Hydrothermal Synthesis and Structure of Neptunium(V) Oxide

Single crystals of Np{sub 2}O{sub 5} have been synthesized by low-temperature hydrothermal reaction of a (NpO{sub 2}){sup +} stock solution with natural calcite crystals. The structure of Np{sub 2}O{sub 5} was solved by direct methods and refined on the basis of F{sup 2} for all unique data collected on a Bruker X-ray diffractometer equipped with an APEX II CCD detector. Np{sub 2}O{sub 5} is monoclinic, space group P2/c, with a = 8.168(2) A, b = 6.584(1) A, c = 9.3130(2) A, {beta} = 116.01(1) deg., V = 449.8(2) A{sup 3}, and Z = 1. The structure contains chains of edge-sharing neptunyl pentagonal bi-pyramids linked into sheets through cation-cation interactions with distorted neptunyl square bi-pyramids. Additional cation-cation interactions connect the sheets into a three-dimensional framework. The formation of Np{sub 2}O{sub 5} on the surface of calcite crystals has important implications for the precipitation of isolated neptunyl phases in natural aqueous systems. (authors)

[1]  P. Burns,et al.  Cation-cation interactions in Sr5(UO2)20(UO6)2O16(OH)6(H2O)6 and Cs(UO2)9U3O16(OH)5. , 2006, Inorganic chemistry.

[2]  P. Burns,et al.  Ba(NpO2)(PO4)(H2O), its relationship to the uranophane group, and implications for Np incorporation in uranyl minerals , 2006 .

[3]  P. Burns,et al.  Crystal Structures and Magnetic Properties of NaK3(NpO2)4(SO4)4(H2O)2 and NaNpO2SO4H2O: Cation−Cation Interactions in a Neptunyl Sulfate Framework , 2006 .

[4]  Peter C. Burns,et al.  U6+ MINERALS AND INORGANIC COMPOUNDS: INSIGHTS INTO AN EXPANDED STRUCTURAL HIERARCHY OF CRYSTAL STRUCTURES , 2005 .

[5]  P. Burns,et al.  Structures and syntheses of four Np5+ sulfate chain structures: Divergence from U6+ crystal chemistry , 2005 .

[6]  N. N. Krot,et al.  Cation—cation interaction in crystalline actinide compounds , 2004 .

[7]  T. Albrecht‐Schmitt,et al.  Cation-cation interactions in neptunyl(V) compounds: hydrothermal preparation and structural characterization of NpO2(IO3) and alpha- and beta-AgNpO2(SeO3). , 2003, Inorganic chemistry.

[8]  John P. Kaszuba,et al.  The aqueous geochemistry of neptunium: Dynamic control of soluble concentrations with applications to nuclear waste disposal , 1999 .

[9]  David R. Janecky,et al.  Neptunium and Plutonium Solubilities in a Yucca Mountain Groundwater , 1998 .

[10]  C. Madic,et al.  Coordination of U4+ in the Complex U(P2W17O61)216- in Solid State and in Aqueous Solution , 1997 .

[11]  H. Nitsche,et al.  Actinide Environmental Chemistry , 1995 .

[12]  H. Nitsche.  Solubility Studies of Transuranium Elements for Nuclear Waste Disposal: Principles and Overview , 1991 .

[13]  M. Saine.  Synthèse et structure de K2U2O7 monoclinique , 1989 .

[14]  H. Nitsche.  Effects of temperature on the solubility and speciation of selected actinides in near-neutral solution , 1987 .

[15]  N. Edelstein,et al.  Solubilities and Speciation of Selected Transuranium Ions. A Comparison of a Non-Complexing Solution with a Groundwater from the Nevada Tuff Site , 1985 .

[16]  G. Choppin,et al.  Crystal structure of a neptunyl cation-cation complex (NpO2+) with mellitic acid: Na4(NpO2)2Cl12O12·8H2O , 1984 .

[17]  T. D. Chikalla,et al.  Decomposition, stoichiometry and structure of neptunium oxides , 1976 .

[18]  A. Zielen,et al.  Specific Interaction between Np(V) and U(VI) in Aqueous Perchloric Acid Media1 , 1961 .