Dimeric uranyl complexes with bridging perrhenates

Effect of Reaction Time on Lanthanide Borate Perrhenate Complexes

Six new trivalent lanthanide borate perrhenate structures─the isostructural series Ln[B₈O₁₁(OH)₄(H₂O)(ReO₄)] (Ln = Ce-Nd, Sm, Eu; 1) and La[B₆O₉(OH)₂(H₂O)(ReO₄)] (2)─have been prepared and structurally characterized. Single-crystal X-ray diffraction analysis reveals that both structures crystallize in the P2₁/n space group, contain 10-coordinated trivalent lanthanides in a capped triangular cupola geometry, are 3D borate framework materials, and contain either terminal (1) or bridging (2) perrhenate moieties. The presence or lack of a bridging perrhenate, along with the identity of the basal ligands, dictates how the layers are tethered together, ultimately leading to the different structures. Furthermore, the formation of 1 is sensitive to the reaction time employed. Herein, the synthesis, structural descriptions, and spectroscopy of these trivalent lanthanide perrhenate borate complexes are presented.

Involvement of 5f Orbitals in the Covalent Bonding between the Uranyl Ion and Trialkyl Phosphine Oxide: Unraveled by Oxygen K-Edge X-ray Absorption Spectroscopy and Density Functional Theory

Monodentate organophosphorus ligands have been used for the extraction of the uranyl ion (UO₂²⁺) for over half a century and have exhibited exceptional extractability and selectivity toward the uranyl ion due to the presence of the phosphoryl group (O═P). Tributyl phosphate (TBP) is the extractant of the world-renowned PUREX process, which selectively recovers uranium from spent nuclear fuel. Trialkyl phosphine oxide (TRPO) shows extractability toward the uranyl ion that far exceeds that for other metal ions, and it has been used in the TRPO process. To date, however, the mechanism of the high affinity of the phosphoryl group for UO₂²⁺ remains elusive. We herein investigate the bonding covalency in a series of complexes of UO₂²⁺ with TRPO by oxygen K-edge X-ray absorption spectroscopy (XAS) in combination with density functional theory (DFT) calculations. Four TRPO ligands with different R substituents are examined in this work, for which both the ligands and their uranyl complexes are crystallized and investigated. The study of the electronic structure of the TRPO ligands reveals that the two TRPO molecules, irrespective of their substituents, can engage in σ- and π-type interactions with U 5f and 6d orbitals in the UO₂Cl₂(TRPO)₂ complexes. Although both the axial (O_yl) and equatorial (O_eq) oxygen atoms in the UO₂Cl₂(TRPO)₂ complexes contribute to the X-ray absorption, the first pre-edge feature in the O K-edge XAS with a small intensity is exclusively contributed by O_eq and is assigned to the transition from O_eq 1s orbitals to the unoccupied molecular orbitals of 1b_1u + 1b_2u + 1b_3u symmetries resulting from the σ- and π-type mixing between U 5f and O_eq 2p orbitals. The small intensity in the experimental spectra is consistent with the small amount of O_eq 2p character in these orbitals for the four UO₂Cl₂(TRPO)₂ complexes as obtained by Mulliken population analysis. The DFT calculations demonstrate that the U 6d orbitals are also involved in the U-TRPO bonding interactions in the UO₂Cl₂(TRPO)₂ complexes. The covalent bonding interactions between TRPO and UO₂²⁺, especially the contributions from U 5f orbitals, while appearing to be small, are sufficiently responsible for the exceptional extractability and selectivity of monodentate organophosphorus ligands for the uranyl ion. Our results provide valuable insight into the fundamental actinide chemistry and are expected to directly guide actinide separation schemes needed for the development of advanced nuclear fuel cycle technologies.

Perrhenate and Pertechnetate Complexes of U(IV), Np(IV), and Pu(IV) with Dimethyl Sulfoxide as an O-Donor Ligand

A series of new dimethyl-sulfoxide-containing pertechnetates and perrhenates of tetravalent U, Np, and Pu were synthesized and structurally characterized by the X-ray diffractometry. In all the synthesized compounds, the actinide atoms were coordinated by eight DMSO molecules with or without an extra XO₄^- anion in the coordination sphere. This resulted in the square antiprismatic or capped square antiprismatic coordination of An atoms. Three or four XO₄^- anions play the role of outer-sphere anions. The electron and IR spectra of the compounds correlated with their crystal structure.

