Alexandre M. Fedosseev

Peculiarities of complex formation of hexavalent Np and Pu with tetrahedral XO42− oxoanions (X=S, Se, Cr, Mo)

Abstract This work was designed for further investigations of coordination compounds of penta- and hexavalent actinides with tetrahedral XO 4 2− -anions. Although a high similarity in the structure and properties of AnO 2 2+ compounds with XO 4 2− -anions (where An=Np, Pu) was expected, our data on the behaviour of AnO 2 2+ compounds in aqueous solutions pointed to marked differences depending on the nature of both actinides and a central X-atom in ligands.

Guanidinium dioxidobis(picolinato-κ2N,O)(picolinato-κO)uranate(VI)

In the title compound, (CH6N3)[U(C6H4NO2)3O2], the uranyl group is coordinated by two O and two N atoms from two chelating picolinate ligands, and one O atom from a third picolinate ligand. The coordination environment of the UVI atom (N2O5) is distorted pentagonal–bipyramidal. In the crystal, all amino groups are involved in the formation of N—H⋯O and N—H⋯N hydrogen bonds, which link cations and anions into layers parallel to the ac plane.

The influence of f-elements' oxidizing potential and ion charge on their stability in aqueous alkaline solution

Abstract The data published on values of redox potentials E of heptavalent Np, Pu, Am, Ru and Mn and octavalent Ru and Pu were analyzed. The half-life (τ1/2) for reduction reactions of heptavalent metal by water in aqueous alkaline solutions was also analyzed. The decrease in the half life stability of actinide in water with the redox potential for 3− charged anions of Np(VII), Pu(VII), and Am(VII) was found. At the same potential, a charge decrease from 3− to 1−reduces the stability approximately two fold. For the redox couple Pu(VIII)/Pu(VII), the estimated value is E > 1.15 V/NHE. If Pu(VIII) existed as PuO4, it would be very unstable (τ1/2 ≈ × 102 s) in 1 M NaOH. For the anionic forms of Pu(VIII), PuO4(OH)22− and PuO64−, the half life was estimated to be very low (τ1/2 < 1 s).

Crystal structure of Th(IV) perchlorate and U(VI) nitrate complexes with trimethyl phosphate: [Th(OP(OCH3)3)4(O2P(OCH3)2)2]2[ClO4]4 and [UO2(OP(OCH3)3)(O2P(OCH3)2)(NO3)]2

Abstract Single crystals of [Th(TMP)4(DMP)2]2[ClO4]4 and [UO2(TMP)(DMP)(NO3)]2 have been synthesized and their structures have been determined by X-ray diffraction analysis. The complexes of Th(IV) and U(VI) contain simultaneously both the molecular ligand trimethyl phosphate (TMP) and the anion dimethyl phosphate. The main structural motif in Th(IV) complex is centrosymmetric dimeric cation [Th(TMP)4(DMP)2]24+, and in U(VI) it is the neutral centrosymmetric dimeric complex [UO2(TMP)(DMP)(NO3)]2. Coordination polyhedron of Th(IV) is tetragonal antiprism, for U(VI) it is pentagonal bipyramid. The structures are compared with those of other Th(IV) and U(VI) complexes containing other trialkyl phosphates.

Capture of Pu(V), Np(V) and Pu(VI) from alkaline solutions by hydroxides of Pu(IV), Th(IV) and La(III)

Abstract In systematic studies of actinide chemistry in alkaline solution, it was found that Pu(IV) hydrous oxide can remove significant amounts of plutonium present in higher oxidation states from solution. By spectrophotometry it was found that the capture of Pu(VI) by Pu(IV) hydrous oxide is negligible whereas Pu(V) and Np(V) are highly adsorbed. Quantitative characterization of the process was investigated by a radiometric method based on 239 Np-labeled neptunium. The influence of temperature, alkali concentration, and the Pu/Np molar ratio on the extent of capture of Np(V) by PuO 2 x H 2 O was investigated.

Crystal structure and spectral properties of complexes of tetravalent Th, U,Np and Pu nitrates with trimethyl phosphate and dimethyl phosphate

Abstract Single crystals of [Th(TMP)6(NO3)2][Th(TMP)2(NO3)5]2 (1), [Th(TMP)4(NO3)3][Th(TMP)2(NO3)5] (2), [U(DMP)3(NO3)] (3), [Np(DMP)3(NO3)] (4), and [Pu(DMP)2(NO3)2(H2O)]·H2O (5) have been synthesized and their structures have been determined by X-ray analysis. IR and optical spectra of polycrystalline compounds 3 and 4 were measured at room temperature. The Th(IV) is crystallized as two complexes with TMP molecular ligands and NO3 anions in coordination environment. The Th atoms in cationic moieties of 1 and 2 are characterized by coordination number of 10 and in the anionic moieties by coordination number of 12. Compounds of U(IV), Np(IV) and Pu(IV) were obtained with two different anions (NO3 and DMP) in coordination environment of the central atom. U(IV) and Np(IV) compounds are isostructural and the main motif of structure is made of infinite chains of [An(DMP)3(NO3)]n, twisted around hexagonal axes. In the structure of Pu(IV) the main structural motif is made of infinite chains [Pu(DMP)2(NO3)2(H2O)]n, extending along the b axis. The coordination numbers of An(IV) are equal to 8 for U and Np, and 9 for Pu. The difference in the structure and composition of formed compounds Th and U, Np, Pu could be explained by hydrolysis of TMP at the synthesis conditions.

Sodium tris(acetato-κ2O,O')dioxidoamericate(VI) and guanidinium tris(cyclopropanecarboxylato-κ2O,O')dioxidoamericate(VI).

The title compounds, Na[{AmO(2)}(C(2)H(3)O(2))(3)], (I), and (CH(6)N(3))[{AmO(2)}(C(4)H(5)O(2))(3)], (II), contain complex anions in which AmO(2)(2+) cations are surrounded by three bidentate-chelating carboxylate groups. The atoms of the AmO(2) group and the Na atoms in (I) are situated on threefold axes. All the atoms in (II) occupy general positions. Both compounds are isomorphous with earlier studied analogous compounds of previous members of the actinide (An) series.

Structure and properties of 2,2-dihydroxymalonates of trivalent Y, lanthanides, Pu and Am

The M-O bond lengths in the lanthanide series show a well-known behaviour due to lanthanide contraction, including so-called “gadolinium break”. All three bond lengths show a good linear correlation with Shannon ionic radii for Y3+ and Ln3+ ions with coordination number 9. Nevertheless, the slopes of these dependences are different (0.957(16) for OH-groups, 0.85(2) for carboxylate groups and 1.080(17) for water molecules) and differ from unity due to a layer nature of the structures. The ionic radii for Pu3+ and Am3+ with coordination number 9 are absent in the Shannon system of ionic radii. From our data, we can propose the values 1.172 and 1.156 Å for Pu3+, and Am3+, respectively. In all crystals the structure is stabilized through extensive hydrogen bonding involving carboxylic and hydroxyl groups and water molecules.