2 research outputs found
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><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 Ln–A bond. The complexes are dimeric through mutual uranyl <i>exo</i>-oxo coordination but can be cleaved to form the trimetallic,
monouranyl “ate” complexes [(py)<sub>3</sub>LiOUOÂ(ÎĽ-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>–A 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 Uranyl–Rare Earth 5f<sup>1</sup>‑4f<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 Ln–A bond. The complexes are dimeric through mutual uranyl <i>exo</i>-oxo coordination but can be cleaved to form the trimetallic,
monouranyl “ate” complexes [(py)<sub>3</sub>LiOUOÂ(ÎĽ-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>–A 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