Showing papers on "Uranyl published in 2001"
TL;DR: In this article, the authors reported a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a nonfluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA 4−.
Abstract: Summary. We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)3(aq.), in uranium mining related waters [1]. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA 4− . Slope analysis of the log (fluorescence intensity) versus log [Ca 2+ ] with both methods have shown that two calcium ions are bound to form the complex Ca2UO2(CO3)3(aq.) .T he formation constants determined from the two independent methods are: i) log β ◦ 213 = 30.45 ± 0.35 and ii) log β ◦ 213 = 30.77 ± 0.25. A bathochrome shift of 0.35 nm between the UO2(CO3)3 4− complex and the Ca2UO2(CO3)3(aq.) complex is observed in the laser-induced photoacoustic spectrum (LIPAS), giving additional evidence for the formation of the calcium uranyl carbonate complex. EXAFS spectra at the LII and LIII-edges of uranium in uranyl carbonate solutions with and without calcium do not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex is obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid. This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.
409 citations
TL;DR: In this article, X-ray absorption and luminescence spectroscopies have been used to characterize the local structure and coordination of uranium(VI) species coprecipitated with calcite (CaCO3) from room-temperature aqueous solutions.
213 citations
TL;DR: Results indicate that the speciation in the solution has minimal influence on the nature of the sorption complex under these experimental conditions, and the primary control on thenature and abundance of the different uranyl sorption complexes appears to be the relative abundance and reactivity of theDifferent sorption sites.
168 citations
TL;DR: The behavior of UO2/water interface under irradiation has been investigated as a function of alpha flux using an alpha beam provided by a cyclotron in this article, and the formation of hydrated uranium peroxide (metastudtite UO4·2H2O) on leached surface was identified by X-ray diffractometry.
148 citations
TL;DR: The uranium desorption rate was unaffected by the aging of uranium-goethite suspensions, and the aging process appears to remove a portion of adsorbed uranium from a readily exchangeable pool.
Abstract: The sorption of uranium on mineral surfaces can significantly influence the fate and transport of uranium contamination in soils and groundwater. The rates of uranium adsorption and desorption on a synthetic goethite have been evaluated in batch experiments conducted at constant pH of 6 and ionic strength of 0.1 M. Adsorption and desorption reactions following the perturbation of initial states were complete within minutes to hours. Surface−solution exchange rates as measured by an isotope exchange method occur on an even shorter time scale. Although the uranium desorption rate was unaffected by the aging of uranium−goethite suspensions, the aging process appears to remove a portion of adsorbed uranium from a readily exchangeable pool. The distinction between sorption control and precipitation control of the dissolved uranium concentration was also investigated. In heterogeneous nucleation experiments, the dissolved uranium concentration was ultimately controlled by the solubility of a precipitated uranyl...
141 citations
TL;DR: The new expanded porphyrin ligand 1 forms stable complexes with both uranyl (UO22+ ) and neptunyl (NpO2+ ) ions and presents a new avenue for waste remediation.
Abstract: Applications of actinide chemistry, whether for energy or defense purposes, have left a legacy of potential waste hazards. The new expanded porphyrin ligand 1 forms stable complexes with both uranyl (UO22+ ) and neptunyl (NpO2+ ) ions and presents a potential new avenue for waste remediation.
141 citations
TL;DR: Solvent effects were shown to give the main contribution to the observed structure variations between the uranium(VI) tetrahydroxide and the tetrafluoride complexes.
Abstract: The structures of the complexes UO2Fn(H2O)5-n2-n, n = 3−5, have been studied by EXAFS. All have pentagonal bipyramid geometry with U−F of and U−H2O distances equal to 2.26 and 2.48 A, respectively. On the other hand the complex UO2(OH)42- has a square bipyramid geometry both in the solid state and in solution. The structures of hydroxide and fluoride complexes have also been investigated with wave function based and DFT methods in order to explore the possible reasons for the observed structural differences. These studies include models that describe the solvent by using a discrete second coordination sphere, a model with a spherical, or shape-adapted cavity in a conductor-like polarizable continuum medium (CPCM), or a combination of the two. Solvent effects were shown to give the main contribution to the observed structure variations between the uranium(VI) tetrahydroxide and the tetrafluoride complexes. Without a solvent model both UO2(OH)4(H2O)2- and UO2F4(H2O)2- have the same square bipyramid geometry...
