Uranium Complexes Research Articles

Can different counter ions and their concentration modify the structural characteristics of aqueous solutions of uranyl ions? Atomistic insights from molecular dynamics simulations

Extensive atomistic molecular dynamics simulation results suggest that probability of counter ion occupying first solvation shell of uranyl ion depends both on its nature and concentration. In general, uranyl-counter ion complexes with pentagonal bi-pyramidal structure with five ligands in the equatorial plane of the linear UO22+ ion are observed. In case of nitrate ion, pure aqua complexes at lower concentrations and mixed mono-nitro aqua complexes are observed at higher concentrations, whereas in case of sulphate and carbonate ions, no pure aqua complexes are observed. The NO3− and SO42− ions act as unidentate, but CO32− acts both as uni- and bi-dentate ligand. In addition, polynuclear uranium complexes with bridging SO42− and CO32− ligands are observed. Relative strength of binding of counter ions with uranyl ion from PMF calculations follows the order CO32− > SO42− > NO3− with the contact pair free energies of about −29.0, −14.0 and −1.1 kcal/mol respectively.

Two‐Electron Oxidative Atom and Group Transfer Reactions at a Well‐Defined Uranium(II) Center

The multi‐electron redox chemistry of uranium(II) compounds remains largely unexplored. Herein, we report a series of two‐electron oxidative atom and group transfer reactions at a well‐defined uranium(II) center. The reactions of uranium(II) complexes [M][(AdTPBN3)U] (M = K(2,2,2‐cryptand) and K(18‐crown‐6)(THF)) with pyridine‐N‐oxide or nitrosobenzene, elemental sulfur/selenium or triphenylphosphine sulfide/selenide, and ditellurium salt led to the isolation of uranium(IV) terminal oxo and chalcogenido complexes [M][(AdTPBN3)UX] (X = O, S, Se, Te). In addition, the reactions of [M][(AdTPBN3)U] with aryl azides ArN3 or diazoalkanes R2CN2 quantitatively yielded uranium(IV) terminal imido [M][(AdTPBN3)UNAr] or hydrazonido(2–) complexes [M][(AdTPBN3)UN2CR2], respectively. Notably, the low‐temperature reaction between [M][(AdTPBN3)U] and mesityl azide allowed the isolation of the first uranium(IV) aryldiazenylimido complex as an intermediate. These uranium(IV)–element multiply bound compounds were fully characterized by X‐ray crystallography, 1H NMR spectroscopy, absorption spectroscopy, solution magnetic susceptibility, and elemental analysis. The controlled two‐electron oxidative reactions at a uranium(II) center not only expand the redox reactivity of uranium(II) but also offer a convenient new route to access uranium–element multiply bound compounds.

Two-Electron Oxidative Atom and Group Transfer Reactions at a Well-Defined Uranium(II) Center.

The multi-electron redox chemistry of uranium(II) compounds remains largely unexplored. Herein, we report a series of two-electron oxidative atom and group transfer reactions at a well-defined uranium(II) center. The reactions of uranium(II) complexes [M][(AdTPBN3)U] (M = K(2,2,2-cryptand) and K(18-crown-6)(THF)) with pyridine-N-oxide or nitrosobenzene, elemental sulfur/selenium or triphenylphosphine sulfide/selenide, and ditellurium salt led to the isolation of uranium(IV) terminal oxo and chalcogenido complexes [M][(AdTPBN3)UX] (X = O, S, Se, Te). In addition, the reactions of [M][(AdTPBN3)U] with aryl azides ArN3 or diazoalkanes R2CN2 quantitatively yielded uranium(IV) terminal imido [M][(AdTPBN3)UNAr] or hydrazonido(2-) complexes [M][(AdTPBN3)UN2CR2], respectively. Notably, the low-temperature reaction between [M][(AdTPBN3)U] and mesityl azide allowed the isolation of the first uranium(IV) aryldiazenylimido complex as an intermediate. These uranium(IV)-element multiply bound compounds were fully characterized by X-ray crystallography, 1H NMR spectroscopy, absorption spectroscopy, solution magnetic susceptibility, and elemental analysis. The controlled two-electron oxidative reactions at a uranium(II) center not only expand the redox reactivity of uranium(II) but also offer a convenient new route to access uranium-element multiply bound compounds.

