Two interpretations of the cerocene electronic ground state

Cerium oxidation state and covalent 4f-orbital contributions in the ground state of bis(η8-pentalene)cerium

“…For a central transition metal with N valence electrons and a d n subconfiguration in a molecule, the oxidation state OS is given as OS ¼ NÀn [31]. Transferring this equation to Ce with N ¼ 4 and the f 1 subconfiguration (n ¼ 1) dominant in bis(h 8 -pentalene)cerium Ce(C 8 H 6 ) 2 , as well as in cerocene Ce(C 8 H 8 ) 2 [15], both compounds clearly have oxidation state OS ¼ 3. Of course this assignment has to be viewed as a simplification of the true situation, which more corresponds to a mixture of a dominating Ce(III) (z 80%) contribution with a small, but for the overall electronic structure very important Ce(IV) (z 20%) admixture.…”

“…In addition, further quantum chemical studies lead to the conclusion that cerocene despite its significant 4f density is better described as a cerium(IV) compound [13,14]. In a recent letter on cerocene we were able to demonstrate that the old [6,7] and new [13,14] electronic structure calculations in fact did not yield entirely different results, but were just interpreted using different sets of molecular orbitals [15]. It is well-known among quantum chemists that unitary transformations of the orbitals used in a full configuration interaction (FCI) scheme, in particular the active orbitals of a complete active space self-consistent field (CASSCF) calculation, leave the wavefunction and the total energy invariant.…”

Quantification of f-element covalency through analysis of the electron density: insights from simulation

“…As a result of density based analysis, the authors assigned a +4 oxidation state, but noted significant charge delocalisation which could account for the reported XANES data. These apparently contradictory interpretations have since been shown to both be valid, 94 and Kerridge has calculated OS Ce to be +3.500 based on analysis of a CASSCF-derived density. 95 Table 5 summarises QTAIM-derived oxidation states for a number of simulated compounds.…”

A Macrocyclic Chelator That Selectively Binds Ln4+ over Ln3+ by a Factor of 1029

“…[68][69] Many "non-classical" tetravalent cerium molecules have also been prepared, including organometallic compounds, [70][71][72] amide, 65,70,[73][74][75][76][77][78] porphyrins [79][80][81][82][83] and a variety of other multidentate N-donor ligands. [84][85][86][87][88][89][90][91] Among these, the lanthanide sandwich molecule cerocene, (C8H8)2Ce, [92][93][94][95][96][97][98][99][100][101][102][103] has played a central role in development of electronic structure models for tetravalent cerium molecules. Theoretical, magnetic, and L3-edge XANES studies of (C8H8)2Ce resulted in observation of the Kondo effect in a single molecule -a phenomenon that is typically reserved for metals.…”