Sterically Congested Uranyl Complexes with Seven-Coordination of the UO2 Unit: the Peculiar Ligation Mode of Nitrate in [UO2(NO3)2(Rbtp)] Complexes

Benchtop access to anhydrous actinide N-donor coordination complexes using ionic liquids

By dehydrating actinide salts with an ionic liquid containing a common anion and subsequent reaction with N-heterocyclic ligands, we challenge the concept that actinides prefer O- over N-donors; rather the acidic hydrogen atoms of protic solvents hinder the formation of more elusive f-element N-donor coordination complexes.

Hexadentate β-Dicarbonyl(bis-catecholamine) Ligands for Efficient Uranyl Cation Decorporation: Thermodynamic and Antioxidant Activity Studies

The special linear dioxo cation structure of the uranyl cation, which relegates ligand coordination to an equatorial plane perpendicular to the O═U═O vector, poses an unusual challenge for the rational design of efficient chelating agents. Therefore, the planar hexadentate ligand rational design employed in this work incorporates two bidentate catecholamine (CAM) chelating moieties and a flexible linker with a β-dicarbonyl chelating moiety (β-dicarbonyl(CAM)₂ ligands). The solution thermodynamics of β-dicarbonyl(CAM)₂ with a uranyl cation was investigated by potentiometric and spectrophotometric titrations. The results demonstrated that the pUO₂²⁺ values are significantly higher than for the previously reported TMA(2Li-1,2-HOPO)₂, and efficient chelation of the uranyl cation was realized by the planar hexadentate β-dicarbonyl(CAM)₂. The efficient chelating ability of β-dicarbonyl(CAM)₂ was attributed to the presence of the more flexible β-dicarbonyl chelating linker and planar hexadentate structure, which favors the geometric arrangement between ligand and uranyl coordinative preference. Meanwhile, β-dicarbonyl(CAM)₂ also exhibits higher antiradical efficiency in comparison to butylated hydroxyanisole. These results indicated that β-dicarbonyl(CAM)₂ has potential application prospects as a chelating agent for efficient chelation of a uranyl cation.

The structural evolution and tunable photoluminescence of f-element bearing coordination polymers of the 2,4,6-tri-α-pyridyl-1,3,5-triazine ligand

An attempt at expanding the family of f-element bearing TPTZ coordination polymers has resulted in fifteen new complexes with topologies that evolved along the periodic table and tunable photoluminescence properties.

Understanding the origins of Oyl–U–Oylbending in the uranyl (UO22+) ion

Although rare, O_yl–U–O_ylbending in the uranyl (UO₂²⁺) ion can be effected by either steric perturbation or electronic perturbation.

Ligand size dependence of U–N and U–O bond character in a series of uranyl hexaphyrin complexes: quantum chemical simulation and density based analysis

A quantum chemical and density based analysis of bonding in uranyl hexaphyrin complexes, looking for trends in stability and covalency.

Assessing covalency in equatorial U–N bonds: density based measures of bonding in BTP and isoamethyrin complexes of uranyl

N-donor complexes of uranyl have been investigated with density-based analytical methods in order to quantify equatorial bond covalency and its effect on axial U–O_yl bonding.

High stability of the He atom confined in a U@C60 fullerene

Electronic structure analysis highlights the high stability of He atom in the actinide metallofullerene U@C₆₀.

Toward equatorial planarity about uranyl: synthesis and structure of tridentate nitrogen-donor {UO2}2+ complexes

The reaction of UO2Cl2·3THF with the tridentate nitrogen donor ligand 2,6-bis(2-benzimidazolyl)pyridine (H2BBP) in pyridine leads to the formation of three different complexes: [(UO2)(H2BBP)Cl2] (1), [(UO)2(HBBP)(Py)Cl] (2), and [(UO2)(BBP)(Py)2] (3) after successive deprotonation of H2BBP with a strong base. Crystallographic determination of 1-3 reveals that increased charge through ligand deprotonation and displacement of chloride leads to equatorial planarity about uranyl as well as a more compact overall coordination geometry. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectra of 1-3 at the U-4d edges have been recorded using a soft X-ray Scanning Transmission X-ray Microscope (STXM) and reveal the uranium 4d5/2 and 4d3/2 transitions at energies associated with uranium in the hexavalent oxidation state. First-principles Density Functional Theory (DFT) electronic structure calculations for the complexes have been performed to determine and validate the coordination characteristics, which correspond well to the experimental results.