137 citations
TL;DR: In this article, the uptake capacity of live and lyophilized Pseudomonas cells was characterized in terms of equilibrium metal loading, effect of solution pH and possible interference by selected co-ions.
Abstract: The biosorptive uranium(VI) uptake capacity of live and lyophilized Pseudomonas cells was characterized in terms of equilibrium metal loading, effect of solution pH and possible interference by selected co-ions. Uranium binding by the test biomass was rapid, achieving >90% sorption efficiency within 10 min of contact and the equilibrium was attained after 1 h. pH-dependent uranium sorption was observed for both biomass types with the maximum being at pH 5.0. Metal uptake by live cells was not affected by culture age and the presence of an energy source or metabolic inhibitor. Sorption isotherm studies at a solution pH of either 3.5 or 5.0 indicated efficient and exceptionally high uranium loading by the test biomass, particularly at the higher pH level. At equilibrium, the lyophilized Pseudomonas exhibited a metal loading of 541 ± 34.21 mg g−1 compared with a lower value by the live organisms (410 ± 25.93 mg g−1). Experimental sorption data showing conformity to both Freundlich and Langmuir isotherm models indicate monolayered uranium binding by the test biomass. In bimetallic combinations a significant interference in uranium loading was offered by cations such as thorium(IV), iron(II and III), aluminium(III) and copper(II), while the anions tested, except carbonate, were ineffective. Uranium sorption studies in the presence of a range of Fe3+ and SO42− concentrations indicate a strong inhibition (80%) by the former at an equimolar ratio while more than 70% adsorption efficiency was retained even at a high sulfate level (30 000 mg dm−3). Overall data indicate the suitability of the Pseudomonas sp biomass in developing a biosorbent for uranium removal from aqueous waste streams.
© 2001 Society of Chemical Industry
107 citations
TL;DR: In this article, the uranyl iodates, UO2(IO3)2 (AU1−8), and UO 2(H2O) (AU2−8) have been prepared from the reaction of UO3 with I2O5 under hydrothermal conditions.
Abstract: The uranyl iodates, UO2(IO3)2 (AU1−8) and UO2(IO3)2(H2O) (AU2−8) have been prepared from the reaction of UO3 with I2O5 under hydrothermal conditions. Equilibrium between AU1−8 and AU2−8 is established after 3 days at 400 °C, resulting in the isolation of an equimolar ratio of these compounds. Lowering of the reaction temperature to 180 °C or shortening of the reaction duration to 1 day allows for the isolation of AU2−8 in pure form. At 327 °C, AU2−8 undergoes dehydration and structural rearrangement to AU1−8, which is a reversible process. Single-crystal X-ray diffraction, bond valence sum calculations, EDX, DSC, TGA, and vibrational and fluorescence spectroscopy have been used to characterize these compounds. Crystallographic data are as follows: AU1−8, monoclinic, space group P21/n, a = 4.2454(8) A, b = 16.636(5) A, c = 5.284(1) A, β = 107.57(2)°, and Z = 2; AU2−8, orthorhombic, space group Pbcn, a = 8.452(2) A, b = 7.707(2) A, c = 12.271(3), and Z = 4. The structure of AU1−8 is pseudo-three-dimensiona...
103 citations
15 Jul 2001
TL;DR: The sorption of uranyl ions onto amorphous silica has been studied in the presence of atmospheric CO(2) by laser-induced time-resolved fluorescence spectroscopy at trace concentrations and three "silent" ternary uranyl-silica-carbonate surface complexes were identified.
Abstract: The sorption of uranyl ions onto amorphous silica has been studied in the presence of atmospheric CO(2) by laser-induced time-resolved fluorescence spectroscopy at trace concentrations (1.0 and 0.1 mM). Two fluorescent uranyl surface complexes have been identified in the pH range 4 to 9. Both complexes could be differentiated by lifetimes (170+/-25 ms at low pH and 360+/-50 ms at high pH) and fluorescence emission spectra. Within the constant capacitance model framework they are described by mononuclear (1 : 1) complexes with release of two and three protons, respectively. When fluorescence data were compared to wet chemistry sorption data, a third "silent" ternary uranyl-silica-carbonate surface complex had to be postulated to account partly for adsorption between pH 8.0 and 9.0. Three independent data sets led therefore to the identification of three surface complexes, postulated as tSiO(2)UO(2) degrees,tSiO(2)UO(2)OH(-), and tSiO(2)UO(2)OHCO(3)(3-). Copyright 2001 Academic Press.
