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

Abstract

The electronic structure of f-element compounds is complex due to a combination of relativistic effects, strong electron correlation and weak crystal field environments. However, a quantitative understanding of bonding in these compounds is becoming increasingly technologically relevant. Recently, bonding interpretations based on analyses of the physically observable electronic density have gained popularity and, in this Feature Article, the utility of such density-based approaches is demonstrated. Application of Bader's Quantum Theory of Atoms in Molecules (QTAIM) is shown to elucidate many properties including bonding trends, orbital overlap and energy degeneracy-driven covalency, oxidation state identification and bond stability, demonstrating the increasingly important role that simulation and analysis play in the area of f-element bond characterisation.

How to Bend the Uranyl Cation via Crystal Engineering

“…Looking first at the Raman spectra of 'bent' complexes 1-3, the 1 symmetric stretch is the most prominent signal in each spectrum at 816 cm -1 , 844 cm -1 , and 839 cm -1 , respectively (Table 4, Figure S11 molecules, which likely increase the ionic interaction between the uranium center and the oxo atoms by increasing electron density transferred from non-planar ligands into the π*antibonding orbitals of the uranyl cation. 22,[53][54]65 Comparing the 1 symmetric stretch frequencies of 1-3 with their non-bent analogues 4-7, we note redshifts between 'bent'…”

Computational analysis of M–O covalency in M(OC6H5)4(M = Ti, Zr, Hf, Ce, Th, U)

“…The metrics employed herein have been used extensively to characterize bonding in situ and have been shown to be particularly useful in f element chemistry. 4,31,[36][37][38][39] Data for the bond critical point (BCP) metrics (electron density, ρBCP, its Laplacian ∇ 2 ρBCP, and the total energy density HBCP) and integrated QTAIM properties (atomic charge, q, and the delocalization index of the M and O atom pair, δ(M,O)) are shown in Table 2 for the optimized M(OC6H5)4 systems (and for the systems at r(M-O) -0.12 Å in Table SI2 of the Supplementary Information). The magnitudes of ρBCP and HBCP are measures of covalency, where values of ρBCP > 0.2 au and HBCP < 0 indicate interactions with significant sharing of electrons, or covalent character.…”

“…The delocalization index is often used as the defining QTAIM metric for covalency, since it provides a measure of the number of electron pairs exchanged in an interaction. 4,9,[43][44][45] It is derived from the expectation value of the exchange operator over two atomic basins and is irrespective of the nature of the interaction. Please do not adjust margins Please do not adjust margins delocalization elsewhere in the molecule.…”

“…Furthermore, there is a lack of understanding of periodic trends in bonding within the lanthanide and actinide series and how they change with oxidation state and ligand environment. [1][2][3][4] The mixing of metal and ligand orbitals is proportional to the spatial overlap between them and inversely proportional to the difference in their energies. [5][6][7][8][9] Strong mixings can therefore arise when there are small energy differences between metal and ligand orbitals (e.g.…”

Transuranic Computational Chemistry

“…[4,6] For an up-todate review of covalency and the QTAIM in the bonding in 5f compounds, including transuranic systems, please see Andrew Kerridge's very nice FeatureArticle. [7] Ir ecently found an exception to the typicallyc ontradictory conclusions of orbital-and electrond ensity-based covalency analyses. [8] Gibsone tal.…”