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This study reports the successful synthesis and characterization of a uranyl nicotinate compound, UO2(C6H4NO2)2·0.25H2O. The compound was synthesized using a metal 1:2 ligand ratio and water as the solvent. The average yield of the compound was 67 %. Thermogravimetric analysis revealed multiple stages of mass loss, including dehydration, nitrogen decomposition and UO2 2+ reduction. Fourier-transform infrared spectroscopy confirmed the coordination of the carboxylate group in the compound. Field emission gun scanning electron microscope analysis showed the particles with a regular oval shape. Energy-dispersive X-ray spectroscopy provided semi-quantitative data on the elemental composition of the compound. The major elements identified were uranium, carbon, oxygen and nitrogen. These results contribute to understanding the compound's synthesis, thermal behaviour, molecular composition, particle morphology and elemental composition. Further research can build upon these findings to explore potential applications and develop new compounds with tailored properties. [ABSTRACT FROM AUTHOR]

This paper reviews not the largest, but at the same time quite an interesting, group of natural and synthetic uranyl molybdate compounds. Nowadays, nine minerals of U and Mo are known, but the crystal structures have only been reported for five of them. Almost an order of magnitude more (69) synthetic compounds are known. A significant discrepancy in the topological types for natural and synthetic phases is shown, which is most likely due to elevated temperatures of laboratory experiments (up to 1000 °C), while natural phases apparently grow at significantly lower temperatures. At the same time, the prevalence of dense topologies (with edge-sharing interpolyhedral linkage) among natural phases can be noted, which is fully consistent with other recently considered mineral groups. Uranyl molybdates demonstrate several similarities with compounds of other U-bearing groups; however, even topological matches do not lead to the appearance of completely isotypic compounds. Structural complexity calculations confirm, in general, crystal chemical observations. Considering the prevalence of dense structures in which coordination polyhedra of uranium and molybdenum are connected through common edges as well as framework architectures, one can expect a less significant influence of interlayer species on the formation of the crystal structure than the main U-bearing complexes. The more structural complexity of the uranyl molybdate units, the more complex of the entire crystal structure is. In addition, there is a tendency for complexity to increase with increasing density of the complex; the simplest structures are vertex-shared, while the complexity increases with the appearance of common edges. [ABSTRACT FROM AUTHOR]

To date, uranyl silicates are mostly represented by minerals in nature. However, their synthetic counterparts can be used as ion exchange materials. A new approach for the synthesis of framework uranyl silicates is reported. The new compounds Rb2[(UO2)2(Si8O19)](H2O)2.5 (1), (K,Rb)2[(UO2)(Si10O22)] (2), [Rb3Cl][(UO2)(Si4O10)] (3) and [Cs3Cl][(UO2)(Si4O10)] (4) were prepared at harsh conditions in "activated" silica tubes at 900 °C. The activation of silica was performed using 40% hydrofluoric acid and lead oxide. Crystal structures of new uranyl silicates were solved by direct methods and refined: 1 is orthorhombic, Cmce, a = 14.5795(2) Å, b = 14.2083(2) Å, c = 23.1412(4) Å, V = 4793.70(13) Å3, R1 = 0.023; 2 is monoclinic, C2/m, a = 23.0027(8) Å, b = 8.0983(3) Å, c = 11.9736(4) Å, β = 90.372(3) °, V = 2230.43(14) Å3, R1 = 0.034; 3 is orthorhombic, Imma, a = 15.2712(12) Å, b = 7.9647(8) Å, c = 12.4607(9) Å, V = 1515.6(2) Å3, R1 = 0.035, 4 is orthorhombic, Imma, a = 15.4148(8) Å, b = 7.9229(4) Å, c = 13.0214(7) Å, V = 1590.30(14) Å3, R1 = 0.020. Their framework crystal structures contain channels up to 11.62 × 10.54 Å filled by various alkali metals. [ABSTRACT FROM AUTHOR]

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Four new hybrid organic‐inorganic uranyl phosphate compounds were structurally characterized after single crystals were grown via ionothermal synthesis using the ionic liquids 1‐ethyl‐3‐methylimidazolium dimethyl phosphate and 1‐ethyl‐3‐methylimidazolium dibutyl phosphate. Three of the new crystal structures presented here incorporate dimethyl or monomethyl phosphate ligands into the structural unit to form one chain‐based compound and two sheet‐based compounds. One of the structures utilizes dibutyl phosphate to form a previously reported uranyl compound, a structural polymorph that crystallized in space group P21/c in contrast to the previously reported P‐1 structure. The structural and topological relationships are compared to those of uranyl phosphate minerals as well as previously reported organophosphate compounds. The roles of the organics on the phosphate anions in impacting uranyl coordination and stabilizing the crystal structures are discussed. [ABSTRACT FROM AUTHOR]

