M. S. Grigor’ev

Synthesis and X-ray diffraction study of complex neptunium(VI) potassium chromate K2[(NpO2)2(CrO4)3(H2O)] · 3H2O

The crystal structure of the K2[(NpO2)2(CrO4)3(H2O)] · 3H2O compound was established. The structure consists of anionic layers [(NpO2)2(CrO4)3(H2O)]n2n, between which K+ ions and crystallization water molecules are located. The coordination polyhedra of Np atoms are distorted pentagonal bipyramids. All chromate ions are bound in a tridentate-bridging fashion.

Phosphoryl-containing acidic podands as extractants for recovery of f-elements

The extraction efficiency of uranium(vi), thorium(iv), and lanthanum(iii) from nitric acid solutions to 1,2-dichloroethane was compared for a series of phosphoryl podands of the acidic type different in polyether chain length and number of oxygen atoms: 2-[(HO)(EtO)(O)P]–C6H4–(OCH2CH2)m–OC6H4–2-[P(O)(EtO)(OH)] (1–3, where m = 1–3) and 2-[(HO)(EtO)(O)P]–C6H4–O(CH2)5O–C6H4–2-[P(O)(EtO)(OH)] (4). The synthesis of podands 1 and 4 obtained for the first time is described. The molecular and crystal structures of podand 1 were determined by X-ray diffraction analysis, and the formation of a strong intramolecular hydrogen bond was observed. Podand 2 is the most efficient extractant for the selective recovery of ThIV in the presence of UVI and LaIII among the studied podands. Micellar aggregates 3–5, 6–90, 3–70, and 7–10 nm in size were found by the dynamic light scattering data in thorium extracts of podands 1–4, respectively.

Complexation of An(VI) (An = U, Np, Pu, Am) with 2,6-pyridinedicarboxylic acid in aqueous solutions. Synthesis and structures of new crystalline compounds of U(VI), Np(VI), and Pu(VI)

Complexation of An(VI) (An = U, Np, Pu, Am) with 2,6-pyridinedicarboxylic (dipicolinic) acid in aqueous solutions was studied. All these actinides form with dipicolinic acid anion, PDC2− 1: 1 and 1: 2 complexes. The PDC2− ion coordinates to actinide(VI) ions in solutions in tridentate fashion. In 1: 2 complexes, the f-f transition bands in the electronic absorption spectra are very weak, which is associated with approximate central symmetry of the coordination polyhedron (CP) of the An atom. The apparent stability constants of Pu(VI) complexes were measured in a wide pH range, and the concentration stability constants of An(VI) (An = U, Np, Pu, Am) were determined. The crystalline complexes [Li2AnO2(PDC)2]·2H2O (An = U, Np, Pu) and [AnO2(PDC)]n (An = Np, Pu) were synthesized, and their structures were determined by single crystal X-ray diffraction. The X-ray data confirmed the conclusion that CP of An atoms in the complex ions AnO2·(PDC)22− is centrosymmetrical. In the isostructural series of [Li2AnO2(PDC)2]·2H2O, the actinide contraction is manifested in shortening of the An-O distances in the “yl” groups in going from U to Pu.

First uranyl methacrylate complexes: Synthesis and structure

Crystals of UO2(mac)2 · 2H2O (I), UO2(mac)2 · 1.5Dmur (II), and UO2(mac)2 · Tmur (III) (mac− is methacrylate ion C3H5COO−, Dmur is N,N-dimethylurea, Tmur is tetramethylurea) have been synthesized and studied by X-ray crystallography and IR spectroscopy. The structural units of I are mononuclear [UO2(mac)2(H2O)2] complexes classified with crystal-chemical group AB201M21 (A = UO22+ B01 = mac−, M1 = H2O). Structure II contains two types of mononuclear uranium-containing complexes: cationic [UO2(mac)(Dmur)3]+ and anionic [UO2(mac)3]−. The crystal-chemical formula of II is AB01M31 + AB301 (A = UO22+, B01 = mac−, M1 = Dmur). The basic structural units of crystal structure III are [UO2(mac)2(Tmur)]2 dimers belonging to crystal-chemical group AB2B01M1 of uranyl complexes (A = UO22+, B2 and B01 = mac−, M1 = Tmur). The composition and possible structures of 14 stable uranyl complexes that can form in the UO22+-mac−-L-H2O system (L is Dmur or Tmur) have been determined on the basis of Voronoi-Dirichlet polyhedron characteristics with the use of the 18-electron rule. It has been demonstrated that, in crystals I–III, uranium-containing complexes are combined into a framework through a system of hydrogen bonds and electrostatic and noncovalent interactions.

Synthesis and structure of U(VI), Np(VI), and Pu(VI) propionates

Crystals of [AnO2(C2H5COO)2(H2O)2], where An = U (I), Np (II), or Pu (III), have been synthesized and studied by X-ray diffraction at 100 K. Compounds I–III are isostructural and crystallize in the monoclinic system, sp. gr. C2/c, Z = 4, with the following unit-cell parameters: a = 7.4677(2), 7.4740(1), 7.512(2) Å, b = 14.2384(4), 14.1681(3), 14.182(4) Å, c = 10.5977(3), 10.5875(2), 10.607(3) Å, β = 92.384(1)°, 92.476(1)°, 92.668(17)°. Crystals I–III are composed of the mononuclear complexes [AnO2(C2H5COO)2(H2O)2] as the main structural units belonging to the crystal-chemical group AB012M12 (A= AnO2+2, B01 = C2H5COO–, M1 = H2O). The crystal-chemical analysis of the structures of compounds of the composition UO2L2 · nH2O, where L is the carboxylate ion, is performed.

