Density functional calculations of 19F and 235U NMR chemical shifts in uranium (VI) chloride fluorides UF6−nCln: Influence of the relativistic approximation and role of the exchange‐correlation functional

Relativistic density functional theory (DFT) has been applied to the calculation of the ¹⁹F nuclear magnetic resonance (NMR) chemical shifts of the title compounds. It is shown that, while large‐core effective core potentials (ECP) fail completely for the calculation of ligand NMR chemical shifts in uranium compounds, small‐core ECPs are a valid relativistic method for this purpose. In an earlier study of the same systems, certain differences between theory and experiment had been observed, for instance, in the relative chemical shift of the A₄ and X sites in UF₅Cl. The reason for these deviations has been investigated further in the current paper. By comparing different relativistic methods, it is shown that the relativistic approximation is not responsible for these deviations. The role of the approximation to the exchange‐correlation (XC) functional of DFT has been probed, and generalized gradient approximations (GGA) as well as hybrid DFT methods have been investigated. None of these methods corrects the mentioned errors. It is argued that the neglect of environmental factors (solvent effects) remains as a possible error source, although the approximate XC functional appears to be the more likely cause of the problem. ²³⁵U NMR shieldings and chemical shifts have been calculated, and the trends predicted earlier have been confirmed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

On search and identification of tracks due to short-lived SHE nuclei in extraterrestrial crystals

The unique approach for search and unambiguous identification of short-lived (T_1/2=10³–10⁷ years) superheavy nuclei in cosmic-ray products of the recent nucleosynthesis in our Galaxy are discussed.It is based on: (a) the ability of non-conducting crystals to register and to store for many million years the tracks due to fast nuclei with atomic number Z20 (“fossil” tracks);(b) calibrations of the said crystals with accelerated heavy ions (20Z92) and on revealing the volume etchable track length (VETL) of the fast nuclei coming to rest inside crystals—both of fossil and “fresh” tracks—to determine the charge distribution of cosmic-ray nuclei tracks and(c) the so-called “four-zone” model of tracks in crystals (and also glasses) which provides not only the VETL track length dependence for 20Z92 nuclei but also demonstrates the regular annealing behavior of VETL of 20Z92 nuclei in a broad temperature interval.This approach was first applied in the early 1980s to investigate the “fossil” tracks due to 22Z92 cosmic-ray nuclei in olivine crystals from meteorites-pallasite Marjalahti and Eagle Station.The discovery of Th–U cosmic-ray nuclei tracks in 1980 was unambiguously confirmed by calibrations of the same crystals with ²³⁸U, ¹⁹⁷Au and ²⁰⁸Pb accelerated ions in the late 1980s. More than 1600 tracks due to cosmic-ray actinide nuclei were measured during the last two decades of the 20th century.Also, 11 anomalously long tracks (track length exceeds by a factor (1.6±0.1) the track length due to Th–U nuclei were measured. The detailed analysis shows that at least 5 of these tracks could not be attributed to the Th–U nuclei. It means that now we have a preliminary proof on the existence Z110 nuclei in cosmic-rays. The abundance is Z110/Th–U=(1–3)×10⁻³ in Z110 freshly formed cosmic-rays (time interval 10³–10⁷ years).The method proposed can provide the necessary and sufficient conditions for the discovery of Z110 nuclei in nature.     

Nucleophilic Reactivity of a Nitride‐Bridged Diuranium(IV) Complex: CO2 and CS2 Functionalization

Thermolysis of the nitride‐bridged diuranium(IV) complex Cs{(μ‐N)[U(OSi(O^tBu)₃)₃]₂} ( 1 ) showed that the bridging nitride behaves as a strong nucleophile, promoting N?C bond formation by siloxide ligand fragmentation to yield an imido‐bridged siloxide/silanediolate diuranium(IV) complex, Cs{(μ‐N^tBu)(μ‐O₂Si(O^tBu)₂)U₂(OSi(O^tBu)₃)₅}. Complex 1 displayed reactivity towards CS₂ and CO₂ at room temperature that is unprecedented in f‐element chemistry, affording diverse N‐functionalized products depending on the reaction stoichiometry. The reaction of 1 with two equivalents of CS₂ yielded the thiocyanate/thiocarbonate complex Cs{(μ‐NCS)(μ‐CS₃)[U(OSi(O^tBu)₃)₃]₂} via a putative NCS^?/S^2? intermediate. The reaction of 1 with one equivalent of CO₂ resulted in deoxygenation and N?C bond formation, yielding the cyanate/oxo complex Cs{(μ‐NCO)(μ‐O)[U(OSi(O^tBu)₃)₃]₂}. Addition of excess CO₂ to 1 led to the unprecedented dicarbamate product Cs{(μ‐NC₂O₄)[U(OSi(O^tBu)₃)₃]₂}.     

Ba4Cr2US9: The First Chalcogenide Analogue of the Perovskite‐related (A3A′BO6)m(A3B3O9)n Family

The compound Ba₄Cr₂US₉, which crystallizes in space group P321, consists of one‐dimensional chains separated by Ba²⁺ cations. Each one‐dimensional chain comprises face‐sharing CrS₆ octahedra and US₆ trigonal prisms in the sequence oct oct tp oct oct tp with the U and Cr centers in a linear chain parallel to [001].     

Heterometallic Uranyl (Hydroxyethyl)iminodiacetic Acid (Heidi) Complexes: Molecular Models for U(VI) Uptake in Complex Media

Amidoximated absorbents (AO-PAN) effectively remove U(VI) from aqueous solution, but previous studies reported more variability for complex natural waters that contain additional confounding ions and molecules. Ternary phases containing U(VI), M(III) (M=Fe(III), Al(III), Ga(III)), and organic molecules exist under these conditions and cause heterogeneous U(VI) uptake on AO-PAN. The goal of the current study is to provide additional insights into the structural features ternary complexes using N-(2-hydroxyethyl)-iminodiacetic acid (HEIDI) as the model organic chelator and explore the relevance of these species on U(VI) capture. Three model compounds ([(UO₂)(Fe)₂(μ₃-O)(C₆NO₅H₈)₂(H₂O)₄] ( UFe₂ ), ([(UO₂)(Al)₂(μ₂-OH)(C₆NO₅H₈)₂(H₂O)₃] ( UAl₂ ) and [(UO₂)(Ga)₂(μ₂-OH)(C₆NO₅H₈)₂(H₂O)₃] ( UGa₂ )) were characterized by single-crystal X-ray diffraction. Raman spectra of the model compounds were compared with solution data and the ternary phases were noted in the case of Al(III) and Ga(III), but not in the Fe(III) system. U(VI) adsorption onto AO-PAN was not impacted by the presence of HEIDI or the trivalent metal species.