Crystals of two new inorganic uranyl silicates, Cs[(UO6)2(UO2)9(Si2O7)F] (1) and Rb2[(PtO4)(UO2)5(Si2O7)] (2), were produced from melts in evacuated silica tubes. Their structures have been solved by direct methods: 1 is trigonal, P-31c, a = 10.2040(3), c = 17.1278(5) Å, V = 1544.45(10) Å3, R1 = 0.042; 2 is tetragonal, P4/mbm, a = 16.0400(24), c = 3.9231(6) Å, V = 1009.34(10) Å3, R1 = 0.045. 1 is the first example of cation–cation interactions between the uranyl polyhedra in uranyl silicates. Therein, UVI adopts three coordination modes, UO6 octahedra, UO6F, and UO7 pentagonal bipyramids, with the latter sharing common edges to form U2O12 dimers. Three dimers associate into six-membered rings via cation–cation interactions. The structure of 1 can be described as a complex uranyl fluoride silicate framework with channels filled by the U1 atoms and disordered Cs+ cations. 2 represents a new type of topology never observed before among the structures of uranyl compounds; it is also a first complex uranium platinum oxide. Therein, the UO6 tetragonal bipyramids share edges to form chains. Five such chains are stitched into a complex ribbon via the silicon polyhedra. The ribbons are connected into a framework by the PtO4 squares; rubidium atoms are located in the channels of the framework. [ABSTRACT FROM AUTHOR]

To date, uranyl silicates are mostly represented by minerals in nature. However, their synthetic counterparts can be used as ion exchange materials. A new approach for the synthesis of framework uranyl silicates is reported. The new compounds Rb2[(UO2)2(Si8O19)](H2O)2.5 (1), (K,Rb)2[(UO2)(Si10O22)] (2), [Rb3Cl][(UO2)(Si4O10)] (3) and [Cs3Cl][(UO2)(Si4O10)] (4) were prepared at harsh conditions in “activated” silica tubes at 900 °C. The activation of silica was performed using 40% hydrofluoric acid and lead oxide. Crystal structures of new uranyl silicates were solved by direct methods and refined: 1 is orthorhombic, Cmce, a = 14.5795(2) Å, b = 14.2083(2) Å, c = 23.1412(4) Å, V = 4793.70(13) Å3, R1 = 0.023; 2 is monoclinic, C2/m, a = 23.0027(8) Å, b = 8.0983(3) Å, c = 11.9736(4) Å, β = 90.372(3) °, V = 2230.43(14) Å3, R1 = 0.034; 3 is orthorhombic, Imma, a = 15.2712(12) Å, b = 7.9647(8) Å, c = 12.4607(9) Å, V = 1515.6(2) Å3, R1 = 0.035, 4 is orthorhombic, Imma, a = 15.4148(8) Å, b = 7.9229(4) Å, c = 13.0214(7) Å, V = 1590.30(14) Å3, R1 = 0.020. Their framework crystal structures contain channels up to 11.62 × 10.54 Å filled by various alkali metals.

[Display omitted] • Phosphate promotes the immobilization of uranyl arsenate under acidic conditions. • Phosphate can induce the transformation of crystalline phases of uranyl arsenate-bearing compounds. • Phosphate improved the chemical stability of the formed uranyl arsenate-bearing compounds. • The formation of Fe(UO 2) 2 (AsO 4) 2 ·H 2 O is relatively thermodynamically favorable in the presence of phosphate. Understanding the formation of uranyl-arsenate compounds (M(UO 2) 2 (AsO 4) 2 ·nH 2 O, M represents divalent metallic cations) is of great importance in controlling the mobility and fate of uranium (U) and arsenic (As) in the natural environment. Phosphate is a ubiquitous coexisting ion with properties similar to arsenate and can complex with uranyl to form uranyl phosphate compounds, thus potentially affecting the formation of uranyl-arsenate compounds. Herein, the effect of phosphate, on the immobilization of uranyl, arsenate and divalent metallic cations (e.g., Fe2+, Mg2+, Ni2+, Cu2+) was explored. Surprisingly, the presence of phosphate promoted the immobilization of uranyl arsenate with the divalent metallic cations under acidic conditions. For example, at pH 3.0, the immobilization efficiency of uranyl and arsenate in the uranyl-arsenate-Fe2+ system increased from 20.6 % and 18.6 % to 82.6 % and 52.2 %, respectively. Moreover, the chemical stability of the formed uranyl arsenate-bearing compounds in the presence of phosphate is significantly improved, and the TCLP leachability of As and U decreased by 81 % and 97 %, respectively. The experimental results illustrated that with PO 4 3- served as a proton acceptor, uranyl and arsenate species were changed and more metallic cations participate in immobilization. Gibbs free energy and Gibbs free energies change also illustrated that the formation of Fe(UO 2) 2 (AsO 4) 2 ·5H 2 O was relatively thermodynamically favorable in the presence of phosphate. The results of thermodynamic calculations could account for the enhancement effects of phosphate on immobilization of uranyl arsenate. The findings have important implications for the mobility and fate of U and As and the solution of their co-contamination, especially in acidic environments. [ABSTRACT FROM AUTHOR]

