Synthesis and structure of actinide(VII) compounds Rb3NpO4(OH)2·3H2O and Rb3PuO4(OH)2·3H2O

Actinide(VII) salts Rb₃[NpO₄(OH)₂]·3H₂O (I) and Rb₃[PuO₄(OH)₂]·3H₂O (II) were prepared as single crystals and examined by X-ray diffraction. The compounds are isostructural and crystallize in the monoclinic system, space group C2/c, Z = 4; unit cell parameters: a = 12.1544(3), b = 10.9942(2), c = 7.789(2) ?, ?? = 91.0930(11)° for I and a = 12.1254(3), b = 10.9506(2), c = 7.7699(2) ?, ?? = 90.8253(12)° for II. The main structural elements of I and II are centrosymmetrical anions [AnO₄(OH)₂]^3? forming together with water molecules, owing to strong hydrogen bonding, chains oriented along [101]. In [AnO₄(OH)₂]^3? anions, the central An(VII) atom has a tetragonal-bipyramidal oxygen surrounding. The An-O(OH) interatomic distances decrease in going from I to II owing to actinide contraction by a factor of ??2 more strongly than the An-O bond lengths in the equatorial planes of the bipyramids. The previously studied structure of Cs₃[NpO₄(OH)₂]·3H₂O (III) was refined.     

Crystal Structure of a Double Oxalate of Np(V) and Co(NH3)

The crystal structure of a dioxalate complex Co(NH₃)₆NpO₂(C₂O₄)₂·1.5H₂O was studied. The structure consists of centrosymmetrical dimeric anions [NpO₂(C₂O₄)₂] ₂ ⁶⁻ , [Co(NH₃)₆]³⁺ cations, and water molecules of crystallization. The NpO ₂ ⁺ dioxocations have close Np-O bond lengths (average 1.824 Å) and are noticeably bent (ONpO angle 175.6°). Each dioxocation in the [NpO₂(C₂O₄)₂] ₂ ⁶⁻ anion is surrounded by five oxygen atoms of three C₂O ₄ ²⁻ anions; the Np coordination polyhedra are pentagonal bipyramids sharing a common edge. __________ Translated from Radiokhimiya, Vol. 47, No. 6, 2005, pp. 495–499. Original Russian Text Copyright ? 2005 by Charushnikova, Krot, Polyakova.     

Reaction of ozone with Np(IV) and Pu(IV) oxalates in water

The reaction of the ozone–oxygen mixture with aqueous suspensions of Np(IV) and Pu(IV) oxalates was studied. Both metal cations and oxalate anions are oxidized in the process. The final products are Np(VI) and Pu(VI) hydroxides. The composition of Np(VI) hydroxide was confirmed by X-ray diffraction analysis. Oxidation of Np(IV) oxalate with oxygen leads to the accumulation of Np(V) oxalate and oxalic acid in the solution. At incomplete oxidation of Np(IV) oxalate with ozone in water, Np(V) is also accumulated. Heating considerably accelerates the ozonation. The possible reaction mechanism is briefly discussed. The Np(V) and Np(VI) ions participate in the catalytic cycle of the decomposition of oxalate ions with ozone.     

Nitrate Complexes of Neptunium(V) with Alkali Metal Cations in the Outer Sphere

Radiochemistry - Nitrate complexes of pentavalent neptunium with alkali cations in the outer sphere, with composition Li[NpO2(NO3)2]·2H2O (I), Na[NpO2(NO3)2]·2H2O (II),...     

Crystal structure of new complexes of Np(V) and Pu(V) propionates with 2,2’-bipyridine, [AnO2(C10H8N2)(OOCC2H5)(H2O)]

The crystal structure of new complexes of Np(V) and Pu(V) propionates with 2,2’-bipyridine (Bipy) was studied. The compounds are isostructural. Their crystals are built of electrically neutral complexes [AnO₂ (C₁₀H₈N₂)(OOCC₂H₅)(H₂O)] (An = Np, Pu). The equatorial surrounding of the actinyl(V) group consists of two nitrogen atoms of Bipy, two oxygen atoms of the propionateion, and oxygen atom of the water molecule. The coordination surrounding of the An(V) atom is a pentagonal bipyramid. In going from Np(V) to Pu(V), the actinide contraction is manifested in a regular decrease in the bond lengths in the pentagonal bipyramids. The water molecule in the An(V) coordination sphere forms strong hydrogen bonds with “yl” oxygen atoms of the adjacent complexes [AnO₂(Bipy)(OOCC2H₅)(H₂O)]. As a result, the complexes in the crystal are bound in infinite chains oriented along the [100] direction.     

