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Title: Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system
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 Tb 3+ 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 Tb 3+ 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 Gd more » 3+ and Tb 3+ 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 La 3+ to 3.7% for Lu 3+ . 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. « less
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Dalton Transactions
Page Range or eLocation-ID:
14318 to 14326
Sponsoring Org:
National Science Foundation
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  1. Abstract

    Lanthanide (Ln) elements are generally found in the oxidation state +II or +III, and a few examples of +IV and +V compounds have also been reported. In contrast, monovalent Ln(+I) complexes remain scarce. Here we combine photoelectron spectroscopy and theoretical calculations to study Ln-doped octa-boron clusters (LnB8, Ln = La, Pr, Tb, Tm, Yb) with the rare +I oxidation state. The global minimum of the LnB8species changes fromCstoC7vsymmetry accompanied by an oxidation-state change from +III to +I from the early to late lanthanides. All theC7v-LnB8clusters can be viewed as a monovalent Ln(I) coordinated by a η8-B82−doubly aromatic ligand. The B73−, B82−, and B9series of aromatic boron clusters are analogous to the classical aromatic hydrocarbon molecules, C5H5, C6H6, and C7H7+, respectively, with similar trends of size and charge state and they are named collectively as “borozenes”. Lanthanides with variable oxidation states and magnetic properties may be formed with different borozenes.

  2. A new series of gallium( iii )/lanthanide( iii ) metallacrown (MC) complexes ( Ln-1 ) was synthesized by the direct reaction of salicylhydroxamic acid (H 3 shi) with Ga III and Ln III nitrates in a CH 3 OH/pyridine mixture. X-ray single crystal analysis revealed two types of structures depending on whether the nitrate counterion coordinate or not to the Ln III : [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 4 (NO 3 )](py) 2 (Ln = Gd III , Tb III , Dy III , Ho III ) and [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 5 ](NO 3 )(py) (Ln = Er III , Tm III , Yb III ). The representative Tb-1 and Yb-1 MCs consist of a Tb/YbGa 4 core with four [Ga III –N–O] repeating units forming a non-planar ring that coordinates the central Ln III through the oxygen atoms of the four shi 3− groups. Two H 2 shi − groups bridge the Ln III to the Ga III ring ions. The Yb III in Yb-1 is eight-coordinated while the ligation of the nine-coordinated Tb III in Tb-1 is completed by one chelating nitrate ion. Ln-1 complexes in the solidmore »state showed characteristic sharp f–f transitions in the visible (Tb, Dy) and near-infrared (Dy, Ho, Er, Yb) spectral ranges upon excitation into the ligand-centered electronic levels at 350 nm. Observed luminescence lifetimes and absolute quantum yields were collected and discussed. For Yb-1 , luminescence data were also acquired in CH 3 OH and CD 3 OD solutions and a more extensive analysis of photophysical properties was performed. This work demonstrates that while obtaining highly luminescent lanthanide( iii ) MCs via a direct synthesis is feasible, many factors such as molar absorptivities, triplet state energies, non-radiative deactivations through vibronic coupling with overtones of O–H, N–H, and C–H oscillators and crystal packing will strongly contribute to the luminescent properties and should be carefully considered.« less
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