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21.
The TiO2 gel doped with UO22 and Eu3 has been prepared by a sol-gel method. The quenching of the UO22 emission by Eu3 and the energy transfer from the excited state of UO22 to the ground state of Eu3 have been investigated. The energy transfer has been studied by the measurement of luminescence lifetime τ, calculations of energy transfer efficiency ηET and energy transfer rate WET. The experimental results indicated that the quenching is combined static and dynamic mechanism, but the static mechanism is dominant. 相似文献
22.
We investigate the vibrational spectra of crystals of ternary orthophosphates Me7Eu2UO2·(PO4)5 (Me–Na, Rb, Cs) obtained by solid-phase synthesis. We show that in these materials the effect of coordination distorts the
geometry of the PO
4
3−
tetrahedron and decreases its symmetry. We conclude that the PO
4
3−
tetrahedrons in Me7Eu2UO2(PO4)5 occupy two nonequivalent positions in the lattice. The character of manifestation and the number of oscillation frequencies
observed allow the assumption that they have the C3v- and C2-symmetry. This symmetry of two crystallographically nonequivalent groups of PO
4
3−
ensures a complete set of bands in the IR absorption spectra of the crystals investigated. We show that these crystals exhibit
chain structural motifs.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol, 64, No. 4, pp. 467–470, July–August, 1997. 相似文献
23.
A. A. Zazhogin A. P. Zazhogin A. I. Komyak A. I. Serafimovich 《Journal of Applied Spectroscopy》2003,70(4):588-592
Based on an analysis of the low-temperature luminescence spectra of tri- and tetranitrate uranyl compounds, the influence exerted by the nature of outer-sphere cations (Na, K, Rb, NH4, and Cs) on the position of a purely electron transition in the uranyl ion has been studied. Linear correlation dependences of the position of a purely electron transition on the value of the ionization potential of cations have been established. It is shown that the upper occupied molecular orbital, whose position is determined by the total donating capacity of ligands and their number, is essentially of ligand character. 相似文献
24.
In the back-end of the nuclear fuel cycle, liquid–liquid extraction is the selected separation method. For an improved design of new extracting agent, the knowledge of the coordination polyhedra of the metal ions is important. In this paper, we investigated the coordination sphere of a series of uranyl complexes with selected organophosphorus extracting molecules: UO2(NO3)2L2 (with L=tri-iso-butylphosphate, tri-n-butylphosphate, trimethylphosphate and triphenylphosphate) using X-ray absorption spectroscopy. FEFF7 calculations of the EXAFS spectra corresponding to the model compound UO2(NO3)2(TiBP)2 (with TiBP=tri-iso-butylphosphate) for which the crystal structure is known led to a multiple scattering approach of the data fitting. EXAFS results show subtle U–O(P) bond distance differences between the different complexes that are discussed in terms of both electronic and steric effects of L. These results are discussed with regards to the extraction ability of L. In the same time, exploratory work has been attempted in order to evaluate U–O–P bond angle variations as a function of L using multiple photon-scattering paths. Satisfactory values have been obtained compared to the crystallographic data. 相似文献
25.
26.
This work is devoted to the study of and Rb2UO2F4.H2O and Cs2UO2F4. H2O IR-spectra with the aim of obtaining a set of vibration frequencies characterising M2U02F4.H2O complexe elucidating the role and nature of water bonds in the structures of the above-mentioned compounds; and receiving preliminary information on the structure of M2UO2F4.H2O. The investigated compounds were synthesized in accord with our previous paper1. M2UO2D2O and M2UO2F4.HDO were obtained by recrystallizing M2UO2F4.H2O from D2O and HDO respectively 相似文献
27.
