Crystal Structure of Double Co(NH3)6 3 + Np(V) Malonates Co(NH3)6(NpO2C3H2O4)2A·H2O (A = OH and NO3)

X-ray diffraction analysis of Co(NH₃)₆(NpO₂C₃H₂O₄)₂NO₃·H₂O (I) and Co(NH₃)₆(NpO₂· C₃H₂O₄)₂OH·H₂O (II) showed that they consist of [NpO₂C₃H₂O₄] _n ^{n -} infinite anionic chains, [Co(NH₃)₆]^{3 +} cations, NO₃ ^- (I) and OH^- (II) anions, and molecules of crystallization water. The anionic chain structure is similar to that in the known compound Co(NH₃)₆(NpO₂C₃H₂O₄)₂C₃H₃O₄. Neptunium(V) atoms occur in hexagonal-bipyramidal environment. The coordination capacity of malonate anions is 6, and they simultaneously coordinate three neptunyl(V) cations NpO₂ ⁺ in the chain.     

Synthesis and structure of dodecamolybdates of tetravalent cerium,thorium, uranium,neptunium, and plutonium

A series of isostructural compounds of the composition Na₇H[EMo₁₂O₄₂]·12H₂O, where E(IV) = Ce, Th, U, Np, or Pu, were synthesized and structurally characterized. In the [EMo₁₂O₄₂]^8– heteropolyanion (HPA), the central E(IV) atom is surrounded by six Mo₂O₉ groups, each constituted by two octahedra sharing a common face. The coordination polyhedron (CP) of the central atom is a weakly distorted icosahedron with the mean E(IV)–О bond lengths of 2.498, 2.529, 2.500, 2.490, and 2.488 Å for Ce, Th, U, Np, and Pu, respectively. In the structure of the compounds Na₇H[EMo₁₂O₄₂]·12H₂O, there are two crystallographically independent sodium atoms: Na(1) and Na(2). The oxygen surrounding of the Na(1) atom is formed by the terminal oxygen atoms of two heteropolyanions adjacent along [001], and its coordination polyhedron is an octahedron. The surrounding of the Na(2) atom (a six-vertex polyhedron) is formed by three terminal oxygen atoms of three Mo₂O₉ groups belonging to the same HPA and by three water molecules. The coordination polyhedra of the Na(2) atoms are linked with each other via common oxygen atoms of O_w(2) water molecules to form a chain “winding” around the 3₁ screw axis. The heteropolyanions and Na⁺ cations in the crystal form a framework constructed in a fashion characteristic of Dexter–Silverton type anions, with the coordination via three terminal oxygen atoms of three Mo₂O₉ groups. Excess negative charge of HPA is compensated by the proton localized on one of the six bridging O atoms. In the Mo₂O₉ doubled octahedra, the Mo–O bonds with the О atoms bonded to E(IV) and forming the edge of the common face are sensitive to the kind of the central atom.     

Synthesis and crystal structure of cesium actinide(VI) tricarbonate complexes Cs4AnO<Subscript>2</Subscript>(CO<Subscript>3</Subscript>)<Subscript>3</Subscript>·6H<Subscript>2</Subscript>O,An(VI) = U,Np, Pu

Tricarbonate complexes of hexavalent U, Np, and Pu with outer-sphere cesium cations, Cs₄AnO₂·(CO₃)₃·6H₂O, were synthesized and studied by single crystal X-ray diffraction analysis. Crystals of Cs₄AnO₂·(CO₃)₃·6H₂O consist of [AnO₂(CO₃)₃]^4– complex anions and hydrated Cs⁺ cations. The coordination polyhedron (CP) of An(VI) atoms is a distorted hexagonal bipyramid with three CO ₃ ^2– anions arranged in the equatorial plane. Four independent Cs+ cations have the coordination surrounding in the form of 11-, 10-, and 9-vertex polyhedra formed by the O atoms of CO ₃ ^2– anions, AnO ₂ ²⁺ cations, and water molecules. Six crystallographically independent water molecules in the structure of Cs₄AnO₂(CO₃)₃·6H₂O form a three-dimensional system of hydrogen bonds in which the O atoms of carbonate ions and water molecules act as proton acceptors. The “yl” oxygen atoms of AnO ₂ ²⁺ cations are not involved in hydrogen bonding. The lengths of the An–O_carb bonds in the equator of the U, Np, and Pu hexagonal bipyramids are noticeably influenced by incorporation of the O atoms of the CO ₃ ^2– anions in the coordination polyhedra of Cs⁺ ions and by involvement of these atoms in hydrogen bonding.     

