Highlights in Uranium Coordination Chemistry

Binuclear Uranium(VI) Complexes with a “Pacman” Expanded Porphyrin: Computational Evidence for Highly Unusual Bis‐Actinyl Structures

“…The early 5f elements such as uranium, neptunium, and plutonium have interesting possibilities that arise from the accessibility of s, p, d, and f orbitals to chemical bonding, thus allowing for exciting coordination chemistry. [2,3] For uranium in the oxidation states of + 5 and + 6, the most characteristic and stable form is the linear UO 2 n + moiety, the uranyl ion.…”

“…[12,[21][22][23][24][25] The U=O bonding in the uranyl dication involves most of the uranium valence orbitals, making the uranium coordination mainly occur in the equatorial plane. [3,26] Besides the Abstract: On the basis of uranyl complexes reacting with a polypyrrolic ligand (H 4 L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO 2 ) 2 (L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum-energy structures.…”

Cation–Cation Complexes of Pentavalent Uranyl: From Disproportionation Intermediates to Stable Clusters

“…[12][13][14] However, because of its low stability only limited information is available on the reactivity and physicochemical properties of molecular pentavalent uranyl complexes relative to other uranium species. [15][16][17] Kinetic and theoretical studies suggest that the disproportionation reaction involves the formation of a dimeric cation-cation complex presenting two mutually coordinated UO 2 + groups, The preparation of stable complexes requires a careful choice of counter ions and reaction conditions. Notably the reaction of 1 with salophen 2À in pyridine leads to immediate disproportionation, but in the presence of [18] which is followed by the protonation of the uranyl oxygen atoms to yield UO 2 2 + and U 4 + species.…”

Stable Pentavalent Uranyl Species and Selective Assembly of a Polymetallic Mixed‐Valent Uranyl Complex by Cation–Cation Interactions

“…We also describe the selective synthesis and the structure of the first mixed-valent UO 2 + ···UO 2 2+ molecular complex, which provides a rare example of functionalization of the U VI =O group. [20,22] By breaking away from the current trend of using steric bulk to prevent dimer formation and the associated disproportionation of UO 2 + complexes, we show that the non-bulky Schiff base ligand salen 2À (N,N'-bis(salicylidene)ethylenediamine) can stabilize pentavalent uranyl ions through the formation of a highly stable cation-cation complex. Moreover, we demonstrate that the resulting tetrameric uranyl(V) complex exhibits unambiguous antiferromagnetic coupling between the uranium centers.…”

“…These interactions can be used in two areas that currently attract great interest, namely the expansion of felement supramolecular chemistry and the enhancement of magnetic interactions in actinide compounds. [1][2][3][4][5][6][7][8][9][10][11][12] Moreover, oligomeric cation-cation species that present mutually coordinated actinyl ions are likely to play a crucial role in nuclear waste reprocessing and in the migration of radioactive actinides in the environment. [1] Cation-cation interactions are known to be important in neptunyl(V) structural chemistry, [13] but are more rarely found in uranyl(VI) compounds because of the lower basicity of the UO 2 2+ oxygen atoms.…”