Uranyl Oxygen Research Articles

Synthesis and structure of bis(β-dibenzoyl methanato -O,O’) (aquo-O) dioxouranium (VI) compound

The compound [UO2(C6H5COCHCOC6H5)2.H2O] was synthesized and characterized by IR, 1H NMR and CHN analysis. Structure of the compound shows that the uranium atom is surrounded by seven oxygen atoms in a pentagonal bi-pyramidal geometry. The water molecule is hydrogen bonded to another molecule via the uranyl and β-diketonate oxygen atoms to give a linear zig-zag arrangement along the ‘a’ axis. The whole molecule is stabilized in solid state by various intermolecular hydrogen bonding interactions. Structure of [UO2(C6H5COCHCOC6H5)2.H2O] shows that the uranium atom is surrounded by seven oxygen atoms in a pentagonal bi-pyramidal geometry. The water molecule is hydrogen bonded to another molecule via the uranyl and β-diketonate oxygen atoms to give a linear zig-zag arrangement along the ‘a’ axis.

First examples of 3d-uranium compounds derived from single-compartment Schiff base ligands: Syntheses, crystal structures and d–d band correlation

This paper deals with the syntheses, characterization, crystal structures and UV–Vis spectroscopy of three diphenoxo-bridged dinuclear CuII(UVIO2) compounds [CuII(MeCN)L1(UVIO2)(NO3)2] (1), [CuII(MeCN)L2(UVIO2)(NO3)2] (2) and [CuII(MeCN)L3(UVIO2)(NO3)2] (3) derived from the single-compartment Schiff base ligands H2L1 (2:1 condensation product of salicylaldehyde and 1,3-diaminopropane), H2L2 (2:1 condensation product of salicylaldehyde and 1-ethyl-1,3-diaminopropane) and H2L3 (2:1 condensation product of 2-hydroxyacetophenone and 1,3-diaminopropane). While copper(II) occupies the N2O2 compartment, uranium(VI) center is linked with Schiff base ligand through the two bridging phenoxo oxygen atoms. Copper(II) is pentacoordinated and distorted square pyramidal, while the uranium(VI) center is octacoordinated and distorted hexagonal bipyramidal in which the two uranyl oxygen atoms occupy the apical positions. Electronic spectra of 1–3 and the corresponding mononuclear CuII compounds have been recorded and a previously reported but practically unexplored correlation regarding d–d band position has been highlighted. Although the correlation is not valid for only mononuclear or only dinuclear compounds derived from different ligands, a nice correlation is found out on comparing the spectra of dinuclear compounds with the corresponding mononuclear compounds.

The structural and spectroscopic studies of [formula omitted] complexes with diethyl benzylphosphonate and diethyl (carboxymethyl)phosphonate in solution and in the solid state

Spectroscopic properties of UO22+ complexes with diethyl benzylphosphonate (C6H5CH2P(O)(OCH2CH3)2) (L1) and diethyl (carboxymethyl)phosphonate ((CH3CH2O)2P(O)CH2COOH) (L2) were investigated using absorption and luminescence spectroscopy. Studied compounds were characterized using CHN microanalytical procedures, infrared spectroscopy and by single crystal X-ray diffraction. Uranyl ion forms with the studied ligands complexes of general formulae [UO2(L1)2(NO3)2] and [UO2(L2)2(NO3)2]. In the crystal structures, the uranyl groups are coordinated in the equatorial plane by six oxygen atoms, and the coordination polyhedra of uranium ions are close to hexagonal bipyramid, with uranyl oxygen atoms in apexes.

ChemInform Abstract: New Reactivity of the Uranyl(VI) Ion

AbstractReview: 117 refs.

