Syntheses, Structures, and Spectroscopic Properties of Plutonium and Americium Phosphites and the Redetermination of the Ionic Radii of Pu(III) and Am(III)

A series of isotypic rare earth phosphites (RE = Ce(III), Pr(III), Nd(III), Pu(III), or Am(III)) with the general formulas RE(2)(HPO(3))(3)(H(2)O) along with a Pu(IV) phosphite, Pu[(HPO(3))(2)(H(2)O)(2)], have been prepared hydrothermally via reactions of RECl(3) with phosphorous acid. The structure of RE(2)(HPO(3))(3)(H(2)O) features a face-sharing interaction of eight- and nine-coordinate rare earth polyhedra. By use of the crystallographic data from the isotypic series along with data from previously reported isotypic series, the ionic radii for higher coordinate Pu(III) and Am(III) were calculated. The (VIII)Pu(III) radius was calculated as 1.112 ± 0.004 ?, and the (IX)Pu(III) radius was calculated to be 1.165 ± 0.002 ?. The (VIII)Am(III) radius was calculated as 1.108 ± 0.004 ?, and the (IX)Am(III) radius was calculated as 1.162 ± 0.002 ?.     

Systematic evolution from uranyl(VI) phosphites to uranium(IV) phosphates

Six new uranium phosphites, phosphates, and mixed phosphate-phosphite compounds were hydrothermally synthesized, with an additional uranyl phosphite synthesized at room temperature. These compounds can contain U(VI) or U(IV), and two are mixed-valent U(VI)/U(IV) compounds. There appears to be a strong correlation between the starting pH and reaction duration and the products that form. In general, phosphites are more likely to form at shorter reaction times, while phosphates form at extended reaction times. Additionally, reduction of uranium from U(VI) to U(IV) happens much more readily at lower pH and can be slowed with an increase in the initial pH of the reaction mixture. Here we explore the in situ hydrothermal redox reactions of uranyl nitrate with phosphorous acid and alkali-metal carbonates. The resulting products reveal the evolution of compounds formed as these hydrothermal redox reactions proceed forward with time.     

Differentiating between trivalent lanthanides and actinides

The reactions of LnCl(3) with molten boric acid result in the formation of Ln[B(4)O(6)(OH)(2)Cl] (Ln = La-Nd), Ln(4)[B(18)O(25)(OH)(13)Cl(3)] (Ln = Sm, Eu), or Ln[B(6)O(9)(OH)(3)] (Ln = Y, Eu-Lu). The reactions of AnCl(3) (An = Pu, Am, Cm) with molten boric acid under the same conditions yield Pu[B(4)O(6)(OH)(2)Cl] and Pu(2)[B(13)O(19)(OH)(5)Cl(2)(H(2)O)(3)], Am[B(9)O(13)(OH)(4)]·H(2)O, or Cm(2)[B(14)O(20)(OH)(7)(H(2)O)(2)Cl]. These compounds possess three-dimensional network structures where rare earth borate layers are joined together by BO(3) and/or BO(4) groups. There is a shift from 10-coordinate Ln(3+) and An(3+) cations with capped triangular cupola geometries for the early members of both series to 9-coordinate hula-hoop geometries for the later elements. Cm(3+) is anomalous in that it contains both 9- and 10-coordinate metal ions. Despite these materials being synthesized under identical conditions, the two series do not parallel one another. Electronic structure calculations with multireference, CASSCF, and density functional theory (DFT) methods reveal the An 5f orbitals to be localized and predominately uninvolved in bonding. For the Pu(III) borates, a Pu 6p orbital is observed with delocalized electron density on basal oxygen atoms contrasting the Am(III) and Cm(III) borates, where a basal O 2p orbital delocalizes to the An 6d orbital. The electronic structure of the Ce(III) borate is similar to the Pu(III) complexes in that the Ce 4f orbital is localized and noninteracting, but the Ce 5p orbital shows no interaction with the coordinating ligands. Natural bond orbital and natural population analyses at the DFT level illustrate distinctive larger Pu 5f atomic occupancy relative to Am and Cm 5f, as well as unique involvement and occupancy of the An 6d orbitals.     

[Hg5O2(OH)4][(UO2)2(AsO4)2]: A complex mercury(II) uranyl arsenate

Under mild hydrothermal conditions UO₂(NO₃)₂·6H₂O, Hg₂(NO₃)₂·2H₂O, and Na₂HAsO₄·7H₂O react to form [Hg₅O₂(OH)₄][(UO₂)₂(AsO₄)₂] (HgUAs-1). Single crystal X-ray diffraction experiments reveal that HgUAs-1 possesses a pseudo-layered structure consisting of two types of layers: and . The layers are complex, and contain three crystallographically unique Hg centers. The coordination environments and bond-valence sum calculations indicate that the Hg centers are divalent. The layers belong to the Johannite topological family. The and layers are linked to each other through μ₂-O bridges that include Hg?O=U=O interactions.     

