I. A. Charushnikova

Crystal Structures of Molecular Adducts between Uranyl Nitrate and 2,2′ : 6′,2′′-Terpyridine or 2,2′-Bipyridyl

Complexes of uranyl nitrate with aromatic molecular ligands : [UO2Terpy(NO3)2] and (H2Terpy)2[UO2(NO3)2(H2O)2](NO3)4 · 4H2O (Terpy 2,2′:6′,2′′-terpyridine), (Hbipy)[UO2(NO3)3] and [(UO2)2(Bipy)2O2(NO3)2] (Bipy—2,2′-bipyridyl) and (HPy)4[(UO2)2(NO3)4(OH)2](NO3)2 (Py—pyridine) were characterized by X-ray diffraction analysis. In all these compounds, the U(VI) atom has the hexagonal bipyramidal environment. The U–O bond lengths in the UO22+ have close values. In the equatorial planes, the U–N bond lengths with the Bipy and Terpy ligands are identical, whereas the U–O bond lengths depend on the type of the ligand. The lengths of the equatorial bonds increase in the sequence U–N > U–Onitr > U–Ohydr > U–Operox. The geometric characteristics of the coordinated and solvate Terpy and Bipy molecules are different. The lengths of the N–O bonds in the NO3– groups depend on the participation of the O atom in the coordination of the central atom, the coordination mode, and the formation of hydrogen bonds.

Crystal and electronic structure of a mixed-valent Np(IV)-Np(V) compound: [BuMeIm]5[Np(NpO2)3(H2O)6Cl12].

A new mixed valent neptunium compound [BuMeIm](5)[Np(NpO(2))(3)(H(2)O)(6)Cl(12)] was synthesized by evaporation of an ethyl acetate-acetone mixture where the salt [BuMeIm](2)[NpCl(6)] was dissolved. The crystal structure was determined using single crystal X-ray diffraction; it consists of four crystallographically unique Np centers with two different coordination environments in two different oxidation states. In addition, five crystallographically independent dialkylimidazolium cations stabilize the crystal through C-H...Cl hydrogen bonds. [Np(NpO(2))(3)(H(2)O)(6)Cl(12)] unit presents a highly symmetric structure with the formation of three Np(IV)-Np(V)O(2)(+) bonds. According to the crystal structure and density functional theory (DFT) calculations, the stability of the three Np(4+)-NpO(2)(+) interactions is due to the presence of chloride ions around NpO(2)(+) which brings electronic charge into the system and also to the presence of water molecules which create hydrogen bond with chloride ions.

Crystal Structure of Two New Molecular Adducts of Uranyl Nitrate with 2,2'-6,2''-Terpyridine

The crystal structures of two uranyl nitrate complexes with 2,2′-6,2″-terpyridine (Trpy), [(UO (Trpy)-[(UO2)2(Trpy)2(OH)2][UO2(NO3)2(OH)2] · 2CH3OH (I) and [(UO2)2(Trpy)2(OH)2]2[UO2(NO3)3(H2O)](NO3)3 · 3H2O (II), were studied. Compound I consists of the centrosymmetric dimeric cations [(UO2)2(Trpy)2(OH)2]2+, the anions [UO2(NO3)2(OH)2]2−, and solvation methanol molecules. Complex II consists of dimeric cations [(UO2)2(Trpy)2(OH)2]2+, the complex anions [UO2(NO3)3(H2O)]−, nitrate anions, and water molecules of crystallization. The uranium atom in the [UO2(NO3)3(H2O)]− anion in II has an unusual coordination polyhedron representing a hexagonal bipyramid in which one oxygen atom in the equatorial plane is replaced by two atoms equidistant from this plane.

