相对论赝势的从头计算法研究铀酰离子电子结构

用相对论赝势的从头算法研究了铀酰离子的几何构和电子结构,得到了与实验数据较一致的键长、键角和ＩＲ振动频率。铀氧间以Ｕ５ｆ与Ｏ２ｐ相互为主,Ｕ６ｄ、Ｏ２ｐ间的键合较小;同时,Ｕ６ｐ、Ｕ７ｓ、Ｕ６ｄ、、Ｕｓｄ杂化轨道与Ｏ２ｓ间也有强的相互作用。不同自旋多重度时对铀酰离了聪以有量计算结果表明,ＵＯ２＾２＋的基态为＾１Σｇ＾＋的基态为＾１Σｇ＾＋的可能性更大。     

A facile synthesis of aminomethylene bisphosphonates through rhodium carbenoid mediated N-H insertion reaction. Application to the preparation of powerful uranyl ligands

A straightforward procedure ensuring the anchoring of bisphosphonate moiety onto aromatic amines is described. The procedure yields aminoaryl 1,1-bisphosphonates known to display multiple biological activities. The described methodology has also been applied to the synthesis of ligands whose uranyl-binding properties have been studied.     

The Photochemical Behavior of the Uranyl Ion (UO$\rm{{_{2}^{2+}}}$): a Dimer Perspective and Outlook

The complex formation of uranyl (UO ) with oxalic acid (HOOC? COOH) in acetone is studied by UV/VIS, absorption, luminescence, and excitation spectroscopy. Based on solid‐state crystallographic data, we propose a dimer structure with D_2h symmetry for the complex in solution. This symmetry is vibrationally distorted to D₂ by the out‐of‐plane equatorial‐ligand vibration. From the spectroscopic point of view, this vibration induces intensity in the transitions Π_g←Σ and one component of Δ_g←Σ . From the photochemical point of view, this vibration induces a twisting mechanism that destroys the complex. From the theoretical point of view, it is worthwhile to notice that the symmetry of the odd out‐of‐plane vibration is the same as the symmetry of the odd LUMO (f_xyz). By vibrating accordingly to the LUMO symmetry, the complex is self‐destroying by absorption of light, and the uranyl is regenerated. A small comment is devoted to a possible δ–δ interaction and the quintuple U₂ bond distance proposed by Gagliardi and Ross [29].     

[Hg5O2(OH)4][(UO2)2(AsO4)2]: A complex mercury(II) uranyl arsenate

Under mild hydrothermal conditions UO₂(NO₃)₂·6H₂O, Hg₂(NO₃)₂·2H₂O, and Na₂HAsO₄·7H₂O react to form [Hg₅O₂(OH)₄][(UO₂)₂(AsO₄)₂] (HgUAs-1). Single crystal X-ray diffraction experiments reveal that HgUAs-1 possesses a pseudo-layered structure consisting of two types of layers: and . The layers are complex, and contain three crystallographically unique Hg centers. The coordination environments and bond-valence sum calculations indicate that the Hg centers are divalent. The layers belong to the Johannite topological family. The and layers are linked to each other through μ₂-O bridges that include Hg?O=U=O interactions.     

熔盐法合成新型硅酸铀K6(UO2)3Si8O22

用熔盐法合成了新型硅酸铀K4(UO2),Si8O22,并用单晶X射线衍射确定结构.结果表明,化合物由UO6 双四角椎及硅酸根四面体构成的(Si8O22)12-单元组成,其中(Si8O22)12-单元的结构形态是最新发现的.29Si MAS NMR测定结果与晶体结构相吻合,而光致发光光谱证实了六价铀的存在.K(UO2),...     