To explore the proximity effect in uranyl coordination of weakly-bonded cucurbit[6]uril(CB[6])-bipyridinium ligands, a new pseudorotaxane precursor C7BPCN3@CB[6] containing 1,1′-(heptyl-1,7-diyl)bis(3-cyanopyridin-1-ium) bromide (C7BPCN3) with elongated alkyl chains and meta-substituted cyano groups, has been synthesized and used to react with uranyl cations. Due to the weak binding affinity between the host and guest components of the supramolecular ligand, five new uranyl-rotaxane coordination polymers URCP1–URCP5 have been prepared, in which the pseudorotaxane linkers have shown great conformation diversity and abundant coordination behaviors. Three different coordination modes are present in the as-synthesized uranyl compounds, one of which is host–guest synergetic coordination due to the proximity effect between the meta-coordination carboxylate groups of C7BPCN3 and the portal carbonyls of CB[6]. Specially, the elongated spacer and weak-bonded feature make both CB[6] host and C7BPCN3 at one end of the pseudorotaxane ligand involved in the synergetic chelating with the uranyl centre. Meanwhile, at the other end, only the C7BPCN3 guest can participate in the first coordination sphere of uranium atom. This is the first time that this unique coordination mode has been observed in uranyl coordinating polyrotaxanes. This work demonstrates the proximity effect on uranyl coordination of weakly-bonded CB[6]-bipyridinium pseudorotaxane linkers, and provides an alternative approach to achieve metal coordination regulation and structure diversity in uranyl coordination polymers involving mechanically interlocked molecules. [ABSTRACT FROM AUTHOR]

New coordination compounds of -phenyl-N-methylnitrone with Cu2+, Mn2+, Ni2+, and UO22+ were synthesized. Complexes were studied by means of IR, NMR and UV-Vis spectroscopies. The crystal and molecular structure of uranyl complex with α-phenyl-Nmethylnitrone was determined by X-ray diffraction study. The monodentate nitrone ligands are coordinated to the metal ion via oxygen atom. The coordination polyhedron of uranium is a distorted hexagonal bipyramide. It was shown that there is dynamic process in the acetone solution in the temperature range of 203-297 K. The ligand exists as a transisomer for both present forms of organic ligand by the NOE difference. Dimeric copper(II) benzoate was obtained via recrystallization of the copper complex with α-phenyl-Nmethylnitrone from methanol solution. According to X-ray diffraction analysis, the environment of each of the copper atoms is octahedral. The coordination sphere is formed by six oxygen atoms. Three anions of benzoic acid are coordinated bidentate-bridged through oxygen atoms of the carboxyl group, while one molecule of benzoic acid is coordinated monodentatically through the carboxyl oxygen atom. [ABSTRACT FROM AUTHOR]

The article presents a study designed to intercalate water during a quasielastic neutron scattering measurement. Information is provided on the sample environment, noting that low-pressure humid air flow along with a controlled relative humidity was used. Particular attention is given to the results related to water dynamics in uranyl fluoride as well as the study's application to systems in which water is a variable in structural or dynamic phase transitions.

Synthesis, IR spectroscopic and X-ray structural studies of crystals [UO2(C4H4O4)(C6H5NO2)2] (I) and a new modification [UO2(C4H4O4)(H2O)] (II), where C4H4O42– are succinate ions, and C6H5NO2 is isonicotinic acid. Structure I is formed by chains in which succinate ions play the role of bridging ligands Q02 and B2, and isonicotinic acid molecules in the form of a zwitterion are monodentate ligands M1. Chains I correspond to the crystal chemical formula АQ020.5B20.5M12, where = UO22+, Q02 and B2 = C4H4O42–, and M1 = C6H5NO2. The reasons of the change in the coordination type of half of the succinate ions in I from characteristic Q02 to rare B2 are explained from the standpoint of the 18-electron rule in uranyl compounds. Structure II, like the two already known modifications, corresponds to the crystal chemical formula АQ4M1, where A = UO22+, Q4 = C4H4O42–, and M1 = H2O. By the example of uranyl succinate monohydrate polymorphs, it was found that, like silica polymorphs, chemically identical 3D uranyl-containing frameworks can differ both in topology (reconstructive isomers) and in the symmetry of the framework (deformation isomers). It was found that the new γ-form of II in the region of ≈180 K reversibly transforms into the already known low-temperature β-modification. It was shown using the Voronoi–Dirichlet polyhedra, that the available data for the fourth polymorph [UO2(C4H4O4)(H2O)] registered in the CSD as {SUCCUR02}, are erroneous. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics simulations with explicit polarization have been successfully used to determine the structural and thermodynamic properties of binary aqueous solutions of uranyl chloride (UO2Cl2). Concentrated aqueous solutions of uranyl chloride have been studied to determine the hydration properties and the ion-ion interactions. The bond distances and the coordination number of the hydrated uranyl are in good agreement with available experimental data. Two stable positions of chloride in the second hydration shell of uranyl have been identified. The UO2+2 -Cl- association constants have also been calculated using a multi-scale approach. First, the ion-ion potential averaged over the solvent configurations at infinite dilution (McMillan-Mayer potential) was calculated to establish the dissociation/association processes of UO2+2 -Cl- ion pairs in aqueous solution. Then, the association constant was calculated from this potential. The value we obtained for the association constant is in good agreement with the experimental result (KUO2Cl+ = 1.48 l mol-1), but the resulting activity coefficient appears to be too low at molar concentration. [ABSTRACT FROM AUTHOR]