DecTree: a physics-based geochemical surrogate for surface complexation of uranium on clay

Abstract. Geochemistry is usually the computational bottleneck in coupled reactive transport simulations, which hampers the complexity of the systems and of the processes they can investigate. In recent years, promising speedups have been obtained by substituting the numerical solution of geochemical models with approximated surrogates borrowed from artificial intelligence and machine learning (AI/ML). In the framework of the DONUT/EURAD project a set of benchmarks were defined to assess the performance and the accuracy of different surrogate approaches in settings relevant to the safety assessment of nuclear waste repositories, such as the surface complexation and exchange of U(VI) on clay. In this context, this work introduces am original surrogate modelling approach based on recursive partitioning of parameter space, which exploits prior domain knowledge for the training. The surrogate, which can be represented as a decision tree, hence the DecTree name, performs dimensionality reduction by identifying functional relationships between outputs and input variables using a straightforward non-monotonic extension of the Spearman's rank correlation coefficient. New predictions are then interpolated from the partitioned training data. Applied to a low-dimensional geochemical model, DecTree shows virtually no training time and excellent accuracy, ensuring a throughput of around 500 000 predictions per second on a single CPU core.

Metal-Metal Bonding in Tri-Actinide Clusters: A DFT Study of [An3Cl6]z (z=1-6) and [An3Cl6Cp3]z (z=-2-+3; An=Ac, Th, Pa, U, Np, Pu).

The actinide-actinide bonding in tri-actinide clusters [An₃Cl₆]z (An=Ac-Pu, z=1-6) and [An₃Cl₆Cp₃]z (z=-2-+3; Cp=(η5-C5H5)) is studied using density functional theory. We find 3-centre bonding similar to the tri-thorium cluster [{Th(η⁸-C₈H₈)(μ₃-Cl)₂}₃{K(THF)₂}₂]∞, as we previously reported (Nature 2021, 598, 72-75). The population of 3-centre molecular orbitals (3c-MOs) by zero, one or two electrons correlates with shortening of the An-An bond lengths, which also decrease with increasing actinide atomic number, consistent with the contraction of the actinide valence atomic orbitals. Mulliken analyses indicate that these 3c-MOs predominantly involve An 6d and 5 f orbitals. Various methods evidence the presence of An-An bonding in most systems with populated 3c-MOs, including bond orders (Mayer and Wiberg), quantum theory of atoms in molecules metrics (ρ, ∇2ρ, -G/V, H, delocalization indices), electron localization function, and electron density assessments. Additionally, we explore the effect of Cp ligand substitution on uranium complexes, finding that bulkier Cp ligands can induce U-U bond distortions and result in slightly longer U-U bonds. Overall, this study advances our understanding of metal-metal bonding in tri-actinide clusters, highlighting its effects on geometric and electronic structures.

Comparison of uranium complexes with methyl-glutarimidedioxime vs. glutarimidedioxime: A methyl change generates different consequences in thermodynamic equilibria and coordination modes

Nuclear power serves as an important source of alternative energy. However, land uranium resources are limited. In contrast, seawater contains an estimated total of 4.5 billion metric tons of uranium, which is more than a thousand times as much as that found in terrestrial ores. Therefore, developing techniques for uranium extraction from seawater is attracting research attention. Amidoxime-functionalized polymer fibers are the most widely utilized sorbents for this purpose. On the surface of amidoxime-based sorbents, cyclic glutarimidedioxime (H2A) is the preferred configuration for sequestration of uranium from seawater. Methyl-glutarimidedioxime (H2Q) forms if a methyl group attaches to the piperidine ring of H2A. The binding strength of uranyl complexes with H2Q and the enthalpy of complexation were investigated via potentiometry and microcalorimetry, respectively. The coordination mode was further revealed by single-crystal X-ray diffraction. It was expected that H2A and H2Q should be identical in terms of coordination as tridentate ligands. However, our investigation revealed that a methyl group attached to the piperidine ring not only altered the chelating mode but also lowered the binding strength of oxime groups. These findings show that developing a mechanism for optimizing molecules that would be formed on fiber surfaces remains challenging, even a methyl structural change would result in major consequences.

