Single-Electron Uranyl Reduction by a Rare-Earth Cation

Heterotrimetallic {LnOVPt} complexes with antiferromagnetic Ln-V coupling and magnetic memory

The new PtVO(SOCR)4 lantern complexes, 1 (R = CH3) and 2 (R = Ph) behave as neutral O-donor ligands to Ln(OR)3 with Ln = Ce, Nd. Four heterotrimetallic complexes with linear {LnOVPt} units were prepared: [Ln(ODtbp)3{PtVO(SOCR)4}] (Ln = Ce, 3Ce (R = CH3), 4Ce (R = Ph); Nd, 3Nd (R = CH3), 4Nd (R = Ph); ODtbp = 2,6-ditertbutylphenolate). Magnetic characterization confirms slow magnetic relaxation behaviour and suggests antiferromagnetic coupling across {Ln-O[double bond, length as m-dash]V} in all four complexes, with variations tunable as a function of Ln and R.

Multinuclear NMR Studies on Lewis Acid-Lewis Base Interactions between Bis(pentafluorophenyl)borinic Acid and Uranyl β-Diketonato Complexes in Toluene

In order to examine the possibility of Lewis acid-Lewis base (LA-LB) interactions between the boron atom of B(C₆F₅)₂OH and the oxo groups ("yl" oxygen atoms) of uranyl β-diketonato complexes, we have measured the ¹H, ¹¹B, ¹⁷O, ¹⁹F NMR and IR spectra of toluene solutions containing β-diketonato complexes [UO₂(acac)₂DMSO or UO₂(dfh)₂DMSO, where acac = 2,4-pentanedionate, dfh = 1,1,1,2,2,6,6,7,7,7-decafluoroheptane-3,5-dionate, and DMSO = dimethyl sulfoxide] and B(C₆F₅)₂OH. ¹¹B and ¹⁷O NMR spectra of solutions containing UO₂(dfh)₂DMSO and B(C₆F₅)₂OH showed no change in their chemical shifts regardless of the [B(C₆F₅)₂OH]/[UO₂(dfh)₂DMSO] ratio. This indicates that there were no apparent interactions between B(C₆F₅)₂OH and UO₂(dfh)₂DMSO. On the other hand, in the corresponding NMR spectra of solutions containing UO₂(acac)₂DMSO and B(C₆F₅)₂OH, new signals were observed at a higher field than signals observed in the solutions containing only B(C₆F₅)₂OH or UO₂(acac)₂DMSO, and their intensity changed with the [B(C₆F₅)₂OH]/[UO₂(acac)₂DMSO] ratio. These results reveal that a complex with LA-LB interaction (B···O═U) between the boron atom of B(C₆F₅)₂OH and the "yl" oxygen atom of UO₂(acac)₂DMSO was formed. IR spectra also supported such complex formation; i.e., the asymmetric O═U═O stretching band of UO₂(acac)₂DMSO was observed to shift from 897 to 810 cm^-1 with the addition of B(C₆F₅)₂OH. Moreover, ¹⁹F NMR spectra indicated that 1:1 and 2:1 LA-LB complexes exist in equilibrium, UO{OB(C₆F₅)₂OH}(acac)₂DMSO + B(C₆F₅)₂OH = U{OB(C₆F₅)₂OH}₂(acac)₂DMSO. The thermodynamic parameters for this equilibrium were obtained as K = (2.5 ± 0.6) × 10² M^-1 (at 25 °C), ΔH = -42.4 ± 5.2 kJ mol^-1, and ΔS = -96.7 ± 19.4 J K^-1 mol^-1. In ¹H NMR spectra, the signal due to -CH groups of UO₂(acac)₂DMSO disappeared, and three signals due to the corresponding -CH groups newly appeared with an increase in the [B(C₆F₅)₂OH]/[UO₂(acac)₂DMSO] ratio. From these phenomena, it is proposed that 1:1 and 2:1 LA-LB complexes having interactions between the -CH groups of acac and the -OH group of coordinated B(C₆F₅)₂OH are formed depending on the [B(C₆F₅)₂OH]/[UO₂(acac)₂DMSO] ratio.

DFT Investigations of the Magnetic Properties of Actinide Complexes

Over the past 25 years, magnetic actinide complexes have been the object of considerable attention, not only at the experimental level, but also at the theoretical one. Such systems are of great interest, owing to the well-known larger spin–orbit coupling for actinide ions, and could exhibit slow relaxation of the magnetization, arising from a large anisotropy barrier, and magnetic hysteresis of purely molecular origin below a given blocking temperature. Furthermore, more diffuse 5f orbitals than lanthanide 4f ones (more covalency) could lead to stronger magnetic super-exchange. On the other hand, the extraordinary experimental challenges of actinide complexes chemistry, because of their rarity and toxicity, afford computational chemistry a particularly valuable role. However, for such a purpose, the use of a multiconfigurational post-Hartree-Fock approach is required, but such an approach is computationally demanding for polymetallic systems—notably for actinide ones—and usually simplified models are considered instead of the actual systems. Thus, Density Functional Theory (DFT) appears as an alternative tool to compute magnetic exchange coupling and to explore the electronic structure and magnetic properties of actinide-containing molecules, especially when the considered systems are very large. In this paper, relevant achievements regarding DFT investigations of the magnetic properties of actinide complexes are surveyed, with particular emphasis on some representative examples that illustrate the subject, including actinides in Single Molecular Magnets (SMMs) and systems featuring metal-metal super-exchange coupling interactions. Examples are drawn from studies that are either entirely computational or are combined experimental/computational investigations in which the latter play a significant role.