93 citations
TL;DR: The Raman spectra reveal nu(U-O) values that correlate with expected trends and structural trends are discussed within the context of classical principles of hard-soft acid-base theory.
Abstract: UO2(C2H3O2)2·2H2O reacts with AX or A(C2H3O2 or ClO4) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)]2[UO2Cl4] (1), [K(18-crown-6)]2[UO2Br4] (2), [Na(15-crown-5)]2[UO2Cl4] (3), [Na(15-crown-5)]2[UO2Br4] (4), [Li(12-crown-4)]2[UO2Cl4] (5), and [Li(12-crown-4)]2[UO2Br4] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO2X4]2- ions coordinate to two [A(crown)]+ cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal νU-O values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard−soft acid−base theory.
TL;DR: In this article, the electronic energy levels of the uranyl ion (UO22+) and the neptunyl ion (NpO 22+) in the crystalline environment of Cs2UO2Cl4 are studied theoretically and compared with the spectroscopic work o...
Abstract: The electronic energy levels of the uranyl ion (UO22+) and the neptunyl ion (NpO22+) in the crystalline environment of Cs2UO2Cl4 are studied theoretically and compared with the spectroscopic work o...
TL;DR: Structural properties of uranyl cations in acidic aqueous perchlorate and triflate solutions were investigated using uranium LIII -edge extended X-ray absorption fine-structure spectroscopy (EXAFS) in conjunction with quantum mechanical calculations of gas-phase model complexes.
Abstract: Structural properties of uranyl cations in acidic aqueous perchlorate and triflate solutions were investigated using uranium L 11 -edge extended X-ray absorption fine-structure spectroscopy (EXAFS) in conjunction with quantum mechancial calculations of gas-phase model complexes. EXAFS spectra were measured in aqueous solutions of up to 10 M triflic and 11.5 M perchloric acid, as well as mixtures of perchloric acid and sodium perchlorate. In no case is the perchlorate anion coordinated to UO 2 2+ . The number of equatorial water molecules bound to UO 2 2+ is always about five In the case of the 10 M CF 3 SO 3 H solution, an inner-sphere complexation of the triflate is observed with a U-S radial distance of 3.62 A These results are in qualitative agreement with quantum mechanical calculations of model uranyl complexes, according to which the interaction energies of anions follow the order perchlorate < triflate << nitrate.
TL;DR: In this paper, the UO22+ coordination chemistry of several prototypic expanded porphyrins is reviewed, and the ability of these expanded polypyrrolic ligands to stabilize complexes containing the uranyl cation is contrasted to that of the porphrin system.
TL;DR: In this paper, UO2Cl2(thf)3 was treated with two equivalents of 1,3dimesitylimidazole-2-ylidene (IMes) and 4,5dichloroimidazoles-2ylidenes (IMeCl2) to obtain the first actinyl carbon bonds.
TL;DR: The ability of the new resin to strongly and selectively retain U(VI) from such a wide range of acid concentrations, along with its favorable physical properties, make it a good candidate for application in the separation and preconcentration of U( VI) from complex environmental, biological, and nuclear waste samples for subsequent determination.
TL;DR: The synthesis and structural characterization of a mixed-valent uranium(V/VI) oxo-imido complex are reported and the structure and bonding in 2 are assessed in the context of metal-ligand multiple bonding in high- valence actinide complexes.