Insight into the complexation of uranium with Bacillus sp. dwc-2 by multi-spectroscopic approaches: FT-IR, TRLF and XAFS spectroscopies

The micromechanisms of the interactions between uranium and microorganisms, especially chemical bonds and bonding numbers between uranium and microbe are not yet clear. In this work, uranium coordination with functional groups in/on Bacillus sp. dwc-2 has been rationally explored by X-ray absorption fine structure (XAFS), Fourier transform infrared (FT-IR), time-resolved laser-induced fluorescence (TRLF) spectroscopies. The results indicate that under acidic condition, 66.8 % of O atoms in coordination shell of U(VI) equatorial plane are provided by organic phosphoryl groups via monodentate coordination, 18.8 % and 15.5 % are provided by water molecules and carboxyl groups via monodentate and bidentate coordination, respectively. While under alkaline condition, these proportions change to 53.1 %, 34.4 % and 22.0 %, respectively. Under neutral condition, U(VI) is mainly deposited by complexing with inorganic phosphates released by microbial cells. Under anaerobic condition, partial U(VI) can be reduced to U(IV) which primarily complex with phosphorus containing groups via monodentate and bidentate coordination, existing as amorphous solids or coordination polymers. This is the first exploration of the binding mechanism between uranium and microorganisms at a semi-quantitative level under different conditions. Our studies will further enhance the contribute to the understanding of coordination mechanism of uranium with microorganism, and demonstrate the potential bioremediation value of this bacterium.

Acid Mediated In‐Situ Catalytic Cleavage/Making of C=N Bonds in Bis‐Hydrazone Uranyl Complexes: Exploration of Photophysical, Electrochemical, Dye Sorption Properties and DFT Studies

AbstractTwo new uranium complexes [UO2L2(H2O)] (where L2=diacetyl bis‐isonicotinoyl hydrazone) complex 1, and [UO2(L1)2] (where L1=diacetylmonoxime isonicotinoylhydrazone) complex 2, have been synthesized by precisely adjusting the pH values of the reaction system. Complex 1 was formed in an acidic ethanolic solution (pH=3) through an in‐situ acid catalytic reaction of diacetylmonoxime isonicotinoylhydrazone and UO2(NO3)2.6H2O, while complex 2 was acquired in a neutral medium (pH=7) through self‐assembly of two ligands and one uranium (VI) metal centre. Both complexes were thoroughly characterized by elemental analysis, UV‐Visible spectroscopy, IR spectroscopy, NMR, TGA, cyclic voltammetry, and powder X‐ray diffraction. The studies indicate that the bis‐hydrazone in complex 1 is a dianionic tetradentate N2O2 donor, whereas in complex 2 it is a monoanionic tridendate N2O donor. The formation of complex 1 was further confirmed by a single‐crystal X‐ray diffraction study, which revealed the role of a water molecule in forming a pentagonal bipyramidal geometry of [UO2L2(H2O)]. Photophysical studies revealed that complexes 1 and 2 exhibited low band gap values of 2.07 and 2.12 eV, respectively, indicating their semiconducting nature. From the CV measurements, the higher negative potentials of the complexes 1 & 2 {1, −0.6 V and 2, −0.5 V vs. ferrocenium/ferrocene (Fc+/Fc)} in DMSO are assigned to the presence of {UO2}2+/{UO2}+ couple signifying their redox active nature. Dye adsorption studies show that both the complexes were able to remove 90 % of Methylene blue (MB) and Rhodamine B (RhB) from the solutions with the concentration of 10−5 M. The structural insights and electronic properties of Ligand HL1 and complex 1 were further explored by density functional theory (DFT) calculations.

Covalency-Driven Differences in the Hydrogenation Chemistry of Lanthanide- and Actinide-Based Frustrated Lewis Pairs.

The electronic organization of Frustrated Lewis Pairs (FLPs) allows them to activate strong bonds in mechanisms that are usually free of redox events at the Lewis acidic site. The unique 6d/5f manifold of uranium could serve as an interesting FLP acceptor site, but to date FLP-like catalysis with actinide ions is unknown. In this paper, the catalytic, FLP-like hydrogenation reactivity of trivalent uranium complexes is explored in the presence of base-stabilized silylenes. Comparison to isoelectronic, isostructural lanthanide and thorium complexes lends insight into the electronic factors governing dihydrogen activation. Mechanistic studies of the uranium- and lanthanide-catalyzed hydrogenations are presented, including discussion of likely intermediates. Computational modeling of the f-element complexes, combined with experimental comparison to p-block Lewis acids, elucidates the relevance of steric hindrance to productive reactivity with dihydrogen. Consideration of the complete experimental and theoretical evidence provides a clear picture of the electronic and steric factors governing dihydrogen activation by these FLPs.