Crystal structure and formula revision of deliensite, Fe[(UO2)2(SO4)2(OH)2](H2O)7

AbstractThe crystal structure of deliensite, Fe[(UO2)2(SO4)2(OH)2](H2O)7, was solved by direct methods and refined toR1= 6.24% for 5211 unique observed reflections [Iobs> 3σ(I)], on a crystal that was found to consist of rotational and inversion (merohedral) twins, from Jeroným mine, Abertamy in the Czech Republic. The presence of four twin domains was taken into account in the refinement. The structure is orthorhombic, space groupPnn2, with unit-cell parametersa= 15.8514(9),b= 16.2478(7),c= 6.8943(3) Å,V= 1775.6(1) Å3andZ= 4. The crystal structure of deliensite contains uranyl-sulfate sheets with a phosphuranylite topology, consisting of dimers of edge-sharing uranyl pentagonal bipyramids linked by corner-sharing with sulfate tetrahedra. The sheets lie in the (100) plane and are decorated by [Fe2+O(H2O)5] octahedra; two weakly bonded H2O molecules are present in the interlayer. The [Fe2+O(H2O)5] octahedron is linked directly to the sheet via the uranyl oxygen atom. Adjacent sheets are linked by hydrogen bonds only. The sheet topology and geometrical isomerism is discussed and a comparison of the composition obtained from electron-probe microanalysis, powder-diffraction data, Raman and infrared spectra of deliensite samples from Mas d'Alary, Lodève, France; L'Ecarpière mine, Gétigné, France; and several localities at Jáchymov, Western Bohemia, Czech Republic is made.

Crystal structures of 2,2′:6′,2″-terpyridine uranyl chlorides molecular assemblies and their luminescence signatures

A series of three compounds bearing uranyl cations and 2,2′:6′,2″-terpyridine (terpy) has been hydrothermally synthesized from uranium tetrachloride aqueous solution. An oxidation process into the hexavalent state has been observed for uranium in these synthesis conditions, together with the crystallization of different phases, which have been characterized by single-crystal X-ray diffraction analysis. The tetrachloridodioxidouranate terpyridinium salts UO2Cl4·H2terpy·H2O (1) and UO2Cl4·(H2terpy)2·2Cl (2) consist of the molecular assemblies of tetrachloro-uranyl anions ([UO2Cl4]2−, square plane bipyramidal environment), isolated to each other via the doubly protonated H2terpy molecules. The latter chelate either water (1) or chlorine anions (2). The addition of organic base such as pyridine favored the crystallization of the complex, UO2Cl2(terpy) (3), with the neutral terpy moiety coordinating one uranyl center via the nitrogen atoms of the pyridyl rings. It resulted in one uranyl center bonded to three nitrogen and two terminal chlorine anions, located in a distorted equatorial plane and two terminal perpendicular uranyl oxygens in apical position of a pentagonal bipyramid ([UO2Cl2N3]). Different π–π interactions between the pyridyl rings of neighboring terpy molecules also occur for these complexes. Fluorescence spectroscopy of these different complexes has been measured at room temperature and 77K showing the various local environments of the emitting centers.

The surface structure of α-uranophane and its interaction with Eu(III) – An integrated computational and fluorescence spectroscopy study

Uranophane is a rare U(VI) secondary silicate mineral that is relevant to the long-term performance of high level nuclear waste repositories. It can be formed under oxidizing conditions, potentially acting as an additional barrier to radionuclide migration through the accessible environment via mineral sorption reactions. To help understand the mechanisms involved in such sorption, a combination of theoretical calculations (classical molecular dynamics and ab initio density functional theory), and experimental work (sorption and laser induced fluorescence spectroscopy studies), have been employed to investigate the uranophane|water interface as well as the interfacial reactivity of the U(VI) silicate toward acidic conditions and radionuclide ion sorption. The combination of theoretical and experimental sorption studies help identify the molecular structure of the surface-sorbed species. Interfacial water is found to orient primarily with the hydrogen-atoms directed towards the negatively charged surface, with sorption sites belonging to three different groups: (1) those involving uranyl oxygen, (2) involving uranyl and silica hydroxyl oxygen atoms, and (3) involving hydroxyl hydrogen. Under basic conditions, deprotonation of the Si–OH groups is predicted to be responsible for uranophane dissolution, while protonation of bridging oxygens is likely responsible for acidic dissolution. Stable inner-sphere sorbed Eu(III) species are observed both experimentally and computationally. Moreover, Eu(III) is found to react with both protonated and deprotonated surface sites, indicating that radionuclides may sorb to the surface of uranophane under a broad range of pH conditions that alter the relative concentrations of protonated and deprotonated surface sites. This is in stark contrast to prior observations regarding other silicate minerals such as quartz, where sorption under basic conditions is enhanced.

