New data on sodium salts of Np(VII) and Pu(VII)

A new Pu(VII) compound, Na₃[PuO₄(OH)₂]·2H₂O, was prepared by X-ray diffraction analysis, and its structure was studied. To reveal the character of actinide contraction in going from Np(VII) to Pu(VII), the geometric parameters of the tetragonal-bipyramidal surrounding of Pu(VII) in the [PuO₄(OH)₂]³⁻ anion were compared with those of Np(VII) in the previously studied isostructural compound Na₃[NpO₄(OH)₂]·2H₂O. To reveal the specific feature of hydrogen bonding in crystals of the general composition Na₃[NpO₄(OH)₂]·nH₂O (n = 0, 2, 4), the structure of the compound Na₃[NpO₄(OH)₂]·4H₂O studied previously by the photographic method was refined. The effect of hydrogen bonds on the geometric characteristics of the coordination polyhedra of the Np and Na atoms was considered.     

Synthesis and single crystal X-ray diffraction study of U(VI), Np(VI), and Pu(VI) perchlorate hydrates

The compounds [AnO₂(H₂O)₅](ClO₄)₂ (An = Np, Pu) and [NpO₂(ClO₄)₂(H₂O)₃] were prepared as single crystals, which were studied by X-ray diffraction at 100 K. The structural type at room temperature was determined. The low-temperature modification of [UO₂(H₂O)₅](ClO₄)₂ was found and structurally studied. The coordination polyhedra in [AnO₂(H₂O)₅]²⁺ are weakly distorted pentagonal bipyramids with averaged interatomic distances An-O of 1.754, 1.744, and 1.732 Å in the “yl” groups and of 2.415, 2.416, and 2.409 Å in the equatorial planes for U, Np, and Pu, respectively. Hence, in the complex cations [AnO₂(H₂O)₅]²⁺ the actinide contraction is manifested only in regular shortening of the An-O interatomic distances in the “yl” groups. The compound [NpO₂(ClO₄)₂(H₂O)₃], isostructural to its known uranyl analog, appeared to be the first, proved by single crystal X-ray diffraction, example of a compound with coordination interaction between the perchlorate ion and the neptunyl(VI) cation.     

Synthesis and study of new complex Pu(V) and Np(V) acetates

Double Pu(V) and Np(V) acetates of the compositions BaPuO₂Ac₃·2H₂O and SrAnO₂Ac₃·3H₂O with An = Pu and Np were synthesized in a well-crystallized form. In the dry state the compounds are stable in prolonged storage and are not hygroscopic. The plutonyl(V) and neptunyl(V) salts of the similar composition are isostructural. The IR spectra of the compounds were measured, and their behavior in heating was studied.     

Synthesis and study of Np(V) and Pu(V) benzoate complexes with bipyridine

Heteroligand compounds AnO₂(bipy)OOCC₆H₅ (An = Np, Pu; bipy = α,α-bipyridine, C¹⁰H⁸N²) were synthesized and studied. It follows from powder X-ray patterns that these compounds are isostructural. Their unit cell parameters, determined by indexing of the powder X-ray patterns, are as follows: a = 9.2162 (7), b = 10.2339(8), c = 17.4083(17) Å, and β = 96.48(1)° for Np and a = 9.1983(18), b = 10.2052(18), c = 17.370(3) Å and β = 96.51(1)° for Pu. The compounds crystallize in the monoclinic system space group P2₁/n, Z = 4. The electronic absorption spectra of crystalline compounds suggest pentagonal-bipyramidal surrounding of the central atom and the prescence of cation-cation bonds with AnO ₂ ⁺ ions acting as monodentate ligands with respect to each other. The IR spectra of the compounds were recorded, and their thermal behavior in air was studied.     

Synthesis and properties of Np(VI) and Pu(VI) monophthalates

Neptunium(VI) and plutonium(VI) monophthalates were prepared and characterized. The complexes AnO₂ (COO)₂C₆H₄ 2H₂O were isolated from cold solutions, and AnO₂ (COO)₂C₆H₄ 1.33H₂O, from hot solutions. NpO₂ (COO)₂C₆H₄ b. 2H₂O and PuO₂ (COO)₂C₆H₄ 2H₂O crystalize in the triclinic and monoclinic systems, respectively. The complexes AnO₂(COO)₂C₆H₄ 1.33H₂O are isostructural and crystallize in the rhombohedral system. The thermal behavior of these complexes was studied. Their IR and electronic absorption spectra were recorded. The properties of these complexes were compared to those of known U(VI) monophthalates.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 389–395.Original Russian Text Copyright © 2004 by Krot, Bessonov, Grigorev, Charushnikova, Makarenkov.     