Behavior of uranium(VI) in the presence of a geomaterial: an aquifer sediment

Sediments from aquatic environments can be contaminated with uranium from natural and anthropogenic sources; the behavior of U(VI) was investigated in two natural (SPT and DS) and gamma-irradiated (SPT-I) aquifer sediments in batch systems. Sediments were characterized, and quartz, albite, and kaolinite were mainly found in both sediments by X-ray diffraction. The points of zero charge were 5.4, 5.3, and 5.5, and the organic matter percentages were 48.0, 46.0, and 4.7% for SPT, SPT-I, and DS, respectively. Uranyl nitrate solutions were put in contact with each sediment considering different parameters (pH, contact time, initial concentration of uranium, and temperature). DS sediment did not adsorb any quantity of uranium at different pH values; SPT and SPT-I, attained the highest q e values at pH 3.5–4. The results show chemisorption on homogenous materials and endothermic processes. Desorption behavior of U(VI)/SPT showed a hundred percent desorption with nitric acid and humic acid solutions; in the last case, it is due to the high stability constant of the complex of uranium with the humic acids. The results help to understand the contamination and decontamination processes of sediments with uranium, the bioavailability of uranium, the ecological risk of U-contaminated sediments, and remediation. Doses of 1 MGy of Co-60 gamma radiation did not affect the uranyl ions behavior in the aquifer sediment.

Comment on “Adsorption of uranium (VI) complexes with polymer-based spherical activated carbon”, published by Y.-A. Boussouga et al. [Water Research 249 (2024) 120825]

Calculation of thermodynamic parameters of adsorption such as Gibbs free energy ΔG°ads from experimentally determined adsorption data can be helpful for elucidation of sorption mechanisms. This approach includes the transformation of adsorption coefficients Kd or KL into dimensionless standard adsorption constants Kads [-]. The present comment reveals recently published misleading approaches and offers thermodynamically sound alternatives.

Enhanced capture of uranyl in simulated seawater by supramolecular PSA@PAO hydrogel through carboxyl synergistic effect

Efficient capture of uranium from seawater is of great significance for promoting the sustainable development of nuclear energy and environmental protection. The preparation of highly efficient adsorbent materials plays a key role in this process. In this study, a composite gel PSA@PAO with ultra-high uranium adsorption capacity and excellent desorption efficiency was successfully designed through the supramolecular crosslinking and synergistic effect of glutaraldehyde, hydrazine oxime, sodium alginate, and polyvinyl alcohol. The gel achieved a uranium adsorption capacity of 348 mg·g−1 in a solution with an extremely low uranium concentration (8 ppm) and exhibited ultra-high adsorption selectivity for uranium oxyanions in simulated seawater containing various metal ions. XPS analysis showed that the acylhydrazone groups and carboxylic acid ligands in the PSA@PAO gel could form more stable synergistic uranium complexes. In the desorption solution, the recovery rate of uranium by the PSA@PAO gel reached 98 %, providing a certain strategy for designing efficient adsorbent materials with multi-functional group synergistic effect.

Unique Selectivity Reversal in the Complexation of Uranium(VI) and Plutonium(IV) with Two Novel C-Pivoted Tripodal Amide Ligands: Extraction and Liquid Membrane Transport Studies

ABSTRACT Two new carbon pivoted tripodal amide-containing ligands with different spacers (L I : -CH2- spacer; L II : -CH2-CH2- spacer) have been investigated for the liquid–liquid extraction of tetravalent plutonium and hexavalent uranium from nitric acid feed solutions. The studies were carried out using the ligand solutions prepared in 95% n-dodecane + 5% isodecanol. Pu(IV) extraction was higher than that of U(VI) at 3 M HNO3 for ligand L I which was just the opposite for ligand L II . Increase of the nitric acid concentration resulted in increasing extraction of both metal ions. Isodecanol variation studies exhibited decrease in the extraction of Pu(IV) and U(VI) with increasing isodecanol content in the organic phase. Greater that 98% stripping of Pu(IV) and U(VI) was obtained from the complexes of L I and L II using 0.5 M HNO3 + 0.1 M HEDTA and 1 M Na2CO3, respectively. The slope analysis study suggested the formation of 1:2 (ML2) species with Pu(IV) as well as U(VI) with both ligands at 3 M HNO3. Temperature variation studies showed that the extraction of U(VI) and Pu(IV) with both ligands is exothermic in nature. Supported liquid membrane transport experiments using 0.11 M ligands (L I and L II ) in 95% n-dodecane + 5% isodecanol indicated poor transport (<10% after 2 h) of U(VI) and Pu(IV).