Crystal structure of neptunium(V) sulfate hexahydrate, (NpO2)2SO4 · 6H2O

Single crystals of (NpO2)2SO4 · 6H2O are obtained, and their structure is determined. The structure is built of NpO2+ dioxo cations, SO42− anions, and molecules of coordination and crystallization water. The NpO2+ ions are linked into cationic ribbons stretched along the [001] direction. In the ribbons, neptunoyl ions of one type act as monodentate ligands, whereas neptunoyl ions of the other type coordinate the neighboring neptunoyl groups by two oxygen atoms. The Np(1) and Np(2) atoms have oxygen environments in the shape of a pentagonal bipyramid whose equatorial plane consists of oxygen atoms of the neighboring dioxo cations, sulfate ions, and water molecules. The sulfate ion acts as a bidentate ligand bridging the two neighboring atoms Np(1) and Np(2). Six water molecules are revealed in the structure; one of them is a crystallization water molecule. Hydrogen bonds link cationic ribbons into a three-dimensional network.

Crystal structure of a Pu(VII) potassium salt, K3PuO4(OH)2·2H2O

A new Pu(VII) compound, K3PuO4(OH)2·2H2O, was synthesized, and its structure was studied by single crystal X-ray diffraction. This compound is isostructural to the previously described K3NpO4(OH)2·2H2O. The structure of the latter compound was redetermined to obtain more precise interatomic distances in the NpO2(OH)23− anion. Changes in An-O bond lengths in the tetragon-bipyramidal coordination polyhedron of the compounds K3AnO4(OH)2·2H2O in going from Np(VII) to Pu(VII) were considered.

Variation of the An-O bond lengths in NaAnO2(OOCCH3)3 and (NH4)4AnO2(CO3)3, An = U(VI), Np(VI), and Pu(VI)

For studying actinide contraction in triacetate and tricarbonate complexes of hexavalent actinides in the series U-Np-Pu, single crystals were prepared and crystal structures of NaPuO2(OOCCH3)3 and (NH4)4. AnO2(CO3)3 (An = Np, Pu) were determined. These compounds are isostructural with NaAnO2(OOCCH3)3 (An = U, Np) and (NH4)4UO2(CO3)3 studied previously. The coordination surrounding of An(VI) is a distorted hexagonal bipyramid. The actinide contraction in An(VI) triacetate and tricarbonate complexes is manifested in shortening of the bond lengths in the AnO22+ cation in the series U-Np-Pu. In triacetate complexes NaAnO2(OOCCH3)3, the average bond lengths in AnO22+ decrease by approximately 2.3% in passing from Np(VI) to Pu(VI). In tricarbonate complexes (NH4)4AnO2(CO3)3, the bond lengths in AnO22+ decrease by approximately 0.7% in passing from U to Np and by approximately 0.4% in passing from Np to Pu. The actinide contraction is less noticeable in the equatorial planes of the bipyramids. The lengths of the An-O bonds with oxygen atoms located around actinyl groups depend on the ligand nature and also on participation of oxygen atoms in the coordination with Na+ cations in the triacetate complexes or in hydrogen bonds with NH4+ ions in the tricarbonate complexes.

Crystal structure of complexes of Np(VI) and Pu(VI) perchlorates with triphenylphosphine oxide, [NpO2(OP(C6H5)3)4](ClO4)2 and [PuO2(OP(C6H5)3)4](ClO4)2

Single crystals of [NpO2(TPPO)4](ClO4)2 and [PuO2(TPPO)4](ClO4)2 isostructural to the complex [UO2(TPPO)4](ClO4)2 [TPPO = OP(C6H5)3] studied previously were prepared, and the structures of these compounds were determined. The coordination polyhedron of these compounds is a tetragonal bipyramid. The geometric characteristics of the tetragonal bipyramids in the compounds are practically the same despite the actinide contraction of the central atoms, whereas the unit cell volume decreases in the series U-Np-Pu. The equality of the volumes of the coordination polyhedra of the U, Np, and Pu atoms is attributed to the influence of TPPO containing phenyl radicals with negative effective charge.