Synthesis and structure of uranyl complexes with malonic acid dianions

The uranyl complexes with malonic acid dianions [UO2(C3H2O4)(CO(NH2)2)]·H2O (1), [UO2(C3H2O4)(CONH2NMe2)]·H2O (2), and [UO2(C3H2O4)(MeCONMe2)] (3) were synthesized and characterized by X-ray crystallography. The structural units [UO2(C3H2O4)L] in the crystals of 1–3 refer to the AK21M1 crystal chemical group (A = UO22+, K21 = C3H2O42−, M1 = L) of uranyl complexes; the crystals of 1 have a framework structure and 2 and 3 have a chain structure. Some structural features of the [UO2(C3H2O4)L] complex groups are discussed.

Synthesis and structure of actinide(VII) compounds Rb3NpO4(OH)2·3H2O and Rb3PuO4(OH)2·3H2O

Actinide(VII) salts Rb3[NpO4(OH)2]·3H2O (I) and Rb3[PuO4(OH)2]·3H2O (II) were prepared as single crystals and examined by X-ray diffraction. The compounds are isostructural and crystallize in the monoclinic system, space group C2/c, Z = 4; unit cell parameters: a = 12.1544(3), b = 10.9942(2), c = 7.789(2) Å, β = 91.0930(11)° for I and a = 12.1254(3), b = 10.9506(2), c = 7.7699(2) Å, β = 90.8253(12)° for II. The main structural elements of I and II are centrosymmetrical anions [AnO4(OH)2]3− forming together with water molecules, owing to strong hydrogen bonding, chains oriented along [101]. In [AnO4(OH)2]3− anions, the central An(VII) atom has a tetragonal-bipyramidal oxygen surrounding. The An-O(OH) interatomic distances decrease in going from I to II owing to actinide contraction by a factor of ∼2 more strongly than the An-O bond lengths in the equatorial planes of the bipyramids. The previously studied structure of Cs3[NpO4(OH)2]·3H2O (III) was refined.

Dimethyl sulfoxide as an O-donor ligand in tetravalent actinide complexes

Four new perchlorate complexes of tetravalent actinides with dimethyl sulfoxide (DMSO) molecules (An4+ = Th, U, Np, Pu) are synthesized and studied. According to the X-ray diffraction data, compounds [Th(DMSO)9](ClO4)4 · 2CH3CN (I), [U(DMSO)8](ClO4)4 · CH3CN (II), [Np(DMSO)8](ClO4)4 · CH3CN (III), and [Pu(DMSO)8](ClO4)4 · CH3CN (IV) crystallize in the triclinic crystal system (space group P1). The crystals of compounds II–IV are isostructural. The absorption spectra of the complexes in the IR and visible regions are measured. All compounds exhibit a decrease in the frequencies of stretching vibrations ν(SO) over the spectrum of free DMSO, indicating the formation of the O-bonded complexes of An4+. The optical spectra of the crystalline compounds exhibit shifts of the bands of electronic f-f transitions of the An4+ ions relative to the hydrated ions: the bathochromic shifts for the U and Np complexes and the hypsochromic shift for the Pu complex. The first coordination sphere of the actinide atoms in the studied complexes is highly stable.

New data on sodium salts of Np(VII) and Pu(VII)

A new Pu(VII) compound, Na3[PuO4(OH)2]·2H2O, was prepared by X-ray diffraction analysis, and its structure was studied. To reveal the character of actinide contraction in going from Np(VII) to Pu(VII), the geometric parameters of the tetragonal-bipyramidal surrounding of Pu(VII) in the [PuO4(OH)2]3− anion were compared with those of Np(VII) in the previously studied isostructural compound Na3[NpO4(OH)2]·2H2O. To reveal the specific feature of hydrogen bonding in crystals of the general composition Na3[NpO4(OH)2]·nH2O (n = 0, 2, 4), the structure of the compound Na3[NpO4(OH)2]·4H2O studied previously by the photographic method was refined. The effect of hydrogen bonds on the geometric characteristics of the coordination polyhedra of the Np and Na atoms was considered.

Synthesis and single crystal X-ray diffraction study of U(VI), Np(VI), and Pu(VI) perchlorate hydrates

The compounds [AnO2(H2O)5](ClO4)2 (An = Np, Pu) and [NpO2(ClO4)2(H2O)3] were prepared as single crystals, which were studied by X-ray diffraction at 100 K. The structural type at room temperature was determined. The low-temperature modification of [UO2(H2O)5](ClO4)2 was found and structurally studied. The coordination polyhedra in [AnO2(H2O)5]2+ are weakly distorted pentagonal bipyramids with averaged interatomic distances An-O of 1.754, 1.744, and 1.732 Å in the “yl” groups and of 2.415, 2.416, and 2.409 Å in the equatorial planes for U, Np, and Pu, respectively. Hence, in the complex cations [AnO2(H2O)5]2+ the actinide contraction is manifested only in regular shortening of the An-O interatomic distances in the “yl” groups. The compound [NpO2(ClO4)2(H2O)3], isostructural to its known uranyl analog, appeared to be the first, proved by single crystal X-ray diffraction, example of a compound with coordination interaction between the perchlorate ion and the neptunyl(VI) cation.