Equatorial coordination of uranyl: Correlating ligand charge donation with the O_yl-U-O_yl asymmetric stretch frequency

Journal Article · Wed Jan 31 23:00:00 EST 2018 · Journal of Organometallic Chemistry

DOI:https://doi.org/10.1016/j.jorganchem.2017.10.010· OSTI ID:1463666

Gibson, John K. ^[1]; de Jong, Wibe A. ^[2]; van Stipdonk, Michael J. ^[3]; Martens, Jonathan ^[4]; Berden, Giel ^[4]; Oomens, Jos ^[5]

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1. Lawrence Berkeley National Laboratory. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
2. Lawrence Berkeley National Laboratory. (LBNL), Berkeley, CA (United States). Computational Research Division
3. Duquesne University, Pittsburgh, PA (United States). Department of Chemistry and Biochemistry
4. Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Nijmegen (The Netherlands).
5. Radboud University, Nijmegen (The Netherlands). Institute for Molecules and Materials, FELIX Laboratory; University of Amsterdam, Amsterdam (The Netherlands). Van‘t Hoff Institute for Molecular Sciences

In uranyl coordination complexes, UO₂(L)_n²⁺, uranium in the formally dipositive [O=U=O]²⁺ moiety is coordinated by n neutral organic electron donor ligands, L. The extent of ligand electron donation, which results in partial reduction of uranyl and weakening of the U=O bonds, is revealed by the magnitude of the red-shift of the uranyl asymmetric stretch frequency, ν₃ . This phenomenon appears in gas-phase complexes in which uranyl is coordinated by electron donor ligands: the ν₃ red-shift increases as the number of ligands and their proton affinity (PA) increases. Because PA is a measure of the enthalpy change associated with a proton-ligand interaction, which is much stronger and of a different nature than metal ion-ligand bonding, it is not necessarily expected that ligand PAs should reliably predict uranyl-ligand bonding and the resulting ν₃ red-shift. In this study, ν₃ was measured for uranyl coordinated by ligands with a relatively broad range of PAs, revealing a surprisingly good correlation between PA and ν₃ frequency. From computed ν₃ frequencies for bare UO₂ cations and neutrals, it is inferred that the effective charge of uranyl in UO₂(L)_n²⁺ complexes can be reduced to near zero upon ligation by sufficiently strong charge-donor ligands. The basis for the correlation between ν₃ and ligand PAs, as well as limitations and deviations from it, are considered. It is demonstrated that the correlation evidently extends to a ligand that exhibits polydentate metal ion coordination.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Energy Frontier Research Centers (EFRC) (United States). Center for Actinide Science & Technology (CAST); Lawrence Berkeley National Laboratory, Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC).
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC-21)
• DOE Contract Number: SC0016568; AC02-05CH11231; AC05-00OR22725
• OSTI ID: 1463666
• Journal Information: Journal of Organometallic Chemistry, Journal Name: Journal of Organometallic Chemistry Journal Issue: C Vol. 857; ISSN 0022-328X
• Publisher: Elsevier
• Country of Publication: United States
• Language: English