分子动力学方法模拟不同温度下铀酰在叶腊石上的吸附和扩散行为

采用分子动力学方法研究了铀酰在叶腊石表面的吸附和扩散。在碳酸根离子存在的情况下,探究了温度对铀酰吸附和扩散的影响。碳酸根离子与铀酰存在较强的作用力,不同数目的碳酸根离子与铀酰结合会形成多种铀酰种态。在不同温度的模拟中,得到了UO_2~(2+)、UO_2CO_3、UO_2(CO_3)_2~(2-)、UO_2(CO_3)_3~(4-)四种铀酰种态和铀酰聚合物。通过原子密度图,观察了粒子在溶液中的分布情况。发现UO_2~(2+)+和UO_2CO_3容易吸附在叶腊石上,而UO_2(CO_3)_2~(2-)和UO_2(CO_3)_3~(4-)主要存在于扩散层中。随着时间的推移,越来越多的碳酸根离子与铀酰配位,使得铀酰在叶腊石上的吸附逐渐减少。本文计算了不同温度下,各铀酰种态的扩散系数。在扩散层中,各种态的扩散系数随温度的变化较为一致,而在吸附层中,UO_2~(2+)和UO_2CO_3的扩散速率随温度的变化较UO_2(CO_3)_2~(2-)和UO_2(CO_3)_3~(4-)慢。但是在同一温度下,同一个吸附层或扩散层中,铀酰种态的扩散系数大小顺序始终保持不变:UO_2~(2+)UO_2CO_3UO_2(CO_3)_2~(2-)UO_2(CO_3)_3~(4-)。说明在碳酸根存在的情况下,UO_2~(2+)可能是主要的扩散形式。     

A Joint Study of Experimental and Computational Chemistry to Probe the Effect of Coordination Modes on the Luminescence of Uranyl-Organic Coordination Polymers

Despite the potential application of uranyl-organic coordination polymers (UOCPs) in detecting metal cations and radiation rays, their luminescence properties have not been sufficiently studied at the molecular level. Herein, we synthesized a series of UOCPs ( UOCP1 – 9 ) with new construction based on bipyridinium salts and diverse auxiliary ligands. The physicochemical properties of the complexes with high purity were systematically characterized, especially the luminescence spectra. A deep theoretical investigation was conducted to illustrate the relation between uranyl coordination and the luminescence spectral property. The results show that the influence of ligand type on the uranyl luminescent spectral properties increases in the order of hydroxide>oxalate>aromatic carboxylate, which can be attributed to the magnitude of orbital interaction between uranyl and ligand. This work helps to profoundly understand uranyl optical properties and electronic structure at the molecular level, providing important hints for recognizing the nature of luminescent spectral features of uranyl-containing materials, as well as the fundamental chemistry of actinide elements.     

Structures and syntheses of framework triuranyl diarsenate hydrates

Two homeotypic hydrated uranyl arsenates, (UO₂)[(UO₂)(AsO₄)]₂(H₂O)₄, UAs4, and (UO₂)[(UO₂)(AsO₄)]₂(H₂O)₅, UAs5 were synthesized by hydrothermal methods. Intensity data were collected at room temperature using MoKα X-radiation and a CCD-based area detector. Their crystal structures were solved by direct methods and refined by full-matrix least-squares techniques on the basis of F² to agreement indices (UAs4, UAs5) wR₂=0.116, 0.060, for all data, and R₁=0.046, 0.033, calculated for 3176, 5306 unique observed reflections (|F_o|>4σ_F) respectively. UAs4 is monoclinic, space group P2₁/c, Z=4, a=11.238(1), b=7.152(1), c=21.941(2)Å, β=104.576(2)°, V=1706.8(1)ų, D_calc=4.51 g/cm³. UAs5 is orthorhombic, space group Pca2₁, Z=4, a=20.133(2), b=11.695(1), c=7.154(1)Å, V=1684.4(1)ų, D_calc=4.65 g/cm³. Both structures contain sheets of arsenate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO₂)(AsO₄)]¹⁻ and the uranophane sheet anion-topology. The sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with an arsenate tetrahedron on each of two adjacent sheets, resulting in open-frameworks with isolated H₂O groups in the larger cavities of the structures. The uranyl arsenate sheet in UAs4 is relatively planar, and is topologically identical with the uranyl phosphate sheet in (UO₂)[(UO₂)(PO₄)]₂(H₂O)₄. The uranyl arsenate sheet in UAs5 is the same geometrical isomer as in UAs4, but is highly corrugated, exhibiting approximately right angle bends of the sheet after every second uranyl arsenate chain repeat.     