New Reactivity of the Uranyl(VI) Ion

The chemistry of the uranyl ion ([UO(2)](2+)) has evolved remarkably over the past few years, with unexpected reactivity observed that challenge our understanding of this ion, and of actinides in general. This review highlights some recent advances in the field, focussing on the organometallic chemistry of the uranyl moiety, which is not well developed in comparison to lower oxidation states of uranium. The use of uranyl as a catalyst is highlighted and the newly developed supramolecular chemistry is described. The uranyl oxygen atoms have been considered as inert, but recent work has shown that is not necessarily the case and is discussed herein. Finally, reduction to the [UO(2)](+) ion will be discussed.

Syntheses, structures, and fluorescent properties of two uranium coordination polymers with carboxylic acids

Two U(VI)-containing coordination polymers, (UO2)2O2(Suc)(2,2′-bipy)2 (1) and UO2(BC)2(DMF) (2) (2,2′-bipy = 2,2′-bipyridine, H2Suc = succinic acid, HBC = benzoic acid, DMF = N,N-dimethylformamide), have been synthesized and characterized via elemental analysis, infrared spectroscopy, UV-Vis spectroscopy, and single-crystal X-ray diffraction. Structural analyses show that 1 is a 1-D chain coordination polymer in which U(VI) ions are connected by succinic acid ligand and the 1-D chain is connected into a 3-D supramolecular network by C⊟H···O hydrogen bonds between carbon of 2,2′-bipyridine and uranyl oxygen. For 2, monomeric entities are further assembled into a 1-D supramolecular network by C–H···O hydrogen bonds between carbon of DMF molecule and coordinated carboxylate oxygen. Thermogravimetric analyses and photoluminescent properties of 1 and 2 are discussed.

Synthesis and structural studies of a new potassium uranyl selenate K(H5O2)[(UO2)2(SeO4)3(H2O)] with strongly deformed layers

Single crystals of a new uranyl selenate, K(H5O2)[(UO2)2(SeO4)3(H2O)] (I), were prepared by isothermal evaporation at room temperature. The crystal structure of I was solved by the direct method (space group P21/c; a = 11.456(2), b = 10.231(1), c = 14.809(2) A; β = 101.901(4)°, V = 1698.4(4) A3; Z = 4) and refined to R1 = 0.0547 (wR2 = 0.0825) for 3375 reflections with |Fo| ≥ 4σF. The structure of I is based on layers of the composition [(UO2)2(SeO4)3(H2O)]2−. The charge of the inorganic layer is compensated by potassium and oxonium ions located in the interlayer space. Each potassium ion is coordinated by seven oxygen atoms belonging to uranyl selenate layers, including uranyl oxygen atoms, which leads to bending of uranyl selenate structural elements.

Synthesis, characterization and molecular structure of 1,1′ bis (diphenyl phosphino ferrocene) dioxide complex of the cis-uranyl dichloride

A 1,1′ bis(diphenyl phosphino ferrocene) dioxide complex of the uranyl dichloride was synthesized and characterized by elemental analysis, 1H, 31P{ 1H} NMR and X-ray diffraction methods. The structure of the compound shows that the uranium(VI) ion is surrounded by four oxygen and two chlorine atoms in an octahedral geometry. Two oxygen atoms from the bis (diphenyl phosphino ferrocene) dioxide and two chlorine atoms form a square planar arrangement. Two uranyl oxygen atoms occupy the axial positions. The bis(diphenyl phosphino ferrocene) dioxide ligand acts as a bidentate chelating ligand with a bite angle of 82.90(16)° around the uranyl group. The two chlorine atoms are mutually cis with a Cl–U–Cl angle of 97.75(7)°.