Structural Role of Isonicotinic Acid in U(VI), Np(VI), and Pu(VI) Complexes with TcO4-, ReO4-, and ClO4- Ions

A series of new pertechnetate, perrhenate, and perchlorate compounds of hexavalent U, Np, and Pu containing isonicotinic acid were synthesized. Their crystal structures were determined by X-ray diffractometry. In all compounds, actinide atoms are found in pentagonal bipyramidal surroundings. They are coordinated by 2 to 4 isonicotinic acid molecules which exist in zwitterionic form as a result of N atom protonation. If only 2 or 3 isonicotinic acid molecules are present in the surroundings of an actinide (An) atom, TcO₄^- or ReO₄^- anions act as monodentate ligands. Otherwise, XO₄^- play the role of outer sphere anions. Electron and IR spectra of the compounds correlate with their crystal structure.

An exploration of homo- and heterometallic UO22+ hybrid materials containing chelidamic acid: synthesis, structure, and luminescence studies

Eight U(vi)–chelidamate compounds highlight the structural significance of modified ligands as sources for direct metal–ligand coordination or halogen-based interaction platforms.

Crystal structure of Th(IV) perchlorate and U(VI) nitrate complexes with trimethyl phosphate: [Th(OP(OCH 3 ) 3 ) 4 (O 2 P(OCH 3 ) 2 ) 2 ] 2 [ClO 4 ] 4 and [UO 2 (OP(OCH 3 ) 3 )(O 2 P(OCH 3)2)(NO3)] 2

Single crystals of [Th(TMP)4(DMP)2]2[ClO4]4 and [UO2(TMP)(DMP)(NO3)]2 have been synthesized and their structures have been determined by X-ray diffraction analysis. The complexes of Th(IV) and U(VI) contain simultaneously both the molecular ligand trimethyl phosphate (TMP) and the anion dimethyl phosphate. The main structural motif in Th(IV) complex is centrosymmetric dimeric cation [Th(TMP)4(DMP)2] 2 4+ , and in U(VI) it is the neutral centrosymmetric dimeric complex [UO2(TMP)(DMP)(NO3)]2. Coordination polyhedron of Th(IV) is tetragonal antiprism, for U(VI) it is pentagonal bipyramid. The structures are compared with those of other Th(IV) and U(VI) complexes containing other trialkyl phosphates.

Heterometallic complexes involving iron(II) and rhenium(VII) centers connected by mu-oxido bridges

The reaction of FeI(2) with two equivalents of AgReO(4) in acetonitrile leads to yellow, crystalline Fe(ReO(4))(2)(CH(3)CN)(3) (1), and the treatment of 1 with four equivalents of CpFe(CO)(2)CN gives orange, crystalline Fe(ReO(4))(2)[CpFe(CO)(2)(CN)](4) (2). Compound 2 can also be prepared in one step by the reaction of FeI(2), AgReO(4) and CpFe(CO)(2)CN in dichloromethane. The structure of 1 consists of infinite chains in which alternating {Fe(CH(3)CN)(4)} and {Fe(ReO(4))(2)(CH(3)CN)(2)} units are linked by perrhenate anions to form a (-ReO(2)-O-Fe(ReO(4))(2)(CH(3)CN)(2)-O-ReO(2)-O-Fe(CH(3)CN)(4)-O-)(n) molecular wire. The structure of 2 shows a monomeric iron complex with a slightly distorted octahedral coordination environment consisting of four organometallic complexes coordinated in the equatorial plane via the cyanide groups and two monodentate perrhenates in the corresponding apical positions. Both compounds were further characterised in the solid state by IR spectroscopy, thermogravimetric analysis and magnetic susceptibility measurements. The magnetic data indicate that 1 behaves as a ferrimagnetic chain with 3D ordering below 8 K due to inter-chain interactions. Compound 2 has antiferromagnetic interactions within the Fe(ReO(4))(2)[CpFe(CO)(2)(CN)](4) clusters.