Alain Cousson

Crystal structure of a neptunyl cation-cation complex (NpO2+) with mellitic acid: Na4(NpO2)2Cl12O12·8H2O

The crystal structure of the compound formed by the neptunyl(V) ion (237NpO2+) and mellitic acid was determined. The stoichiometric formula of the compound was Na4(NpO2)2C12O12·8H2O with the following crystal data: Z = 4; Vc = 2486.7 A3;Dcalc = 2.96 g cm−3; a = 12.53(1) A; b = 11.58(2) A; c = 17.81(2) A; β = 105.79°; space group, C2/c. The structure was obtained using classical methods with R = 0.044 and Rw = 0.056 for 2372 independent reflections. The most interesting result was the evidence for neptunyl dimers in the lattice, possibly as a result of cation-cation interactions. The two neptunium atoms in such dimers are 3.4824(8) A apart. The neptunyl dinier is associated with four mellitate ligands. The sodium ions and the water molecules serve as bridging species to increase the crystalline cohesion.

Crystal structure and Mössbauer studies of neptunium(V) complexes with polycarboxylic acids

Abstract Complexes of the neptunyl ion ( 237 NpO 2 + ) with pyromellitic acid and mellitic acid were prepared with the formulae (Na 3 NpO 2 (C 10 O 8 H 2 )) 2 ·11H 2 O and Na 4 (NpO 2 ) 2 (C 12 O 12 )·8H 2 O respectively. These solids were studied using X-ray diffraction, Mossbauer spectroscopy and magnetic susceptibility measurements. The crystal structure of (Na 3 NpO 2 (C 10 O 8 H 2 )) 2 ·11H 2 O was refined to R = 0.027 for 6793 independent reflections (structural data: a = 14.46(1) A ; b = 9.404(8) A ; c = 6.768(4) A ; α = 95.08°; β = 103.23°; γ = 87.47°; space group, P1; Z = 1). The NpO 2 + ion is coordinated to four pyromellitate anions. The Mossbauer spectra exhibited magnetic hyperfine splitting which was attributed to paramagnetic relaxation phenomena.

Crystal structure of uranyl benzene 1,2,4,5-tetracarboxylate dihydrate: UO2C10O8H4•2H2O

The crystal structure of the complex in the title was determined by X-ray crystallography from single-crystal diffractometer data. Crystal data: UO2C10O8H4 · 2H2O, triniclic, P1, a = 6.355(6) A, b = 11.531(9) A, c = 5.548(5) A, α = 104.07 °, β = 109.06 °, γ = 81.85 °, M = 558.192, Z = 1, V =371.875 A3, dcalc = 2.49 g cm−3, R (F) = 0.106, Rw = 0.134 for 3413 independent reflections. The hexagonal dipyramid around the uranium atom contains two carboxyl ligands and two water molecules in the equatorial plane of the uranyl ion. The U—O (uranyl bond) is 1.70(2) A, 〈U—O〉 in the equatorial plane is 2.48 A, and other distances and angles are similar to those in the literature.

Systematic trends in the237neptunium Mössbauer isomer shift: Overlap of IV, V and VI neptunium oxidation states and correlation between isomer shift and crystal structure

The influence of the neptunium ion environment on the237Np Mössbauer isomer shifts has been studied in various metal coordination complexes: fluorides, oxides, oxide fluorides and polycarboxylates. A linear dependence between the isomer shift and the mean neptunium-ligand distance in a series of hexavalent Np compounds has been evidenced and the feasibility of overlapped isomer shift areas, namely Np(IV), Np(V) and Np(VI) has been established.