Axially Symmetric U-O-Ln- and U-O-U-Containing Molecules from the Control of Uranyl Reduction with Simple f-Block Halides

The reduction of U^VI uranyl halides or amides with simple Ln^II or U^III salts forms highly symmetric, linear, oxo-bridged trinuclear U^V /Ln^III /U^V , Ln^III /U^IV /Ln^III , and U^IV /U^IV /U^IV complexes or linear Ln^III /U^V polymers depending on the stoichiometry and solvent. The reactions can be tuned to give the products of one- or two-electron uranyl reduction. The reactivity and magnetism of these compounds are discussed in the context of using a series of strongly oxo-coupled homo- and heterometallic poly(f-block) chains to better understand fundamental electronic structure in the f-block.

Subtle Interactions and Electron Transfer between U(III) , Np(III) , or Pu(III) and Uranyl Mediated by the Oxo Group

A dramatic difference in the ability of the reducing An(III) center in AnCp3 (An=U, Np, Pu; Cp=C5 H5 ) to oxo-bind and reduce the uranyl(VI) dication in the complex [(UO2 )(THF)(H2 L)] (L="Pacman" Schiff-base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At-first contradictory electronic structural data are explained by combining theory and experiment. Complete one-electron transfer from Cp3 U forms the U(IV) -uranyl(V) compound that behaves as a U(V) -localized single molecule magnet below 4 K. The extent of reduction by the Cp3 Np group upon oxo-coordination is much less, with a Np(III) -uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np(IV) U(V) but single-crystal X-ray diffraction and SQUID magnetometry suggest a Np(III) -U(VI) assignment. DFT-calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu(III) -U(VI) interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.

The Renaissance of Non-Aqueous Uranium Chemistry

Prior to the year 2000, non-aqueous uranium chemistry mainly involved metallocene and classical alkyl, amide, or alkoxide compounds as well as established carbene, imido, and oxo derivatives. Since then, there has been a resurgence of the area, and dramatic developments of supporting ligands and multiply bonded ligand types, small-molecule activation, and magnetism have been reported. This Review 1) introduces the reader to some of the specialist theories of the area, 2) covers all-important starting materials, 3) surveys contemporary ligand classes installed at uranium, including alkyl, aryl, arene, carbene, amide, imide, nitride, alkoxide, aryloxide, and oxo compounds, 4) describes advances in the area of single-molecule magnetism, and 5) summarizes the coordination and activation of small molecules, including carbon monoxide, carbon dioxide, nitric oxide, dinitrogen, white phosphorus, and alkanes.

A uranium-based UO2(+)-Mn2+ single-chain magnet assembled trough cation-cation interactions

Single-chain magnets (SCMs) are materials composed of magnetically isolated one-dimensional (1D) units exhibiting slow relaxation of magnetization. The occurrence of SCM behavior requires the fulfillment of stringent conditions for exchange and anisotropy interactions. Herein, we report the synthesis, the structure, and the magnetic characterization of the first actinide-containing SCM. The 5f-3d heterometallic 1D chains [{[UO2(salen)(py)][M(py)4](NO3)}]n, (M=Cd (1) and M=Mn (2); py=pyridine) are assembled trough cation-cation interaction from the reaction of the uranyl(V) complex [UO2(salen)py][Cp*2Co] (Cp*=pentamethylcyclopentadienyl) with Cd(NO3)2 or Mn(NO3)2 in pyridine. The infinite UMn chain displays a high relaxation barrier of 134±0.8 K (93±0.5 cm(-1)), probably as a result of strong intra-chain magnetic interactions combined with the high Ising anisotropy of the uranyl(V) dioxo group. It also exhibits an open magnetic hysteresis loop at T<6 K, with an impressive coercive field of 3.4 T at 2 K.

Oxo-group-14-element bond formation in binuclear uranium(V) Pacman complexes

Simple and versatile routes to the functionalization of uranyl-derived U(V)-oxo groups are presented. The oxo-lithiated, binuclear uranium(V)-oxo complexes [{(py)3LiOUO}2(L)] and [{(py)3LiOUO}(OUOSiMe3)(L)] were prepared by the direct combination of the uranyl(VI) silylamide "ate" complex [Li(py)2][(OUO)(N")3] (N" = N(SiMe3)2) with the polypyrrolic macrocycle H4L or the mononuclear uranyl (VI) Pacman complex [UO2(py)(H2L)], respectively. These oxo-metalated complexes display distinct U-O single and multiple bonding patterns and an axial/equatorial arrangement of oxo ligands. Their ready availability allows the direct functionalization of the uranyl oxo group leading to the binuclear uranium(V) oxo-stannylated complexes [{(R3Sn)OUO}2(L)] (R = nBu, Ph), which represent rare examples of mixed uranium/tin complexes. Also, uranium-oxo-group exchange occurred in reactions with [TiCl(OiPr)3] to form U-O-C bonds [{(py)3LiOUO}(OUOiPr)(L)] and [(iPrOUO)2(L)]. Overall, these represent the first family of uranium(V) complexes that are oxo-functionalised by Group 14 elements.

Controlled deprotection and reorganization of uranyl oxo groups in a binuclear macrocyclic environment

Switching on uranium(V) reactivity: The silylated uranium(V) dioxo complex [(Me(3)SiOUO)(2)(L)(2)] (A) is inert to oxidation, but after two-electron reduction to [(Me(3)SiOUO)(2)(L)](2-) (1), it can be desilylated to form [OU(μ-O)(2)UO(L)(2)](2-) (2) with reinstated uranyl character. Removal of the silyl group uncovers new redox and oxo rearrangement chemistry for uranium, thus reforming the uranyl motif and involving the U(VI/V) couple in dioxygen reduction.