Aqueous Solutions Of Uranyl Nitrate Research Articles

Unveiling Structural Diversity of Uranyl Compounds of Aprotic 4,4'-Bipyridine N,N'-Dioxide Bearing O-Donors.

As an aprotic O-donor ligand, 4,4'-bipyridine N,N'-dioxide (DPO) shows good potential for the preparation of uranyl coordination compounds. In this work, by regulating reactant compositions and synthesis conditions, diverse coordination assembly between uranyl and DPO under different reaction conditions was achieved in the presence of other coexisting O-donors. A total of ten uranyl-DPO compounds, U-DPO-1 to U-DPO-10, have been synthesized by evaporation or hydro/solvothermal treatment, and the possible competition and cooperation of DPO with other O-donors for the formation of these uranyl-DPO compounds are discussed. Starting with an aqueous solution of uranyl nitrate, it is found that an anionic nitrate or hydroxyl group is involved in the coordination sphere of uranyl in U-DPO-1 ((UO2)(NO3)2(H2O)2·(DPO)), U-DPO-2 ((UO2)(NO3)2(DPO)), and U-DPO-3 ((UO2)(DPO)(μ2-OH)2), where DPO takes three different kinds of coordination modes, i.e. uncoordinated, monodentate, and biconnected. The utilization of UO2(CF3SO3)2 in acetonitrile, instead of an aqueous solution of uranyl nitrate, precludes the participation of nitrate and hydroxyl, and ensures the engagement of DPO ligands (4-5 DPO ligands for each uranyl) in a uranyl coordination sphere of U-DPO-4 ([(UO2)(CF3SO3)(DPO)2](CF3SO3)), U-DPO-5 ([UO2(H2O)(DPO)2](CF3SO3)2) and U-DPO-6 ([(UO2)(DPO)2.5](CF3SO3)2). Moreover, when combined with anionic carboxylate ligands, terephthalic acid (H2TPA), isophthalic acid (H2IPA), and succinic acid (H2SA), DPO works well with them to produce four mixed-ligand uranyl compounds with similar structures of two-dimensional (2D) networks or three-dimensional (3D) frameworks, U-DPO-7 ((UO2)(TPA)(DPO)), U-DPO-8 ((UO2)2(DPO)(IPA)2·0.5H2O), U-DPO-9 ((UO2)(SA)(DPO)·H2O), and U-DPO-10 ((UO2)2(μ2-OH)(SA)1.5(DPO)). Density functional theory (DFT) calculations conducted to probe the bonding features between uranyl ions and different O-donor ligands show that the bonding ability of DPO is better than that of anionic CF3SO3 -, nitrate, and a neutral H2O molecule and comparable to that of an anionic carboxylate group. Characterization of physicochemical properties of U-DPO-7 and U-DPO-10 with high phase purity including infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and luminescence properties is also provided.

Linear energy transfer of fission fragments of 235U and nucleation of gas bubbles in aqueous solutions of uranyl nitrate

Fission fragments emitted in a fissile solution create tiny gas bubbles, the size of which is determined by the linear energy transfer (LET) of the particles. The LET of fission fragments of 235U in aqueous solutions of uranyl nitrate has been determined, and using methods adapted from the literature, the size of gas bubbles generated along the tracks of these particles has been estimated, revealing important variations with respect to particle LET and solution properties. Empirical correlations are presented for the maximum radius of radiolytic gas bubbles in unsaturated solutions of uranyl nitrate as a function of solution temperature and concentration. These can be used to predict the critical concentration of dissolved hydrogen necessary for the appearance of gas voids during nuclear criticality transients. The findings are intended for use in a future model of nuclear criticality transients in aqueous fissile solutions for the purposes of nuclear criticality safety assessment.

