Details

Autor(en) / Beteiligte

• Smiles, Danil E
• Batista, Enrique R
• Booth, Corwin H
• Clark, David L
• Keith, Jason M
• Kozimor, Stosh A
• Martin, Richard L
• Minasian, Stefan G
• Shuh, David K
• Stieber, S. Chantal E
• Tyliszczak, Tolek

Titel

The duality of electron localization and covalency in lanthanide and actinide metallocenes

Ist Teil von

• Chemical science (Cambridge), 2020-02, Vol.11 (1), p.2796-289

Ort / Verlag

England: Royal Society of Chemistry

Erscheinungsjahr

2020

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Previous magnetic, spectroscopic, and theoretical studies of cerocene, Ce(C 8 H 8 ) 2 , have provided evidence for non-negligible 4f-electron density on Ce and implied that charge transfer from the ligands occurs as a result of covalent bonding. Strong correlations of the localized 4f-electrons to the delocalized ligand π-system result in emergence of Kondo-like behavior and other quantum chemical phenomena that are rarely observed in molecular systems. In this study, Ce(C 8 H 8 ) 2 is analyzed experimentally using carbon K-edge and cerium M 5,4 -edge X-ray absorption spectroscopies (XAS), and computationally using configuration interaction (CI) calculations and density functional theory (DFT) as well as time-dependent DFT (TDDFT). Both spectroscopic approaches provide strong evidence for ligand → metal electron transfer as a result of Ce 4f and 5d mixing with the occupied C 2p orbitals of the C 8 H 8 2− ligands. Specifically, the Ce M 5,4 -edge XAS and CI calculations show that the contribution of the 4f 1 , or Ce 3+ , configuration to the ground state of Ce(C 8 H 8 ) 2 is similar to strongly correlated materials such as CeRh 3 and significantly larger than observed for other formally Ce 4+ compounds including CeO 2 and CeCl 6 2− . Pre-edge features in the experimental and TDDFT-simulated C K-edge XAS provide unequivocal evidence for C 2p and Ce 4f covalent orbital mixing in the δ-antibonding orbitals of e 2u symmetry, which are the unoccupied counterparts to the occupied, ligand-based δ-bonding e 2u orbitals. The C K-edge peak intensities, which can be compared directly to the C 2p and Ce 4f orbital mixing coefficients determined by DFT, show that covalency in Ce(C 8 H 8 ) 2 is comparable in magnitude to values reported previously for U(C 8 H 8 ) 2 . An intuitive model is presented to show how similar covalent contributions to the ground state can have different impacts on the overall stability of f-element metallocenes. Unequivocal experimental evidence for carbon 2p and cerium 4f orbital mixing in cerocene, Ce(C 8 H 8 ) 2 is provided from carbon K-edge and Ce M 5,4 -edge X-ray absorption spectroscopies and corroborated with DFT and configuration interaction calculations.