We present here the synthesis of a novel fluorescent actinide polyrotaxane compound URCP1 through the utilization of an end‐cutting pseudorotaxane precursor with only the cucurbit[6]uril (CB[6]) macrocyclic components acting as linking struts. The non‐coordinating guest motif in the obtained polyrotaxane, with increased freedom and structural flexibility, can display intriguing temperature‐triggered conformational variations inside the cavity of CB[6], which was clearly evidenced by crystallographic snapshots at different temperatures. Notably, this observation of temperature‐triggered structural dynamics in URCP1 represents the first report of actinide polyrotaxane with such feature in solid‐state. Moreover, URCP1 has a high photoluminescence quantum yield (PLQY) of 49.8 %, comparable to other luminescent uranyl compounds, and can work as a fluorescent probe to selectively detect Fe3+ over other eight competing cations in aqueous solution, with the limit of detection being as low as 4.4×10−3 ppm. [ABSTRACT FROM AUTHOR]

Six hybrid uranyl–transition metal compounds [UO2Ni(cptpy)2(HCOO)2(DMF)(H2O)] (1), [UO2Ni(cptpy)2(BTPA)2] (2), [UO2Fe(cptpy)2(HCOO)2(DMF)(H2O)] (3), [UO2Fe(cptpy)2(BTPA)2] (4), [UO2Co(cptpy)2(HCOO)2(DMF)(H2O)] (5), and [UO2Co(cptpy)2(BTPA)2] (6), based on bifunctional ligand 4′‐(4‐carboxyphenyl)‐2,2′:6′,2′′‐terpyridine (Hcptpy) are reported (H2BTPA = 4,4′‐biphenyldicarboxylic acid). Single‐crystal XRD revealed that all six compounds feature similar metalloligands, which consist of two cptpy− anions and one transition metal cation. The metalloligand M(cptpy)2 can be considered to be an extended linear dicarboxylic ligand with length of 22.12 Å. Compounds 1, 3, and 5 are isomers, and all of them feature 1D chain structures. The adjacent 1D chains are connected together by hydrogen bonds and π–π interactions to form a 3D porous structure, which is filled with solvent molecules and can be exchanged with I2. Compounds 2, 4, and 6 are also isomers, and all of them feature 2D honeycomb (6,3) networks with hexagonal units of dimensions 41.91×26.89 Å, which are the largest among uranyl compounds with honeycomb networks. The large aperture allows two sets of equivalent networks to be entangled together to result in a 2D+2D→3D polycatenated framework. Remarkably, these uranyl compounds exhibit high catalytic activity for cycloaddition of carbon dioxide. Moreover, the geometric and electronic structures of compounds 1 and 2 are systematically discussed on the basis of DFT calculations. [ABSTRACT FROM AUTHOR]

A uranyl compound [(UO2)(C10H8N2O2)2][HPW12O40] has been hydrothermally synthesized (150 °C for 72 h) in the presence of typical Keggin‐phosphotungstic acid. This compound exhibits a regular layered structure which is composed of [UO2]2+ and bridging ligand 4,4'‐bipyridine‐N‐dioxide (4,4'‐BPDO). The nanosized cavities are occupied by Keggin‐anions [HPW12O40]2– through covalent bonds and hydrogen bonds, in order to hold the charge equilibrium and enhance the stability of the structure. The adsorption properties of this compound have been primarily investigated. The results indicate that the incorporation of Keggin‐anions plays an important role in the fast capture of cationic dye MB+. Compound 1 is the first case of uranyl coordination network decorated by POMs, which evidently provides a feasible strategy for controlling the structural connectivity and functionality of uranyl organic framework. [ABSTRACT FROM AUTHOR]

New complexes of U(VI) with p-methoxybenzoic acid were synthesized and their crystal structures were determined. Three uranyl-based structural units were found: a simple 1 : 3 complex anion, a dimeric two-nuclear complex, and an infinite coordination polymer. Two of the obtained compounds contained two different structural units simultaneously. One of the compounds exhibited an unprecedented structure for uranyl compounds based on 0D and 1D structural units. Electron and IR spectra of the compounds were correlated with the crystal structure of the obtained complexes. [ABSTRACT FROM AUTHOR]

