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 5f¹-4fⁿ Complexes

Abstract

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 Ln(III)(A)3 (A = N(SiMe3)2, OC6H3Bu(t)2-2,6) via homolysis of a Ln-A bond. The complexes are dimeric through mutual uranyl exo-oxo coordination but can be cleaved to form the trimetallic, monouranyl "ate" complexes [(py)3LiOUO(μ-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 Ln(III)-A homolysis allows [5f(1)-4f(n)]2 and Li[5f(1)-4f(n)] complexes with oxo-bridged metal cations to be made for all possible 4f(n) 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(V)Sm(III) monomer, whereas the dimeric U(V)Dy(III) complex was found to show magnetic bistability at 3 K, a property required for the development of single-molecule magnets.

Cation‐Mediated Conversion of the State of Charge in Uranium Arene Inverted‐Sandwich Complexes

“…68, 72 Moreover, examples of unambiguous magnetic coupling between uranium ions in molecular systems remain very limited41, 73–77 although such interactions are at the origins of the single‐molecule magnet behavior recently reported for few multinuclear U III and U V complexes 19. 78, 79…”

Oxo Ligand Substitution in a Cationic Uranyl Complex: Synergistic Interaction of an Electrophile and a Reductant

“…[2][3][4][5][6][7] For example, Arnold and co-workers demonstrated that sequential reaction of U VI O 2 (THF)(H 2 L) (L = polypyrrolic macrocycle) with KN(SiMe 3 ) 2 and FeI 2 resulted in formation of the U(V) silyloxide, [U V O(OSiMe 3 )(THF)Fe 2 I 2 L]. 7 Similarly, our research group has demonstrated that reaction of U VI O 2 ( Ar acnac) 2 ( Ar acnac = ArNC(Ph)CHC(Ph)O, Ar = 3,5-t Bu 2 C 6 H 3 ), 8 with a mixture of B(C 6 F 5 ) 3 and HSiR 3 (R = Ph, Et), 9,10 or with Ph 3 SiOTf alone, 11 results in formation of the reductive silylation products, U V (OSiR 3 )(OB{C 6 11 respectively.…”

Future Directions for Transuranic Single Molecule Magnets

“…The slow progress in the field is in part due to the relative smallness of the actinide scientific community, and to the fact that only a handful of laboratories are equipped to handle transuranic elements, so that most of the reported work concerns uranium complexes only. SMM behaviour has actually been observed in several monometallic U III [13] and U V [14] complexes and in heterometallic coordination compounds containing U V and either Mn II or Dy III cations [15][16][17].…”