Density Functional calculations have been performed to calculate the one-electron oxidation potential for ferrocene and the redox couples for a series of small transition metal compounds of the first-, second-, and third-row elements. The solvation effects are incorporated via a self-consistent reaction field (SCRF), using the polarized continuum model (PCM). From our study of seven different density functionals combined with three different basis sets for ferrocene, we find that no density functional method can reproduce the redox trends from experiment when referencing our results to the experimental absolute standard hydrogen electrode (SHE) potential. In addition, including additional necessary assumptions such as solvation effects does not lead to any conclusion regarding the appropriate functional. However, we propose that if one references their transition metal compounds results to the calculated absolute half-cell potential of ferrocene, they can circumvent the additional assumptions necessary to predict a redox couple. Upon employing this method on several organometallic and inorganic complexes, we obtained very good correlation between calculated and experimental values (R(2) = 0.97), making it possible to predict trends with a high level of confidence. The hybrid functional B3LYP systematically underestimates the redox potential; however, the linear correlation between DFT and experiment is good (R(2) = 0.96) when including a baseline shift. This protocol is a powerful tool that allows theoretical chemists to predict the redox potential in solution of several transition metal complexes a priori and aids in the rational design of redox-active catalysts.

Covalency in Ln-Cl bonds of Oh-LnCl6(x-) (x = 3 for Ln = Ce(III), Nd(III), Sm(III), Eu(III), Gd(III); x = 2 for Ln = Ce(IV)) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6(x-) (x = 2, 3). The M5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce(III) and Ce(IV)). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce(III) to Ce(IV) had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl6(3-) (formally Ln(III)), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce(IV) 4f-orbital mixing (t1u* + t2u*) in CeCl6(2-). This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl6(2-) (M = Ti, Zr, Hf, U).

Chlorine K-edge X-ray absorption spectroscopy (XAS) and ground-state and time-dependent hybrid density functional theory (DFT) were used to probe the electronic structures of O(h)-MCl(6)(2-) (M = Ti, Zr, Hf, U) and C(4v)-UOCl(5)(-), and to determine the relative contributions of valence 3d, 4d, 5d, 6d, and 5f orbitals in M-Cl bonding. Spectral interpretations were guided by time-dependent DFT calculated transition energies and oscillator strengths, which agree well with the experimental XAS spectra. The data provide new spectroscopic evidence for the involvement of both 5f and 6d orbitals in actinide-ligand bonding in UCl(6)(2-). For the MCl(6)(2-), where transitions into d orbitals of t(2g) symmetry are spectroscopically resolved for all four complexes, the experimentally determined Cl 3p character per M-Cl bond increases from 8.3(4)% (TiCl(6)(2-)) to 10.3(5)% (ZrCl(6)(2-)), 12(1)% (HfCl(6)(2-)), and 18(1)% (UCl(6)(2-)). Chlorine K-edge XAS spectra of UOCl(5)(-) provide additional insights into the transition assignments by lowering the symmetry to C(4v), where five pre-edge transitions into both 5f and 6d orbitals are observed. For UCl(6)(2-), the XAS data suggest that orbital mixing associated with the U 5f orbitals is considerably lower than that of the U 6d orbitals. For both UCl(6)(2-) and UOCl(5)(-), the ground-state DFT calculations predict a larger 5f contribution to bonding than is determined experimentally. These findings are discussed in the context of conventional theories of covalent bonding for d- and f-block metal complexes.

Evidence for metal-carbon orbital mixing in thorocene and uranocene was determined from DFT calculations and carbon K-edge X-ray absorption spectra (XAS) collected with a scanning transmission X-ray microscope (STXM). Both the experimental and computational results showed that the 5f orbitals engaged in significant d-type mixing with the C 8 H 8 2À ligands, which increased as the 5f orbitals dropped in energy on moving from Th 4+ to U 4+. The first experimental evidence for extensive f-orbital interactions has been provided by the C K-edge XAS analysis of thorocene; however, f-type covalency in uranocene was negligible. The results highlighted two contrasting trends in orbital mixing from one pair of highly symmetric molecules, and showed that covalency does not increase uniformly for different molecular orbital interactions with later actinides.

Here we describe the synthesis of two imido analogs of the uranyl ion, UO 2+ 2 , in which the oxygens are replaced by divalent alkyl or aryl nitrogen groups: U(N t Bu) 2 I 2 (THF) 2 (1) and U(NPh) 2 I 2 (THF) 3 (2) (where t Bu is tert -butyl and THF is tetrahydrofuran). Both compounds have been fully characterized by standard analytical techniques, including x-ray crystallography, and the chemical bonding between the metal center and the nitrogen ligands was quantified by using hybrid density functional theory calculations. As expected for a uranyl analog, these complexes exhibit linear N-U-N linkages and very short U-N bonds. In addition, the theoretical calculations show strong involvement of the 5f and 6d electrons in the U-N bonding.