Biological samples are mainly composed of elements with a low atomic number which show a relatively low electron scattering power. For Transmission Electron Microscopy analysis, biological samples are generally embedded in resins, which allow thin sectioning of the specimen. Embedding resins are also composed by light atoms, thus the contrast difference between the biological sample and the surrounding resin is minimal. Due to that reason in the last decades, several staining solutions and approaches, performed with heavy metal salts, have been developed with the purpose of enhancing both the intrinsic sample contrast and the differences between the sample and resin. The best staining was achieved with the uranyl acetate (UA) solution, which has been the election method for the study of morphology in biological samples. More recently several alternatives for UA have been proposed to get rid of its radiogenic issues, but to date none of these solutions has achieved efficiencies comparable to UA. In this work, we propose a different staining solution (X Solution or X SOL), characterized by lanthanide polyoxometalates (LnPOMs) as heavy atoms source, which could be used alternatively to UA in negative staining (NS), in en bloc staining, and post sectioning staining (PSS) of biological samples. Furthermore, we show an extensive chemical characterization of the LnPOM species present in the solution and the detailed work for its final formulation, which brought remarkable results, and even better performances than UA. [ABSTRACT FROM AUTHOR]

The molten flux synthesis of a uranium gallophosphate and a uranium gallate, Cs4[UO2Ga2(PO4)4] (1) and Cs2UO2Ga2O5 (2), and four uranium phosphates, [Rb2Rb3.93Cl0.93][(UO2)5(PO4)5] (3), Rb11[(UO2)8(PO4)9] (4), Rb7.6[(UO2)8O8.6F0.4(PO4)2] (5), and Rb6[(UO2)5O2(PO4)4] (6), is reported. A systematic exploration of the UF4–GaPO4–ACl (A = Cs, Rb) phase space resulted in the synthesis of targeted Cs4[UO2Ga2(PO4)4] (1) and Cs2UO2Ga2O5 (2), which are gallium analogs of the previously reported aluminates, Cs4[UO2Al2(PO4)4] and Cs2UO2Al2O5. The exploration of this phase space simultaneously led to the synthesis and characterization of four new uranium phosphate phases: [Rb2Rb3.93Cl0.93][(UO2)5(PO4)5] (3), a salt inclusion material, and Rb11[(UO2)8(PO4)9] (4), both of which have complex 3D, porous, framework structures, and Rb7.6[(UO2)8O8.6F0.4(PO4)2] (5) and Rb6[(UO2)5O2(PO4)4] (6), both of which are layered structures related to the U3O8 topology. Fluorescence spectroscopy data are reported for all the compositions and are found to be typical for uranyl compounds. [ABSTRACT FROM AUTHOR]

In this work, a new 2D layered silver uranyl phosphonate compound Ag01.51[AgI4(UO2)3(O3PC6H4PO3)(O3PC6H4PO3H)2] (denoted as compound 1) was synthesized by reaction of 1,2-phenylenediphosphonic acid (H4PDPA) with UO2(NO3)2·6H2O and AgNO3 under mild hydrothermal conditions. The uranyl layered framework consists of two types of UO8 and UO7 coordination units simultaneously connected by two kinds of phenylenediphosphonate linkers. To our surprise, the presence of both silver ions and metallic silver atoms in the free space between the layers is identified by the single crystal X-ray diffraction, EDS, and XPS techniques. The ratio of Ag+ and Ag0 was estimated to be 2.81 : 1, based on the primary peak area of Ag 3d5/2 from the XPS results, which corroborates with the ratio of 2.65 : 1 obtained from the XRD results. More importantly, the incorporation of the mixed-valent silver sites results in the quenching of the fluorescent emission of the uranyl phosphonate compound as evidenced by its single crystal fluorescence spectrum. [ABSTRACT FROM AUTHOR]

Nine new templated uranyl sulfates and selenates, [(H9O4)2(H2O)][(UO2)2(SO4)3(H2O)2] (H9US), [(C5H7 NO)2(H2O)][(UO2)2(SeO4)3(H2O)2](H2O) (OUSe), [C6H6N3][H5O2] [(UO2)2(SeO4)3(H2O)] (BH5USe), [C6H6N3][H7O3][(UO2)2(SO4)3 (H2O)](H2O) (BH7US), [C6H16N][H5O2][(UO2)2(SeO4)3(H2O)] (TeH5USe), [C6H18N2][(UO2)2(SO4)3(H2O)] (TmUS), [H5O2]2 [(UO2)2(SeO4)3(H2O)](H2O) (H5USe-1), [H5O2]2[(UO2)2(SeO4)3 (H2O)2](H2O)9 (H5USe-2), and [C4H14N2][(UO2)2(SeO4)3(H2O)](H2O) (DmUSe) have been prepared by isothermal evaporation of aqueous solutions containing extra sulfuric or selenic acid. Their crystal structures can be considered as organo-inorganic hybrids constructed of alternating [(UO2)2 (TO4)3(H2O)n]2− slabs (T = Se6+, S6+, n = 1, 2) and layers containing templating organic moieties and/or hydronium ions and water molecules. The organic and inorganic parts of the structures are linked by multiple hydrogen bonds. Besides structure description, we offer topological analysis of the inorganic fragments with UO2:TO4 ratio of 2:3 as modular units resulting from self-assembly of fundamental chains formed by [(UO2)2(TO4)2] tetramers and TO4 tetrahedra. [ABSTRACT FROM AUTHOR]