Les hydrovydes de neptunium(IV): Structure cristalline de NH4Np(OH)5 et etude par resonance mössbauer de Np(OH)4

NH4Np(OH)5 crystallives in the monoclinic system, space group P21, with cell parameters a = 8.704(3) A, b = 8.704(3) A, c = 7.067(2) A and γ = 127.16°; V = 426.7 A3, d(calc) = 5.29 g cm−3, M = 340, v = 4. The structure was refined to R = 0.030 and Rp = 0.040 for 1130 independent reflevions such that I ⩾ σ(I). The neptunium atoms have a nine coordination (McClure polyhedron). Packing gives a layer structure. Layers of (Np2(OH)10)n2− are separated by ammonium ions. NH4Np(OH)5 is the structural model for Np(OH)4 which has been studied using magnetic susceptibility measurements and Mossbauer (237Np) spectrometry.

Mössbauer (237Np) and structural studies of some oxouranates and oxoneptunates

Two oxoneptunates have been investigated using237Np Mössbauer spectroscopy. The crystal structures of Na2U2O7 and β-Na2UO4 were recently determined by one of us. The two isotypic compounds Na2Np2O7 and β-Na2NpO4 were prepared. For β-Na2NpO4 the Mössbauer spectrum confirms the structural study. For Na2Np2O7 the structural study enabled the fit of the complex Mössbauer spectrum recorded at 77K.

Étude du système BaF2NpF3 par diffraction X et spectroscopie Mössbauer (237Np)

Resume Le systeme BaF 2 NpF 3 a ete etudie par diffraction X et spectroscopie Mossbauer ( 237 Np). Deux solutions solides ont ete mises en evidence. La premiere de type fluorine a pour formule Ba 1 − x Np III x F 2 + x (0 x ⩽ 0,25), la seconde est de type hexagonal LaF 3 de formule Ba 0,05 + x Np III 0,95 − 2 x Np IV x F 2,95 (0 ⩽ x ⩽ 0,475). La spectroscopie Mossbauer ( 237 Np) a permis de proposer un mecanisme de substitution original du neptunium trivalent par le baryum dans cette solution solide.

Experimental evaluation of the sternheimer quadrupole antishielding factor γ∞ for the tetravalent neptunium ion

Abstract Using a point charge model, the lattice contribution to the electric field gradient (EFG) was calculated for the isotypic hydrated neptunium fluorides MNpF6 · 3H2O (M = Mn, Fe, Co, Ni, Zn). The atomic coordinates in these compounds were computed from prescribed interatomic distances using a least squares procedure, the positional parameters in CoNpF6 · 3H2O and the ionic radii differences between the M2+ ions. With our structural determinations, calculations of the EFG and the experimental Mossbauer data, we can propose for the Sternheimer antishielding factor γ∞ (Np4+) the value γ∞ = −126(13). This result is in good agreement with the calculated value deduced from theoretical considerations.

Mössbauer 237Np and crystallographic studies of MIINpF6·3H2O (MII = Mn, Fe, Co) compounds

Abstract The compounds M II NpF 6 3H 2 O with M II = Mn, Fe, Co were prepared as single crystals by hydrothermal synthesis (T = 400°C, P = 2000 bars). CoNpF 6 3H 2 O crystallises in a monoclinic system with C2 space group. Cell parameters are a = 12.143(9) Ā; b = 6.922(5) Ā; c = 7.942(5) Ā; β = 92.84°. The Mossbauer measurements were performed in a conventional He Cryostat. The Mossbauer source used in the experiments was a 500 mCi 241 Am metal with a conventional sine mode drive system. A microbalance magnetometer attached to a varying temperature Cryostat was used for the susceptibility measurements. The maximum applied magnetic field was 14KG. The Mossbauer spectroscopy of 237 Np shows a magnetically split hyperfine spectrum at 4.2K for all those compounds. The spectra can be fitted with a magnetic hyperfine field associated to a quadrupole splitting using the linear correlation between B eff and e 2 qQ. From isomer shift measurements, we confirm the IV charge state of Np in these 3 compounds. The magnetic susceptibility shows antiferromagnetic type transition. 1/ξ = f(T) follows a Curie-Weiss law above T N .