[en] The behavior of Am in acidic and basic solutions containing the Fe(CN)^3-₆/Fe(CN)^4-₆ redox system is studied. In mineral acids, K₃Fe(CN)₆ and Am(III) form the poorly soluble compound AmFe(CN)₆, which with time undergoes a change owing to radiolytic reduction of Fe(CN)^3-₆ to Fe(CN)^4-₆. In basic solutions of K₃Fe(CN)₆, Am(III) is oxidized to AmO⁺₂, forming the soluble complex (AmO₂)₃Fe(CN)₆, which gradually decomposes to produce the solid double hydroxide Na₂AmO₂(OH)₃·nH₂O. An Am(IV) hydroxide is formed if [Am] and [K₃Fe(CN)₆] are equal

No abstract available

[en] The Moessbauer spectra of complexes between Np(V) and Cr(III) or Rh(III) ions absorbed on cation exchange resin were measured at 4.2⁰K with a constant acceleration Moessbauer spectrometer. The spectrum of the Np(V)-Cr(III) complex showed a strong magnetic splitting with Moessbauer parameters of g₀μ/sub N/H/sub eff/ 9.91 cm/sec, ¹/₄ eqQ = -2.9 cm/sec, and delta = 1.69 cm/sec. The spectrum of the Np(V)-Rh(III) complex was dominated by quadrupole splitting with a minor fraction showing magnetic hyperfine structure. The results of these measurements are consistent with the suggested structure of the complexes--substituting NpO₂⁺ in the transition metal ion coordination sphere--and the magnetic properties of paramagnetic Cr(III) ion (3d³, high spin) and diamagnetic Rh(III) ion

[en] Early actinides (U, Np, Pu, Am) show a particular linear bond actinyl type structure in higher oxidation state. The multiple bond nature of this chemical pattern contributes to a drastic diminution of the charge at the metallic core inducing a strong stabilisation of these high oxidation states. The potential participation of the early actinide 5f orbitals in the valence molecular shell is supposed to be one of the most important engines of this chemical specificity. In order to progress in the comprehension of this behaviour, a study of the electronic and the geometric structure of some actinyl complexes with different electronic configuration is undertaken using theoretical and experimental approaches. (authors)

[en] The +5 oxidation state of U, Np, Pu, and Am is a linear dioxo cation (AnO₂⁺) with a formal charge of +1. These cations form complexes with a variety of other cations, including actinide cations. Other oxidation states of actinides do not form these cation-cation complexes with any cation other than AnO₂⁺; therefore, cation-cation complexes indicate something unique about AnO₂⁺ cations compared to actinide cations in general. The first cation-cation complex, NpO₂⁺·UO₂²⁺, was reported by Sullivan, Hindman, and Zielen in 1961. Of the four actinides that form AnO₂⁺ species, the cation-cation complexes of NpO₂⁺ have been studied most extensively while the other actinides have not. The only PuO₂⁺ cation-cation complexes that have been studied are with Fe³⁺ and Cr³⁺ and neither one has had its equilibrium constant measured. Actinides have small molar absorptivities and cation-cation complexes have small equilibrium constants; therefore, to overcome these obstacles a sensitive technique is required. Spectroscopic techniques are used most often to study cation-cation complexes. Laser-Induced Photacoustic Spectroscopy equilibrium constants for the complexes NpO₂⁺·UO₂²⁺, NpO₂⁺·Th⁴⁺, PuO₂⁺·UO₂²⁺, and PuO₂⁺·Th⁴⁺ at an ionic strength of 6 M using LIPAS are 2.4 ± 0.2, 1.8 ± 0.9, 2.2 ± 1.5, and ∼0.8 M^-1

[en] Formation constants are listed for standard conditions, i.e., 298.15K (25⁰C), 10⁵ Pa, and zero ionic strength for a number of species containing selected elements (Am, Cs, Np, Pa, Pb, Pd, Pu, Ra, Sn, Sr, Tc, Th, U) and ligands (hydroxide, fluoride, chloride, bromide, iodide, iodate, sulphate, ammonia, nitrate, hydrogen phosphate, dihydrogen phosphate, carbonate, bicarbonate, oxalate, formate, thiocyanate, acetate, benzoate, catecholate, ethylenediamine, glycinate, glycollate and phenolate) that have been considered important for nuclear technology. 16 refs

[en] Rates of complex formation and dissociation in NpO₂⁺- Chlorophosphonazo III (2,7-bis(4-chloro-2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studies were made of the rates of reaction of La³⁺, Eu³⁺, Dy³⁺, and Fe³⁺ with CLIII. Rate determining step in each system is an intramolecular process, the NpO₂⁺-CLIII reaction proceeding by a first order approach to equilibrium in the acid range from 0.1 to 1.0 M. Complex formation occurs independent of acidity, while both acid dependent and independent dissociation pathways are observed. Activation parameters for the complex formation reaction are ΔH=46.2±0.3 kJ/m and ΔS=7± J/mK (I=1.0 M); these for the acid dependent and independent dissociation pathways are ΔH=38.8±0.6 kJ/m, ΔS=-96±18 J/mK, ΔH=70.0± kJ/m, and ΔS=17±1 J/mK, respectively. An isokinetic relationship is observed between the activation parameters for CLIII complex formation with NpO₂⁺, UO₂²⁺, Th⁴⁺, and Zr⁴⁺. Rates of CLIII complex formation reactions for Fe³⁺, Zr⁴⁺, NpO₂⁺, UO₂²⁺, Th⁴⁺, La³⁺, Eu³⁺, and Dy³⁺ correlate with cation radius rather than charge/radius ratio

[en] Chelates of pyridine azopyrazolin-5-one derivatives with Zr(IV), La(III), Y(III) and UO₂²⁺ have been prepared and characterized on the basis of microanalysis, electronic, IR, ¹H NMR spectra. The thermogravimetric analysis confirms the presence of coordinated water molecules. The 1:1 and 1:2 (Mⁿ⁺:L) ratios are suggested on the basis of spectrophotometric and conductometric data. It is concluded that the ligand L₁ and L₃ can act, as neutral bidentate ligands while L₂ acts as monobasic bidentate. All complexes are thermally stable up to ∼ 200⁰C

No abstract available

[en] The single-crystal X-ray structure of (NpO₂)₂C₃H₂O₄·3H₂O (I) is solved (Siemens P3/PC, graphite monochromator, Mo Kα-radiation). The unit-cell parameters are a = 6.596(1), b = 8.320(1), c = 10.308(2) angstrom β = 90.24(2)degrees, Z = 2, space group P2₁, d_calc = 4.07 g/cm³, 2239 reflections with I > 3σ(I), R = 0.049, R_w = 0.073. The crystal structure of I is constructed of NpO₂⁺, C₃H₂O^2-₄, coordinated water, and water of crystallization. The two crystallographically unique NpO₂ groups (Np coordination number 7, pentagonal bipyramidal coordination polyhedron) are joined into planar open-quotes squareclose quotes cationic networks in which both groups act as bidentate ligands. The malonate ion additionally joins Np atoms of one network that are bonded to each other by cation-cation (CC) interactions. The structure of I is compared to that of the previously described (NpO₂)₂C₃H₂O₄·4H₂O (II). The change from II (crystallized from cold solutions) to I (crystallized from hot solutions) is accompanied by the exclusion of water from the Np coordination sphere and produces a structure rearrangement with formation of new CC bonds