Understanding the Scarcity of Thorium Peroxide Clusters

The reaction of Th­(NO₃)₄·5H₂O with 3 equiv of 2,2′,6′,2″-terpyridine (terpy) in a mixture of acetonitrile and methanol results in formation of the trinuclear thorium peroxide cluster [Th­(O₂)­(terpy)­(NO₃)₂]₃. This cluster is assembled via bridging by μ–η²:η² peroxide anions between thorium centers. It decomposes upon removal from the mother liquor to yield Th­(terpy)­(NO₃)₄ and Th­(terpy)­(NO₃)₄(EtOH). The peroxide formation appears to be radiolytic in origin and is, most likely, generated from radiolysis of water by short-lived daughters generated from ²³²Th decay. This cluster does not form when freshly recrystallized Th­(NO₃)₄·5H₂O is used as the starting material and requires an aged source of thorium. Analysis of the bonding in these clusters shows that, unlike uranium­(VI) peroxide interactions, thorium­(IV) complexation by peroxide is quite weak and largely ionic. This explains its much lower stability, which is more comparable to that observed in similar zirconium­(IV) peroxide clusters

Characterization of Lanthanide Complexes with Bis-1,2,3-triazole-bipyridine Ligands Involved in Actinide/Lanthanide Separation

The complexation of selected trivalent lanthanide ions with derivatives of the tetranitrogen donor ligands 6,6′-bis-1R,1<i>H</i>-1,2,3-triazol-4-yl-2,2′-bipyridines (BTzBPs, R = alkyl or aryl) was investigated in solid state and in solution. An anhydrous solid [Ce­(Bn-BTzBP)­(NO₃)₃] (Bn = benzene) complex was synthesized and characterized by single-crystal X-ray diffraction. Eu­(III) complexes with the 2-ethyl­(hexyl) derivative EH-BTzBP in methanol were studied by time-resolved fluorescence spectroscopy. Earlier studies have identified the EH-BTzBP as a potentially useful solvent extraction reagent for the separation of americium from lanthanide metal ions, a challenging component of advanced nuclear fuel cycles for actinide transmutation. To help identify species formed in the extraction process, the influence of 2-bromohexanoic acid (identified as an essential component of the separation system) on Eu­(III) complexes was investigated. Comparison with an organic phase after extraction of Eu­(III) by EH-BTzBP and 2-bromohexanoic acid showed that both 1:1 and 1:2 (Eu/EH-BTzBP) complexes are involved in the extraction. UV–visible spectrophotometry was used to compare Eu­(III) stability constants with those of other Ln­(III) complexes

Uncovering the Origin of Divergence in the CsM(CrO4)2 (M = La, Pr, Nd, Sm, Eu; Am) Family through Examination of the Chemical Bonding in a Molecular Cluster and by Band Structure Analysis

A series of f-block chromates, CsM­(CrO₄)₂ (M = La, Pr, Nd, Sm, Eu; Am), were prepared revealing notable differences between the Am^III derivatives and their lanthanide analogs. While all compounds form similar layered structures, the americium compound exhibits polymorphism and adopts both a structure isomorphous with the early lanthanides as well as one that possesses lower symmetry. Both polymorphs are dark red and possess band gaps that are smaller than the Ln^III compounds. In order to probe the origin of these differences, the electronic structure of α-CsSm­(CrO₄)₂, α-CsEu­(CrO₄)₂, and α-CsAm­(CrO₄)₂ were studied using both a molecular cluster approach featuring hybrid density functional theory and QTAIM analysis and by the periodic LDA+GA and LDA+DMFT methods. Notably, the covalent contributions to bonding by the f orbitals were found to be more than twice as large in the Am^III chromate than in the Sm^III and Eu^III compounds, and even larger in magnitude than the Am-5f spin–orbit splitting in this system. Our analysis indicates also that the Am–O covalency in α-CsAm­(CrO₄)₂ is driven by the degeneracy of the 5f and 2p orbitals, and not by orbital overlap