Aryloxide anions can form outer sphere complexes with metals as electropositive as uranium

2009 ◽  
pp. 7342 ◽  
Author(s):  
William J. Evans ◽  
Justin R. Walensky ◽  
Joseph W. Ziller
Keyword(s):  
Outer Sphere ◽  
Outer Sphere Complexes

Surface Complexation of Neptunium(V) with Goethite

2006 ◽  
Vol 985 ◽  
Author(s):  
James L Jerden ◽  
A Jeremy Kropf
Keyword(s):  
Sodium Chloride ◽  
Sodium Silicate ◽  
Outer Sphere ◽  
Distribution Coefficients ◽  
Batch Adsorption ◽  
Inner Sphere ◽  
Show Evidence ◽  
X Ray Absorption ◽  
Outer Sphere Complexes ◽  
Inner Sphere Complexes

AbstractBatch adsorption experiments in which neptunium bearing solutions were reacted with goethite (alpha-FeOOH) have been performed to study uptake mechanisms in sodium chloride and calcium-bearing sodium silicate solutions. This paper presents results identifying and quantifying the mechanisms by which neptunium is adsorbed as a function of pH and reaction time (aging). Also presented are results from tests in which neptunium is reacted with goethite in the presence of other cations (uranyl and calcium) that may compete with neptunium for sorption sites. The desorption of neptunium from goethite has been studied by resuspending the neptunium-loaded goethite samples in solutions containing no neptunium. Selected reacted sorbent samples were analyzed by x-ray absorption spectroscopy (XAS) to determine the oxidation state and molecular speciation of the adsorbed neptunium. Results have been used to establish the pH adsorption edge of neptunium on goethite in sodium chloride and calcium-bearing sodium silicate solutions. The results indicate that neptunium uptake on goethite reaches 95% at a pH of approximately 7 and begins to decrease at pH values greater than 8.5. Distribution coefficients for neptunium sorption range from less than 1000 (moles/kg)sorbed / (moles/kg)solution at pH less than 5.0 to greater than 10,000 (moles/kg)sorbed / (moles/kg)solution at pH greater than 7.0. Distribution coefficients as high as 100,000 (moles/kg)sorbed / (moles/kg)solution were recorded for the tests done in calcite equilibrated sodium silicate solutions. XAS results show that neptunium complexes with the goethite surface mainly as Np(V) (although Np(IV) is prevalent in some of the longer-duration sorption tests). The neptunium adsorbed to goethite shows Np-O bond length of approximately 1.8 angstroms which is representative of the Np-O axial bond in the neptunyl(V) complex. This neptunyl(V) ion is coordinated to 5 or 6 equatorial oxygens with Np-O bond lengths of 2.45 angstroms. The absence of a clearly recognizable Np-Fe interaction for the sodium chloride sorption tests suggests that neptunium in these solutions adsorbs as an outer-sphere complex. XAS results from the calcium-bearing sodium silicate sorption tests show evidence for a neptunyl(V) inner-sphere surface complex with a Np-Fe interaction at 3.5 angstroms. Desorption tests indicate that samples in which neptunium is bound as inner-sphere complexes show significant sorption hysteresis relative to samples in which neptunium is bound largely as outer-sphere complexes.

A Spectroscopic Characterization and Quantification of M(III)/Clay Mineral Outer-Sphere Complexes

2008 ◽  
Vol 42 (20) ◽  
pp. 7601-7606 ◽  
Author(s):  
Eva Hartmann ◽  
Bart Baeyens ◽  
Michael H. Bradbury ◽  
Horst Geckeis ◽  
Thorsten Stumpf
Keyword(s):  
Clay Mineral ◽  
Outer Sphere ◽  
Spectroscopic Characterization ◽  
Outer Sphere Complexes

Ion association and charge-transfer excitation between N-heterocyclic cations and cyanoiron complexes

1979 ◽  
Vol 57 (16) ◽  
pp. 2079-2084 ◽  
Author(s):  
Henrique E. Toma
Keyword(s):  
Charge Transfer ◽  
Equilibrium Constants ◽  
Ion Association ◽  
Outer Sphere ◽  
Binding Properties ◽  
Donor And Acceptor ◽  
Charge Transfer Excitation ◽  
Optical Charge ◽  
Heterocyclic Cations ◽  
Outer Sphere Complexes

N-Heterocyclic cations form with substituted pentacyanoferrates a series of outer-sphere complexes of general formula Fe(CN)5L//N-Het, suitable for systematic studies in aqueous solution. The equilibrium constants for the association of dipositive cations (e.g. N,N′-dimethyl-4,4-bipyridyl, or paraquat ion) and monopositive cations (e.g. N-methylpyrazinium) with the hexacyanoferrate(II) anion are typically in the range of 30–40 M−1and 10–13 M−1. The optical charge-transfer energies depend on the nature of the N-heterocyclic acceptor, and on the binding properties of the ligand L as they modify the ionization potentials of the Fe(CN)5Ln− complexes. A linear correlation between the optical charge-transfer energies and ΔE0 was found, with a slope (ΔEop/ΔG0) of 1.03 ± 0.03. The results were interpreted on the light of Hush's theory for intervalence transitions, with the aid of the equation Eop = 2(ΔG11* + ΔG22*) + ΔG120, which correlates the optical energy (Eop) for electron-transfer with the intrinsic barriers (ΔG11* + ΔG22*) of the donor and acceptor ions, and the free energy change (ΔG120) for the process.

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