Abstract: The synthesis and structural characterization of a mixed-valent uranium(V/VI) oxo−imido complex are reported Reaction of the uranyl chloride complex [K(18-crown-6)]2[UO2Cl4] (1) with the triamidoamine ligand Li3[N(CH2CH2NSiButMe2)3] yields oxo−imido [K(18-crown-6)(Et2O)][UO(μ2-ΝCΗ2CH2N(CH2CH2NSiButMe2)2)]2 (2) as the major isolated uranium product in moderate yield The reaction that forms 2 involves activation of both the triamidoamine ligand and the uranyl dioxo unit of 1 An X-ray crystal structure determination of 2 reveals a dimeric complex in which the coordination geometry at each uranium center is that of a capped trigonal bipyramid The multidentate triamidoamine ligand coordinates to uranium through the capping amine and two of the three pendant amido ligands, while the third pendant amido donor has been activated to generate a bridging imido ligand by loss of the silyl substituent One of the uranyl oxo groups is retained as a terminal ligand to complete the coordination sphere for each uraniu
TL;DR: Density functional theory (DFT) calculations demonstrate that the approximate C2v geometry of the [IO4]3- anion can be attributed to a second-order Jahn-Teller distortion.
Abstract: The hydrothermal reaction of elemental Ag, or water-soluble silver sources, with UO3 and I2O5 at 200 °C for 5 days yields Ag4(UO2)4(IO3)2(IO4)2O2 in the form of orange fibrous needles. Single-cryst...
TL;DR: In this paper, the authors investigated the hydration of uranyl ion (UO 2 2+ ) in aqueous system using hybrid density functional theory B3LYP method Gibbs free energies and solvation energies for different UO 2 (H 2 O) n 2+ (n = 4, 5, and 6) (including the first and second solvation shell) clusters were calculated Polarized continuum model (PCM) was used to calculate the solvation energy.
TL;DR: In this article, the authors showed that K2[(UO2)3(IO3)4O2] is more stable than Ba[(H2O2)-I2O5 under mild and supercritical conditions.
Abstract: The alkali metal and alkaline-earth metal uranyl iodates K2[(UO2)3(IO3)4O2] and Ba[(UO2)2(IO3)2O2](H2O) have been prepared from the hydrothermal reactions of KCl or BaCl2 with UO3 and I2O5 at 425 and 180 °C, respectively. While K2[(UO2)3(IO3)4O2] can be synthesized under both mild and supercritical conditions, the yield increases from <5% to 73% as the temperature is raised from 180 to 425 °C. Ba[(UO2)2(IO3)2O2](H2O), however, has only been isolated from reactions performed in the mild temperature regime. Thermal measurements (DSC) indicate that K2[(UO2)3(IO3)4O2] is more stable than Ba[(UO2)2(IO3)2O2](H2O) and that both compounds decompose through thermal disproportionation at 579 and 575 °C, respectively. The difference in the thermal behavior of these compounds provides a basis for the divergence of their preparation temperatures. The structure of K2[(UO2)3(IO3)4O2] is composed of [(UO2)3(IO3)4O2]2- chains built from the edge-sharing UO7 pentagonal bipyramids and UO6 octahedra. Ba[(UO2)2(IO3)2O2](H2O) ...
TL;DR: The results of a study on the ground states of tricarbonato complexes of dioxouranate using multiconfigurational second-order perturbation theory (CASSCF/CASPT2) are presented and only minor geometrical rearrangements occur in the one-electron reduction, confirming the reversibility of this reduction.
Abstract: The results of a study on the ground states of tricarbonato complexes of dioxouranate using multiconfigurational second-order perturbation theory (CASSCF/CASPT2) are presented. The equilibrium geometries of the complexes corresponding to uranium in the formal oxidation states VI and V, [UO2(CO3)3]4- and [UO2(CO3)3],5- have been fully optimized in D3h symmetry at second-order perturbation theory (MBPT2) level of theory in the presence of an aqueous environment modeled by a reaction field Hamiltonian with a spherical cavity. The uranyl fragment has also been optimized at CASSCF/CASPT2, to obtain an estimate of the MBPT2 error. Finally, the effect of distorting the D3h symmetry to C3 has been investigated. This study shows that only minor geometrical rearrangements occur in the one-electron reduction of [UO2(CO3)3]4- to [UO2(CO3)3],5- confirming the reversibility of this reduction.
TL;DR: In this article, an extended X-ray absorption fine structure spectroscopy (EXAFS) study was conducted to understand the surface interactions between citrate, UO22+, and goethite between pH 3.5 and pH 5.5.
