Does the 4f-shell contribute to bonding in tetravalent lanthanide halides?

Abstract

Lanthanide tetrahalide molecules LnX4 (Ln = Ce, Pr, Tb; X = F, Cl, Br, I) have been investigated by density functional theory at the levels of the relativistic Zero Order Regular Approximation and the relativistic energy-consistent pseudopotentials, using frozen small- and medium-cores. The calculated bond lengths and vibrational frequencies are close to the experimental data. Our calculations indicate 4f shell contributions to bonding in LnX4, in particular for the early lanthanides, which show significant overlap between the Ln 4f-shell and the halogen np-shells. The 4f shells contribute to Ln-X bonding in LnX4 about one third more than in LnX3.

The electronic configurations of LnX (Ln=La–Eu, X=O, S, Se, Te): A FON–DFT investigation

“…Since our results agree with popular theoretical programs and approaches, we think this work is still acceptable and reliable. Similar DFT calculations on lanthanide systems have been reported in our recently works [26,59,60].…”

General synthesis of 2D rare-earth oxide single crystals with tailorable facets

“…In addition, the interaction between the RE ions and X ions decreased because of the lower bond energy in sequence (Fig. 3 a) [ 37 ]. Thus, the weaker the alkalinity of the active X ions, the higher corresponding FCA concentration is required to realize the 2D growth and facet-controllability of the REO (Table S1).…”

Role of La 5p in Bulk and Quantum-Confined Solids Probed by the La 5p54f1 3D1 Excitonic Final State of Resonant Inelastic X-ray Scattering

“…37,38 5d and 6s shells' participation in chemical bonding, on the other hand, is generally accepted. 34,39,40 The contribution to covalency from pseudocore (inner valence) 5p shell is still unclear. 41,42 In lanthanides, the 5p shell is spatially extended and penetrates into the core (Figure 1) which effectively screens the 4f shell; 43 hence it is more favorable than the 4f shell to form a spatial-driven covalent bond.…”

“…It is known and established experimentally and theoretically from the RE series that in general the 4f states are barely perturbed by the host material, causing narrow 4f bands − and being considered “chemically inert”. In the case of La, the unoccupied 4f shell lies even higher in energy scale and 4f orbital mixing with the ligand states is energetically highly unfavorable. , Even though some work suggested the contribution of RE 4f to chemical bond, − it appears mostly in higher oxidation states instead of typical trivalent compounds or in specific systems such as heavy fermions. , 5d and 6s shells’ participation in chemical bonding, on the other hand, is generally accepted. ,, The contribution to covalency from pseudocore (inner valence) 5p shell is still unclear. , In lanthanides, the 5p shell is spatially extended and penetrates into the core (Figure ) which effectively screens the 4f shell; hence it is more favorable than the 4f shell to form a spatial-driven covalent bond. Previous experimental and theoretical studies indicate that the 5p in the electronic structure yields a ≈20 eV shallow potential that makes covalent bonding possible through inner valence molecular orbital formation. ,, Note that throughout this article, we define the intraactomic orbital hybridization (e.g., sp 3 of carbon in CH 4 ) as “hybridization”, and interatomic metal–ligand bond as ”orbital mixing”.…”

“…In the case of La, the unoccupied 4f shell lies even higher in energy scale and 4f orbital mixing with the ligand states is energetically highly unfavorable. 32,33 Even though some work suggested the contribution of RE 4f to chemical bond, 34−36 it appears mostly in higher oxidation states instead of typical trivalent compounds or in specific systems such as heavy fermions. 37,38 5d and 6s shells' participation in chemical bonding, on the other hand, is generally accepted.…”