Synthesis and crystal structure of new Np(VI) and Pu(VI) phthalates, Na4{AnO2[(OOC)2C6H4]3} · nH2O

Double phthalates of Np(VI) and Pu(VI) of the composition Na4[AnO2L3] · nH2O [L = (OOC)2C6H4] were synthesized in the crystalline form and studied by X-ray diffraction. The compounds are isostructural, their crystals consist of complex anions [AnO2L3]4− and Na+ cations, forming neutral layers; water molecules are located between the layers. The coordination polyhedra of An(VI) are hexagonal bipyramids, whose average planes are formed by oxygen atoms of three phthalate anions. In passing from Np(VI) to Pu(VI), the actinide contraction is reflected to a greater extent in the variation of the bond lengths with apical oxygen atoms of the bipyramids, whereas the An-O bond lengths in the equatorial plane of the bipyramids vary insignificantly.

Crystal structure of complexes of pentavalent neptunium with 1,8-bis[2-(diphenylphosphinylmethyl)]phenoxy-3,6-dioxaoctane (L) and hexavalent actinides (U, Np, Pu) with 1,8-bis[2-(diphenylphosphinyl)]phenoxy-3,6-dioxaoctane (L1)

Complexes of pentaand hexavalent actinides with phosphoryl-containing podands incorporating a triethylene glycol fragment and 2-(diphenylphosphinyl)phenyl (L1) or 2-(diphenylphosphinylmethyl)phenyl (L) end groups were synthesized and structurally characterized. The complexes can be described by the following formulas: [NpO2L(C2H5OH)(NO3)] (I) for pentavalent neptunium and [AnO2(L1)2](OH)2 · nH2O (II), where An is U (IIa), Np (IIb), and Pu (IIc), for the isostructural compounds of hexavalent actinides. In I, L is a bidentate bridging ligand. The Np5+ coordination polyhedron is a pentagonal bipyramid. The bipyramid equatorial plane is formed by the oxygen atoms of two podands L, the bidentate nitrate ion, and the ethanol OH group. The oxygen atoms of the phosphoryl groups of the podand are involved in the coordination environment of two NpO2+ cations where they connect the electrically neutral neptunoyl nitrate fragments to infinite chains along the [100] direction, which are in turn connected into ribbons by strong hydrogen bonds. The crystal of II consists of the complex cations [AnO2(L1)2]2+, hydroxyl ions, and water molecules of crystallization. The environment of AnO22+ is formed by four ligands L1 whose oxygen atoms form a tetragonal-bipyramidal coordination environment. Each of the two crystallographically independent ligands L1 is connected to two AnO2+ cations. This gives positively charged layers of actinyl cations perpendicular to the [010] direction connected by molecular ligands. The layers contain channels accommodating hydroxyl ions and crystallization water molecules.

Synthesis and structure of crystalline complexes of Np(V) with 1,10-phenanthroline-2,9-dicarboxylic acid. Complexation in solution and spectral studies

Complexes of Np(V) with 1,10-phenanthroline-2,9-dicarboxylic acid, C12H6N2(COOH)2 (H2PDA), of the compositions [(NpO2)2(PDA)(H2O)3]·H2O (I), (NH4)2[NpO2(PDA)]2·3H2O (II), and [C(NH2)3]2[NpO2·(PDA)]2·4H2O (III) were synthesized. The Np atoms in the crystal lattices of all the compounds have the pentagonal bipyramidal coordination surrounding, with the [C12H6N2(COO)2]2− anions acting as chelate-bridging N,O-donor ligands. In the structure of I, two crystallographically independent NpO2+ dioxocations participate in the cation-cation interaction leading to the formation of tetrameric cation-cation complexes. The nonequivalence of the Np atoms is manifested in splitting of the main absorption band of Np(V) in the electronic spectrum of solid compound I. The structures of II and III are based on dimeric anionic complexes [NpO2(C12H6N2(COO)2)]22−. Only one kind of complexes, NpO2(PDA)−, was detected in the solution, and high value of the concentration stability constant β, ∼1012 L mol−1, is due to tetradentate coordination of the ligand.