dramatic extraction selectivity for the phenyl substituted ligand was achieved upon modification of the ligand to metal ratio, with a 100 : 1 ratio resulting in a near linear decrease in %E from 41% for La3+ to 3.7% for Lu3+. Finally, modification of the TREN capping scaffold by adding an oxygen atom to the central nitrogen led to consistently low %E values, revealing the effect of TREN cap oxidation on Ln extraction for this tripodal CMPO ligand system.
RESUMEN
We report here the characterization in solution (NMR, luminescence, MS) and the solid-state (X-ray crystallography, IR) of complexes between phenacyldiphenylphosphine oxide and five Ln(iii) ions (Sm, Eu, Gd, Tb, Dy). Four single crystal X-ray structures are described here showing a 1 : 2 ratio between the Ln3+ ions Eu, Dy, Sm and Gd and the ligand, where the phosphine oxide ligands are bound in a monodentate manner to the metal center. A fifth structure is reported for the 1 : 2 Eu(NO3)3-ligand complex showing bidentate binding between the two ligands and the metal center. The solution coordination chemistry of these metal complexes was probed by 1H, 13C and 31P NMR, mass spectrometry, and luminescence experiments. The title ligand has the capability to sensitize Tb3+, Dy3+, Eu3+ and Sm3+ leading to metal-centered emission in solutions of acetonitrile and methanol and in the solid state.