Linear Energy Transfer of Fission Fragments of U-235 and Nucleation of Gas Bubbles in Aqueous Solutions of Uranyl Nitrate

Linear Energy Transfer of Fission Fragments of U-235 and Nucleation of Gas Bubbles in Aqueous Solutions of Uranyl Nitrate

Synthesis and crystal structures of two new uranyl coordination compounds obtained in aqueous solutions of 1-butyl-2,3-dimethylimidazolium chloride

Two new uranyl coordination compounds, [C9H17N2]3[(UO2)2(CrO4)2Cl2(H2O)2]Cl·5H2O (1) and (C9H17N2)[(UO2)(C2O4)Cl] (2), have been synthesized by adding potassium dichromate (K2Cr2O7) or oxalic acid dihydrate (H2C2O4·2H2O) solution into an aqueous solution of uranyl nitrate and 1-butyl-2,3-dimethylimidazolium chloride [Bmmim]Cl. [Bmmim]Cl provides the charge balance and Cl ions that coordinate with uranyl ions. The fundamental building units of 1 and 2 are UO6Cl pentagonal bipyramidal structures. Compound 1 exhibits a graphene-like structure with a system molar ratio of 1:1 for U:Cr and crystallizes in the orthorhombic space group Pbca, with a = 25.644(3) Å, b = 12.996(14) Å and c = 29.198(4) Å. 16-Membered rings are formed by CrO42− and UO22+ in the crystal structure of 1. Compound 2 crystallizes in monoclinic space group P21/n, with a = 10.759(3) Å, b = 11.395(3) Å, c = 14.149(4) Å, β = 102.962(9)° and shows one-dimensional (1D) serrated chains. Within the crystal structures of 1 and 2, C–H[Bmmim]Cl⋯O hydrogen bonds are identified. O–Hwater⋯Cl hydrogen bonds are also detected in the crystal structure for 1.

Photophysics and photochemistry of uranyl ions in aqueous solutions: Refining of quantitative characteristics

The photochemistry and photophysics of aqueous solutions of uranyl nitrate have been investigated by nanosecond laser photolysis with excitation at 266 and 355 nm and by time-resolved fluorescence spectroscopy. The quantum yield has been determined for (UO 2 2+ )* formation under excitation with λ = 266 and 355 nm light (φ = 0.35). The quantum yield of uranyl luminescence under the same conditions is 1 × 10–2 and 1.2 × 10–3, respectively, while the quantum yield of luminescence in the solid state is unity, irrespective of the excitation wavelength. The decay of (UO 2 2+ )* in the presence of ethanol is biexponential. The rate constants of this process at pH 3.4 are k 1 = (2.7 ± 0.2) × 107 L mol–1 s–1 and k 2 = (5.4 ± 0.2) × 106 L mol–1 s–1. This biexponential behavior is explained by the existence of different complex uranyl ion species in the solution. The addition of colloidal TiO2 to the solution exerts no effect on the quantum yield of (UO 2 2+ )* formation or on the rate of the reaction between (UO 2 2+ )* and ethanol. The results of this study have been compared with data available from the literature.

Extraction and Preconcentration of dissolved dibutyl phosphoric acid (HDBP) from aqueous uranyl nitrate solutions for gas chromatographic analysis

With a view to mitigate the complexities associated with aqueous solubility of Organophosphorous solvent, accurate estimation of dissolved organic in aque- ous streams assumes great importance. Present method employs solvent extraction using 10 % (v/v) mixture of benzyl alcohol-benzene (BBA) for selective enrichment/ extraction of dissolved Dibutyl phosphosphoric acid (HDBP), the target analyte, in presence of tributyl phos- phate from nitric acid solutions containing bulk amount of uranyl ions. The extracted HDBP after methylation is subjected to gas chromatographic analysis using thermal conductivity detector. A calibration plot of HDBP esti- mation in the concentration range of 10-100 ppm, yields a precision with RSD of ± 5% . Graphical Abstract

