N. N. Krot

Dimeric dioxocations, (NpO2+)2, in the structure of bis­(μ-2-fluoro­benzoato-κ2O:O′)di-μ-oxo-bis­[(2,2′-bipyridine-κ2N,N′)oxoneptunium(V)]

The centrosymmetric title compound, [(NpO2)2(C7H4FO2)2(C10H8N2)2], contains the dimeric dioxocation (NpO2+)2 in which two of the four O atoms bridge the Np atoms. Two bidentate chelating-bridging fluoroxadbenzoate anions link the Np atoms of the dimeric cation. The N atoms of the 2,2′-bipyridine ligand occupy two positions in the equatorial plane of the distorted pentaxadgonal bipyramid, forming a five-membered metallacycle.

Novel heptavalent actinide compounds: tetrasodium dihydroxidotetraoxidoneptunate(VII) hydroxide dihydrate and its plutonium analogue

The title compounds, Na(4)[NpO(4)(OH)(2)]OH.2H(2)O and Na(4)[PuO(4)(OH)(2)]OH.2H(2)O, are isostructural and isomorphous, and contain complex [AnO(4)(OH)(2)](3-) anions (Ac is an actinide) in the form of distorted tetragonal bipyramids, Na(+) cations, crystallization water molecules and outer-sphere OH groups. The complex [AnO(4)(OH)(2)](3-) anions occupy general positions and the coordinated OH groups deviate significantly from a centrosymmetric relative orientation. The [AnO(4)(OH)(2)](3-) anions exhibit anisotropic actinide contraction; the shortening of the An-O(hydroxide) bonds on going from Np to Pu is greater than that of the AnO(4) groups.

Tricaesium dihydroxotetra­oxoplutonate(VII) trihydrate

The title compound, Cs3[PuO4(OH)2]·3H2O, contains centrosymmetric [PuO4(OH)2]3− anions. The Pu atom in this anion has an almost ideal tetraxadgonal bipyramidal oxygen environment. The Pu—O distances are 1.8889u2005(14) and 1.8685u2005(15)u2005A in the PuO4 group and 2.3726u2005(15)u2005Au2005to the OH groups. In the isostructural NpVII compound, Cs3[NpO4(OH)2]·3H2O, the Np—O distances in the NpO4 group are nearly the same as the Pu—O distances here, but the distances to the OH groups are about 0.04u2005A longer.

Development of Alkaline Oxidative Dissolution Methods for Chromium (III) Compounds Present in Hanford Site Tank Sludges

The high-level radioactive waste sludge in the underground storage tanks at the Hanford Site contains various chromium(III)solid phases. Dissolution and removal of chromium from tank waste sludges is desirable prior to high-level waste vitrification because increased volume is required to incorporate the residual chromium. Unfortunately, dissolution of chromium from the sludge to form Cr(OH){sub 4}{sup {minus}} through treatment with heated NaOH solution (also used to dissolve aluminum phases and metathesize phosphates to sodium salts) generally has been unsuccessful in tests with both simulated and genuine Hanford waste sludges. Oxidative dissolution of the Cr(III) compounds to form soluble chromate has been proposed as an alternative chromium solid phase dissolution method and results of limited prior testing have been reported.

Reinvestigation of trisodium dihydroxidotetraoxidoneptunate(VII)

The title compound, Na3[NpO4(OH)2], contains complex [NpO4(OH)2]3− anions, having a distorted tetraxadgonal bixadpyramidal form. The Np atom occupies a special position on a twofold axis. The Np—O distances are 1.8981u2005(13) and 1.9012u2005(12)u2005A in the NpO4 group and 2.3145u2005(11)u2005A to the OH groups. The main distortion of the tetraxadgonal bipyramid is a shift of the O atoms of the OH groups from ideal positions, the corresponding O—Np—O angle being 173.80u2005(7)°. The orientation of the OH groups differs significantly from the centrosymmetric arrangement found in other compounds with [NpO4(OH)2]3− anions.

