Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 134, Issue 12, Pages 5586-5597Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja2105015
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Funding
- LANL by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy
- Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences of the U.S. Department of Energy at Lawrence Berkeley National Laboratory [DE-AC02-05CH11231]
- LANL by Glenn T. Seaborg Institute
- National Nuclear Security Administration of the U.S. Department of Energy [DE-AC52-06NA25396]
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Chlorine K-edge X-ray absorption spectroscopy (XAS) and ground-state and time-dependent hybrid density functional theory (DFT) were used to probe the electronic structures of O-h-MCl62- (M = Ti, Zr, Hf, U) and C-4 nu-UOCl5-, and to determine the relative contributions of valence 3d, 4d, 5d, 6d, and 5f orbitals in M-Cl bonding. Spectral interpretations were guided by time-dependent DFT calculated transition energies and oscillator strengths, which agree well with the experimental XAS spectra. The data provide new spectroscopic evidence for the involvement of both 5f and 6d orbitals in actinide-ligand bonding in UCl62-. For the MCl62-, where transitions into d orbitals of t(2g) symmetry are spectroscopically resolved for all four complexes, the experimentally determined Cl 3p character per M-Cl bond increases from 8.3(4)% (TiCl62-) to 10.3(5)% (ZrCl62-), 12(1)% (HfCl62-), and 18(1)% (UCl62-). Chlorine K-edge XAS spectra of UOCl5- provide additional insights into the transition assignments by lowering the symmetry to C-4 nu, where five pre-edge transitions into both 5f and 6d orbitals are observed. For UCl62, the XAS data suggest that orbital mixing associated with the U 5f orbitals is considerably lower than that of the U 6d orbitals. For both UCl62- and UOCl5-, the ground-state DFT calculations predict a larger 5f contribution to bonding than is determined experimentally. These findings are discussed in the context of conventional theories of covalent bonding for d- and f-block metal complexes.
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