Novel type of molecular connectivity in one-dimensional uranyl compounds: [K@(18-crown-6)(H2O)][(UO2)(SeO4)(NO3)], a new potassium uranyl selenate with 18-crown-6 ether

New hybrid organic–inorganic uranyl selenate, [K(C12H24O6)(H2O)][(UO2)(SeO4)(NO3)] (I), has been prepared by a room-temperature evaporation from the aqueous solutions of uranyl nitrate, selenic acid, potassium nitrate and 18-crown-6 ether. The crystal structure of I [monoclinic, P21/c, a=7.2404(2), b=21.2024(7), c=15.7322(5)Å, β=91.5810(10)°, V=2414.19(13)Å3, Z=4, R1=0.023] is based upon the [(UO2)(SeO4)(NO3)]− one-dimensional uranyl nitrate–selenate chains consisting of UO7 pentagonal bipyramids, SeO4 tetrahedra and nitrate groups. The chains are linked to the [K@(18-crown-6)(H2O)]+ complexes via the K+O bonds to form a “multi-axis transporter” {[K@(18-crown-6)(H2O)][(UO2)(SeO4)(NO3)]} bands that are linked together via weak hydrogen bonds only. The infrared spectroscopy data support the structural data.

The role of potassium atoms in the formation of uranyl selenates: the crystal structure and synthesis of two novel compounds

*Corr esponding author Single crystals of two new uranyl selenates K 3 (H 3 O)[(UO 2 ) 4 (SeO 4 ) 6 (H 2 O) 4 ]∙5H 2 O (I) and K 2.5 (NO 3 ) 0.5 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)]∙4H 2 O (II) have been prepared by room-temperature evaporation from aqueous solution of uranyl nitrate, selenic acid, potassium carbonate and (for the compound I) carbamide. The crystal structure of I has been solved by direct methods [monoclinic, P2 1 /m, a = 12.001(3), b = 13.613(3), c = 13.753(3) A, β = 109.187(4)°, V = 2122.0(8) A 3 and Z = 2] and refined to R 1 = 0.029 (wR 2 = 0.084) for 4865 reflections with |F o| ≥ 4σF using least-square methods. The crystal structure of II has been solved by direct methods [monoclinic, С2/с, a = 20.290(4), b = 10.380(2), c = 21.436(4) A, β = 103.446(3)°, V = 4391.0(13) A 3 and Z = 4] and refined to R 1 = 0.027 (wR 2 = 0.066) for 7944 reflections with | F o | ≥ 4σF using least-square techniques. The structures of I and II are based upon the [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O) 2 ] 2– and [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] 2– layers, respectively, consisting of UO 7 pentagonal bipyramids sharing corners with SeO 4 tetrahedra. Potassium cations induce curvature of the uranyl selenate layers, which is mediated by the interlayer water molecules, hydronium ions and nitrate groups. The topology of the 2D units in the structure of I is novel for the structural chemistry of uranyl selenates.

First Organic–Inorganic Uranyl Chloroselenate: Synthesis, Crystal Structure and Spectroscopic Characteristics

Single crystals of the new uranyl selenate hydrate (C5H12NO)[(UO2)(SeO4)Cl(H2O)] (1) have been prepared by evaporation at room temperature from aqueous solution of uranyl nitrate, selenic acid, potassium hydroxide and choline chloride. The crystal structure of 1 has been solved by direct methods [monoclinic, P21/n, a = 10.745(4), b = 11.236(4), c = 12.477(4) A, β = 114.580(5)°, V = 1,369.9(8) A3, Z = 4] and refined to R 1 = 0.022 (wR 2 = 0.058) for 4,350 reflections with |Fo| ≥ 4σ F using least square techniques. The structure is based upon the [(UO2)(SeO4)Cl(H2O)]− layers consisting of UO6Cl pentagonal bypyramids sharing corners with SeO4 tetrahedra. The presence of the Cl− ions in the system leads to the formation of a mixed-ligand coordination of uranyl ions. The topology of the 2D layer in the structure of 1 is based upon 4- and 8-membered rings of polyhedra and is related to the one observed in the structure of apophyllite-group minerals. Single crystals of the new uranyl selenate chloride (C5H12NO)[(UO2)(SeO4)Cl(H2O)] have been prepared by evaporation at room temperature; the structure based upon 2D [(UO2)(SeO4)Cl(H2O)]− units whereas uranyl ions are coordinated by both O atoms of selenate anions and Cl atoms and description of its unprecedented structural topology reported herein.

