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Title: Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory

Abstract

We describe the use of Cl K-edge X-ray Absorption Spectroscopy (XAS) and both ground state and time-dependent hybrid density functional theory (DFT) to probe electronic structure and determine the degree of orbital mixing in M-Cl bonds for (C5Me5)2MCl2 (M = Ti, 1; Zr, 2; Hf, 3; Th, 4; and U, 5), where we can directly compare a class of structurally similar compounds for d- and f-elements. We report direct experimental evidence for covalency in M-Cl bonding, including actinides, and offer insight into the relative roles of the valence f- and dorbitals in these systems. The Cl K-edge XAS data for the group IV transition metals, 1 – 3, show slight decreases in covalency in M-Cl bonding with increasing principal quantum number, in the order Ti > Zr > Hf. The percent Cl 3p character per M-Cl bond was experimentally determined to be 25, 23, and 22% per M-Cl bond for 1-3, respectively. For actinides, we find a shoulder on the white line for (C5Me5)2ThCl2, 4, and distinct, but weak pre-edge features for 2 (C5Me5)2UCl2, 5. The percent Cl 3p character in Th-Cl bonds in 4 was determined to be 14 %, with high uncertainty, while the U-Cl bonds in 5more » contains 9 % Cl 3p character. The magnitudes of both values are approximately half what was observed for the transition metal complexes in this class of bent metallocene dichlorides. Using the hybrid DFT calculations as a guide to interpret the experimental Cl K-edge XAS, these experiments suggest that when evaluating An- Cl bonding, both 5f- and 6d-orbitals should be considered. For (C5Me5)2ThCl2, the calculations and XAS indicate that the 5f- and 6d-orbitals are nearly degenerate and heavily mixed. In contrast, the 5f- and 6d-orbitals in (C5Me5)2UCl2 are no longer degenerate, and fall in two distinct energy groupings. The 5f-orbitals are lowest in energy and split into a 5-over-2 pattern with the high lying U 6d-orbitals split in a 4-over-1 pattern, the latter of which is similar to the dorbital splitting in group IV transition metal (C5R5)2MCl2 (R = H, Me) compounds. Time dependent-DFT (TD-DFT) was used to calculate the energies and intensities of Cl 1s transitions into empty metal based orbitals containing Cl 3p character, and provide simulated Cl K-edge XAS spectra for 1 - 4. However, for 5, which has two unpaired electrons, analogous information was obtained from transition dipole calculations using ground state Kohn-Sham orbitals. The simulations provide additional confidence in the interpretation of spectra based on ground state calculations. Overall, this study demonstrates that Cl K-edge XAS and DFT calculations represent powerful tools that can be used to evaluate electronic structure and covalency in actinide metal-ligand bonding. In addition, these results provide a framework that can be used in future studies to evaluate actinide covalency in compounds that contain transuranic elements.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
965554
Report Number(s):
PNNL-SA-65228
Journal ID: ISSN 0002-7863; JACSAT; KP1704020; TRN: US0903778
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society, 131(34):12125-12136
Additional Journal Information:
Journal Volume: 131; Journal Issue: 34; Journal ID: ISSN 0002-7863
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; X-RAY SPECTROSCOPY; ABSORPTION SPECTROSCOPY; CHLORIDES; DENSITY FUNCTIONAL METHOD; TITANIUM COMPLEXES; ZIRCONIUM COMPLEXES; HAFNIUM COMPLEXES; THORIUM COMPLEXES; URANIUM COMPLEXES; COVALENCE; ELECTRONIC STRUCTURE; GROUND STATES; QUANTUM NUMBERS