Two three-dimensional uranyl framework compounds consisting of 1,2,4-benzenetricarboxylic ligands and uranyl units have been synthesized under mild solvothermal conditions. Compound 1 adopts an open framework structure built from uranyl pentamers, which is a rare topology for uranyl structures. Compound 2 is constructed from UO8 and UO7 bipyramids that are connected by the ligand to form a three-dimensional framework. As a consequence, compound 1 exhibits an unusual photoluminescence spectrum of one broad peak at 545 nm with a significant red shift compared to the typical uranyl emissive peaks as shown in the spectra of uranyl nitrate and compound 2. In addition, since compound 1 crystallizes in the noncentrosymmetric space group Cc, its secondary-harmonic generation property was measured under 1064 nm laser radiation, showing a moderate SHG signal response of 0.91 × KDP. [ABSTRACT FROM AUTHOR]

Experimental investigations of crystallization in a family of uranyl triacetate compounds with Na, K, Rb and Cs were performed. The crystal structures of two novel Cs- and Rb-bearing tri(acetato)uranylates were solved, and the content of H2O molecules in the crystal structure of K-bearing uranyl triacetate was refined. Synthesized compounds were analyzed using IR spectroscopy and single-crystal X-ray diffraction. Crystal chemical analysis of the M[(UO2)(CH3COO)3](H2O)n family (M = Na, K, Rb, Cs; n = 0–1.0) reveals the sequence of structural transformations depending on the size of alkali cation resulting in the symmetry reduction from cubic P 213 (for Na), through tetragonal I 41/a (for K and Rb) to triclinic P 1̅ space groups (for Cs), which is in accordance with the principle of morphotropism, suggested by Paul von Groth, founder of the Zeitschrift für Krystallographie journal, in 1870. [ABSTRACT FROM AUTHOR]

Five centrosymmetric uranyl germanate compounds, K8BrF(UO2)3(Ge2O7)2, Rb6(UO2)3(Ge2O7)2·0.5H2O, Cs6(UO2)2Ge8O21 and A+2(UO2)3(GeO4)2 (A+ = Rb+, Cs+), were synthesized in this work. K8BrF(UO2)3(Ge2O7)2 and Rb6(UO2)3(Ge2O7)2·0.5H2O were obtained under mixed KF–KBr flux and hydrothermal conditions, respectively. Both structures crystallized in the triclinic P1¯ space group and have similar anionic frameworks featuring novel hexagon shaped 12-membered channels. The condensation of two different types of SBU [UGe4] pentamers (A) and (A2) results in the formation of K8BrF(UO2)3(Ge2O7)2 and Rb6(UO2)3(Ge2O7)2·0.5H2O frameworks. Cs6(UO2)2Ge8O21 was obtained from a CsF–CsCl high temperature flux, and it also crystallized in the centrosymmetric triclinic P1¯ space group. The structure of Cs6(UO2)2Ge8O21 has a novel oxo-germanate layer composed of germanate tetrahedra and trigonal bipyramids. Two new SBU types, (42·52-A2) and (54-A2) [UGe4] pentamers, were found in the structure of Cs6(UO2)2Ge8O21. A+2(UO2)3(GeO4)2 (A+ = Rb+, Cs+) were synthesized by a high temperature/high pressure (HT/HP) technique, and both structures with oval-shaped 12-membered channels crystallized in the centrosymmetric orthorhombic Pnma space group. The extreme conditions led to the formation of [U2Ge2] tetramers (E), which consist of 7-coordinated U and 5-coordinated Ge. Different synthetic methods of uranyl germanate compounds resulted in a distinct coordination environment of the uranyl cations and a variety of U＝O and U−O bond lengths, further affecting the dimensionality and types of uranyl units and SBUs. The Raman and IR spectra of the five new phases were collected and analyzed. [ABSTRACT FROM AUTHOR]

The uranyl ion extraction properties of an octaphosphinoylated para-tert-butylcalix [8] arene (B8bL8) in CHCl3 from an aqueous–acidic–saline medium containing a uranyl nitrate salt were investigated. UV–Vis and luminescence techniques allowed us to evaluate the extraction capability and loading capacity of B8bL8 towards uranyl ions. Both techniques revealed a 2 UO22+:1 B8bL8 stoichiometry for the main extracted species in the organic phases. IR, NAA, and XPS analyses of the pure solid recovered from the extracts demonstrated such a stoichiometry. B8bL8 in CHCl3 would be highly useful for the treatment of nuclear or radioactive wastes containing uranium in rich aqueous–acidic–saline media. [ABSTRACT FROM AUTHOR]

