Gas Phase Computational Studies on the Competition between Nitrile and Water Ligands in Uranyl Complexes^†

Abstract

The gas phase formation of uranyl dicationic complexes containing water and nitrile (acetonitrile, propionitrile, and benzonitrile) ligands, [UO2(H2O)m(RCN)n]2+, has been studied using density functional theory with a relativistic effective core potential to account for scalar relativistic effects on uranium. It is shown that nitrile addition is favored over the addition of water ligands. Decomposition of these complexes to [UO2OH(H2O)m(RCN)n]+ by the loss of either H3O+ or (RCN + H)+ is also examined. It is found that this reaction is competitive with the ligand addition when the coordination sphere of uranyl is unsaturated. Additionally, this reaction is influenced by the size of the nitrile ligand with reactions involving acetonitrile being the most prevalent. Finally, ligand addition to the monocation shows trends similar to that of the dication with energetic differences being smaller for the addition to the monocation. The gas phase formation of uranyl dicationic complexes containing water and nitrile (acetonitrile, propionitrile, and benzonitrile) ligands,, has been studied using density functional theory with a relativistic effective core potential to account for scalar relativistic effects on uranium. It is shown that nitrile addition is favored over the addition of water ligands. Decomposition of these complexes to+ by the loss of either H 3 O + or (RCN + H) + is also examined. It is found that this reaction is competitive with the ligand addition when the coordination sphere of uranyl is unsaturated. Additionally, this reaction is influenced by the size of the nitrile ligand with reactions involving acetonitrile being the most prevalent. Finally, ligand addition to the monocation shows trends similar to that of the dication with energetic differences being smaller for the addition to the monocation.

Cluster-Models for Uranyl(VI) Adsorption on α-Alumina

“…Overall, the equatorial U−O eq distances lie within the range of 2.32 (partial first solvation shell) to 2.49 Å for the fully solvated five-coordinate species with 2+ charge. The binding energies for the one-, three-, and five-coordinate clusters correspond to −73.9, −193.3, and −264.2 kcal/mol, respectively, pointing to a nonlinear trend (nonaddtivity) in the total hydration energy of these systems. − On average, each additionall water reduces the hydration energy by ∼5 kcal/mol.…”

Formation of Bare UO22+and NUO+by Fragmentation of Gas-Phase Uranyl–Acetonitrile Complexes

“…The charge-exchange reactions to produce ligated uranyl–hydroxide have also been modeled computationally . In general, the formation of hydroxide species was modeled with the assumption that uranyl must first have two ligands bound to it, with at least one being H 2 O.…”

“…53 The charge-exchange reactions to produce ligated uranyl− hydroxide have also been modeled computationally. 63 In general, the formation of hydroxide species was modeled with the assumption that uranyl must first have two ligands bound to it, with at least one being H 2 O. The reaction energies of the charge-exchange reactions were found by DFT to be on the order of 10−25 kcal/mol less exoergic than the alternative ligand addition reactions.…”

Uranium Oxo and Superoxo Cations Revealed Using Infrared Spectroscopy in the Gas Phase

“…However, most other gas-phase experiments produce only singly charged uranium species. Recent spectroscopy experiments have isolated uranium and its oxides in rare gas matrixes or in the gas phase to probe the structure and bonding in these systems, − and computational studies have complemented this work. − Selected complexes of uranium or its oxide ions have been investigated with mass spectrometry to explore solvation and coordination. − In the present work, we investigate mass-selected uranium oxide ions with infrared spectroscopy in the oxide stretching region.…”