Quantifying the σ and π Interactions between U(V) f Orbitals and Halide, Alkyl, Alkoxide, Amide and Ketimide Ligands

Abstract

f Orbital bonding in actinide and lanthanide complexes is critical to their behavior in a variety of areas from separations to magnetic properties. Octahedral f(1) hexahalide complexes have been extensively used to study f orbital bonding due to their simple electronic structure and extensive spectroscopic characterization. The recent expansion of this family to include alkyl, alkoxide, amide, and ketimide ligands presents the opportunity to extend this study to a wider variety of ligands. To better understand f orbital bonding in these complexes, the existing molecular orbital (MO) model was refined to include the effect of covalency on spin orbit coupling in addition to its effect on orbital angular momentum (orbital reduction). The new MO model as well as the existing MO model and the crystal field (CF) model were applied to the octahedral f(1) complexes to determine the covalency and strengths of the σ and π bonds formed by the f orbitals. When covalency is significant, MO models more precisely determined the strengths of the bonds derived from the f orbitals; however, when covalency was small, the CF model was better than either MO model. The covalency determined using the new MO model is in better agreement with both experiment and theory than that predicted by the existing MO model. The results emphasize the role played by the orbital energy in determining the strength and covalency of bonds formed by the f orbitals.

Covalency in Lanthanides. An X-ray Absorption Spectroscopy and Density Functional Theory Study of LnCl6x–(x= 3, 2)

“…Our results for the 4f 1 CeCl 6 3− , which showed only 1(1)% Cl 3p-character per Ln−Cl bond, were in reasonable agreement with the analysis by Edelstein and Lukens using UV−vis spectroscopy that also showed only marginal involvement of the t 1u and t 2u orbitals in Ce III −Cl bonding. 141 Moving across the lanthanide series from left to right, both experiment and theory indicated that the energy of the orbitals decreased while the amount of Cl 3p-character determined in the combined 4f-orbitals remained relatively constant ( Figure 14 and Table 2). The DFTdetermined amount of Cl 3p-character per bond in the 4f-orbitals fluctuated between 1.1 and 3.8% for Ce III , Nd III , Sm III , and Gd III , while the calculated value for Eu III 4f 6 was increased to 6.4%.…”

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2013

“…The covalency determined using the new MO model was in better agreement with both experiment and theory than that predicted by the existing MO model. The results emphasized the role played by the orbital energy in determining the strength and covalency of bonds formed by the f orbitals [152]. Thermally stable uranium(VI)-methyl and -acetylide complexes: U VI OR[N(SiMe 3 ) 2 ] 3 (R = Me, C≡CPh) have been prepared in which coordination of the hydrocarbyl group is directed trans to the uranium-oxo multiple bond.…”

Spectroscopic and magnetic investigations of actinide‐based nanomagnets

“…2) has been thoroughly studied for octahedral and pseudooctahedral U V complexes by a combination of spectroscopic (UVvis-NIR and EPR), and magnetic measurements [8] ; this analysis succeeds in reliably describing the fundamental properties from a microscopic point of view, and, therefore, gives valuable information on the bonding and covalency in these systems. [9] A rich subset of the recent advances in U V chemistry deals with the [UO 2 ] 1 cation [10] ; The uranium centers in uranyl complexes tend to conserve an almost linear OAUAO arrangement with short distances, which is expected to give rise to a strongly axial field (and, therefore, to an energy spectra similar to that in the right-hand panel of Fig. 2).…”