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

Abstract

Unequivocal experimental evidence for carbon 2p and cerium 4f orbital mixing in cerocene, Ce(C8H8)2 is provided from carbon K-edge and Ce M5,4-edge X-ray absorption spectroscopies and corroborated with DFT and configuration interaction calculations.

Comparison of tetravalent cerium and terbium ions in a conserved, homoleptic imidophosphorane ligand field

“…This structured white-line feature, oen a resolved doublet, has been thought to be a consequence of a multicongurational ground state that consists of partial 4f n 5d 0 L and 4f n+1 5d 0 L (where L is a ligand hole) character that transition to excited states 4f n 5d 1 L and 4f n+1 5d 1 L, respectively. 13,41,48,49 The spectrum of 2-Ce(PN), reported previously, 31 is unique in that the intensity of the lower energy feature of the white line doublet, attributed to the 4f n+1 5d 1 L nal statei.e. partial trivalent characterwas signicantly decreased in comparison to other Ce 4+ compounds, such as ceria (CeO 2 ).…”

Isolation and characterization of a covalent CeIV-Aryl complex with an anomalous 13C chemical shift

“…However, modern spectroscopic and computational techniques have challenged this simple assumption [3][4][5][6] . The covalency in M − X interactions can result in anomalous and diagnostic nuclear magnetic resonance shifts, X = 13 C, 15 N, 19 F, 77 Se, 125 Te, resulting from participation of f-element orbital angular momentum [7][8][9][10][11][12][13] . Another important aspect of detailed f-element electronic structure is multiconfigurational character, as described in the model example of cerocene, Ce(COT) 2 , COT = cyclooctatetraene ligand 14 .…”

“…Another important aspect of detailed f-element electronic structure is multiconfigurational character, as described in the model example of cerocene, Ce(COT) 2 , COT = cyclooctatetraene ligand 14 . The case for multiconfigurational character in cerocene has been made through X-ray absorption, SQUID magnetometry, and multireference computational studies and tied strongly to the characteristics of the cerium-carbon bonding 15 . Despite the interest surrounding f-element covalency and multiconfigurational effects, there are few examples of organometallic Ce IV complexes 16 .…”

Understanding Periodic and Non-periodic Chemistry in Periodic Tables

“…Covalent contributions to the bonds of all these elements are dominantly based on the ( n −1)d orbital overlap interactions. In period 6, the energy and radius of the 4f shell lends itself to additional covalent bond contribution in Ce(III) and in a few praseodymium compounds (Dolg and Moossen, 2015 ; Moossen and Dolg, 2016 ; Zhang et al, 2016 ; Hu et al, 2017 ; Smiles et al, 2020 ). Elsewise, the 4f level is too contracted, sitting inside the atomic core with outer ( n −1)p 6 shell ( Figure 8 ), but can store electrons thereby changing the oxidation state, the number of d-valence electrons and the ionic core radius (Dognon, 2014 , 2017 ; Liu et al, 2017 ; Pathak et al, 2017 ; Lu et al, 2019 ).…”