A Metallocene Bis(phosphoranocarbene) of Uranium and a Probe of Its Reactivity with Alcohols.

The addition of 2 equiv of the phosphaylide H2C═PPh3 to the dimethyl uranium metallocene Cp*2UMe2 (Cp* = η5-C5Me5) in toluene with gentle heating at 40 °C generates the phosphorano-stabilized bis(carbene) Cp*2U[C(H)PPh3]2 (1) in good yield. Characterization of 1 by X-ray crystallographic analysis reveals two short uranium-carbon bonds, ranging from 2.301(5) to 2.322(5) Å, consistent with the presence of U═C carbene-type bonds. Monitoring the reaction by NMR spectroscopy suggests that it proceeds through the intermediate formation of the methyl carbene complex Cp*2U[C(H)PPh3](Me) (1Int); however, prolonged heating of these solutions leads to the ortho-cyclometalated carbene species Cp*2U{κ2-[C(H)PPh2(C6H4)]} (2) via intramolecular C-H activation. Rapid conversion from 1 to 2 occurs within hours upon heating its toluene solutions to 100 °C. Preliminary reactivity studies of 1 show that it readily reacts with alcohols, such as HODipp (Dipp = 2,6-diisopropylphenyl) and HOC(CF3)3, to give the mixed carbene alkoxide compounds Cp*2U[C(H)PPh3](OR) (R = Dipp (4Dipp), C(CF3)3 (5CF3)). In one case, the reaction of 1 with HODipp in the presence of adventitious water led to the formation of a few crystals of the terminal U(IV) oxo complex, [Ph3PCH3][Cp*2U(O)(ODipp)] (3oxo). The isolation of 1 marks the first instance of an unchelated, heteroatom-stabilized bis(carbene) complex of uranium that also provides an entryway to the synthesis of its monocarbene derivatives through protonolysis.

Unraveling complexation and enantioseparation of a new chiral‐at‐uranium complex to chiral pesticides R/S‐malaoxons

Unraveling uranium complexes has become a popular study topic in recent years to address the problem of spent fuel treatment. An important and promising investigation is the enantiomer separation of chiral organophosphorus pesticides (OPs) via uranyl‐containing receptors. Among them, malaoxon (MLX), as a chiral OP with high toxicity and good selectivity, is controversial because of the different toxicity differences caused by the R and S configurations to target and non‐target organisms. Therefore, it is crucial to explore effective methods for separating its enantiomers. In this work, a novel 2‐(9‐[1H‐pyrazole‐1‐carbonyl]‐1,10‐phenanthrolin‐2‐yl)‐1H‐inden‐1‐one (HPIDO) ligand, which combines with uranyl to form the chiral‐at‐uranium complex (Uranyl‐HPIDO receptor), was designed for the enantioseparation of R/S‐malaoxons (R/S‐MLXs). Based on density functional theory (DFT), we explored the potential coordination modes between the Uranyl‐HPIDO receptor and R/S‐MLXs at various sites. The analyses of bonding properties, orbital interactions, and weak interactions of intramolecular groups of the complexes, along with the study of thermodynamic properties, revealed that the Uranyl‐HPIDO receptor preferred to bind to the phosphoryl oxygen (O5) of R/S‐MLXs to form stable complexes. Good enantioseparations of the two enantiomers were achieved in various solvents (water, n‐Butanol, n‐Octanol, dichloromethane, propanoic acid, toluene, and cyclohexane); the separation factors (SFR/S) ranged 21–853, and the enantioselectivity coefficients (ESCR/S) were more than 95%. The findings could theoretically offer useful information and guidance for the separation of R/S‐MLXs, in addition to providing fresh concepts for the creation of novel uranyl receptors.

Safety assessment in the disposal of high-level radioactive wastes (HLWs): a geochemical study of uranium complexes in deep groundwater in granites from Beishan, China

Safety assessment in the disposal of high-level radioactive wastes (HLWs): a geochemical study of uranium complexes in deep groundwater in granites from Beishan, China

Combined experimental and theoretical studies of some uranium(VI) complexes derived from imidazole-based carbenes