Synthesis and structural features of Np(VI) and Pu(VI) isophthalates

New An(VI) isophthalate complexes [PuO₂(C₈H₄O₄)] (I), Cs₂[(NpO₂)₂(C₈H₄O₄)₃]·4H₂O (II), [H₃O]₂[(NpO₂)₂(C₈H₄O₄)₃]·nH₂O (III), and [H₃O][NpO₂(C₈H₄O₄)(C₈H₅O₄)]·2H₂O (IV) with the An(VI): Lig ratios of 1: 1 (I), 1: 1.5 (II, III), and 1: 2 (IV) were synthesized and studied by single crystal X-ray diffraction. In complex I, the coordination polyhedron of the Pu(1) atom is a pentagonal bipyramid whose equatorial plane is formed by the oxygen atoms of four [C₈H₄O₄]^2– anions. The coordination capacity of the ligand in complex I is maximal among compounds I–IV and equal to 5, with each [C₈H₄O₄]^2– anion binding four PuO₂²⁺ cations into electrically neutral layers. In the structures of II and III, the coordination polyhedra of the Np(1) atoms are hexagonal bipyramids whose equatorial planes are formed by the oxygen atoms of three [C₈H₄O₄]^2– anions. Two crystallographically independent [C₈H₄O₄]^2– anions exhibit the coordination capacity equal to 4, each binding two NpO₂²⁺ cations in the chelate fashion. As a result, doubled anionic layers are formed in the crystals of II and III. Outer-sphere cations influence the packing of doubled layers in the crystals: Complex II crystallizes in the monoclinic system, and complex III, in the orthorhombic system. In the structure of IV, the coordination polyhedron of the Np(1) atom is a hexagonal bipyramid whose equatorial plane is formed by the oxygen atoms of two [C₈H₄O₄]^2– anions and one [C₈H₅O₄]^– anion. The crystallographically independent bridging anion [C₈H₄O₄]^2– exhibits the coordination capacity equal to 4 and binds in the chelate fashion two NpO₂²⁺ cations to form chains, and the independent hydrogen isophthalate anion [C₈H₅O₄]^– binds one neptunyl(VI) cation in the chain in the chelate fashion, exhibiting the coordination capacity equal to 2.     

Synthesis and properties of complexes of Np(V) and Pu(V) benzoates with phenanthroline

Complexes of 1,10-phenanthroline (phen) with Np(V) and Pu(V) benzoates of the compositions NpO₂(phen)(OOCC₆H₅) and PuO₂(phen)(OOCC₆H₅) were synthesized. A powder X-ray diffraction study showed that these compounds, depending on the preparation conditions, exist in the form of two phases having essentially the same composition but different powder patterns. The phases isolated from hot (70–100°C) solutions are isostructural with the previously described complexes AnO₂(bipy)(OOCC₆H₅) (An = Np and Pu, bipy = 2,2′-bipyridine), i.e., in their structure there are dimeric (AnO₂) ₂ ²⁺ cations formed by mutual coordination of two AnO ₂ ⁺ ions via “yl” oxygen atoms. The compounds AnO₂(phen)(OOCC₆H₅) prepared by slow crystallization in the cold or at weak (up to 45°C) heating are isostructural with each other but appreciably differ in the structure from the high-temperature phases. The electronic absorption spectra of the compounds and their thermal behavior were examined.     

Synthesis and study of Np(V) sesquioxalates

Neptunium(V) at its relatively high concentrations in oxalate solutions forms, along with the mono-and bioxalate complexes, the intermediate binuclear anion (NpO₂)₂(C₂O₄) ₃ ^4? . This anion gradually crystallizes from cold aqueous-ethanol solutions in the form of the compound Na₄(NpO₂)₂(C₂O₄)₃ · 6H₂O, and from hot aqueous-ethanol solutions, in the form of a lower hydrate, Na₄(NpO₂)₂(C₂O₄)₃ · 2H₂O. Both compounds were characterized by powder X-ray diffraction and by electronic absorption and IR spectra. The thermal behavior of the hexahydrate in air was studied. Attempts to prepare the related crystalline compounds M₄(NpO₂)₂(C₂O₄)₃ · nH₂O with M = Li or NH₄ failed.     