Reversible growth of UO2 nanoparticles in aqueous solutions through 7 MeV electron beam irradiation

Uranium dioxide (UO2) nanoparticles of rod-shaped structures with diameter 80nm and length 500nm, have been grown in aqueous solutions of uranyl nitrate with electron beam irradiation using a 7MeV linear electron accelerator. These nanoparticles were found to be stable under de-aerated condition; however they decomposed upon exposure to air or oxygen. The bimolecular rate constant for decomposition of these nanoparticles has been estimated to be 4.3×10−1M−1s−1, in the aerated and oxygen saturated solutions, assuming these to be of pseudo-first order processes. The nitrogen-purged decomposed solution again produced the black coloured UO2 sol upon such irradiation and these reversible phenomena could be repeated for several cycles. There was also decomposition of the UO2 nanoparticles along with evolution of hydrogen upon addition of acid in the de-aerated condition.

Electrochemical Behavior of the System of Uranium(VI) Extraction with CMPO-Ionic Liquid

The electrochemical behavior of U(VI) extracted from an aqueous solution of uranyl nitrate by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in an ionic liquid was investigated. The hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C4mimNTf2) was used in this study. Using an equimolar series method, we found that CMPO and U(VI) formed a 3:1 molar complex during the extraction process. Cyclic voltammetry was used to investigate the electrochemical behavior of the U(VI)-CMPO complex in C4mimNTf2. The U(VI)-CMPO complex was found to be quasi-reversibly reduced to a U(V)-CMPO complex. The formal redox potential (E �� , vs Fc/Fc + ) for the U(VI)/ U(V) couple was determined to be (-0.885±0.008) V. Controlled-potential electrolysis of the extract gave a deposit on the surface of a platinum plate. X-ray photoelectron spectroscopy showed that the deposit contained only U(VI), U(IV), and oxygen, and the CMPO extractant and the ionic liquid were not trapped in the deposit.

Thermodynamic properties of electrolyte solutions. Compressibility studies in aqueous solutions of urayl nitrate

Sound velocities in aqueous solutions of uranyl nitrate were measured at 5 K intervals from T = (283.15 to 323.15) K, within the (0.1 to 2.8) mol · kg −1 concentration range. The sound velocities determined then served to evaluate the isentropic and isothermal compressibilities, the apparent molar compressibilities, the isochoric thermal pressure coefficients, changes of the cubic expansion coefficients with pressure and the heat capacities with volume and these parameters are qualitatively correlated with the changes in the structure of water when uranyl nitrate is dissolved in it.

ChemInform Abstract: Rapid Self‐Assembly of Uranyl Polyhedra into Crown Clusters.

AbstractThree chemically distinct clusters built from 32 uranyl peroxide polyhedra, (NH4)40 [(UO2)32(O2)40(OH)24] (I), (NH4)40 [(UO2)32(O2)44(OH)26] (II), and a third one with a composition consistent with coprecipitation of (I) and (II), self‐assemble and crystallize within 15 min from aqueous solutions of uranyl nitrate, ammonium hydroxide, and hydrogen peroxide in different molar ratios under ambient conditions.