Current synthetic pathways for uranyl peroxide materials introduce high initial concentrations of aqueous H2O2 that decline over time. Alternatively, in situ generation of organic peroxide would maintain constant concentrations of peroxide over prolonged periods of time and open new pathways to novel uranyl peroxide compounds. Herein, we demonstrate this concept through the synthesis of a nanotube‐like uranyl peroxide phosphate (NUPP), Na12[(UO2)(μ‐O2)(HPO4)]6(H2O)40, making use of the inhibited autoxidation of benzaldehyde in benzyl alcohol solutions in the presence of phosphonate ligands. The unique feature of NUPP is the bent dihedral angle U‐(μ‐O2)‐U (123.9°±0.4° to 124.6°±0.5°), which allows hexameric uranyl peroxide macrocycles to adopt the nanotubular topology and prevents the formation of nanocapsules. Raman spectroscopy of the solution phase confirms our mechanistic understanding of the reaction pathway and confirms that consistent levels of peroxide are generated in situ over an extended period of time. [ABSTRACT FROM AUTHOR]

The uranyl compound UO2(L')EtOH (L' = benzyl N-(2-(oxidanyl)benzylidene)-N'-((2-(1-oxidanyl)phenyl)ethylidene) carbamohydrazonothioate) was synthesized and its molecular and crystal structure was determined by X-ray diffraction. The compound crystallizes in the triclinic sp. gr. P , Z = 2. The coordination geometry about the uranium atom is distorted pentagonal bipyramidal consisting of a UO2O4N2 polyhedron where the oxido ligands occupy axial positions with a symmetric linear structure (O=U=O angle = 179.11(12)°). The pentagonal plane (N2O3) is formed by the dinegative, tetradentate Schiff base ligand (N2O2) and the oxygen atom of the coordinated alcohol ligand. In the complex, the ligand adopts a propeller-like conformation. [ABSTRACT FROM AUTHOR]

Regularities in the Raman spectra of acetate uranyl compounds CsUO2(CH3COO)3, CsUO2(CD3COO)3, NaUO2(CH3COO)3, NaUO2(CD3COO)3, UO2(CH3COO)2, and RbUO2(CH3COO)3 have been analyzed. The Raman spectra are excited by 785-nm laser radiation and recorded using a miniature fiber-optic spectrometer with a multielement detector. It is established that the spectra of all these compounds contain a strong Raman satellite with a frequency in the range of 850–860 cm–1. This satellite corresponds to symmetric stretching vibrations (type A1) of the uranyl group. The obtained results make it possible to detect and analyze small amounts of uranyl compounds. [ABSTRACT FROM AUTHOR]

Uranyl vanadate compounds with divalent cations, M(UO2)(V2O7) (M = Ca, Sr) and Sr3(UO2)(V2O7)2, were synthesized by flux crystal growth, and their crystal structures were solved using single‐crystal X‐ray diffraction data. Ca(UO2)V2O7 and Sr(UO2)V2O7 were synthesized from reactants with molar ratios M:U:V of 1:1:2 and identical heating conditions, and increasing the M:U:V ratio to 3:1:4 resulted in Sr3(UO2)(V2O7)2. Crystallographic data for M(UO2)V2O7 compounds are: a = 7.1774(18) Å, b = 6.7753(17) Å, c = 8.308(2) Å; V = 404.01(18) Å3; space group Pmn21, Z = 2 for Ca; a = 13.4816(11) Å, b = 7.3218(6) Å, c = 8.4886(7) Å; V = 837.91(12) Å3; space group Pnma, Z = 4 for Sr. Compound Sr3(UO2)(V2O7)2 has a = 6.891(3) Å, b = 7.171(3) Å, c = 14.696(6) Å, α = 85.201(4)˚, β = 78.003(4)˚, γ = 89.188(4)˚; V = 707.9(5) Å3; space group P1, Z = 2. The framework structure of Sr(UO2)(V2O7) is related to that of Pb(UO2)(V2O7) reported previously, while that of Ca(UO2)(V2O7) has a different topology. The topological polymorphism of the [(UO2)(V2O7)]‐type framework may be due to the differing ionic radii of the guest M2+ cations. Compound Sr3(UO2)(V2O7)2 has a modular structure based on two different types of electroneutral layers: [Sr(UO2)(V2O7)] and [Sr2(V2O7)]. Structural complexities were calculated, and Raman spectra were collected and their peaks were assigned. [ABSTRACT FROM AUTHOR]

