Crystal Chemistry of Uranyl Compounds

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Mineralogical Crystallography and Biomineralization".

Deadline for manuscript submissions: closed (1 July 2021) | Viewed by 6838

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Faculty of Geology, Saint Petersburg State University, 199034 Saint Petersburg, Russia
Interests: minerals; crystal structures; actinide compounds; uranyl crystal chemistry, layered minerals and materials
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Special Issue Information

Dear Colleagues,

Uranyl compounds are known as important constituents of spent nuclear fuel and oxidation zones of mineral deposits. A large amount of structural and chemical data on uranyl compounds has been accumulated recently due to their importance for catalysis, ion-exchange, and absorption applications. Hence, understanding the trends in chemistry and structural diversity of alteration products of primary (or first formed) uranium compounds is important for predicting long-term behavior of radioactive wastes in geological repositories, since some of the alteration products may incorporate radionuclides into their structures. The compounds of hexavalent uranium have witnessed increasing interest not only due to their essential role in energy production but also because of the particular abundance and non-triviality of their crystal chemistry. These compounds are often considered as transporting agents both in geological media and in deposits of spent nuclear fuel. Not only minerals and their analogs are of interest, but also a wide range of synthetic uranium compounds including hybrid and templated materials. This Special Issue is devoted to all aspects of the crystal chemistry of uranium compounds and aims to combine important surveys covering topics indicated in the keywords below. 

We invite you to participate in this Special Issue and to contribute your research results in the fields of uranyl compounds crystal chemistry, structural studies of uranium minerals and related synthetic compounds, structural topology and relationships between compounds, studies of their physical properties, descriptions (including mechanistic) of growth processes, and the properties of the natural and synthetic uranyl compounds.

Dr. Evgeny Nazarchuk
Guest Editor

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Keywords

  • Uranium minerals
  • Uranyl compounds
  • Crystallography
  • Crystal chemistry
  • X-ray diffraction
  • Crystal structures
  • Crystal growth

Published Papers (3 papers)

