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The interaction of Np(v) with borate was investigated in 0.1-5.0 M NaCl and 0.25-4.5 M MgCl2 solutions with 7.2 ≤ pHm ≤ 10.0 (pHm = -log[H+]) and 0.004 M ≤ [B]tot ≤ 0.16 M. Experiments were performed under an Ar-atmosphere at T = (22 ± 2) °C using a combination of under- and oversaturation solubility experiments, NIR spectroscopy, and extensive solid phase characterization. A bathochromic shift (≈5 nm) in the Np(v) band at λ = 980 nm indicates the formation of weak Np(v)-borate complexes under mildly alkaline pHm-conditions. The identification of an isosbestic point supports the formation of a single Np(v)-borate species in dilute MgCl2 systems, whereas a more complex aqueous speciation (eventually involving the formation of several Np(v)-borate species) is observed in concentrated MgCl2 solutions. The solubility of freshly prepared NpO2OH(am) remained largely unaltered in NaCl and MgCl2 solutions with [B]tot = 0.04 M within the timeframe of this study (t ≤ 300 days). At [B]tot = 0.16 M, a kinetically hindered but very significant drop in the solubility of Np(v) (3-4 log10-units, compared to borate-free systems) was observed in NaCl and dilute MgCl2 solutions with pHm ≤ 9. The drop in the solubility was accompanied by a clear change in the colour of the solid phase (from green to white-greyish). XRD and TEM analyses showed that the amorphous NpO2OH(am) "starting material" transformed into crystalline solid phases with similar XRD patterns in NaCl and MgCl2 systems. XPS, SEM-EDS and EXAFS further indicated that borate and Na/Mg participate stoichiometrically in the formation of such solid phases. Additional undersaturation solubility experiments using the newly formed Na-Np(v)-borate(cr) and Mg-Np(v)-borate(cr) compounds further confirmed the low solubility ([Np(v)]aq ≈ 10-6-10-7 M) of such solid phases in mildly alkaline pHm-conditions. The formation of these solid phases represents a previously unreported retention mechanism for the highly mobile Np(v) under boundary conditions (pHm, [B]tot, ionic strength) of relevance to certain repository concepts for nuclear waste disposal.

We report on synthesis and characterization of the compounds A

Magnetic susceptibility, electrical resistivity, and heat capacity results are reported for the chemical substitution series URu

Sulfur dioxide reacts with [PPN](2)[MFe(3)(CO)(14)] (M = Cr, Mo, W) (PPN = bistriphenylphosphonium iminium) to produce [PPN](2)[Fe(3)(CO)(9)(mgr;(3),eta(2)-SO(2))] (I) and [PPN](2)[Fe(3)(CO)(8)(mgr;-SO(2))mgr;(3)-S] (II), which were characterized by infrared spectroscopy, (13)C NMR, and X-ray crystallography. Further reaction of I with sulfur dioxide results in the formation of II in 48% yield. Reaction of SO(2) with [PPN](2)[Fe(4)(CO)(13)] yields [PPN](2)[Fe(2)(CO)(6)(mgr;-SO(2))(2)] (III) which was characterized by infrared spectroscopy, (13)C NMR, mass spectrometry, and X-ray crystallography. One equivalent of sulfur dioxide with [PPN](2)[MFe(3)(CO)(14)C] (M = Cr, W) produces [PPN](2)[Fe(3)(CO)(8)(mgr;-SO(2))(mgr;(3)-CCO)] (IV), which on further reaction with SO(2) gives the known cluster [PPN](2)[Fe(3)(CO)(7)(mgr;-SO(2))(2)(mgr;(3)-CCO)] (V). An excess of sulfur dioxide with [MFe(3)(CO)(n)()C](x)()(-) (M = Cr, W: n =13, x = 2; M = Rh: n = 12, x = 1; M = Mn: n = 13, x = 1) produced V as the only identified product. Crystallographic data for I.0.5CH(2)Cl(2): monoclinic, Cc (no. 9), a = 29.7648(3) Å, b = 14.6496(1) Å, c = 21.7620(3) Å, beta = 123.397(1) degrees, V = 7922.3 Å(3); Z = 4. Crystallographic data for III.NCCH(3): monoclinic P2(1) (no. 4), a = 10.0295(5) Å, b = 26.356(1) Å, c = 14.1032(7) Å, beta = 94.691 degrees, V = 3715.6(3) Å(3); Z = 4.

The alkali metal and alkaline-earth metal uranyl iodates K(2)[(UO(2))(3)(IO(3))(4)O(2)] and Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) have been prepared from the hydrothermal reactions of KCl or BaCl(2) with UO(3) and I(2)O(5) at 425 and 180 degrees C, respectively. While K(2)[(UO(2))(3)(IO(3))(4)O(2)] can be synthesized under both mild and supercritical conditions, the yield increases from5% to 73% as the temperature is raised from 180 to 425 degrees C. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), however, has only been isolated from reactions performed in the mild temperature regime. Thermal measurements (DSC) indicate that K(2)[(UO(2))(3)(IO(3))(4)O(2)] is more stable than Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) and that both compounds decompose through thermal disproportionation at 579 and 575 degrees C, respectively. The difference in the thermal behavior of these compounds provides a basis for the divergence of their preparation temperatures. The structure of K(2)[(UO(2))(3)(IO(3))(4)O(2)] is composed of [(UO(2))(3)(IO(3))(4)O(2)](2)(-) chains built from the edge-sharing UO(7) pentagonal bipyramids and UO(6) octahedra. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) consists of one-dimensional [(UO(2))(2)(IO(3))(2)O(2)](2)(-) ribbons formed from the edge sharing of distorted UO(7) pentagonal bipyramids. In both compounds the iodate groups occur in both bridging and monodentate binding modes and further serve to terminate the edges of the uranium oxide chains. The K(+) or Ba(2+) cations separate the chains or ribbons in these compounds forming bonds with terminal oxygen atoms from the iodate ligands. Crystallographic data: K(2)[(UO(2))(3)(IO(3))(4)O(2)], triclinic, space group P_1, a = 7.0372(5) A, b = 7.7727(5) A, c = 8.9851(6) A, alpha = 93.386(1) degrees, beta = 105.668(1) degrees, gamma = 91.339(1) degrees, Z = 1; Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), monoclinic, space group P2(1)/c, a = 8.062(4) A, b = 6.940(3) A, c = 21.67(1), beta= 98.05(1) degrees, Z = 4.