TL;DR: In this paper, a novel open framework U−O material with composition (NH4)3(H2O)2{[(UO2)10O10(OH)][ (UO4)(H2Os)2]} was synthesized hydrothermally, and the structure was solved by direct methods and refined on the basis of F2 for all 4230 unique reflections in space group C2/c.
Abstract: A novel open framework U−O material with composition (NH4)3(H2O)2{[(UO2)10O10(OH)][(UO4)(H2O)2]} was synthesized hydrothermally. The structure [monoclinic, a = 11.627(2) A, b = 21.161(3) A, c = 14.706(2) A, β = 103.930(3)°, V = 3511.97 A3] was solved by direct methods and refined on the basis of F2 for all 4230 unique reflections in space group C2/c to an agreement factor (R1) of 7.7%, calculated using 2180 unique observed reflections (|Fo| ≥ 4σF). The structure contains six symmetrically distinct U6+ sites, five of which occur as approximately linear (UO2)2+ uranyl ions that are coordinated by four or five additional ligands, giving square and pentagonal bipyramids. One U6+ cation occurs in distorted octahedral coordination. The structure contains β-U3O8-type sheets parallel to (001) that are cross-linked through U2O12 pentagonal bipyramid dimers, resulting in an open framework structure composed only of uranium polyhedra. The (NH4)+ and H2O groups are located in the interconnected three-dimensional chan...
TL;DR: Amberlite XAD-2 has been functionalized by coupling it to quinalizarin by means of an -N = N- spacer to characterize the resulting new polymer matrix, and the matrix has been used to preconcentrate Cu(II), Cd (II), Co( II), Pb (II, Pb(II, Zn) and Mn(II) before their determination by flame atomic absorption spectrometry (FAAS).
Abstract: Amberlite XAD-2 has been functionalized by coupling it to quinalizarin [1,2,5,8-tetrahydroxyanthraquinone] by means of an -N = N- spacer. Elemental analysis, thermogravimetric analysis, and infrared spectra were used to characterize the resulting new polymer matrix. The matrix has been used to preconcentrate Cu(II), Cd(II), Co(II), Pb(II), Zn(II), and Mn(II) before their determination by flame atomic absorption spectrometry (FAAS). UO2(II) has been preconcentrated for fluorimetric determination. The optimum pH values for maximum adsorption of the metals are between 5.0 and 7.0. All these metal ions are desorbed (recovery 91–99%) with 4 mol L–1 HNO3. The adsorptive capacity of the resin was found to be in the range 0.94–5.28 mg metal g–1 resin and loading half-life (t1/2) between 5.3 and 15.0 min. The effects of NaF, NaCl, NaNO3, Na2SO4, Na3PO4, Ca(II), and Mg(II) on the adsorption of these metal ions (0.2 μg mL–1) are reported. The lower limits of detection for these metal ions are between 1 and 15.0 μg L–1. After enrichment on this matrix flame AAS has been used to determine these metal ions (except the uranyl ion) in river water samples (RSD ≤ 6.5%); fluorimetry was used to determine uranyl ion in well water samples (RSD ≤ 6.3%). Cobalt from pharmaceutical vitamin tablets was preconcentrated by use of this chelating resin and estimated by FAAS (RSD ∼ 4%).
TL;DR: In this paper, the equilibrium solubility of uranyl nitrate in supercritical fluid carbon dioxide (SF-CO 2 ) in the absence and presence of different modifiers was investigated.
Abstract: The equilibrium solubility of uranyl nitrate in supercritical fluid carbon dioxide (SF-CO 2 ) in the absence and presence of different modifiers was investigated. In the presence of methanol and HNO 3 , uranyl nitrate showed a considerable solubility in SF-CO 2 . SF-CO 2 modified with different co-extractants such as tributylphosphate (TBP), methylisobutyl ketone (MIBK), acetylacetone (AA) and methanol (MeOH) at 60°C and 250 atm was used for the extraction of uranyl nitrate from cellulose-based filter papers. The extraction efficiency of the system for uranyl ion was found to decrease in the order TBP>MIBK>AA>MeOH. The use of eight potential chelating agents bis (2-ethylhexyl)hydrogen phosphate (HDEPH), tri- n -octylphosphine oxide (TOPO), dicyclohexyl-18-crown-6 (DC18C6), dibenzoylmethane (DBM), 8-hydroxyquinoline (HOX), diphenylaminesulfonic acid (DPASA) 1,4- bis -[4-methyl-5-phenyl-2-oxazolyl]benzene (DMPOPOP) and TBP for uranyl ion extraction from filter paper samples by methanol modified SF-CO 2 was investigated. The organophosphorous reagents TOPO and HDEPH showed the highest extraction efficiency in the series. The synergistic extraction of uranyl nitrate with HDEPH and TOPO in the presence of DC18C6 was also studied.