Tetra-μ2-acetato-tetraaquadi-μ3-oxido-octaoxidotetrauranium(VI) methanol disolvate tetrahydrate

The centrosymmetric title tetra­mer, [U4(C2H3O2)4O10(H2O)4]·2CH4O, has a near planar core [maximum deviation from the least squares plane of 0.294 (6) Å]. It consists of two hexa­gonal–bipyramidally coordinated UVI atoms connected via μ2-O (acetate) and μ3-O (oxide) bridges in the equatorial plane to two penta­gonal–bipyramidally coordinated UVI atoms. The equatorial plane of each UVI atom is completed by a bound water mol­ecule, while the axial positions are occupied by uranyl (UO2)2+ O atoms. Multiple O—H⋯O hydrogen bonds are present, including a lattice methanol mol­ecule bound to one of the penta­gonal bipyramidal uranyl O atoms, as well as two different C 1 1(6) chains orginating from a donor water mol­ecule, via a uranyl oxygen acceptor and an acetate acceptor on different, adjacent tetra­mers. Finally, the unit cell contains four UVI tetra­mers, all connected by hydrogen bonding, forming a supra­molecular R 4 4(24) ring.

La(UO2)V2O7][(UO2)(VO4)] the first lanthanum uranyl-vanadate with structure built from two types of sheets based upon the uranophane anion-topology

The new lanthanum uranyl vanadate divanadate, [La(UO2)V2O7][(UO2)(VO4)] was obtained by reaction at 800°C between lanthanum chloride, uranium oxide (U3O8) and vanadium oxide (V2O5) and the structure was determined from single-crystal X-ray diffraction data. This compound crystallizes in the orthorhombic system with space group P212121 and unit-cell parameters a=6.9470(2)Å, b=7.0934(2)Å, c=25.7464(6)Å, V=1268.73(5)Å3, Z=4. A full matrix least-squares refinement yielded R1=0.0219 for 5493 independent reflections. The crystal structure is characterized by the stacking of uranophane-type sheets [(UO2)(VO4)]−∞2 and double layers [La(UO2)(V2O7)]+∞2 connected through La–O bonds involving the uranyl oxygen of the uranyl-vanadate sheets. The double layers result from the connection of two [La(UO2)(VO4)2]−∞2 sheets derived from the uranophane anion-topology by replacing half of the uranyl ions by lanthanum atoms and connected through the formation of divanadate entities.

On the Mechanism of Oxygen Exchange Between Uranyl(VI) Oxygen and Water in Strongly Alkaline Solution as Studied by 17O NMR Magnetization Transfer

The mechanism, rate constant, and activation parameters for the exchange between uranyl(VI) oxygen and water oxygen in tetramethyl ammonium hydroxide solution, TMA-OH, have been determined using (17)O NMR magnetization transfer technique. In the concentration range investigated, the predominant complex is UO(2)(OH)(4)(2-). The experimental rate equation, rate = k(ex)[TMA-OH](free)[U(VI)](2)(total) indicates that the exchange takes place via a binuclear complex or transition state with the stoichiometry [(UO(2)(OH)(4)(2-))(UO(2)(OH)(5)(3-)]. The rate-determining step most likely takes place between the axial "yl" oxygens and the equatorial hydroxides. The experimental Gibbs energy of activation, DeltaG(++) = 60.8 +/- 2.4 kJ/mol is in good agreement with the value, DeltaA(++) approximately DeltaG(++) = 52.3 +/- 5.4 kJ/mol, found by Buhl and Schreckenbach in a recent Car-Parrinello molecular dynamics study, indicating that their proposed "shuttle" mechanism may be applicable also on the proposed binuclear transition state.

