8 research outputs found
Single-Electron Uranyl Reduction by a Rare-Earth Cation
Reducing the irreducible. Incorporation of a lanthanide cation into the bottom coordination pocket of a uranyl Pacman complex results in single electron reduction to form stable pentavalent uranyl-lanthanide complexes with uranyl-oxo-lanthanide bonds.JRC.E.6-Actinides researc
Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis:Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced Uranyl-Rare Earth 5f<sup>1</sup>-4f<sup><em>n</em></sup> Complexes
The heterobimetallic complexes [{UO2Ln-(py)2(L)}2], combining a singly reduced uranyl cation and a rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle (Pacman) and bridged through a uranyl oxo-group, have been prepared for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds are formed by the single-electron reduction of the Pacman uranyl complex [UO2(py)(H2L)] by the rare-earth complexes LnIII(A)3 (A = N(SiMe3)2, OC6H3But 2-2,6) via homolysis of a LnâA bond. The complexes are dimeric through mutual uranyl exo-oxo coordination but can be cleaved to form the trimetallic, monouranyl âateâ complexes [(py)3LiOUO(ÎŒ-X)Ln(py)(L)] by the addition of lithium halides. X-ray crystallographic structural characterization of many examples reveals very similar features for monomeric and dimeric series, the dimers containing an asymmetric U2O2 diamond core with shorter uranyl U=O distances than in the monomeric complexes. The synthesis by LnIIIâA homolysis allows [5f1-4fn]2 and Li[5f1-4fn] complexes with oxobridged metal cations to be made for all possible 4fn configurations. Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies on the complexes are utilized to provide a basis for the better understanding of the electronic structure of f-block complexes and their f-electron exchange interactions. Furthermore, the structures, calculated by restricted-core or allelectron methods, are compared along with the proposed mechanism of formation of the complexes. A strong antiferromagnetic coupling between the metal centers, mediated by the oxo groups, exists in the UVSmIII monomer, whereas the dimeric UVDyIII complex was found to show magnetic bistability at 3 K, a property required for the development of single-molecule magnets.JRC.E.6-Actinide researc
Uranyl oxo activation and functionalization by metal cation coordination
International audienceThe oxo groups in the uranyl ion [UO] , one of many oxo cations formed by metals from across the periodic tableâare particularly inert, which explains the dominance of this ion in the laboratory and its persistence as an environmental contaminant. In contrast, transition metal oxo (M=O) compounds can be highly reactive and carry out difficult reactions such as the oxygenation of hydrocarbons. Here we show how the sequential addition of a lithium metal base to the uranyl ion constrained in a âPacmanâ environment results in lithium coordination to the U=O bonds and single-electron reduction. This reaction depends on the nature and stoichiometry of the lithium reagent and suggests that competing reduction and CâH bond activation reactions are occurring
Control of Oxo-Group Functionalization and Reduction of the Uranyl Ion
yesUranyl complexes of a large, compartmental
N8-macrocycle adopt a rigid, âPacmanâ geometry that stabilizes
the UV oxidation state and promotes chemistry at a single
uranyl oxo-group. We present here new and straightforward
routes to singly reduced and oxo-silylated uranyl Pacman
complexes and propose mechanisms that account for the
product formation, and the byproduct distributions that are
formed using alternative reagents. Uranyl(VI) Pacman
complexes in which one oxo-group is functionalized by a
single metal cation are activated toward single-electron
reduction. As such, the addition of a second equivalent of a
Lewis acidic metal complex such as MgNâł2 (Nâł = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg
functionalized as a result of MgâN bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(Nâł)Cl] favor
the formation of weaker UâOâZn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to
metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated
by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxogroup
The development and application of new polydentate ligands in early thransition metal chemistry
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Single-Electron Uranyl Reduction by a Rare-Earth Cation
Unlike their transition-metal analogues, the oxo groups of the uranyl dication, [UO2]2+, which has a linear geometry and short, strong U-O bonds are commonly considered inert.[1] Very little Lewis base character has been demonstrated for the uranyl oxo groups,[2,3] which makes them poor models for the heavier, highly radioactive transuranic actinyl cations such as neptunyl [NpO2]n+ (n=1, 2).[4, 5] The heavier actinyls are important components in nuclear waste and demonstrate oxo basicity that can give rise to poorly understood cluster formation and problems in nuclear waste PUREX separation processes.[6] However, it has been shown recently that the
