Exploring the Interaction Natures in Plutonyl (VI) Complexes with Topological Analyses of Electron Density

Adsorption and diffusion of actinyls on the basal gibbsite (001) surface: a theoretical perspective

Actinides are an important component of nuclear fuel for nuclear power and affect human health, and a key process in the transport of radionuclides in the environment is adsorption on mineral surfaces. In this work, we have used density functional theory (DFT) to investigate the microscopic adsorption and diffusion mechanisms of actinyls, U(V), U(VI), Np(V), Np(VI) Pu(V), and Pu(VI), on the gibbsite (001) surface. Actinyls(VI) are attached to the gibbsite surface through two An-Os bonds, which results in a bidentate inner sphere mode, while actinyls(V) favor a monodentate inner sphere adsorption mode with the gibbsite (001) surface. The solvent effects were considered through an explicit water cluster model. All the actinyls studied can be efficiently adsorbed on the gibbsite (001) surface with binding energies ranging from -113.9 kJ mol-1 to -341.2 kJ mol-1. Electronic structure analyses indicate that the cooperation of the An-Os bonds and hydrogen bonds leads to high adsorption stability of the actinyls with the gibbsite surface. The diffusion barriers of the actinyls on the gibbsite surface were determined, and the high energy barriers indicate that this type of gas-phase diffusion process is not likely to take place.

Flux Crystal Growth of the Extended Structure Pu(V) Borate Na2(PuO2)(BO3)

As part of our exploration of plutonium-containing materials as potential nuclear waste forms, we report the first extended structure Pu(V) material and the first Pu(V) borate. Crystals of Na₂(PuO₂)(BO₃) were grown out of mixed hydroxide/boric acid flux and found to crystallize in the orthorhombic space group Cmcm with lattice parameters of a = 9.9067(4) Å, b = 6.5909(2) Å, and c = 6.9724(2) Å. Na₂(PuO₂)(BO₃) adopts a layered structure in which layers of PuO₂(BO₃)^2- are separated by sodium cations. Plutonium is found in a pentagonal bipyramidal coordination environment, with axial Pu(V)-O plutonyl bond lengths of 1.876(3) Å and equatorial Pu-O bond lengths ranging from 2.325(5) to 2.467(3) Å. We find that the Pu(V)-O plutonyl bond lengths are approximately 0.1 Å longer than the reported Pu(VI)-O plutonyl bond lengths and shorter by approximately 0.033 Å than the corresponding U(V) uranyl bond lengths. Raman spectroscopy on single crystals was used to determine the PuO₂⁺ plutonyl stretching and the equatorial breathing mode frequencies of the pentagonal bipyramidal coordination environment around plutonium. Density functional theory calculations were used to calculate the Raman spectrum to help identify the Raman bands at 690 and 630 cm^-1 as corresponding to the plutonyl(V) ν1 stretch and the equatorial PuO₅ breathing mode, respectively. UV-vis measurements on single crystals indicate semiconducting behavior with a band gap of ∼2.60 eV.

Covalent Triazine Framework C6N6 as an Electrochemical Sensor for Hydrogen-Containing Industrial Pollutants. A DFT Study

Industrial pollutants pose a serious threat to ecosystems. Hence, there is a need to search for new efficient sensor materials for the detection of pollutants. In the current study, we explored the electrochemical sensing potential of a C₆N₆ sheet for H-containing industrial pollutants (HCN, H₂S, NH₃ and PH₃) through DFT simulations. The adsorption of industrial pollutants over C₆N₆ occurs through physisorption, with adsorption energies ranging from -9.36 kcal/mol to -16.46 kcal/mol. The non-covalent interactions of analyte@C₆N₆ complexes are quantified by symmetry adapted perturbation theory (SAPT0), quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analyses. SAPT0 analyses show that electrostatic and dispersion forces play a dominant role in the stabilization of analytes over C₆N₆ sheets. Similarly, NCI and QTAIM analyses also verified the results of SAPT0 and interaction energy analyses. The electronic properties of analyte@C₆N₆ complexes are investigated by electron density difference (EDD), natural bond orbital analyses (NBO) and frontier molecular orbital analyses (FMO). Charge is transferred from the C₆N₆ sheet to HCN, H₂S, NH₃ and PH₃. The highest exchange of charge is noted for H₂S (-0.026 e^-). The results of FMO analyses show that the interaction of all analytes results in changes in the E_H-L gap of the C₆N₆ sheet. However, the highest decrease in the E_H-L gap (2.58 eV) is observed for the NH₃@C₆N₆ complex among all studied analyte@C₆N₆ complexes. The orbital density pattern shows that the HOMO density is completely concentrated on NH₃, while the LUMO density is centred on the C₆N₆ surface. Such a type of electronic transition results in a significant change in the E_H-L gap. Thus, it is concluded that C₆N₆ is highly selective towards NH₃ compared to the other studied analytes.

Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study

Uranyl Pacman takes them all: the bonding of s- and d-block cations to uranyl is compared by experiment, spectroscopy and theory.

The uranyl(vi) ‘Pacman’ complex [(UO₂)(py)(H₂L)] A (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp₂Ti(η²-Me₃SiC Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CSiMe₃) and [Cp₂TiCl]₂ to oxo-titanated uranyl(v) complexes [(py)(Cp₂Ti^IIIOUO)(py)(H₂L)] 1 and [(ClCp₂Ti^IVOUO)(py)(H₂L)] 2. Combination of Zr^II and Zr^IV synthons with A yields the first Zr^IV–uranyl(v) complex, [(ClCp₂ZrOUO)(py)(H₂L)] 3. Similarly, combinations of Ae⁰ and Ae^II synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)₂(ClMgOUO)(py)(H₂L)] 4, [(py)₂(thf)₂(ICaOUO)(py) (H₂L)] 5; the zinc complexes [(py)₂(XZnOUO)(py)(H₂L)] (X = Cl 6, I 7) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with A generate the first mono-rubidiated and mono-caesiated uranyl(v) complexes; monomeric [(py)₃(RbOUO)(py)(H₂L)] 8 and hexameric [(MOUO)(py)(H₂L)]₆ (M = Rb 8b or Cs 9). In these uranyl(v) complexes, the pyrrole N–H atoms show strengthened hydrogen-bonding interactions with the endo-oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M₄ edge HR-XANES (High Energy Resolution X-ray Absorption Near Edge Structure) and 3d4f RIXS (Resonant Inelastic X-ray Scattering) have been used (the latter two for the first time for uranyl(v) in 7 (ZnI)) to compare the covalent character in the U^V–O and O–M bonds and show the 5f orbitals in uranyl(vi) complex A are unexpectedly more delocalised than in the uranyl(v) 7 (ZnI) complex. The O_exo–Zn bonds have a larger covalent contribution compared to the Mg–O_exo/Ca–O_exo bonds, and more covalency is found in the U–O_exo bond in 7 (ZnI), in agreement with the calculations.

Systematic analysis of structural and topological properties: new insights into PuO2(H2O)n2+ (n = 1–6) complexes in the gas phase

In this study, the equilibrium, electronic structures, bonding and topological properties of PuO₂(H₂O)_n²⁺ (n = 1–6) complexes were systematically investigated.