Synthesis, characterization and molecular structure of 1,1′ bis(diphenylphosphino ferrocene)dioxide complex of uranyl nitrate

A 1,1′ bis(diphenylphosphino ferrocene)dioxide complex of uranyl nitrate was synthesized and characterized by IR, 1H and 31P{ 1H} NMR spectroscopic and X-ray diffraction methods. The structure of the compound shows that the uranium atom is surrounded by eight oxygen atoms in a hexagonal bi-pyramidal geometry. Two oxygen atoms from 1,1′ bis(diphenylphosphino ferrocene)dioxide ligand and four oxygen atoms from the nitrate groups form a planar hexagon. The two uranyl oxygen atoms occupy the axial position. The 1,1′ bis(diphenylphosphino ferrocene)dioxide ligand acts as a bidentate chelating ligand with a bite angle of 71.56(8)° around the uranium(VI) atom, which is much smaller in value compare to any of the previously reported values (90.1°–154.0°) for this ligand.

Probing the oxygen environment in UO22+ by solid-state O17 nuclear magnetic resonance spectroscopy and relativistic density functional calculations

A combined theoretical and solid-state (17)O nuclear magnetic resonance (NMR) study of the electronic structure of the uranyl ion UO(2)(2+) in (NH(4))(4)UO(2)(CO(3))(3) and rutherfordine (UO(2)CO(3)) is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens and the latter exemplifying a uranyl environment without hydrogens. Relativistic density functional calculations reveal unique features of the U-O covalent bond, including the finding of (17)O chemical shift anisotropies that are among the largest for oxygen ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state (17)O NMR measurements in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the (17)O echo signal of U (17)O(2)(2+).

Synthesis, spectroscopic characterization and X-ray structure analyses of two uranyl complexes

Abstract The synthesis, spectroscopic characterization and crystal structures of two uranyl complexes, [UO2(SALEN)(DMF)] (1) and [UO2(BPHA)2(DMF)] (2) {SALEN = N,N′-ethylenebis(salicylimine), DMF = N,N-dimethylformamide, BPHA = N-phenyl benzohydroxamate} are described. The coordination geometry around the metal center in the mononuclear complexes can be best described as distorted pentagonal bipyramidal with an almost linear uranyl moiety. In addition to the van der Waal´s interactions, the crystal packing in the complexes is stabilized by weak intermolecular C–H…O hydrogen bonds involving the uranyl oxygen atoms, so generating two-dimensional arrays in both crystal structures.

An ab Initio Theoretical Study of the Electronic Structure of UO2+ and [UO2(CO3)3]5−

The electronic spectra up to 50,000 cm(-1) of uranyl(V) both as a bare ion, UO2(+), and coordinated with three carbonate ligands, [UO2(CO3)3]5-, are presented. Solvent effects were treated by a nonequilibrium continuum solvent model. The transition energies were obtained at the spin-orbit level using relativistic wave function based multiconfigurational methods such as the complete active space self-consistent field method (CASSCF)and the complete active space with second-order perturbation theory (CASPT2) followed by a calculation of the spin-orbit effects at the variation-perturbation level. Earlier relativistic intermediate Hamiltonian Fock space coupled-cluster calculations on the spectrum of the bare uranyl(V) ion were extended to investigate the influence of electron correlation effects on spacings between the electronic states. This study is an attempt to contribute to an enhanced understanding of the electronic structure of actinyl ions. Both spectra show transitions within nonbonding orbitals and between nonbonding and antibonding orbitals as well as charge transfers from the uranyl oxygens to uranium. The ground state in UO2(+) is found to be 2Φ(5/2u), corresponding to the σ(u)(2)φ(u)(1) configuration, while in [UO2(CO3)3]5-, it is 2Δ(3/2u), arising from the σ(u)(2)δ(u)(1) configuration. It is remarkable that the excited state corresponding to an excitation from the nonbonding δ(u) to the uranyl antibonding 3π(u)* molecular orbital is significantly lower in energy in the carbonate complex, 6623 cm(-1), than that in the bare ion, 17,908 cm(-1). The first ligand (carbonate) to metal charge-transfer excitation is estimated to occur above 50,000 cm(-1). The reported results compare favorably with experiment when available.