more Lewis basic, pentavalent uranyl cation, [UO2]+, can be stabilized indefinitely using suitable equatorial-binding ligands and anaerobic conditions.[7,8] Usually the [UO2]+ cation decomposes by disproportionation, which is also a poorly understood process, but is important in the precipitation of uranium salts out of aqueous environments.[9, 10] The disproportionation is suggested, by analogy with the transuranic metal oxo Lewis base behavior, to involve the formation of cationâcation interactions (CCIs)[11, 12] in which the oxo groups ligate to adjacent actinyl centers forming diamond (A) or T-shaped (B) dimers or clusters which can then allow the transfer of protons and electrons between metals, such as in C.JRC.E.6-Actinides researc
Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis: Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced UranylâRare Earth 5f<sup>1</sup>â4f<sup><i>n</i></sup> Complexes
The heterobimetallic
complexes [{UO<sub>2</sub>LnÂ(py)<sub>2</sub>(L)}<sub>2</sub>], combining
a singly reduced uranyl cation and a
rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle
(Pacman) and bridged through a uranyl oxo-group, have been prepared
for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds
are formed by the single-electron reduction of the Pacman uranyl complex
[UO<sub>2</sub>(py)Â(H<sub>2</sub>L)] by the rare-earth complexes Ln<sup>III</sup>(A)<sub>3</sub> (A = NÂ(SiMe<sub>3</sub>)<sub>2</sub>, OC<sub>6</sub>H<sub>3</sub>Bu<sup>t</sup><sub>2</sub>-2,6) via homolysis
of a LnâA bond. The complexes are dimeric through mutual uranyl <i>exo</i>-oxo coordination but can be cleaved to form the trimetallic,
monouranyl âateâ complexes [(py)<sub>3</sub>LiOUOÂ(ÎŒ-X)ÂLnÂ(py)Â(L)]
by the addition of lithium halides. X-ray crystallographic structural
characterization of many examples reveals very similar features for
monomeric and dimeric series, the dimers containing an asymmetric
U<sub>2</sub>O<sub>2</sub> diamond core with shorter uranyl Uî»O
distances than in the monomeric complexes. The synthesis by Ln<sup>III</sup>âA homolysis allows [5f<sup>1</sup>-4f<sup><i>n</i></sup>]<sub>2</sub> and LiÂ[5f<sup>1</sup>-4f<sup><i>n</i></sup>] complexes with oxo-bridged metal cations to be
made for all possible 4f<sup><i>n</i></sup> configurations.
Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies
on the complexes are utilized to provide a basis for the better understanding
of the electronic structure of f-block complexes and their f-electron
exchange interactions. Furthermore, the structures, calculated by
restricted-core or all-electron methods, are compared along with the
proposed mechanism of formation of the complexes. A strong antiferromagnetic
coupling between the metal centers, mediated by the oxo groups, exists
in the U<sup>V</sup>Sm<sup>III</sup> monomer, whereas the dimeric
U<sup>V</sup>Dy<sup>III</sup> complex was found to show magnetic bistability
at 3 K, a property required for the development of single-molecule
magnets
Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis: Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced UranylâRare Earth 5f<sup>1</sup>â4f<sup><i>n</i></sup> Complexes
The heterobimetallic
complexes [{UO<sub>2</sub>LnÂ(py)<sub>2</sub>(L)}<sub>2</sub>], combining
a singly reduced uranyl cation and a
rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle
(Pacman) and bridged through a uranyl oxo-group, have been prepared
for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds
are formed by the single-electron reduction of the Pacman uranyl complex
[UO<sub>2</sub>(py)Â(H<sub>2</sub>L)] by the rare-earth complexes Ln<sup>III</sup>(A)<sub>3</sub> (A = NÂ(SiMe<sub>3</sub>)<sub>2</sub>, OC<sub>6</sub>H<sub>3</sub>Bu<sup>t</sup><sub>2</sub>-2,6) via homolysis
of a LnâA bond. The complexes are dimeric through mutual uranyl <i>exo</i>-oxo coordination but can be cleaved to form the trimetallic,
monouranyl âateâ complexes [(py)<sub>3</sub>LiOUOÂ(ÎŒ-X)ÂLnÂ(py)Â(L)]
by the addition of lithium halides. X-ray crystallographic structural
characterization of many examples reveals very similar features for
monomeric and dimeric series, the dimers containing an asymmetric
U<sub>2</sub>O<sub>2</sub> diamond core with shorter uranyl Uî»O
distances than in the monomeric complexes. The synthesis by Ln<sup>III</sup>âA homolysis allows [5f<sup>1</sup>-4f<sup><i>n</i></sup>]<sub>2</sub> and LiÂ[5f<sup>1</sup>-4f<sup><i>n</i></sup>] complexes with oxo-bridged metal cations to be
made for all possible 4f<sup><i>n</i></sup> configurations.
Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies
on the complexes are utilized to provide a basis for the better understanding
of the electronic structure of f-block complexes and their f-electron
exchange interactions. Furthermore, the structures, calculated by
restricted-core or all-electron methods, are compared along with the
proposed mechanism of formation of the complexes. A strong antiferromagnetic
coupling between the metal centers, mediated by the oxo groups, exists
in the U<sup>V</sup>Sm<sup>III</sup> monomer, whereas the dimeric
U<sup>V</sup>Dy<sup>III</sup> complex was found to show magnetic bistability
at 3 K, a property required for the development of single-molecule
magnets