Reinvestigation of tris­odium dihydroxido­tetra­oxidoneptunate(VII) dihydrate

The title compound, Na3[NpO4(OH)2]·2H2O, contains distorted tetragonal–bipyramidal centrosymmetric [NpO4(OH)2]3− complex anions. The Np—O distances are 1.8975u2005(7) and 1.8891u2005(7)u2005Å in the NpO4 group and 2.3451u2005(7)u2005Å to the OH group. Both Na atoms (one in a general position, the second in a special position on an inversion centre) have a distorted octahedral oxygen environment.

Behavior of Anhydrous Uranyl Acetate at Heating in CH3CN. Crystal Structures of New Uranyl Acetates

Finely crystalline anhydrous uranyl acetate UO2(OOCCH3)2 (I) was prepared by recrystallization from acetonitrile at 140-145°C. Its X-ray diffraction pattern was indexed in the monoclinic system: a = 7.4311(5), b = 12.6622(9), c = 4.1985(2) Å, β = 92.01(1)°, V = 394.8(2) Å3, Z = 2, ρcalc = 3.265 g cm-3; probable space group C2, Cm, or C2/m. Presumably, in structure I, the coordination polyhedra of U atoms (hexagonal bipyramids), sharing common equatorial edges, are linked to form infinite chains via bridging oxygen atoms of acetate ions. Under the same conditions, the presence of water in acetonitrile results in formation of crystalline [UO2(OOCCH3)2·HOOCCH3] (II) and (NH4)2[(UO2)5(μ3-O)2(OOCCH3)8] (III), whose composition and structure were determined by single crystal X-ray analysis. In the structure of II, one acetate ion is bidentate chelate and the other, bidentate bridging; the coordination number (CN) of the U atom is 7. In the structure of III, there are three crystallographically independent U atoms with CN 7 and 8. The coordination polyhedra of the U atoms, sharing common edges and vertices, are linked via bridging O2- ions and oxygen atoms of acetate ions.

Diacetatodiaqua­dioxouranium(VI) acetic acid disolvate

The coordination polyhedron of the U atom in the title compound, [U(C2H3O2)2O2(H2O)2]·2CH3COOH, is a distorted hexaxadgonal bipyramid, with the equatorial positions occupied by four O atoms of two bidentate-chelating acetate anions and two O atoms of coordinated water molxadecules. The complex lies on an inversion centre. A two-dimensional network of hydrogen bonds is present in the crystal structure.

Synthesis, Crystal Structure, and Absorption Spectra of Neptunium(V) Di(acetamido) Nitrate (NpO2)(NO3)(CH3CONH2)2

The crystal structure of (NpO2)(NO3)(CH3CONH2)2 was determined. The crystallographic data were are follows: a = 5.766(3) Å, b = 13.154(5) Å, c = 14.027(6) Å, V = 1064.0(8) Å3, space group Pnma, Z = 4, ρcalcd = 2.804 g/cm3, R = 0.046, Rw = 0.102. The coordination polyhedron of Np is a pentagonal bipyramid whose equatorial positions are occupied by the oxygen atoms of the neighboring NpO2 group, acetamide molecules, and of the nitrate ion. The IR and electronic absorption spectra of the compound were measured.

Catalytic Decomposition of Organic Anions in Alkaline Radioactive Waste: 1. EDTA Oxidation

Decomposition of ethylenediaminetetraacetate in alkaline solutions with H2O2, Na2S2O8, NaClO, and NaBrO was studied titrimetrically. EDTA is oxidized in solutions heated above 60°C in the presence of cobalt salts at stepwise addition of excess H2O2. The reaction between persulfate and EDTA has an induction period decreasing with increasing NaOH concentration and temperature and with decreasing initial EDTA content or with adding AgNO3, K4Fe(CN)6, or NaNO2. The process involves thermal dissociation of the persulfate ions into radical ions and the subsequent development of a chain reaction. Hypochlorite ions oxidize EDTA in 0.5-5.0 M NaOH at 25-60°C. The process efficiency can be improved by fractional addition of the oxidant in the presence of Co(II) or Ni(II) salts. EDTA is oxidized in alkaline solutions with hypobromite ions only on heating to 95°C. Salts of Co(II), Ni(II), and Cu(II) accelerate the process.