Complex Topology of Uranyl Polyphosphate Frameworks: Crystal Structures of α‐, β‐K[(UO2)(P3O9)] and K[(UO2)2(P3O10)]

Three new uranyl polyphosphates, α‐K[(UO₂)(P₃O₉)] ( 1 ), β‐K[(UO₂)(P₃O₉)] ( 2 ), and K[(UO₂)₂(P₃O₁₀)] ( 3 ), were prepared by high‐temperature solid‐state reactions. The crystal structures of the compounds have been solved by direct methods: 1 – monoclinic, P2₁/m, a = 8.497(1), b = 15.1150(1), c = 14.7890(1) Å, β = 91.911(5)°, V = 1898.3(3) ų, Z = 4, R₁ = 0.0734 for 4181 unique reflections with |F₀| ≥ 4σ_F; 2 – monoclinic, P2₁/n, a = 8.607(1), b = 14.842(2), c = 14.951(1) Å, β = 95.829(5)°, V = 1900.0(4) ų, Z = 4, R₁ = 0.0787 for 3185 unique reflections with |F₀| ≥ 4σ_F; 3 – Pbcn, a = 10.632(1), b = 10.325(1), c = 11.209(1) Å, V = 1230.5(2) ų, Z = 4, R₁ = 0.0364 for 1338 unique reflections with |F₀| ≥ 4σ_F. In the structures of 1 and 2 , phosphate tetrahedra share corners to form infinite [PO₃]^? chains, whereas, in the structure of 3 , tetrahedra form linear [P₃O₁₀]^5? trimers. The structures are based upon 3‐D frameworks of U and P polyhedra linked by sharing common O corners. The infinite [PO₃]^? chains in the structures of 1 and 2 are parallel to [100] and [–101], respectively. The uranyl polyphosphate frameworks are occupied by host K⁺ cations.     

Stoichiometry of uranyl hydrolysis reaction in acidic aqueous solutions from the evidence of oxygen exchange kinetics

The kinetics of uranyl oxygen exchange with water molecules in aqueous solutions was studied in the pH range 1–4 and uranium concentration range 10^–4–0.1 M. It was confirmed that the exchange is stimulated by hydrolyzed uranyl species. From the evidence of data on the kinetics of uranyl oxygen exchange the reaction stoichiometry of uranyl hydrolysis was determined. The scheme of uranyl hydrolysis involving formation of (UO₂)₂(OH)₂²⁺, (UO₂)₂(OH)₃⁺, and other hydrolyzed species was proposed. To cite this article: L.G. Mashirov et al., C. R. Chimie 336 (2004).

Résumé

Étude de l'hydrolyse de l'uranium hexavalent en milieu acide par échange isotopique de l'oxygène. L'échange isotopique de l'oxygène de l'ion uranyle avec les molécules d'eau a été étudié dans le domaine de pH de 1 à 4 et de concentration en uranium de 10^–4 à 0,1 M. Cet échange a lieu par l'intermédiaire d'espèces hydrolysées de U(VI). La stoechiométrie des formes hydrolysées de U(VI) est déduite des vitesses d'échange isotopique. En particulier, les espèces (UO₂)₂(OH)₂²⁺ et (UO₂)₂(OH)₃⁺ ont été clairement identifiées. Un schéma d'hydrolyse est proposé. Pour citer cet article : L.G. Mashirov et al., C. R. Chimie 336 (2004).