A spectrophotometric study of the reduction of Pu(VIII) and Pu(VII) in alkaline solutions

The reduction of Pu(VIII) with water in ozonized 15 and 6 MNaOH solutions after termination of the ozone bubbling was studied by spectrophotometry. Kinetic curves reflecting the whole set of processes that occur in NaOH solutions of different concentrations were obtained. Calculations performed with the experimental curves made it possible to construct the kinetic curves describing the behavior of plutonium in higher oxidation states in solution and to obtain the individual absorption spectra of Pu(VII) and Pu(VIII). The processes occurring in ozonized solutions of Pu(VI) in 6 and 15 M NaOH after termination of the ozone bubbling were found to occur by different mechanisms, yielding in 4 days Pu(VI) and Pu(V), respectively.     

Kinetics of Redox Reactions of U, Pu, and Np in TBP Solutions: VII. Kinetics of Reduction of Pu(IV) and Np(VI) with Butanal Oxime in Undiluted TBP

The kinetics of reduction of Pu(IV) and Np(VI) with butanal oxime in undiluted TBP containing HNO₃ was studied spectrophotometrically. In the range [HNO₃] = 0.08-0.75 M the rate of Pu(IV) reduction is described by the equation -d[Pu(IV)]/dt = k[Pu(IV)]²[C₃H₇CHNOH]/{[Pu(III)][HNO₃]²} with the rate constant k = 0.068±0.017 mol l^-1 min^-1 at 20°C. The kinetic equation of the reduction of Np(VI) to Np(V) in the range [HNO₃] = 0.01-0.27 M is -d[Np(VI)]/dt = k[Np(VI)][C₃H₇CHNOH][H₂O]²/[HNO₃]0.5, where k = 0.058±0.007 l2.5 mol-2.5 min^-1 at 25°C, and the activation energy is 79±9 kJ mol^-1.     

Synthesis and Structure of U(VI), Np(VI), and Pu(VI) Phenylacetates

Radiochemistry - Phenylacetates [AnO2(C6H5CH2COO)2], where An = U (I), Np (II), or Pu (III), were synthesized and studied by single crystal X-ray diffraction. Compounds I–III are...     

X-ray photoelectron study of murataite ceramics containing Th, U, Np, and Pu

The structure of X-ray photoelectron spectra of actinide-containing (An = Th, U, Np, and Pu) murataite ceramic (Ti-Mn-Ca-An-Zr-Al-Fe-O) samples as potential matrices for immobilization of actinide radioactive waste was studied. The elemental composition of the sample surface was analyzed, and comparison with the calculated data for the bulk of the samples was made. The binding energies of the An4f electrons and the parameters of the fine structure of their X-ray photoelectron spectra were determined. These parameters were compared with the corresponding values for the dioxides.     

Synthesis and study of complexes of Pu(V) and Np(V) formates and acetates with α,α′-bipyridine

Crystalline NpO₂OOCH·C₁₀H₈N₂·nH₂O and NpO₂OOCCH₃·C₁₀H₈N₂·H₂O were synthesized by the addition of a small excess of α,α′-bipyridine to neutral Np(V) formate and acetate solutions. In the wet state and after drying in air, these compounds have essentially different powder X-ray patterns. In the dry state, these compounds are monohydrates. In formate solutions with addition of α,α′-bipyridine, Pu(V) behaves similarly, whereas attempts to prepare the related Pu(V) acetate complexes failed. The Np(V) and Pu(V) compounds AnO₂OOCCH₃·C₁₀H₈N₂·nH₂O are isostructural. According to the results of spectrophotometric studies, the coordination polyhedron of the central atom in all the compounds studied is a pentagonal bipyramid. The IR spectra were recorded and the thermal behavior of the compounds was studied.     

Synthesis and Structure of U(VI), Np(VI), and Pu(VI) 2-Fluorobenzoates

The compounds NH₄[AnO₂(C₆H₄FCOO₃], where An = U (I), Np (II), or Pu (III), CgH₄COO^? is the 2-fluorobenzoate anion, were synthesized and studied by single crystal X-ray diffraction. Compounds I–III are isostructural and crystallize in the cubic system, space group P2₁3, Z = 4. The main structural units of I–III are mononuclear complexes [AnO₂(C₆H₄COO)₃]^? belonging to crystal-chemical group AB₃¹ (A = AnO₂²⁺, B⁰¹ = C₆H₄FCOO^?). The actinide contraction in the structures of I–III is manifested in a regular decrease in the lengths of the An=0 bonds in the AnO₂²⁺ cations and in the volumes of the Voronoi-Dirichlet polyhedra (VDPs) of the An atoms in the series U-Np-Pu. The intermolecular interactions in crystal structures of I–III were analyzed by the method of molecular VDPs.