Influence of diluent alkyl substitution on the extraction of Am(III) and Eu(III) by a 6,6´-bis(1,2,4-triazin-3-yl)-2,2´-bipyridine ligand dissolved in alkylated cyclohexanone diluents

Several alkylated cyclohexanones were investigated as potential diluents for the selective extraction of Am(III) from Eu(III) from nitric acid solutions by the CyMe4-BTBP ligand. No significant extraction of either of the metal ions was observed for these diluents themselves. In the extractions from 1 M HNO3, 3-methylcyclohexanone and 4-methylcyclohexanone gave comparable results to cyclohexanone whereas in the extractions from 4 M HNO3, 2-methylcyclohexanone, 3-methylcyclohexanone and 4-methylcyclohexanone all gave superior results. For the monomethylated diluents, D Am and SFAm/Eu decreased in the order of alkyl substitution 2 > 4 ∼ 3. However, alkyl substitution of cyclohexanone significantly slows down the extraction kinetics compared to cyclohexanone, and the position of alkyl substitution was found to play an important role in the solvents properties. 3-Methylcyclohexanone was identified as the most promising of the diluents.

Bis(methanol-κO)dioxido[3,3'-(1H-1,2,4-triazole-3,5-diyl)diphenolato-κ3O,N4,O']uranium(VI) methanol monosolvate

The structure of the title compound, [U(C(14)H(9)N(3)O(2))O(2)(CH(3)OH)(2)]·CH(3)OH, is the first to be reported for an actinide complex including triazole ligands. The U(VI) atom exhibits a pentagonal-bipyramidal NO(6) coordination environment, involving two axial oxide ligands [U=O = 1.766 (3) and 1.789 (3) Å], four equatorial O atoms [U-O = 2.269 (3)-2.448 (3) Å] from the ligand and the two coordinated methanol molecules, and one equatorial N atom [U-N = 2.513 (4) Å] from the ligand. In the crystal structure, the complex molecules are linked via intermolecular N-H...O and O-H...O hydrogen bonds to form a two-dimensional structure.

Exploring the uranyl organometallic chemistry: from single to double uranium-carbon bonds

Uranyl organometallic complexes featuring uranium(VI)-carbon single and double bonds have been obtained from uranyl UO(2)X(2) precursors by avoiding reduction of the metal center. X-ray diffraction and density functional theory analyses of these complexes showed that the U-C and U=C bonds are polarized toward the nucleophilic carbon.

The influence of linker geometry in bis(3-hydroxy-N-methyl-pyridin-2-one) ligands on solution phase uranyl affinity

Seven water-soluble, tetradentate bis(3-hydroxy-N-methyl-pyridin-2-one) (bis-Me-3,2-HOPO) ligands were synthesized that vary only in linker geometry and rigidity. Solution-phase thermodynamic measurements were conducted between pH 1.6 and pH 9.0 to determine the effects of these variations on proton and uranyl cation affinity. Proton affinity decreases by introduction of the solubilizing triethylene glycol group as compared to unsubstituted reference ligands. Uranyl affinity was found to follow no discernable trends with incremental geometric modification. The butyl-linked 4 li-Me-3,2-HOPO ligand exhibited the highest uranyl affinity, consistent with prior in vivo decorporation results. Of the rigidly-linked ligands, the o-phenylene linker imparted the best uranyl affinity to the bis-Me-3,2-HOPO ligand platform.

Linear uranium metallocenes with polydentate aromatic nitrogen ligands

Treatment of [Cp*(2)U(NCMe)(5)]X(2) [Cp* = C(5)Me(5), X = BPh(4) (1) or I (1')] or Cp*(2)UI(2) in acetonitrile with the polydentate aromatic nitrogen bases phen, terpy and R(4)btbp led to the formation of the linear uranium metallocenes [Cp*(2)U(NCMe)(3)(phen)]X(2) [X = BPh(4) (2), I (2')], [Cp*(2)U(NCMe)(2)(terpy)][BPh(4)](2) (4), [Cp*(2)U(NCMe)(Me(4)btbp)][BPh(4)](2) (5) and [Cp*(2)U(NCMe)(CyMe(4)btbp)][X](2), [X = BPh(4) (6), I (6')], [phen = 1,10-phenanthroline, terpy = 2,2':6,2''-terpyridine, Me(4)btbp = 6,6'-bis-(3,3,6,6-tetramethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine, CyMe(4)btbp = 6,6'-bis-(3,3,6,6-tetramethyl-cyclohexane-1,2,4-triazin-3-yl)-2,2'-bipyridine]. The bent metallocene [Cp*(2)U(phen)(2)][BPh(4)](2) (3) was isolated from the reaction of 1 and two molar equivalents of phen in THF. The X-ray crystal structures of 2.2MeCN, 3.2THF, and 6'.2MeCN were determined.