A series of bidentate, viz., 1,1'-(1,2-ethylene)-3,3'-dimethyldiimidazoline-2,2'-diylidene (L1), 1-methyl-3-(2-pyridylmethyl)-imidazoline-2-ylidene (L2) and tridentate, viz., 1,3-bis(2-pyridyl)-imidazoline-2-ylidene (L3) ligands have been obtained from their corresponding imidazolium salts through deprotonation reactions. Treatment of UO2Cl2(THF)3 with one equivalent L3 produces air-stable U(VI)-carbene complex 3, characterized by elemental analysis, FTIR, NMR spectroscopy as well as extended X-ray absorption fine structure (EXAFS) analysis. EXAFS result indicates that the ligand is bonded through one C and two N-atoms to the uranium atom. Attempts to synthesize uranyl complexes derived from L1 and L2 were also successful but these complexes are decomposed quickly within one hour at room temperature. 3 produces pure UO2 powder when heated under an argon atmosphere from room temperature to 600 °C with constant heating rate of 5 °C/min. The solid-state UV–Vis spectrum of the compound shows absorption peaks at 332 and 450 nm. The excitation spectrum of 3 (at λ em = 520 nm) exhibits two almost symmetrical peaks at 273 and 368 nm. Density functional theory-based quantum mechanical calculations indicate that a partial covalent interaction exists between the carbene C and U while a weak non-covalent interaction exists between carbene N and U atoms.

Synthesis and Characterization of Uranium Complexes Supported by Substituted Aryldimethylsilylanilide Ligands

Synthesis and Characterization of Uranium Complexes Supported by Substituted Aryldimethylsilylanilide Ligands

Actinide Triamidoamine (TrenR) Chemistry: Uranium and Thorium Derivatives Supported by a Diphenyl‐tert‐Butyl‐Silyl‐Tren Ligand

AbstractWe report the synthesis and characterisation of thorium(IV), uranium(III), and uranium(IV) complexes supported by a sterically demanding triamidoamine ligand with N‐diphenyl‐tert‐butyl‐silyl substituents. Treatment of ThCl4(THF)3.5 or UCl4 with [Li3(TrenDPBS)] (TrenDPBS={N(CH2CH2NSiPh2But)3}3−) afforded [An(TrenDPBS)Cl] (An=Th, 1Th; U, 1U). Complexes 1An react with benzyl potassium to afford the cyclometallates (TrenDPBScyclomet) [An{N(CH2CH2NSiPh2But)2(CH2CH2NSiPhButC6H4)}] (An=Th, 2Th; U, 2U). Treatment of 1An with sodium azide affords [An(TrenDPBS)N3] (An=Th, 3Th; U, 3U). Reaction of 3Th with potassium graphite affords 2Th. In contrast, 3Th reacts with cesium graphite to afford the doubly‐cyclometallated (TrenDPBSd‐cyclomet) ate complex [Th{N(CH2CH2NSiPh2But)(CH2CH2NSiPhButC6H4)}2Cs(THF)3] (4). In contrast to 3Th, reaction of 3U with potassium graphite produces the uranium(III) complex [U(TrenDPBS)] (5), and 5 can also be prepared by reaction of potassium graphite with 1U. The loss of azide instead of conversion to nitrides contrasts to prior work when the silyl group is iso‐propyl silyl, underscoring how ligand substituents profoundly drive the reaction chemistry. Several complexes exhibit T‐shaped meta‐C−H⋅⋅⋅phenyl and staggered parallel π–π‐stacking interactions, demonstrating subtle weak interactions that drive ancillary ligand geometries. Compounds 1An–3An, 4, and 5 have been variously characterised by single crystal X‐ray diffraction, multi‐nuclear NMR spectroscopy, infrared spectroscopy, UV/Vis/NIR spectroscopy, and elemental analyses.

A Genuine Trivalent Bis‐Acylphosphide (BAP) Complex of Uranium

AbstractThe genuine trivalent uranium complex, K[UIII(mesBAP)4], employing four bidentate bis(2,4,6‐trimethylbenzoyl)phosphide (mesBAP) chelating ligands, is reported and obtained by the reduction of the literature‐known tetravalent analog [UIV(mesBAP)4]. Hence, the bis(acyl)phosphide mesBAP ligand allowed to establish a fully reversible redox couple with uranium in the oxidation states +III and +IV. In both complexes [U(mesBAP)4]0/−, the uranium ions are coordinated to four mesBAP ligands in a square antiprismatic geometry. All new compounds have been characterized by single‐crystal XRD analysis, 1H and 31P NMR, and UV/Vis/NIR electronic absorption spectroscopy, as well as SQUID magnetization and electrochemical measurements, and CW X‐band EPR in the case of the trivalent complex.