Decomposition of uranyl nitrate in the silica gel matrix under the action of microwave radiation

Decomposition of aqueous solutions of uranyl nitrate in a matrix of granulated silica gel of KSKG grade under the action of microwave radiation (MWR) was studied. Microwave irradiation leads not only to formation of solid decomposition products UO3, UO2(OH)NO3, and their hydrates in pores of KSKG granules, but also to accumulation of gaseous NOx and H2O. The presence of NOx in KSKG pores leads to HNO3 formation in the course of washing of sorbent granules with water. This prevents hydrolysis of uranyl nitrate and formation of UO2(OH)2·H2O in KSKG pores. Washout of uranium with water and HClO4 solutions from the KSKG fraction containing products of decomposition of 2 and 10 g of the initial UO2(NO3)2·6H2O under the action of MWR (hereinafter denoted as KSKG-P-I) was studied. Upon ∼7-day contact of the solid and liquid phases at the total ratio S : L = 1 : 20, from 5 to 14% of U passes into the aqueous phase from KSKG-P-I samples obtained in experiments with 10 and 2 g of UO2(NO3)2·6H2O, respectively. In the course of repeated treatments of KSKG-P-I with water, pH of the wash water increased from 3 to 6, owing to removal of NOx from KSKG pores. Then an insoluble phase of uranyl hydroxide UO2(OH)2·H2O, which can also be presented as hydroxylated uranium trioxide UO3·2H2O, is gradually formed from the solution obtained by treatment of KSKG-P-I with water. On treatment of KSKG-P-I with HClO4 solutions (pH 1–2), virtually all uranium species formed by MWR treatment of aqueous uranyl nitrate solutions in KSKG matrix dissolve (at a contact time of the solid and liquid phases of ∼21 days, the amount of U that passed into HClO4 solutions is ∼90%). The amount of the U form that is not extracted with HClO4 solutions and remains in KSKG granules is ∼12% of its initial amount. X-ray phase analysis suggests that the uranium species remaining in KSKG are silicate compounds formed by sorbent saturation with a uranyl nitrate solution and subsequent MWR treatment.

Characterization of alumina-supported uranium oxide catalysts in methane oxidation

Synthesis of alumina-supported uranium oxide catalysts and their characterization in methane oxidation have been performed. The catalysts containing 5% U were prepared by impregnation, solid-phase synthesis and mechanical mixing techniques. Samples were studied using BET, XRD, HRTEM and XPS methods. It was shown that physicochemical properties and activity of the catalysts depend on the preparation procedure and calcination temperature and are determined by the extent of the interaction between active component and support. Most active are the catalysts prepared by impregnation of alumina with an aqueous solution of uranyl nitrate. It was found that the 5%U/Al 2O 3 catalyst calcined at 1000 °C has the highest catalytic activity, and it is explained by the formation of highly active nanodispersed state of uranium on the surface of the support.

Amine-templated uranyl selenates with chiral [(UO2)2(SeO4)3(H2O)]2– layers: topology, isomerism, structural relationships

Abstract Eleven new amine-templated uranyl selenate hydrates have been prepared by evaporation from aqueous solution of uranyl nitrate, selenic acid and the respective amines. The structures of the compounds have been solved by direct methods and refined using least-squares techniques. Each structure is based upon [(UO2)2(SeO4)3(H2O)]2– layers of corner-sharing UO7 pentagonal bipyramids and SeO4 tetrahedra. The layers are based upon 4- and 6-membered rings arranged in different fashion. In topology I, 6-membered rings form edge-sharing chains, whereas, in topology II, they form corner-sharing chains. Layers with the topology II exist in two geometrical isomers that differ in the system of ‘up’ and ‘down’ orientations of tetrahedra relative to the plane of the layer. There are two isomers, one of which is chiral and the other is achiral. The layers with the topology II are chiral. Chirality is induced by the combination of orientations of tetrahedra and direction of the U → H2O bond. The analysis of the relationships between composition and shape of amine molecules and layer topology reveals two important regularities. 1. Aliphatic components of amine molecules tend to associate with 6-MRs of the inorganic layers. 2. Molecules with longer and spacious aliphatic components favor formation of the layers with topology II, whereas those with shorter aliphatic components prefer layers with the topology I.