TL;DR: In this paper, a polyvinyl 2-pyrrolidone (PVP)/acrylonitrile interpenetrating polymer networks (IPNs) were synthesized and amidoximated for the purpose of uranyl ion adsorption.
Abstract: Poly(N-vinyl 2-pyrrolidone) (PVP)/acrylonitrile (AN) interpenetrating polymer networks (IPNs) were synthesized and amidoximated for the purpose of uranyl ion adsorption. The adsorption of amidoximated IPNs was studied from different uranyl ion solutions (850, 1000, 1200, 1400, and 1600 ppm). The result of all our adsorption studies showed that the bonding between UO-amidoxime groups complied with the Langmuir-type isotherm. The adsorption capacity was found as 0.75 g UO/g dry amidoximated IPN. In order to increase the UO ion adsorption capacity the amidoximated IPN was treated with alkali, but no significant increase could be observed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2324–2329, 2001
TL;DR: The structure of weeksite, K 1.26Ba0.25Ca0.869(4) A, V 7262(2) A 3, space group Cmmb, has been solved by direct methods using data collected with Mo KX-radiation and a CCD-based detector and refined by full-matrix least-squares techniques, on the basis of F 2 for all unique reflections, to an agreement factor (R1) of 7.0% and a goodness-of-fit (S) of 1.04, calculated
Abstract: The structure of weeksite, K 1.26Ba0.25Ca0.12((UO2)2(Si5O13))H2O, orthorhombic, a 14.209(2), b 14.248(2), c 35.869(4) A, V 7262(2) A 3 , space group Cmmb, has been solved by direct methods using data collected with Mo KX-radiation and a CCD- based detector and refined by full-matrix least-squares techniques, on the basis of F 2 for all unique reflections, to an agreement factor (R1) of 7.0% and a goodness-of-fit ( S) of 1.04, calculated using the 1565 unique observed reflections ( Fo ≤ 4� F). The structure contains four unique U 6+ positions, each of which is part of a nearly linear (UO 2) 2+ uranyl ion. The uranyl ions ( Ur) are further coordinated by five atoms of oxygen arranged at the equatorial corners of UrO5 pentagonal bipyramids. There are ten silicon atoms, each of which is tetrahedrally coordinated by oxygen atoms. The uranyl polyhedra share equatorial edges to form chains, which in turn share polyhedron edges with silicate tetrahedra. The uranyl silicate chains are linked to crankshaft-like chains of vertex-sharing silicate tetrahedra, resulting in layers that are connected by the sharing of vertices between silicat e tetrahedra to form an open framework. Potassium, barium, calcium and H 2O are located in the channels within the uranyl silicate framework. Displacement of some atoms from their corresponding special positions indicates that the results represent an averag e structure.
TL;DR: The structure of uranopilite has been solved and refined on the basis of F 2 for all unique data collected with monochromatic MoK X-radiation and a CCD-based detector to an agreement factor (R1) of 7.0%, calculated using 3907 unique observed reflections ( Fo ≥ 4F) as mentioned in this paper.