GUO Hong–Xu WENG Wen LI Xi–Zhong 《结构化学》2008,27(12):1455-1458
An organically templated 2-D uranyl sulfate, {(C2H8N)[(UO2)Cl(SO4)(H2O)] }n 1, has been hydrothermally synthesized. The crystal and molecular structures have been determined by X-ray crystallography method and spectral techniques. 1 belongs to monoclinic, space group P21/c with a = 8.3545(17), b = 10.550(2), c = 12.370(3)A, β = 102.64(3)°, V = 1063.9(4)A3, Mr = 464.64, De= 2.901 g/cm^3, F(000) = 836,μ = 15.710 mm^-1, Z= 4, the final R = 0.0286 and wR = 0.0685 for 10164 observed reflections with Ⅰ 〉 2σ(Ⅰ). 1 presents a two-dimensional layer-like structure constructed from infinite anionic [(UO2)Cl(H2O)(SO4)]^- layers with [C2H8N]^+ cations balancing the charge and a number of intermoleeular hydrogen bonds (C-H…O and O-H…Cl) existing in the solid state. The fluorescence properties of 1 have also been discussed. 相似文献
28.
Linjuan Zhang Jing Zhou Jianyong Zhang Jing Su Shuo Zhang Ning Chen Yunpeng Jia Jiong Li Yu Wang Jian-Qiang Wang 《Journal of synchrotron radiation》2016,23(3):758-768
Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoretical L3‐edge X‐ray absorption near‐edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE1 = 168.3/R(U—Oax)2 ? 38.5 (for the axial plane) and ΔE2 = 428.4/R(U—Oeq)2 ? 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the U L3‐edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X‐ray absorption fine‐structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl–ligand complexes, such as the uranyl–carbonate complex. Most importantly, the XANES research method could be extended to low‐concentration uranyl systems, as indicated by the results of the uranyl–amidoximate complex (~40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides. 相似文献
29.
Wen-Bo Lan Sha Gao Ying-Wu Lin Guo-Wen Peng 《Journal of Coordination Chemistry》2016,69(18):2775-2784
Uranyl–salophen (U–S) complexes, as modified by unilateral benzene and coordinated with cyclohexenones substituted by methyls or fluorines in E/Z-types, were investigated using density functional theory calculations at the level of B3LYP/6–311G** basis set. The results indicated that the O of substituted cyclohexenones could coordinate with U of the asymmetric U–S complexes. When the C=C bond of cyclohexenones was located upward in the twisted salophen plane, the binding energies of the cyclohexenones to the asymmetric U–S and Wiberg bond indices (WBIs) of carbonyl oxygen to uranium (U–O) were higher than those of the C=C bonds located downward. It could be concluded that when cyclohexenones were coordinated to the asymmetric U–S, the major products would be the complexes in which the C=C bond of cyclohexenones locates upward in the configuration. Binding energies of the E-type substituted cyclohexenones to the asymmetric U–S were higher than those for the Z-type ones. 相似文献
30.
Olivier Renier Dr. Clément Falaise Harrison Neal Karoly Kozma Prof. Dr. May Nyman 《Angewandte Chemie (International ed. in English)》2016,55(43):13480-13484
Uranyl polyoxometalate clusters are both fundamentally fascinating and potentially relevant to nuclear energy applications. With only ten years of development, there is still much to be discovered about heterometal derivatives and aqueous speciation and behavior. Herein, we show that it is possible to encapsulate the polyoxocations [Bi6O8]2+ and [Pb8O6]4+ in [(UO2)(O2)(OH)]2424? (denoted Bi@U24 and Pb@U24) in pure form and high yields despite the fact that under aqueous conditions, these compounds are stable on opposite ends of the pH scale. Moreover, [Pb8O6]4+ is a formerly unknown PbII polynuclear species, both in solution and in the solid state. Raman spectroscopic and mass spectrometric analysis of the reaction solutions revealed the very rapid assembly of the nested clusters, driven by bismuth‐ or lead‐promoted decomposition of excess peroxide, which inhibits U24 formation. Experimental and simulated small‐angle X‐ray scattering data of Bi@U24 and Pb@U24 solutions revealed that this technique is very sensitive not only to the size and shape of the clusters, but also to the encapsulated species. 相似文献