Charge-density matching in organic–inorganic uranyl compounds

Abstract Single crystals of [C10H26N2][(UO2)(SeO4)2(H2O)](H2SeO4)0.85(H2O)2 (1), [C10H26N2][(UO2)(SeO4)2] (H2SeO4)0.50(H2O) (2), and [C8H20N]2[(UO2)(SeO4)2(H2O)] (H2O) (3) were prepared by evaporation from aqueous solution of uranyl nitrate, selenic acid and the respective amines. The structures of the compounds have been solved by direct methods and structural models have been obtained. The structures of the compounds 1, 2, and 3 contain U and Se atoms in pentagonal bipyramidal and tetrahedral coordinations, respectively. The UO7 and SeO4 polyhedra polymerize by sharing common O atoms to form chains (compound 1) or sheets (compounds 2 and 3). In the structure of 1, the layers consisting of hydrogen-bonded [UO2(SeO4)2(H2O)]2− chains are separated by mixed organic–inorganic layers comprising from [NH3(CH2)10NH3]2+ molecules, H2O molecules, and disordered electroneutral (H2SeO4) groups. The structure of 2 has a similar architecture but a purely inorganic layer is represented by a fully connected [UO2(SeO4)2]2− sheet. The structure of 3 does not contain disordered (H2SeO4) groups but is based upon alternating [UO2(SeO4)2(H2O)]2− sheets and 1.5-nm-thick organic blocks consisting of positively charged protonated octylamine molecules, [NH3(CH2)7CH3]+. The structures may be considered as composed of anionic inorganic sheets (2D blocks) and cationic organic blocks self-organized according to competing hydrophilic–hydrophobic interactions. Analysis of the structures allows us to conclude that the charge-density matching principle is observed in uranyl compounds. In order to satisfy some basic peculiarities of uranyl (in general, actinyl) chemistry, it requires specific additional mechanisms: (a) in long-chain-amine-templated compounds, protonated amine molecules interdigitate; (b) in long-chain-diamine-templated compounds, incorporation of acid–water interlayers into an organic substructure is necessary; (c) the inclination angle of the amine chains may vary in order to modify surface area of an organic substructure.

Charge density matching in organic-inorganic uranyl compounds

Abstract Single crystals of [C10H26N2][(UO2)(SeO4)2(H2O)](H2SeO4)0.85(H2O)2 (1), [C10H26N2][(UO2)(SeO4)2] (H2SeO4)0.50(H2O) (2), and [C8H20N]2[(UO2)(SeO4)2(H2O)] (H2O) (3) were prepared by evaporation from aqueous solution of uranyl nitrate, selenic acid and the respective amines. The structures of the compounds have been solved by direct methods and structural models have been obtained. The structures of the compounds 1, 2, and 3 contain U and Se atoms in pentagonal bipyramidal and tetrahedral coordinations, respectively. The UO7 and SeO4 polyhedra polymerize by sharing common O atoms to form chains (compound 1) or sheets (compounds 2 and 3). In the structure of 1, the layers consisting of hydrogen-bonded [UO2(SeO4)2(H2O)]2− chains are separated by mixed organic–inorganic layers comprising from [NH3(CH2)10NH3]2+ molecules, H2O molecules, and disordered electroneutral (H2SeO4) groups. The structure of 2 has a similar architecture but a purely inorganic layer is represented by a fully connected [UO2(SeO4)2]2− sheet. The structure of 3 does not contain disordered (H2SeO4) groups but is based upon alternating [UO2(SeO4)2(H2O)]2− sheets and 1.5-nm-thick organic blocks consisting of positively charged protonated octylamine molecules, [NH3(CH2)7CH3]+. The structures may be considered as composed of anionic inorganic sheets (2D blocks) and cationic organic blocks self-organized according to competing hydrophilic–hydrophobic interactions. Analysis of the structures allows us to conclude that the charge-density matching principle is observed in uranyl compounds. In order to satisfy some basic peculiarities of uranyl (in general, actinyl) chemistry, it requires specific additional mechanisms: (a) in long-chain-amine-templated compounds, protonated amine molecules interdigitate; (b) in long-chain-diamine-templated compounds, incorporation of acid–water interlayers into an organic substructure is necessary; (c) the inclination angle of the amine chains may vary in order to modify surface area of an organic substructure.

