Structural investigations of three actinide(IV) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(IV), U(IV), Np(IV)) and their cerium(IV) analogue display the same metal coordination in the solid state. The mononuclear complexes show...

To reduce high-level radiotoxic waste generated by nuclear power plants, highly selective separation agents for minor actinides are mandatory. The mixed N,O-donor ligand N,N,N′,N′-tetrakis­[(6-carboxypyridin-2-yl)­methyl]­ethylenediamine (H4TPAEN; 1) has shown good performance as a masking agent in Am3+/Eu3+ separation studies. Adjustments on the pyridyl backbone to raise the hydrophilicity led to a decrease in selectivity and a decrease in M3+–Nam interactions. An enhanced basicity of the pyridyl N-donors was given as a cause. In this work, we examine whether a decrease in O-donor basicity can promote the M3+–Nam interactions. Therefore, we replace the deprotonated “charged” carboxylic acid groups of TPAEN4– by neutral amide groups and introduce N,N,N′,N’-tetrakis­[(6-N″,N′′-diethylcarbamoylpyridin-2-yl)­methyl]­ethylenediamine (TPAMEN; 2) as a new ligand. TPAMEN was crystallized with Eu­(OTf)3 and Eu­(NO3)3·6H2O to form positively charged 1:1 [Eu­(TPAMEN)]3+ complexes in the solid state. Alterations in the M–O/N bond distances are compared to [Eu­(TPAEN)]− and investigated by DFT calculations to expose the differences in charge/energy density distributions at europium­(III) and the donor functionalities of the TPAEN4– and TPAMEN. On the basis of estimations of the bond orders, atomic charges spin populations, and density of states in the Eu and potential Am and Cm complexes, the specific contributions of the donor–metal interaction are analyzed. The prediction of complex formation energy differences for the [M­(TPAEN)]− and [M­(TPAMEN)]3+ (M3+ = Eu3+, Am3+) complexes provide an outlook on the potential performance of TPAMEN in Am3+/Eu3+ separation.

Two N,N′-bis(3-alkoxy-2-hydroxybenzyl)cyclohexane-1,2-diamine proligands, H2L1 (R = OCH3) and H2L2 (R = OC2H5), and five heterodinuclear ZnII/LnIII complexes, [Zn(L)(µ-CH3COO)Ln(NO3)2], containing [L1]2– and Gd3+, Tb3+, Er3+, or Yb3+ and [L2]2– and Yb3+ have been synthesised and structurally characterised. The complexes are isostructural and crystallise in the P21/n monoclinic space group. Zinc(ii) is coordinated by the inner N2O2 donor set of the ligand and an oxygen of the bridging acetate anion; the lanthanide(iii) ions possess an O9 coordination environment involving the interaction with the ligand’s outer O4 donor set, two bidentate nitrate ions, and the bridging acetate.

Highly selective rare-earth separation has become increasingly important due to the indispensable role of these elements in various cutting-edge technologies including clean energy. However, the similar physicochemical properties of rare-earth elements (REEs) render their separation very challenging, and the development of new selective receptors for these elements is potentially of very considerable economic and environmental importance. Herein, we report the development of a series of 4-phosphoryl pyrazolone receptors for the selective separation of trivalent lanthanum, europium, and ytterbium as the representatives of light, middle, and heavy REEs, respectively. X-ray crystallography studies were employed to obtain solid-state structures across 11 of the resulting complexes, allowing comparative structure–function relationships to be probed, including the effect of lanthanide contraction that occurs along the series from lanthanum to europium to ytterbium and which potentially provides a basis for REE ion separation. In addition, the influence of ligand structure and lipophilicity on lanthanide binding and selectivity was systematically investigated via n-octanol/water distribution and liquid–liquid extraction (LLE) studies. Corresponding stoichiometry relationships between solid and solution states were well established using slope analyses. The results provide new insights into some fundamental lanthanide coordination chemistry from a separation perspective and establish 4-phosphoryl pyrazolone derivatives as potential practical extraction reagents for the selective separation of REEs in the future.

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