The shortest Th–Th distance from a new type of quadruple bond

Very short Th–Th distances, featuring a previously unreported 6dδ2 electronic configuration, are predicted quantum chemically for LThThL compounds.</p

Towards Hydrazine Based Hydrogen Storage Materials Incorporating Late Transition Metals: a DFT Study

AbstractOur established method of modeling transition metal based H2 storage materials is extended to include the desirable and achievable targets of hydrazine linked Cu(I), Cu(II) and Ni(II). Two coordinate Cu(I) H2 binding site representations bind two H2 molecules through the reversible Kubas interaction with a theoretical maximum storage capacity of 4.27%wt

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

Metal-Metal Bonding in Uranium-Group 10 Complexes

Heterobimetallic complexes containing short uranium–group 10 metal bonds have been prepared from monometallic IU^IV(OAr^P-κ²<i>O</i>,<i>P</i>)₃ (<b>2</b>) {[Ar^PO]⁻ = 2-<i>tert</i>-butyl-4-methyl-6-(diphenylphosphino)­phenolate}. The U–M bond in IU^IV(μ-OAr^P-1κ¹<i>O</i>,2κ¹<i>P</i>)₃M⁰, M = Ni (<b>3–Ni</b>), Pd (<b>3–Pd</b>), and Pt (<b>3–Pt</b>), has been investigated by experimental and DFT computational methods. Comparisons of <b>3–Ni</b> with two further U–Ni complexes XU^IV(μ-OAr^P-1κ¹<i>O</i>,2κ¹<i>P</i>)₃Ni⁰, X = Me₃SiO (<b>4</b>) and F (<b>5</b>), was also possible via iodide substitution. All complexes were characterized by variable-temperature NMR spectroscopy, electrochemistry, and single crystal X-ray diffraction. The U–M bonds are significantly shorter than any other crystallographically characterized d–f-block bimetallic, even though the ligand flexes to allow a variable U–M separation. Excellent agreement is found between the experimental and computed structures for <b>3–Ni</b> and <b>3–Pd</b>. Natural population analysis and natural localized molecular orbital (NLMO) compositions indicate that U employs both 5f and 6d orbitals in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules analysis reveals U–M bond critical point properties typical of metallic bonding and a larger delocalization index (bond order) for the less polar U–Ni bond than U–Pd. Electrochemical studies agree with the computational analyses and the X-ray structural data for the U–X adducts <b>3–Ni</b>, <b>4</b>, and <b>5</b>. The data show a trend in uranium–metal bond strength that decreases from <b>3–Ni</b> down to <b>3–Pt</b> and suggest that exchanging the iodide for a fluoride strengthens the metal–metal bond. Despite short U–TM (transition metal) distances, four other computational approaches also suggest low U–TM bond orders, reflecting highly transition metal localized valence NLMOs. These are more so for <b>3–Pd</b> than <b>3–Ni</b>, consistent with slightly larger U–TM bond orders in the latter. Computational studies of the model systems (PH₃)₃MU­(OH)₃I (M = Ni, Pd) reveal longer and weaker unsupported U–TM bonds vs <b>3</b>

Electronic structure of bulk AnO2 (An = U, Np, Pu) and water adsorption on the (111) and (110) surfaces of UO2 and PuO2 from hybrid density functional theory within the periodic electrostatic embedded cluster method

Generalised gradient approximation (PBE) and hybrid (PBE0) density functional theory (DFT) within the periodic electrostatic embedded cluster method have been used to study AnO2 bulk and surfaces (An = U, Np, Pu). The electronic structure has been investigated by examining the projected density of states (PDOS). While PBE incorrectly predicts these systems to be metallic, PBE0 finds them to be insulators, with the composition of the valence and conduction levels agreeing well with experiment. Molecular and dissociative water adsorption on the (111) and (110) surfaces of UO2 and PuO2 has been investigated, with that on the (110) surface being stronger than on the (111). Similar energies are found for molecular and dissociative adsorption on the (111) surfaces, while on the (110) there is a clear preference for dissociative adsorption. Adsorption energies and geometries on the (111) surface of UO2 are in good agreement with recent periodic DFT studies using the GGA+U approach, and our data for dissociative adsorption on the (110) surface of PuO2 match experiment rather well, especially when dispersion corrections are included

Oxygen Vacancy Formation and Water Adsorption on Reduced AnO2 {111}, {110} and {100} Surfaces (An = U, Pu); A Computational Study

The substoichiometric {111}, {110} and {100} surfaces of UO2 and PuO2 are studied computationally using two distinct yet related approaches based on density functional theory; the periodic electrostatic embedded cluster method (PEECM) and Hubbard-corrected periodic boundary condition DFT. First and second layer oxygen vacancy formation energies and geometries are presented and discussed; the energies are found to be substantially larger for UO2 vs PuO2, a result traced to the substantially more positive An(IV)/An(III) reduction potential for Pu, and hence relative ease of Pu(III) formation. For {110} and {100}, the significantly more stable dissociative water adsorption seen previously for stoichiometric surfaces [J. Nucl. Mater. 2016, 482, 124–134; J. Phys. Chem. C 2017, 121, 1675-1682] is also found for the defect surfaces. By contrast, vacancy creation substantially changes the most stable mode of water adsorption on the {111} surface, such that the almost degenerate molecular and dissociative adsorptions on the pristine surface are replaced by a strong preference for dissociative adsorption on the substoichiometric surface. The implications of this result for the formation of H2 are discussed. The generally very good agreement between the data from the embedded cluster and periodic DFT approaches provides additional confidence in the reliability of the results and conclusions

Exceptional uranium(VI)-nitride triple bond covalency from ¹⁵N nuclear magnetic resonance spectroscopy and quantum chemical analysis.

From Europe PMC via Jisc Publications RouterHistory: ppub 2021-09-01, epub 2021-09-24Publication status: PublishedFunder: RCUK | Engineering and Physical Sciences Research Council (EPSRC); Grant(s): EP/M027015/1, EP/K024000/1, EP/S033181/1Funder: European Research Council; Grant(s): 612724Determining the nature and extent of covalency of early actinide chemical bonding is a fundamentally important challenge. Recently, X-ray absorption, electron paramagnetic, and nuclear magnetic resonance spectroscopic studies have probed actinide-ligand covalency, largely confirming the paradigm of early actinide bonding varying from ionic to polarised-covalent, with this range sitting on the continuum between ionic lanthanide and more covalent d transition metal analogues. Here, we report measurement of the covalency of a terminal uranium(VI)-nitride by 15N nuclear magnetic resonance spectroscopy, and find an exceptional nitride chemical shift and chemical shift anisotropy. This redefines the 15N nuclear magnetic resonance spectroscopy parameter space, and experimentally confirms a prior computational prediction that the uranium(VI)-nitride triple bond is not only highly covalent, but, more so than d transition metal analogues. These results enable construction of general, predictive metal-ligand 15N chemical shift-bond order correlations, and reframe our understanding of actinide chemical bonding to guide future studies