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Research

16 pages, 4333 KiB  
Article
The Role of Acidity in the Synthesis of Novel Uranyl Selenate and Selenite Compounds and Their Structures
by Gabriel L. Murphy, Philip Kegler, Eike M. Langer and Evgeny V. Alekseev
Crystals 2021, 11(8), 965; https://doi.org/10.3390/cryst11080965 - 16 Aug 2021
Cited by 2 | Viewed by 1745
Abstract
Herein, the novel uranyl selenate and selenite compounds Rb2[(UO2)2(SeO4)3], Rb2[(UO2)3(SeO3)2O2], Rb2[UO2(SeO4)2(H2O)]·2H [...] Read more.
Herein, the novel uranyl selenate and selenite compounds Rb2[(UO2)2(SeO4)3], Rb2[(UO2)3(SeO3)2O2], Rb2[UO2(SeO4)2(H2O)]·2H2O, and (UO2)2(HSeO3)2(H2SeO3)2Se2O5 have been synthesized using either slow evaporation or hydrothermal methods under acidic conditions and their structures were refined using single crystal X-ray diffraction. Rb2[(UO2)2(SeO4)3] synthesized hydrothermally adopts a layered 2D tetragonal structure in space group P42/ncm with a = 9.8312(4) Å, c = 15.4924(9) Å, and V = 1497.38(15) Å, where it consists of UO7 polyhedra coordinated via SeO4 units to create units UO2(SeO4)58− moieties which interlink to create layers in which Rb+ cations reside in the interspace. Rb2[(UO2)3(SeO3)2O2] synthesized hydrothermally adopts a layered 2D triclinic structure in space group P1¯ with a = 7.0116(6) Å, b = 7.0646(6) Å, c = 8.1793(7) Å, α = 103.318(7)°, β = 105.968(7)°, γ = 100.642(7)° and V = 365.48(6) Å3, where it consists of edge sharing UO7, UO8 and SeO3 polyhedra that form [(UO2)3(SeO3)2O2] layers in which Rb+ cations are found in the interlayer space. Rb2[UO2(SeO4)2(H2O)]·2H2O synthesized hydrothermally adopts a chain 1D orthorhombic structure in space group Pmn21 with a = 13.041(3) Å, b = 8.579(2) Å, c = 11.583(2) Å, and V = 1295.9(5) Å3, consisting of UO7 polyhedra that corner share with one H2O and four SeO42− ligands, creating infinite chains. (UO2)2(HSeO3)2(H2SeO3)2Se2O5 synthesized under slow evaporation conditions adopts a 0D orthorhombic structure in space group Cmc21 with a = 28.4752(12) Å, b = 6.3410(3) Å, c = 10.8575(6) Å, and V = 1960.45(16) Å3, consisting of discrete rings of [(UO2)2(HSeO3)2(H2SeO3)2Se2O5]2. (UO2)2(HSeO3)2(H2SeO3)2Se2O5 is apparently only the second example of a uranyl diselenite compound to be reported. A combination of single crystal X-ray diffraction and bond valance sums calculations are used to characterise all samples obtained in this investigation. The structures uncovered in this investigation are discussed together with the broader family of uranyl selenates and selenites, particularly in the context of the role acidity plays during synthesis in coercing specific structure, functional group, and topology formations. Full article
(This article belongs to the Special Issue Crystal Chemistry of Uranyl Compounds)
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9 pages, 8091 KiB  
Article
Alkali Uranyl Borates: Bond Length, Equatorial Coordination and 5f States
by Myrtille O.J.Y. Hunault, Denis Menut and Olivier Tougait
Crystals 2021, 11(1), 56; https://doi.org/10.3390/cryst11010056 - 12 Jan 2021
Cited by 5 | Viewed by 2110
Abstract
Three uranyl borates, UO2B2O4, LiUO2BO3 and NaUO2BO3, have been prepared by solid state syntheses. The influence of the crystallographic structure on the splitting of the empty 5f and 6d states [...] Read more.
Three uranyl borates, UO2B2O4, LiUO2BO3 and NaUO2BO3, have been prepared by solid state syntheses. The influence of the crystallographic structure on the splitting of the empty 5f and 6d states have been probed using High Energy Resolved Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS) at the uranium M4-edge and L3-edge respectively. We demonstrate that the 5f splitting is increased by the decrease of the uranyl U-Oax distance, which in turn correlates with an increased bond covalency. This is correlated to the equatorial coordination change of the uranium. The role of the alkalis as charge compensating the axial oxygen of the uranyl is discussed. Full article
(This article belongs to the Special Issue Crystal Chemistry of Uranyl Compounds)
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14 pages, 2742 KiB  
Article
Uranyl Nitrates: By-Products of the Synthetic Experiments or Key Indicators of the Reaction Progress?
by Vladislav V. Gurzhiy, Olga S. Tyumentseva and Ilya V. Kornyakov
Crystals 2020, 10(12), 1122; https://doi.org/10.3390/cryst10121122 - 9 Dec 2020
Cited by 2 | Viewed by 2211
Abstract
Six novel uranyl nitrate compounds K3[(UO2)(NO3)Cl3](NO3) (1, 2), α-Cs2[(UO2)(NO3)Cl3] (3), [(UO2)(NO3)2(H2O)2 [...] Read more.
Six novel uranyl nitrate compounds K3[(UO2)(NO3)Cl3](NO3) (1, 2), α-Cs2[(UO2)(NO3)Cl3] (3), [(UO2)(NO3)2(H2O)2][(CH3NH3)2(NO3)2] (4), Cs2[(UO2)(NO3)4] (5), and [(UO2)2(OH)2(NO3)2(H2O)3](H2O) (6) have been prepared from aqueous solutions. Their structures were analyzed using single-crystal X-ray diffraction technique. Structural studies have shown that the crystals of 1 and 2 are isotypic but differ in the distortion at the counter ion’s sites. The crystal of 3 is a low-temperature polymorph modification of the recently studied compound. The crystal structure of 4 is composed of uranyl-dinitrate-dihydrate and methylamine-nitrate electroneutral complexes linked through the system of H-bonds. The crystal structure of 5 is based on the finite [(UO2)(NO3)4]2− clusters that are arranged in pseudo-chained complexes extended along [100] and are arranged according to a hexagonal packing or rods. The crystal of 6 is also a novel polymorph modification of previously studied compound, the structure of which is based on the very rare topological type of the finite clusters. Nowadays, uranyl nitrate finite clusters of nine various topological types are known. We give herein a short review of their topological features and relationships. Crystallization of uranyl nitrates usually occurs when all other competitive anions in the system have already formed crystalline phases, or the reaction of reagents have slowed down or even stopped. Thus it is suggested that crystallization of uranyl nitrates can be used as a key indicator of the reaction progress, which points to the necessity of the initial concentrations of reagents correction, or to the replacement of reagents and adjustment of the thermodynamic (P,T) parameters of the synthesis. Full article
(This article belongs to the Special Issue Crystal Chemistry of Uranyl Compounds)
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