Issue 40, 2018

Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system

Abstract

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.

Graphical abstract: Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system

Supplementary files

Article information

Article type
Paper
Submitted
31 5 2018
Accepted
19 7 2018
First published
27 7 2018

Dalton Trans., 2018,47, 14318-14326

Author version available

Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system

M. G. Patterson, A. K. Mulville, E. K. Connor, A. T. Henry, M. L. Hudson, K. Tissue, S. M. Biros and E. J. Werner, Dalton Trans., 2018, 47, 14318 DOI: 10.1039/C8DT02239A

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