Citation Formats

Kozimor, Stosh A, Yang, Ping, Batista, Enrique R, Boland, Kevin S, Burns, Carol J, Clark, David L, Conradson, Steven D, Martin, Richard L, Wikerson, Marianne P, and Wolfsberg, Laura E. Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory. United States: N. p., 2009. Web. doi:10.1021/ja9015759.
Kozimor, Stosh A, Yang, Ping, Batista, Enrique R, Boland, Kevin S, Burns, Carol J, Clark, David L, Conradson, Steven D, Martin, Richard L, Wikerson, Marianne P, & Wolfsberg, Laura E. Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory. United States. https://doi.org/10.1021/ja9015759
Kozimor, Stosh A, Yang, Ping, Batista, Enrique R, Boland, Kevin S, Burns, Carol J, Clark, David L, Conradson, Steven D, Martin, Richard L, Wikerson, Marianne P, and Wolfsberg, Laura E. Wed . "Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory". United States. https://doi.org/10.1021/ja9015759.
@article{osti_965554,
title = {Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory},
author = {Kozimor, Stosh A and Yang, Ping and Batista, Enrique R and Boland, Kevin S and Burns, Carol J and Clark, David L and Conradson, Steven D and Martin, Richard L and Wikerson, Marianne P and Wolfsberg, Laura E},
abstractNote = {We describe the use of Cl K-edge X-ray Absorption Spectroscopy (XAS) and both ground state and time-dependent hybrid density functional theory (DFT) to probe electronic structure and determine the degree of orbital mixing in M-Cl bonds for (C5Me5)2MCl2 (M = Ti, 1; Zr, 2; Hf, 3; Th, 4; and U, 5), where we can directly compare a class of structurally similar compounds for d- and f-elements. We report direct experimental evidence for covalency in M-Cl bonding, including actinides, and offer insight into the relative roles of the valence f- and dorbitals in these systems. The Cl K-edge XAS data for the group IV transition metals, 1 – 3, show slight decreases in covalency in M-Cl bonding with increasing principal quantum number, in the order Ti > Zr > Hf. The percent Cl 3p character per M-Cl bond was experimentally determined to be 25, 23, and 22% per M-Cl bond for 1-3, respectively. For actinides, we find a shoulder on the white line for (C5Me5)2ThCl2, 4, and distinct, but weak pre-edge features for 2 (C5Me5)2UCl2, 5. The percent Cl 3p character in Th-Cl bonds in 4 was determined to be 14 %, with high uncertainty, while the U-Cl bonds in 5 contains 9 % Cl 3p character. The magnitudes of both values are approximately half what was observed for the transition metal complexes in this class of bent metallocene dichlorides. Using the hybrid DFT calculations as a guide to interpret the experimental Cl K-edge XAS, these experiments suggest that when evaluating An- Cl bonding, both 5f- and 6d-orbitals should be considered. For (C5Me5)2ThCl2, the calculations and XAS indicate that the 5f- and 6d-orbitals are nearly degenerate and heavily mixed. In contrast, the 5f- and 6d-orbitals in (C5Me5)2UCl2 are no longer degenerate, and fall in two distinct energy groupings. The 5f-orbitals are lowest in energy and split into a 5-over-2 pattern with the high lying U 6d-orbitals split in a 4-over-1 pattern, the latter of which is similar to the dorbital splitting in group IV transition metal (C5R5)2MCl2 (R = H, Me) compounds. Time dependent-DFT (TD-DFT) was used to calculate the energies and intensities of Cl 1s transitions into empty metal based orbitals containing Cl 3p character, and provide simulated Cl K-edge XAS spectra for 1 - 4. However, for 5, which has two unpaired electrons, analogous information was obtained from transition dipole calculations using ground state Kohn-Sham orbitals. The simulations provide additional confidence in the interpretation of spectra based on ground state calculations. Overall, this study demonstrates that Cl K-edge XAS and DFT calculations represent powerful tools that can be used to evaluate electronic structure and covalency in actinide metal-ligand bonding. In addition, these results provide a framework that can be used in future studies to evaluate actinide covalency in compounds that contain transuranic elements.},
doi = {10.1021/ja9015759},
url = {https://www.osti.gov/biblio/965554}, journal = {Journal of the American Chemical Society, 131(34):12125-12136},
issn = {0002-7863},
number = 34,
volume = 131,
place = {United States},
year = {2009},
month = {9}
}