Structure and properties of the thorium vanadyl tellurate, Th(VO2)2(TeO6)(H2O)2

The hydrothermal reaction of Th(NO3)4.xH2O with V2O5 and H6TeO6 at 200 degrees C under autogenously generated pressure results in the formation of Th(VO2)2(TeO6)(H2O)2 as a pure phase. The single-crystal X-ray data indicate that Th(VO2)2(TeO6)(H2O)2 possesses a three-dimensional structure constructed from ThO9 tricapped trigonal prisms, VO5 distorted square pyramids, VO4 distorted tetrahedra, and TeO6 distorted octahedra. Both of the vanadium polyhedra contain VO2+ vanadyl units with two short V=O bond distances. The tellurate octahedron is tetragonally distorted and utilizes all of its oxygen atoms to bond to adjacent metal centers, sharing edges with ThO9 and VO5 units, and corners with two ThO9, one VO5, and two VO4 polyhedra. Crystallographic data: Th(VO2)2(TeO6)(H2O)2, orthorhombic, space group Pbca, a = 12.6921(7), b = 11.5593(7), c = 13.0950(8) A, Z = 8 (T = 193 K). The UV-vis diffuse reflectance spectrum of Th(VO2)2(TeO6)(H2O)2 shows vanadyl-based charge-transfer absorption features. Th(VO2)2(TeO6)(H2O)2 decomposes primarily to Th(VO3)4 when heated at 600 degrees C in air.     

A new oxoanion: [IO]3- containing I(V) with a stereochemically active lone-pair in the silver uranyl iodate tetraoxoiodate(V), Ag4(UO2)4(IO3)2(IO4)2O2

The hydrothermal reaction of elemental Ag, or water-soluble silver sources, with UO3 and I2O5 at 200 degrees C for 5 days yields Ag4(UO2)4(IO3)2(IO4)2O2 in the form of orange fibrous needles. Single-crystal X-ray diffraction studies on this compound reveal a highly complex network structure consisting of three interconnected low-dimensional substructures. The first of these substructures are ribbons of UO8 hexagonal bipyramids that edge-share to form one-dimensional chains. These units further edge-share with pentagonal bipyramidal UO7 units to create ribbons. The edges of the ribbons are partially terminated by tetraoxoiodate(V), [IO4]3-, anions. The uranium oxide ribbons are joined by bridging iodate ligands to yield two-dimensional undulating sheets. These sheets help to form, and are linked together by, one-dimensional chains of edge-sharing AgO7 capped octahedral units and ribbons formed by corner-sharing capped trigonal planar AgO4 polyhedra, AgO6 capped square pyramids, and AgO6 octahedra. The [IO4]3- anions in Ag4(UO2)4(IO3)2)(IO4)2O2 are tetraoxoiodate(V), not metaperiodate, and contain I(V) with a stereochemically active lone-pair. Bond valence sum calculations are consistent with this formulation. Differential scanning calorimetry measurements show distinctly different thermal behavior of Ag4(UO2)4(IO3)2(IO4)2O2 versus other uranyl iodate compounds with endotherms at 479 and 494 degrees C. 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. DFT optimized geometry for the [IO4]3- anion is in good agreement with those measured from single-crystal X-ray diffraction studies on Ag4(UO2)4(IO3)2(IO4)2O2.     

Hydrothermal syntheses, structures, and properties of the new uranyl selenites Ag(2)(UO(2))(SeO(3))(2), M[(UO(2))(HSeO(3))(SeO(3))] (M = K, Rb, Cs, Tl), and Pb(UO(2))(SeO(3))(2)

The transition metal, alkali metal, and main group uranyl selenites, Ag(2)(UO(2))(SeO(3))(2) (1), K[(UO(2))(HSeO(3))(SeO(3))] (2), Rb[(UO(2))(HSeO(3))(SeO(3))] (3), Cs[(UO(2))(HSeO(3))(SeO(3))] (4), Tl[(UO(2))(HSeO(3))(SeO(3))] (5), and Pb(UO(2))(SeO(3))(2) (6), have been prepared from the hydrothermal reactions of AgNO(3), KCl, RbCl, CsCl, TlCl, or Pb(NO(3))(2) with UO(3) and SeO(2) at 180 degrees C for 3 d. The structures of 1-5 contain similar [(UO(2))(SeO(3))(2)](2-) sheets constructed from pentagonal bipyramidal UO(7) units that are joined by bridging SeO(3)(2-) anions. In 1, the selenite oxo ligands that are not utilized within the layers coordinate the Ag(+) cations to create a three-dimensional network structure. In 2-5, half of the selenite ligands are monoprotonated to yield a layer composition of [(UO(2))(HSeO(3))(SeO(3))](1-), and coordination of the K(+), Rb(+), Cs(+), and Tl(+) cations occurs through long ionic contacts. The structure of 6 contains a uranyl selenite layered substructure that differs substantially from those in 1-5 because the selenite anions adopt both bridging and chelating binding modes to the uranyl centers. Furthermore, the Pb(2+) cations form strong covalent bonds with these anions creating a three-dimensional framework. These cations occur as distorted square pyramidal PbO(5) units with stereochemically active lone pairs of electrons. These polyhedra align along the c-axis to create a polar structure. Second-harmonic generation (SHG) measurements revealed a response of 5x alpha-quartz for 6. The diffuse reflectance spectrum of 6 shows optical transitions at 330 and 440 nm. The trailing off of the 440 nm transition to longer wavelengths is responsible for the orange coloration of 6.     