Interaction of Aluminum with Am(III) and Certain REE(III) Ions in Alkaline Solutions

Precipitates prepared by addition of ammonia or NaOH into solutions containing Al and REE(III) (La, Nd) or Al and Am(III) were studied by thermogravimetry, UV-Vis and IR spectroscopy, X-ray diffraction analysis, and measurement of the dissolution rate. It was shown that the properties of the precipitates containing Al and the second element noticeably differ from the properties of straight aluminum hydroxide precipitate. In the IR spectra, new vibrational bands appear. In the electronic spectra, small shifts of Nd(III) and Am(III) absorption bands relative to the bands of the individual f-element hydroxides are observed. The rates of dissolution of the precipitates in HCl solutions noticeably differ. With increasing pH of coagulation to 13-14, a part of aluminum is captured with the precipitate. However, this fraction is small. In the precipitates obtained from 0.1-1 M NaOH, the interaction of f elements with aluminum is practically lacking.     

Synthesis of New Crystalline Pu(V) Compounds from Solutions: II. Double Pu(V) Oxalates with Co(NH<Subscript>3</Subscript>)<Subscript>6</Subscript><Superscript>3+</Superscript> Ions in the Outer Sphere

Crystalline compounds of the general composition Co(NH³)⁶PuO₂(C₂O₄)²·nH₂O (n = 2, 3, 5) were isolated from freshly prepared neutral oxalate solutions of Pu(V) by addition of Co(NH₃)₆³⁺ ions. These compounds are fairly stable in storage in air and poorly soluble in water. Previously unknown double Np(V) oxalates Co(NH₃)₆NpO₂(C₂O₄)·nH₂O (n = 2, 5) were also synthesized and studied. All the compounds of Pu(V) and Np(V) of the same composition are mutually isostructural. The behavior of these compounds at heating was studied, and their IR spectra were measured. The optical spectra of new Np(V) compounds were measured.     

Variation of the An-O bond lengths in NaAnO2(OOCCH3)3 and (NH4)4AnO2(CO3)3, An = U(VI), Np(VI), and Pu(VI)

For studying actinide contraction in triacetate and tricarbonate complexes of hexavalent actinides in the series U-Np-Pu, single crystals were prepared and crystal structures of NaPuO₂(OOCCH₃)₃ and (NH₄)₄. AnO₂(CO₃)₃ (An = Np, Pu) were determined. These compounds are isostructural with NaAnO₂(OOCCH₃)₃ (An = U, Np) and (NH₄)₄UO₂(CO₃)₃ studied previously. The coordination surrounding of An(VI) is a distorted hexagonal bipyramid. The actinide contraction in An(VI) triacetate and tricarbonate complexes is manifested in shortening of the bond lengths in the AnO ₂ ²⁺ cation in the series U-Np-Pu. In triacetate complexes NaAnO₂(OOCCH₃)₃, the average bond lengths in AnO ₂ ²⁺ decrease by approximately 2.3% in passing from Np(VI) to Pu(VI). In tricarbonate complexes (NH₄)₄AnO₂(CO₃)₃, the bond lengths in AnO ₂ ²⁺ decrease by approximately 0.7% in passing from U to Np and by approximately 0.4% in passing from Np to Pu. The actinide contraction is less noticeable in the equatorial planes of the bipyramids. The lengths of the An-O bonds with oxygen atoms located around actinyl groups depend on the ligand nature and also on participation of oxygen atoms in the coordination with Na⁺ cations in the triacetate complexes or in hydrogen bonds with NH ₄ ⁺ ions in the tricarbonate complexes. Original Russian Text ? I.A. Charushnikova, N.N. Krot, Z.A. Starikova, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 6, pp. 495–499.     

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.     

Crystal structure of a complex of Pu(VI) nitrate with triphenylphosphine oxide, [PuO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>(OP(C<Subscript>6</Subscript>H<Subscript>5</Subscript>)<Subscript>3</Subscript>)<Subscript>2</Subscript>]

Single crystals of [PuO₂(NO₃)₂(TPPO)₂] (TPPO = OPPh₃) isostructural to the related compounds of uranyl and neptunyl were isolated, and the structure of this complex was determined. Contrary to the complexes [AnO₂(TPPO)₄](ClO₄)₂ studied previously, the interatomic distances and volumes of coordination polyhedra of An in these compounds somewhat decrease in the series U-Np-Pu. This difference was attributed to a change in the number of TPPO ligands in the compounds and weakening of their interaction with oxygen atoms of the AnO ₂ ²⁺ groups in passing from [AnO₂(TPPO)₂](ClO₄)₂ to [AnO₂(No₃)₂(TPPO)₂].     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

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.