Assessing covalency in Cerium and Uranium hexachlorides:a correlated wavefunction and density functional theory study

The electronic structure of a series of uranium and cerium hexachlorides in a variety of oxidation states was evaluated at both the correlated wavefunction and density functional (DFT) levels of theory. Following recent experimental observations of covalency in tetravalent cerium hexachlorides, bonding character was studied using topological and integrated analysis based on the quantum theory of atoms in molecules (QTAIM). This analysis revealed that M–Cl covalency was strongly dependent on oxidation state, with greater covalency found in higher oxidation state complexes. Comparison of M–Cl delocalisation indices revealed a discrepancy between correlated wavefunction and DFT-derived values. Decomposition of these delocalisation indices demonstrated that the origin of this discrepancy lay in ungerade contributions associated with the f-manifold which we suggest is due to self-interaction error inherent to DFT-based methods. By all measures used in this study, extremely similar levels of covalency between complexes of U and Ce in the same oxidation state was found

Dithio- and Diselenophosphinate Thorium(IV) and Uranium(IV) complexes:molecular and electronic structure, spectroscopy, and transmetalation reactivity

We report a comparison of the molecular and electronic structures of dithio- and diselenophosphinate, (E2PR2)1– (E = S, Se; R = iPr, tBu), with thorium(IV) and uranium(IV) complexes. For the thorium dithiophosphinate complexes, reaction of ThCl4(DME)2 with 4 equiv of KS2PR2 (R = iPr, tBu) produced the homoleptic complexes, Th(S2PiPr2)4 (1S-Th-iPr) and Th(S2PtBu2)4 (2S-Th-tBu). The diselenophosphinate complexes were synthesized in a similar manner using KSe2PR2 to produce Th(Se2PiPr2)4 (1Se-Th-iPr) and Th(Se2PtBu2)4 (2Se-Th-tBu). U(S2PiPr2)4, 1S-U-iPr, could be made directly from UCl4 and 4 equiv of KS2PiPr2. With (Se2PiPr2)1–, using UCl4 and 3 or 4 equiv of KSe2PiPr2 yielded the monochloride product U(Se2PiPr2)3Cl (3Se-UiPr-Cl), but using UI4(1,4-dioxane)2 produced the homoleptic U(Se2PiPr2)4 (1Se-U-iPr). Similarly, the reaction of UCl4 with 4 equiv of KS2PtBu2 yielded U(S2PtBu2)4 (2S-U-tBu), whereas the reaction with KSe2PtBu2 resulted in the formation of U(Se2PtBu2)3Cl (4Se-UtBu-Cl). Using UI4(1,4-dioxane)2 and 4 equiv of KSe2PtBu2 with UCl4 in acetonitrile yielded U(Se2PtBu2)4 (2Se-U-tBu). Transmetalation reactions were investigated with complex 2Se-U-tBu and various CuX (X = Br, I) salts to yield U(Se2PtBu2)3X (6Se-UtBu-Br and 7Se-UtBu-I) and 0.25 equiv of [Cu(Se2PtBu2)]4 (8Se-Cu-tBu). Additionally, 2Se-U-tBu underwent transmetalation reactions with Hg2F2 and ZnCl2 to yield U(Se2PtBu2)3F (6) and U(Se2PtBu2)3Cl (4Se-UtBu-Cl), respectively. The molecular structures were analyzed using 1H, 13C, 31P, and 77Se NMR and IR spectroscopy and structurally characterized using X-ray crystallography. Using the QTAIM approach, the electronic structure of all homoleptic complexes was probed, showing slightly more covalent bonding character in actinide–selenium bonds over actinide–sulfur bonds

Assessing covalency in equatorial U-N bonds:density based measures of bonding in BTP and isoamethyrin complexes of uranyl

Calculations performed at the density functional level of theory have been used to investigate complexes of uranyl with the expanded porphyrin isoamethyrin and the bis-triazinyl-pyridine (BTP) ligands, the latter of which is well-known to be effective in the separation of trivalent lanthanides and actinides. Analysis has been performed using a range of density-based techniques, including the Quantum Theory of Atoms in Molecules (QTAIM), the Electron Localisation Function (ELF) and the reduced density gradient (RDG). The effects of peripheral alkyl substituents on UO2-isoamethyrin, known to be vital for proper replication of the experimental geometry, are considered. Evidence for comparable amounts of covalent character has been found in the largely ionic U–N bonds of UO2-isoamethyrin and [UO2(BTP)2]2+ and examination of the variation in the electronic characteristics of the uranyl unit upon complexation in both of these cases reveal striking similarities in the nature of the U–N bonding and the effect of this bonding on the U–Oyl interaction, as well as evidence of donation into the U–N bonding region from the uranyl unit itself

U−Oyl stretching vibrations as a quantitative measure of the equatorial bond covalency in uranyl complexes:a quantum-chemical investigation

The molecular structures of a series of uranyl (UO22+) complexes in which the uranium center is equatorially coordinated by a first-row species are calculated at the density functional theory level and binding energies deduced. The resulting electronic structures are investigated using a variety of density-based analysis techniques in order to quantify the degree of covalency in the equatorial bonds. It is shown that a consideration of the properties of both the one-electron and electron-pair densities is required to understand and rationalize the variation in axial bonding effected by equatorial complexation. Strong correlations are found between density-based measures of the covalency and equatorial binding energies, implying a stabilizing effect due to covalent interaction, and it is proposed that uranyl U–Oyl stretching vibrational frequencies can serve as an experimental probe of equatorial covalency