Structural and spectroscopic trends in actinyl iodates of uranium,neptunium, and plutonium

Two neptunyl(VI) iodates, NpO(2)(IO(3))(2)(H(2)O) (1) and NpO(2)(IO(3))(2).H(2)O (2), have been prepared from the aqueous reactions of Np(V) in HCl with KIO(4) or H(5)IO(6) at 180 degrees C and have been characterized by single crystal X-ray diffraction and Raman spectroscopy. Both compounds consist of two-dimensional arrangements of pentagonal bipyramidal [NpO(7)] polyhedra with axial neptunyl, NpO(2)(2+), dioxocations. In 1, the neptunium centers are bound in the equatorial plane by four bridging iodate anions and one terminal water molecule. The iodate anions link the [NpO(7)] units into corrugated sheets that interact with one another through intermolecular IO(3)(-)...IO(3)(-) interactions as also observed in UO(2)(IO(3))(2)(H(2)O). Compound 2 is isostructural with the recently reported PuO(2)(IO(3))(2).H(2)O, where oxygen atoms from bridging iodate anions occupy the five equatorial sites around the neptunyl moieties. The iodate anions occur as both mu(2)- and mu(3)-units and link the neptunyl polyhedra into sheets. Both types of iodate anions have their stereochemically active lone-pair of electrons aligned on one side of each layer creating a polar structure. Raman spectra of 1, UO(2)(IO(3))(2)(H(2)O), and PuO(2)(IO(3))(2).H(2)O show a sequential shift of the nu(1)(AnO(2)(2+)) stretch to lower wavenumber as the atomic number of the actinide is increased. Crystallographic data: 1, orthorhombic, space group Pcan, a = 7.684(2) A, b = 8.450(2) A, c = 12.493(3) A, Z = 4; 2, orthorhombic, space group Pna2(1), a = 7.314(1) A, b = 11.631(2) A, c = 9.449(2) A, Z = 4.     

Hydrothermal preparation,structures, and NLO properties of the rare earth molybdenyl iodates,RE(MoO2)(IO3)4(OH) [RE = Nd,Sm, Eu

The reactions of RE(IO3)3 [RE = Nd, Sm, Eu] with I2O5 and MoO3 in a 1:2:2 molar ratio at 200 degrees C in aqueous media provide access to RE(MoO2)(IO3)4(OH) [RE = Nd (1), Sm (2), Eu (3)] as pure phases as determined from powder X-ray diffraction data. Single crystal X-ray diffraction experiments demonstrate that these compounds are isostructural and crystallize in the chiral and polar space group P2(1). The structures are composed of three-dimensional networks formed from eight-coordinate, square antiprismatic RE3+ cations and MoO2(OH)+ moieties that are bound by bridging iodate anions. The Mo(VI) centers are present in distorted octahedral environments composed of two cis-oxo atoms, a hydroxo group, and three bridging iodate anions arranged in a fac geometry. There are four crystallographically unique iodate anions in the structures of 1-3, one of these is actually present in the form of a IO3+1 polyhedron where a short interaction of 2.285(4) A is formed between the iodate anion and the hydroxo group bound to the Mo(VI) center. This interaction results in significant distortions of the iodate anion similar to those found in tellurites with TeO3+1 units. Two of the four iodate anions are aligned along the polar b-axis, imparting the required polarity to these compounds. Second-harmonic generation (SHG) measurements on sieved powders of 1 show a response of 350 x alpha-quartz. Crystallographic data: 1, monoclinic, space group P2(1), a = 6.9383(5) A, b = 14.0279(9) A, c = 7.0397(5) A, beta = 114.890(1) degrees, Z = 2; 2, monoclinic, space group P2(1), a = 6.9243(6) A, b = 13.963(1) A, c = 7.0229(6) A, beta = 114.681(1) degrees, Z = 2; 3, monoclinic, space group P2(1), a = 6.9169(6) A, b = 13.943(1) A, c = 7.0170(6) A, beta = 114.542(1) degrees, Z = 2.