Uranyl vanadate compounds with divalent cations, M(UO2)(V2O7) (M = Ca, Sr) and Sr3(UO2)(V2O7)2, were synthesized by flux crystal growth, and their crystal structures were solved using single‐crystal X‐ray diffraction data. Ca(UO2)V2O7 and Sr(UO2)V2O7 were synthesized from reactants with molar ratios M:U:V of 1:1:2 and identical heating conditions, and increasing the M:U:V ratio to 3:1:4 resulted in Sr3(UO2)(V2O7)2. Crystallographic data for M(UO2)V2O7 compounds are: a = 7.1774(18) Å, b = 6.7753(17) Å, c = 8.308(2) Å; V = 404.01(18) Å3; space group Pmn21, Z = 2 for Ca; a = 13.4816(11) Å, b = 7.3218(6) Å, c = 8.4886(7) Å; V = 837.91(12) Å3; space group Pnma, Z = 4 for Sr. Compound Sr3(UO2)(V2O7)2 has a = 6.891(3) Å, b = 7.171(3) Å, c = 14.696(6) Å, α = 85.201(4)˚, β = 78.003(4)˚, γ = 89.188(4)˚; V = 707.9(5) Å3; space group P1, Z = 2. The framework structure of Sr(UO2)(V2O7) is related to that of Pb(UO2)(V2O7) reported previously, while that of Ca(UO2)(V2O7) has a different topology. The topological polymorphism of the [(UO2)(V2O7)]‐type framework may be due to the differing ionic radii of the guest M2+ cations. Compound Sr3(UO2)(V2O7)2 has a modular structure based on two different types of electroneutral layers: [Sr(UO2)(V2O7)] and [Sr2(V2O7)]. Structural complexities were calculated, and Raman spectra were collected and their peaks were assigned. [ABSTRACT FROM AUTHOR]

Crystal structures of three new uranyl compounds were solved using single crystal X‐ray diffraction and studied using FTIR spectroscopy. Although the syntheses conditions were very similar differing only in the alkaline earth metal (Mg, Ca or Sr), the resulting structures are different, containing, respectively, mono‐, tri‐ and hexanuclear metal‐containing building units. This fact proves the profound crystal‐chemical role of secondary metal atoms on the formation of crystal structures. Parameters of alkaline earth metal cations in the three newly synthesized compounds as well as in the earlier reported Ba‐containing analog are discussed in detail using Voronoi–Dirichlet polyhedra and the method of intersecting spheres. Differences in packing of building units in the four mentioned compounds, as well as inter‐ and intramolecular noncovalent interactions in their structures are reported. The results of analysis are consistent with the stereoatomic model of crystal structures. [ABSTRACT FROM AUTHOR]

We have measured photoluminescence spectra of uranyl nitrate (UO2(NO3)2) crystals and a UO2(NO3)2-filled opal crystal. The spectra have been compared to the corresponding photoluminescence spectrum of photonic glass. The photoluminescence spectra were excited by semiconductor light-emitting diodes, a cw laser, and repetitive laser pulses. The excitation wavelengths were located in the resonance absorption band of the uranyl compound. This has offered the possibility of measuring the photoluminescence spectrum of UO2(NO3)2 at an acquisition time of 1 ms, using the smallest possible amount of the substance (down to 10–9 g). The spectra have been obtained in the range 200–1000 nm using a fiber-optic minispectrometer. [ABSTRACT FROM AUTHOR]

Adsorption of uranyl (UO22+) ions to mineral surfaces is a potentially effective method for removing this hazardous metal from water, but other toxic trace metal ions (Xn+: Rb+, Sr2+, Cr3+, Mn2+, Ni2+, Zn2+, Cd2+) in uraniferous wastewaters compete with UO22+ for adsorption sites and thus may diminish the capacity of adsorbents to sequester UO22+. A better understanding of competitive adsorption among these metal ions and the development of better adsorbents are, therefore, of critical importance. The purpose of the present study was to synthesize and characterize magnetic adsorbents, consisting of MFe2O4 (M = Mn, Fe, Zn, Co, or Ni) nanoparticles synthesized on montmorillonite (Mnt) edge sites, and to investigate their use as adsorbents for UO22+, including competitive adsorption with trace metal ions. Selective adsorption was studied using Langmuir, Freundlich, and Dubinin-Radushkevich isotherms, and the results showed that Xn+ ions were adsorbed primarily on MFe2O4-montmorillonite surfaces, and the UO22+ ions were adsorbed on the interfaces between montmorillonite edge surfaces and MFe2O4 nanoparticles. Using the Freundlich model, the interface adsorption capacity of UO22+ reached 25.1 mg·g–1 in mixed solution. Further, the UO22+ and Cr3+ ions had a redox reaction on the interfaces with synergistic adsorption. Herein, the adsorption capacity of Cr3+ was 60.2 mg·g–1 using the Freundlich isotherm. The results demonstrated that the MFe2O4-montmorillonite with highly selective adsorption of UO22+ ions is applicable to UO22+ treatment in the presence of toxic trace metal ions. [ABSTRACT FROM AUTHOR]

We have measured photoluminescence spectra of uranyl nitrate (UO2(NO3)2) crystals and a UO2(NO3)2-filled opal crystal. The spectra have been compared to the corresponding photoluminescence spectrum of photonic glass. The photoluminescence spectra were excited by semiconductor light-emitting diodes, a cw laser, and repetitive laser pulses. The excitation wavelengths were located in the resonance absorption band of the uranyl compound. This has offered the possibility of measuring the photoluminescence spectrum of UO2(NO3)2 at an acquisition time of 1 ms, using the smallest possible amount of the substance (down to 10–9 g). The spectra have been obtained in the range 200–1000 nm using a fiber-optic minispectrometer. [ABSTRACT FROM AUTHOR]