     

Synthesis and study of Pu(V) formates

New double formates MPuO₂(OOCH)₂ (M = NH₄ and K) were isolated from neutral aqueous solutions. These compounds are isostructural to the Np(V) analogs. The unit cell parameters of the salts were determined by powder X-ray diffraction. The symmetry of the crystal lattice decreases from rhombic to monoclinic in going from the ammonium to the potassium salt. The electronic absorption spectra were recorded and analyzed. The thermal behavior of the Pu(V) compounds was studied. Their IR spectra were recorded. The hexagonal bipyramidal oxygen surrounding in the solid compounds was determined. Preparation of simple Pu(V) formates was attempted. The reasons preventing preparation of these compounds were analyzed.     

Behavior of Pu(VI) and Np(VI) in malonate solutions

Complexation of PuO ₂ ²⁺ in solutions containing malonate anions C₃H₂O ₄ ^2? (L^2?) is studied by spectrophotometry. Mono-and bimalonate complexes are formed. The monomalonate complex was isolated as PuO₂L · 3H₂O. It is isostructural to UO₂L · 3H₂O and forms rhombic crystals with the unit cell parameters a = 9.078(2), b = 7.526(2), and c = 6.2005(15) Å, space group Pmn2₁. The electronic absorption spectrum of the monomalonate complex is characterized by a strong band at 843 nm. In malonate solutions, Pu(VI) is slowly reduced to the pentavalent state even in the cold. The reduction of Np(VI) is considerably faster and more sensitive to increasing temperature. Some kinetic features of the reduction are discussed.     

Synthesis and X-ray diffraction study of radium plumbate

Previously unknown mixed oxide RaPbO₃ was prepared by thermal decomposition of a mixture of radium and lead carbonates. An X-ray diffraction study showed that radium plumbate crystallizes in the cubic perovskite structural type. The unit cell parameter (a = 4.303 Å) and crystallographic density (ρ = 10.42 g cm^?3) were determined. Formation of a new compound, RaPtO_3?x , upon sintering of mixtures of radium and lead carbonates at 800°C in a platinum crucible was detected. A similar barium compound can be formed upon calcination of barium compounds in platinum vessels in air.     

Disproportionation of Pu(VI) and reproportionation of Pu(V), Pu(VII) in aqueous alkali solutions

Disproportionation of Pu(VI) and reproportionation of Pu(V) and Pu(VII) in aqueous NaOH solutions was studied. With an increase in the NaOH concentration in solution over 7.5 M, the equilibrium of the reaction Pu(VII) + Pu(V)?2Pu(VI) is gradually shifted toward formation of Pu(V) and Pu(VII) as products of Pu(VI) disproportionation, and at [NaOH] + 13 M, Pu(VI) disproportionates virtually completely. At [NaOH] + 7.5 M, the equilibrium of the above reaction is shifted toward formation of Pu(VI). Based on the experimental data, the equilibrium constants of the reaction at various alkali concentrations in the solution and the formal potentials ?_{f[Pu(VII)/Pu(VI)]} were calculated. The data obtained showed that, with respect to reduction with water, Pu(VII) is stable in aqueous alkali solutions at NaOH concentrations exceeding 7.5 M.     

Synthesis and X-ray diffraction study of uranyl malonate monohydrate

Uranyl malonate monohydrate [UO₂(mal)(H₂O)], where mal^2– is malonate ion, was synthesized and studied by single crystal X-ray diffraction. The main structural units are electrically neutral [UO₂(mal)(H₂O)] layers belonging to crystal-chemical group AQ²¹М¹ (A = UO ₂ ²⁺ , Q²¹ = mal^2–, M¹ = H₂O) of uranyl complexes. Specific features of the packing of the uranium-containing complexes are discussed on the basis of Voronoi–Dirichlet tessellation. The structural differences between the monohydrate synthesized and the known uranyl malonate trihydrate are considered.     

Synthesis and high-temperature X-ray diffraction study of thorium orthosilicate

The α-ThSiO₄ phase, a synthetic analog of thorite mineral, was prepared by hydrothermal synthesis and converted to β-ThSiO₄, a synthetic analog of huttonite mineral. The temperature dependences of the unit cell parameters were studied by high-temperature X-ray diffraction, and the thermal expansion coefficients of the compounds were determined.