Density Functional Studies on the Complexation and Spectroscopy of Uranyl Ligated with Acetonitrile and Acetone Derivatives

Abstract

The coordination of nitrile (acetonitrile, propionitrile, and benzonitrile) and carbonyl (formaldehyde, acetaldehyde, and acetone) ligands to the uranyl dication (UO22+) has been examined using density functional theory (DFT) utilizing relativistic effective core potentials (RECPs). Complexes containing up to six ligands have been modeled in the gas phase for all ligands except formaldehyde, for which no minimum could be found. A comparison of relative binding energies indicates that 5-coordinate complexes are predominant, while 6-coordinate complexes involving propionitrile and acetone ligands might be possible. Additionally, the relative binding energy and the weakening of the uranyl bond is related to the size of the ligand, and in general, nitriles bind more strongly to uranyl than carbonyls. Disciplines Chemistry CommentsReprinted (adapted) The coordination of nitrile (acetonitrile, propionitrile, and benzonitrile) and carbonyl (formaldehyde, acetaldehyde, and acetone) ligands to the uranyl dication (UO 2 2+ ) has been examined using density functional theory (DFT) utilizing relativistic effective core potentials (RECPs). Complexes containing up to six ligands have been modeled in the gas phase for all ligands except formaldehyde, for which no minimum could be found. A comparison of relative binding energies indicates that 5-coordinate complexes are predominant, while 6-coordinate complexes involving propionitrile and acetone ligands might be possible. Additionally, the relative binding energy and the weakening of the uranyl bond is related to the size of the ligand, and in general, nitriles bind more strongly to uranyl than carbonyls.

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

“…8 The present work builds upon the previous results by allowing water, as well as nitrile ligands, to bind to uranyl.…”

“…As noted in previous work, 8 the sixth ligand can be a direct ligand (although weakly bound), or it can add to the first solvent shell. There are three possibilities when two, three, and four nitrile ligands are present.…”

Gas-Phase Coordination Complexes of UVIO22+, NpVIO22+, and PuVIO22+ with Dimethylformamide

“…Our hypothesis was that DMF as the co-solvent, with a gas-phase basicity of 857 kJ/mol, compared to basicities of 660, 748, and 782 kJ/mol, for water, acetonitrile, and Figure S1) acetone, respectively [20] [21], and the high basicity of DMF relative to acetonitrile or acetone should result in greater electron donation to the metal center by the first four ligands, which may render addition of a fifth DMF ligand energetically unfavorable. Similar shifts to higher stability of complexes with four ligands relative to those with five have been observed previously with gas-phase uranyl-nitrile complexes [12].…”

On the “yl” bond weakening in uranyl(VI) coordination complexes

“…Kaltsoyannis et al, however, did not find any evidence of the "p competition", confirming only in part the claims by Clark et al 3 Windus et al studied the uranyl(VI)-acetonitrile bonding interaction and found that the ligand p donation to the U 5f orbital lead to the weakening of the U-O yl bond. 7 Denning and coauthors 8-9 made an extensive series of spectroscopic and theoretical investigations on the electronic structures of UO 2 Cl 4 2and Cs 2 UO 2 Cl 4 . They discussed the equatorial ligand interaction with the uranyl molecular orbitals (MOs) in these complexes.…”