Assigning the Cerium Oxidation State for CH₂CeF₂ and OCeF₂ Based on Multireference Wave Function Analysis

Abstract

The geometric and electronic structure of the recently experimentally studied molecules ZCeF2 (Z = CH2, O) was investigated by density functional theory (DFT) and wave function-based ab initio methods. Special attention was paid to the Ce-Z metal-ligand bonding, especially to the nature of the interaction between the Ce 4f and the Z 2p orbitals and the possible multiconfigurational character arising from it, as well as to the assignment of an oxidation state of Ce reflecting the electronic structure. Complete active space self-consistent field (CASSCF) calculations were performed, followed by orbital rotations in the active orbital space. The methylene compound CH2CeF2 has an open-shell singlet ground state, which is characterized by a two-configurational wave function in the basis of the strongly mixed natural CASSCF orbitals. The system can also be described in a very compact way by the dominant Ce 4f(1) C 2p(1) configuration, if nearly pure Ce 4f and C 2p orbitals are used. In the basis of these localized orbitals, the molecule is almost monoconfigurational and should be best described as a Ce(III) system. The singlet ground state of the oxygen OCeF2 complex is of closed-shell character when a monoconfigurational wave function with very strongly mixed Ce 4f and O 2p CASSCF natural orbitals is used for the description. The transformation to orbitals localized on the cerium and oxygen atoms leads to a multiconfigurational wave function and reveals characteristics of a mixed valent Ce(IV)/Ce(III) compound. Additionally, the interactions of the localized active orbitals were analyzed by evaluating the expectation values of the charge fluctuation operator and the local spin operator. The Ce 4f and C 2p orbital interaction of the CH2CeF2 compound is weakly covalent and resembles the interaction of the H 1s orbitals in a stretched hydrogen dimer. In contrast, the interaction of the localized active orbitals for OCeF2 shows ionic character. Calculated vibrational Ce-C and Ce-O stretching frequencies at the DFT, CASSCF, second-order Rayleigh-Schrödinger perturbation theory (RS2C), multireference configuration interaction (MRCI), as well as single, doubles, and perturbative triples coupled cluster (CCSD(T)) level are reported and compared to experimental infrared absorption data in a Ne and Ar matrix.

Synthesis, Characterization, and Electrochemistry of the Homoleptic f Element Ketimide Complexes [Li]2[M(N═CtBuPh)6] (M = Ce, Th)

“…[8][9][10][11][12][13][14][15][16] This redox chemistry is relevant to both fundamental and applied research. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] For example, multi-configurational ground states have recently been revealed in several molecular and solid-state Ce(IV) materials. 25,[29][30][31][32][33][34][35][36][37] Moreover, X-ray absorption spectroscopy and density functional theory studies on tetravalent cerium have revealed considerable covalency and f orbital participation in Ce(IV)-L bonding.…”

“…[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] For example, multi-configurational ground states have recently been revealed in several molecular and solid-state Ce(IV) materials. 25,[29][30][31][32][33][34][35][36][37] Moreover, X-ray absorption spectroscopy and density functional theory studies on tetravalent cerium have revealed considerable covalency and f orbital participation in Ce(IV)-L bonding. [24][25][26][27][28][29]38 In addition, the Ce(IV/III) redox couple has proved instrumental for separation of cerium from mineral ores and in the mechanism of action of several ceria-supported catalysts.…”

“…The chemistry of high-valent lanthanide ions has remained enigmatic. − Indeed, cerium is the only lanthanide element that can easily form stable molecular +4 complexes, which has paved the way for extensive study of its redox properties, both in solid state and solution. − This redox chemistry is relevant to both fundamental and applied research. − For example, multiconfigurational ground states (GSs) have recently been revealed in several molecular and solid-state Ce­(IV) materials. ,− Moreover, X-ray absorption spectroscopy and density functional theory (DFT) studies on tetravalent cerium have revealed considerable covalency and f orbital participation in Ce­(IV)-L bonding. − , In addition, the Ce­(IV/III) redox couple has proved instrumental for separation of cerium from mineral ores and in the mechanism of action of several ceria-supported catalysts. ,,,, Despite these successes, there still are only a handful of ligands that are capable of stabilizing high oxidation states in the lanthanides, especially in nonaqueous environments. Examples include nitroxide, tetraazaannulene, imidophosphorane, , atrane, binolate, silyloxide, and methanediide. ,, …”

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(Dognon, , 2017Liu et al, 2017;Pathak et al, 2017;Lu et al, 2019).…”