Abstract: The structure of uranopilite, ((UO 2)6(SO4)O2(OH)6(H2O)6)(H2O)8, space group Pa 8.896(2), b 14.029(3), c 14.339(3) A, 96.610(4), 98.472(4), 99.802(4)°, V 1726.1(4) A 3 , Z = 2, has been solved and refined on the basis of F 2 for all unique data collected with monochromatic MoK X-radiation and a CCD-based detector to an agreement factor ( R1) of 7.0%, calculated using 3907 unique observed reflections ( Fo ≥ 4F). The structure contains six symmetrically distinct U 6+ cations, each of which is part of an approximately linear (UO 2) 2+ uranyl ion (Ur). The uranyl ions are each coordinated by five ligands arranged at the equatorial vertices of Ur5 (: O 2- , (OH) - , H2O) pentagonal bipyramids that are capped by OUr atoms. The single symmetrically unique S 6+ cation is coordinated by four O atoms in a tetrahedral arrangement. The Ur5 pentagonal bipyramids share vertices and edges, resulting in a cluster of composition ((UO 2)6O6(OH)6(H2O)6) 6- . These clusters are linked through SO 4 tetrahedra, which share each of their vertices with different Ur5 pentagonal bipyramids, resulting in electroneutral uranyl sulfate chains of composition ((UO2)6(SO4)O2(OH)6(H2O)6) that extend along (100). The uranyl sulfate chains are linked to form the extended structure by hydrogen bonds bridging directly between the chains and to interstitial H 2O groups. The uranyl sulfate chain in uranopilite is novel in minerals and synthetic compounds.
TL;DR: It is shown that both dynamic and structural information can be obtained from spectral and kinetic data in uranyl ion spectroscopy studies.
TL;DR: The crystal structure of marthozite has been solved by direct methods and refined to an R index of 5.7% for 4364 observed (| F o | > 4σ F ) reflections collected with a four-circle diffractometer fitted with Mo K α X-radiation and a CCD detector.
Abstract: The crystal structure of marthozite, Cu 2+ [(UO 2 ) 3 (SeO 3 ) 2 O 2 ] (H 2 O) 8 , a 6.9879(4), b 16.4537(10), c 17.2229(10) A, V 1980.2(3) A 3 , Pbn 2 1 , Z = 4, D calc = 4.37 g/cm 3 , has been solved by direct methods and refined to an R index of 5.7% for 4364 observed (| F o | > 4σ F ) reflections collected with a four-circle diffractometer fitted with Mo K α X-radiation and a CCD detector. There are three unique U sites, each occupied by U 6+ with two short U –O uranyl bonds (1.76–1.82 A) and coordination numbers of [8], [7] and [7], respectively. There are two unique Se sites, each occupied by Se 4+ and coordinated by three O atoms ( Se –O ≈ 1.70 A), forming a triangular pyramid with Se at the apex, indicative of stereoactive lone-pair behavior in Se 4+ . There is one Cu site, occupied by Cu 2+ in octahedral coordination by four (H 2 O) groups ( Cu –H 2 O ≈ 2.0 A) and two O atoms ( Cu –O ≈ 2.4 A). The structural unit is a sheet of composition [(UO 2 ) 3 (SeO 3 ) 2 O 2 ], comprised of chains of edge-sharing (Uϕ n ) polyhedra extending along [100] that are cross-linked in the [001] direction by (SeO 3 ) groups; this sheet is topologically identical to the structural unit in guilleminite, Ba [(UO 2 ) 3 (SeO 3 ) 2 O 2 ] (H 2 O) 3 . Adjacent sheets are linked through interstitial Cu 2+ cations via Cu 2+ –O apical bonds and via H bonds that involve both (H 2 O) groups bonded to Cu 2+ and interstitial (H 2 O) groups not bonded to any cation. The principal differences between marthozite and guilleminite involve the interlayer species. In guilleminite, the Ba atom is centrally positioned with respect to the chain of (UO n ) polyhedra, whereas in marthozite, the Cu 2+ atom is located off the pseudo-mirror plane of the chain of (UO n ) polyhedra. This differential positioning of the interstitial cations results in an intersheet separation in marthozite that is nearly 1 A greater than that in guilleminite, despite the fact that Ba (in guilleminite) is much larger than Cu 2+ (in marthozite). The H-bond arrangement in marthozite is very different from that in guilleminite. In marthozite, there are eight unique interlayer (H 2 O) groups; four of these (H 2 O) groups bond directly to Cu 2+ and four are held in the structure solely by H bonds. In guilleminite, there are two unique interlayer (H 2 O) groups, both of which bond to the interlayer Ba atoms.