Synthesis,Crystal Structure,and Spectral Characteristics of the Np(V) Complex with Triphenylphosphine Oxide [NpO2(PO(C6H5)3)4]ClO4

Single crystals of [NpO₂(PO(C₆H₅)₃)₄]ClO₄ were grown and the structure of this compound was studied (CAD4 diffractometer, MoK ; triclinic unit cell: a = 9.140(2), b = 13.528(3), c = 13.918(3) Å, = 97.14(3)°, = 108.17(3)°, = 91.75(3)°, space group P-1, Z = 1, V = 1618.0 ų, d _{c a l c} = 1.521 g cm^-3; R ₁ = 0.0245 for 5342 observed reflections with F ₀ > 4(F ₀), wR ₂ = 0.0677 for 5601 unique reflections, 419 refined parameters). [NpO₂(PO(C₆H₅)₃)₄]ClO₄ consists of complex cations [NpO₂(PO(C₆H₅)₃)₄]⁺ and disordered ClO_4- anions. The Np(V) atom has tetragonal-bipyramidal oxygen surrounding with coordination number (CN) 6. The NpO₂ group is linear, the O = Np = O bond angle is 180.0°, and the Np = O bond length is 1.797(2) Å. The equatorial coordination plane of the bipyramid is formed by oxygen atoms of four triphenylphosphine oxide (TPPO) molecules. The Np-O_eq bond lengths vary from 2.434(2) to 2.442(2) Å (average 2.438 Å). The O_eq-Np-O_eq bond angle is close to the right angle (88.98°). The average bond lengths in TPPO ligands are P-O 1.498, P-C 1.798, and C-C 1.376 Å; the average bond angles are O-P-O 111.12°, C-P-C 107.78°, P-C-C 120.2, and C-C-C 120.0°. The electronic absorption spectra (Shimadzu UV-3100, 900-1050 nm) and IR spectra (Specord-M80, 400-4000 cm^{- 1}) of crystalline [NpO₂(PO(C₆H₅)₃)₄] were measured in an NaCl matrix. The absence of the main characteristic absorption band of the NpO₂ ⁺ dioxocation (980 nm) in the electronic absorption spectrum suggests centrosymmetrical equatorial surrounding of the Np(V) atom. The narrow absorption band ta_{a s}(NpO₂ ⁺) in the IR spectra in the region of 860 cm^-1 suggests the absence of cation-cation interaction, and its position is consistent with a short Np-O bond length in neptunyl(V) groups.     

Synthesis of New Crystalline Pu(V) Compounds from Solutions: III. Synthesis and Study of NaPuO2C2O4·nH2O with n = 3, 1, and 0

NaPuO₂C₂O₄·3H₂O was isolated from a freshly prepared oxalate solution of Pu(VI) by reduction with a stoichiometric amount of hydrazine hydrate. Heating of the compound results in its stepwise dehydration with successive formation of the monohydrate and anhydrous salt. According to powder X-ray patterns, NaPuO₂C₂O₄·nH₂O (n = 3, 4) is isostructural to the corresponding analogs NaNpO₂C₂O₄·nH₂O. The unit cell parameters of NaNpO₂C₂O₄·H₂O and NaPuO₂C₂O₄·nH₂O (n = 3, 1) were determined. The results of the X-ray analysis and the electronic and IR spectra of the neptunyl(V) and plutonyl(V) crystalline compounds suggest the presence of cation-cation bonds in NaPuO₂C₂O₄·nH₂O (n = 1, 0). __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 105–109. Original Russian Text Copyright ? 2005 by Krot, Bessonov, Grigor’ev, Charushnikova, Makarenkov.     

Cation–Cation Interaction in the Np(V) Complex with Cyclobutanecarboxylic Acid Anions,Na[NpO2(cbc)2]

Radiochemistry - The Np(V) complex Na[NpO2(cbc)2] was isolated in the crystalline form and studied by single crystal X-ray diffraction. The coordination surrounding of the Np(1) atom is a...     

Crystal structure of mixed-valent Np(IV)/Np(V) chloride, [Np(NpO2)6(H2O)8(OH)Cl9]·H2O

A new mixed-valent Np(IV)/Np(V) chloride, [Np(NpO₂)₆(H₂O)₈(OH)Cl₉]·H₂O, was synthesized, and its crystal structure was determined. The crystals consist of NpO ₂ ⁺ and Np⁴⁺ cations, of Cl^? and OH^? anions, of coordination-bonded water molecules, and of water molecules of crystallization. The Np(V) atom, Np(1), has pentagonal bipyramidal coordination surrounding with O atoms in the apical position and with the equatorial plane formed by three Cl^? anions, O atom of the adjacent NpO ₂ ⁺ cation, and O atom of water molecule. The mutual coordination of the neptunyl(V) ions, cation-cation (CC) interaction, links the Np(1) coordination polyhedra via common vertices into rings around sixfold axes, with the Np(V)?Np(V) distance in these fragments of 4.276 Å. The ring fragments are linked with each other via common equatorial edges of the bipyramids into layers perpendicular to c-axis. The Np(IV) atom, Np(2), has coordination surrounding in the form of tricapped trigonal prism (CN 9) with the tetragonal lateral faces formed by the O atoms of the NpO ₂ ⁺ cations and the capping positions occupied by the O atoms of two water molecules and one hydroxy group. The Np(2) atoms act in CC interactions as coordination center for six NpO ₂ ⁺ ions, with the Np(IV)?Np(V) distance of 4.183 Å. The Np(2) polyhedra are arranged in the crystal between layers of the Np(1) coordination polyhedra, linking them with each other.