Polynuclear Cation−Cation Complexes of Pentavalent Uranyl: Relating Stability and Magnetic Properties to Structure

Reaction of {[UO2Pys][mu-KI2Py2]}n (1) with 2 equiv of potassium dibenzoylmethanate (Kdbm) in pyridine or acetonitrile affords, respectively, the corresponding tetranuclear complexes of pentavalent uranyl ([UO2(dbm),2]2[mu-K(Py)2]2[mu8-K(Py)]}2I2 x Py2 (2) (in 70% yield) and {[UO2(dbm)2]2[mu-K(MeCN)2][mu8-K]}2 (3) (in 40% yield) in which four UO2+ are mutually coordinated (T-shaped "cation-cation" interaction). The X-ray structures of 2 and 3 show also the presence of, respectively, six and four potassium cations involved in UO2+...K+ interactions. Reaction of 2 with an excess of 18-crown-6 (18C6) affords the dimeric complex [UO2(dbm)2K(18C6)]2 (4) presenting a diamond-shaped interaction between two UO2+ groups, in 45% yield. 1H and PFGSTE diffusion NMR spectroscopy of 2 and 3 in pyridine show unambiguously the presence of UO2+...UO2+ and UO2+...K+ interactions (tetrametallic species) in solution, which leads to a rapid (7 days) disproportionation of pentavalent uranyl to afford [U(dbm)4] and [UO2(dbm)2] species. The UO2+...K+ interaction plays an important synergistic role in the stabilization of the UO2+...UO2+ interactions. Accordingly, the lower affinity of (K(18C6))+ for the uranyl(V) oxygen in complex 4 results in a lower number of coordinated K+ and therefore in a weakened UP2+...UO2+ interaction. The UO24+...UO2+ interactions is completely disrupted in dmso or in the presence of Kdbm, preventing disproportionation of pentavalent uranyl. Solid-state variable-temperature magnetic susceptibility studies showed the unambiguous presence of antiferromagnetic coupling between the two oxo-bridged uranium centers of complex 4, with the appearance of a maximum in chi versus T at approximately 5 K. The different behavior of the tetrameric complex 3, which probably involves a magnetic coupling occurring at lower temperature, can be ascribed to the different geometric arrangement of the interacting uranyl(V) groups.

Syntheses, structures, and electrochemistry of a dinuclear compound and a mononuclear–mononuclear cocrystalline compound of uranyl(VI)

AbstractSyntheses, structures, and electrochemistry of a dialkoxo‐bridged diuranyl(VI) compound [(UO2)2(L1)2(dimethylformamide)2] (1) and a mononuclear–mononuclear cocrystalline compound [(UO2)(L2)(H2O)⊂(H2O)]·[(UO2)(L2)(H2O)] (2) derived from Schiff base ligands are reported (H2L1 = Schiff base ligand obtained on condensation of 3‐ethoxysalicylaldehyde with 2‐aminoethanol; H2L2 = N,N ′‐o ‐phenylenebis(3‐ethoxysalicylaldimine)). The compounds 1 and 2 crystallize in the space groups P 21/c and P 1, respectively. Compound 1 is a dialkoxo‐bridged dinuclear compound of uranium(VI) containing two deprotonated ligands, [L]2–, two dimethylformamide (dmf) molecules and two UO22+ centers. Three C–H···O type hydrogen bonds involving one uranyl oxygen, two dmf hydrogens, and the imine hydrogen link the dinuclear units into a two‐dimensional network. Compound 2 is a cocrystal of two mononuclear units, [(UO2)(L2)(H2O)⊂(H2O)] (unit 1) and [(UO2)(L2)(H2O)] (unit 2). In unit 1, the non‐coordinated water molecule forms hydrogen bonds with oxygens of phenoxo, ethoxy, and coordinated water molecules resulting in the formation of an inclusion product. The overall supramolecular structure of compound 2 is one‐dimensional and consists of interlinked self‐assembled dimeric unit of unit 1 and unit 2. Cyclic voltammetric measurements reveal that the uranium(VI) center in [(UO2)2(L1)2(dimethylformamide)2] (1) is reduced quasireversibly at E1/2 = –773 mV with ΔEP = 121 mV, while the metal center in [(UO2)(L2)(H2O)⊂(H2O)]·[(UO2)(L2)(H2O)] (2) is reduced reversibly with E1/2 = –765 mV with ΔEP = 68 mV. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)