Should environmental effects be included when performing QTAIM calculations on actinide systems?:a comparison of QTAIM metrics for Cs2UO2Cl4, U(Se2PPh2)4 and Np(Se2PPh2)4 in gas phase, COSMO and PEECM

Quantum Theory of Atoms–in–Molecules bond critical point and delocalisation index metrics are calculated for the actinide-element bonds in Cs2UO2Cl4, U(Se2PPh2)4 and Np(Se2PPh2)4, in gas-phase, continuum solvent (COSMO) and via the periodic electrostatic embedded cluster method. The effects of the environment are seen to be very minor, suggesting that they do not account for the differences previously observed between the experimental and theoretical QTAIM ρb and ∇2ρb for the U-O bonds in Cs2UO2Cl4. With the exception of the local density approximation, there is only a small dependence of the QTAIM metrics on the exchange–correlation functional employed

Optical excitation of MgO nanoparticles:a computational perspective

The optical absorption spectra of magnesium oxide (MgO) nanoparticles, along with the atomic centres responsible, are studied using a combination of time-dependent density functional theory (TD-DFT) and coupled-cluster methods. We demonstrate that TD-DFT calculations on MgO nanoparticles require the use of range-separated exchange–correlation (XC-) functionals or hybrid XC-functionals with a high percentage of Hartree–Fock like exchange to circumvent problems related to the description of charge-transfer excitations. Furthermore, we show that the vertical excitations responsible for the experimentally studied range of the spectra of the MgO nanoparticles typically involve both 3-coordinated corner sites and 4-coordinated edge sites. We argue therefore that to label peaks in these absorption spectra exclusively as either corner or edge features does not provide insight into the full physical picture

White phosphorus activation by a Th(III) complex

[Th(Cp′′)3] (Cp′′ = {C5H3(SiMe3)2-1,3}) activates P4 to give [{Th(Cp′′)3}2(μ–η1:η1-P4)] (1), which has an unprecedented cyclo-P4 binding mode. DFT studies were performed on a model of 1 to probe the bonding in this system

Topological study of bonding in aquo and bis(triazinyl)pyridine complexes of trivalent lanthanides and actinides:does covalency imply stability?

The geometrical and electronic structures of Ln[(H2O)9]3+ and [Ln(BTP)3]3+, where Ln = Ce–Lu, have been evaluated at the density functional level of theory using three related exchange-correlation (xc-)functionals. The BHLYP xc-functional was found to be most accurate, and this, along with the B3LYP functional, was used as the basis for topological studies of the electron density via the quantum theory of atoms in molecules (QTAIM). This analysis revealed that, for both sets of complexes, bonding was almost identical across the Ln series and was dominated by ionic interactions. Geometrical and electronic structures of actinide (An = Am, Cm) analogues were evaluated, and [An(H2O)9]3+ + [Ln(BTP)3]3+ → [Ln(H2O)9]3+ + [An(BTP)3]3+ exchange reaction energies were evaluated, revealing Eu ↔ Am and Gd ↔ Cm reactions to favor the An species. Detailed QTAIM analysis of Eu, Gd, Am, and Cm complexes revealed increased covalent character in M–O and M–N bonds when M = An, with this increase being more pronounced in the BTP complexes. This therefore implies a small electronic contribution to An–N bond stability and the experimentally observed selectivity of the BTP ligand for Am and Cm over lanthanides

Coordination Chemistry and QTAIM Analysis of Homoleptic Dithiocarbamate Complexes, M(S2CNiPr2)4, M = Ti, Zr, Hf, Th, U, Np

In a systematic approach to comparing the molecular structure and bonding in homoleptic transition-metal and actinide complexes, a series of dithiocarbamates, M(S2CNiPr2)4 (M = Ti, Zr, Hf, Th, U, Np), have been synthesized. These complexes have been characterized through spectroscopic and X-ray crystallographic analysis, and their bonding has been examined using density functional theory calculations. Computational results indicate that the covalent character associatedSave with the M-S bonds shows the trend of Hf < Zr < Th < Ti < U ≈ Np. © 2018 American Chemical Society

Probing Hydrogen and Halogen-Oxo Interactions in Uranyl Coordination Polymers:A Combined Crystallographic and Computational Study

The syntheses and crystal structures of four compounds containing the UO22+ cation and either benzoic acid (1), m-chlorobenzoic acid (2), m-bromobenzoic acid (3), or m-iodobenzoic acid (4) are described and the vibrational spectroscopic properties for compounds 3 and 4 are reported. Single crystal X-ray diffraction analysis of these materials shows that uranyl oxo atoms are engaged in non-covalent assembly via either hydrogen (1 and 2) or halogen bonding (3 and 4) interactions. The halogen bonding in compounds 3 and 4 is notable as the crystallographic metric percentage of the sum of the van der Waals radii indicates these interactions are of similar strength. Characteristics of the halogen-oxo interactions of 3 and 4 were probed via Raman and infrared spectroscopy, which revealed significant differences in stretching frequency values for the two compounds. Additionally, compounds 3 and 4 were characterized via quantum chemical calculations and density-based quantum theory of atoms in molecules (QTAIM) analysis, which indicated that the I-oxo interaction in 4 is likely the stronger of the two interactions, with differences between the two interactions resulting from both inductive effects and halogen polarizability