Uranyl(VI) Nitrate Salts: Modeling Thermodynamic Properties Using the Binding Mean Spherical Approximation Theory and Determination of “Fictive” Binary Data

This work is aimed at a description of the thermodynamic properties of highly concentrated aqueous solutions of uranyl nitrate at 25 degrees C. A new resolution of the binding mean spherical approximation (BIMSA) theory, taking into account 1-1 and also 1-2 complex formation, is developed and used to reproduce, from a simple procedure, experimental uranyl nitrate osmotic coefficient variation with concentration. For better consistency of the theory, binary uranyl perchlorate and chloride osmotic coefficients are also calculated. Comparison of calculated and experimental values is made. The possibility of regarding the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O as a "simple" solution (in the sense of Zdanovskii, Stokes, and Robinson) is examined from water activity and density measurements. Also, an analysis of existing uranyl nitrate binary data is proposed and compared with our obtained data. On the basis of the concept of "simple" solution, values for density and water activity for the binary system UO(2)(NO(3))(2)/H(2)O are proposed in a concentration range on which uranyl nitrate precipitates from measurements on concentrated solutions of the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O. This new set of binary data is "fictive" in the sense that the real binary system is not stable chemically. Finally, a new, interesting predictive capability of the BIMSA theory is shown.

Amine‐Templated Uranyl Selenates with Layered Structures. I Structural Diversity of Sheets with a U:Se ratio of 1:2

AbstractCrystals of four amine‐templated layered uranyl selenates, [C2H10N2][(UO2)(SeO4)2(H2O)](H2O) (1), [CH6N3]2[(UO2)(SeO4)2(H2O)](H2O)1.5 (2), [C4H12N]2[(UO2)(SeO4)2(H2O)] (3), and [CH6N3]3[(UO2)2(SeO4)2(H(SeO4)2)](H2O)2 (4) were prepared by evaporation from aqueous solution of uranyl nitrate, selenic acid and the respective amine. The structures of all four compounds have been solved by direct methods. The structures of 1 (monoclinic, C2/c, a = 11.787(2), b = 7.7007(10), c = 16.600(3) Å, β = 102.016(14)°, V = 1473.7(4) Å3, R1 = 0.037 for 1743 unique observed reflections), 2 (monoclinic, C2/c, a = 37.314(4), b = 7.1771(6), c = 13.2054(14) Å, β = 109.267(8)°, V = 3338.4(6) Å3, R1 = 0.088 for 3005 unique observed reflections) and 3 (monoclinic, C2/c, a = 27.212(10), b = 7.372(3), c = 23.113(7) Å, β = 117.75(2)°, V = 4103(3) Å3, R1 = 0.073 for 2111 unique observed reflections) are based on sheets of the composition [(UO2)(SeO4)2(H2O)]2− consisting of pentagonal [UO7]8− pentagonal bipyramids linked via [SeO4]2− tetrahedra. The sheets have the same chemical composition but different topologies. The structure of 4 (orthorhombic, P212121, a = 10.7261(9), b = 13.918(2), c = 18.321(2) Å, V = 2735.1(5) Å3, R1 = 0.050 for 5683 unique observed reflections) contains [(UO2)2(SeO4)2(H(SeO4)2)]3− sheets parallel to (001). In all four structures, the layers are connected via protonated amine and H2O molecules.