Mixed-Valence NpV/AnVI Molybdate Complexes with Single-Charge Outer-Sphere Cations.

Five new mixed-valence NpV/AnVI molybdates of the composition [C(NH2)3]3[(NpVO2)(NpVIO2)(MoO4)3(H2O)]·H2O (1), [C(NH2)3]3[(NpVO2)(NpVIO2)(MoO4)3(H2O)]·3H2O (2), Na3[(NpVO2)(PuVIO2)(MoO4)3(H2O)]·nH2O (3), Na6[(NpVO2)2(UVIO2)(MoO4)5]·13H2O (4), and LiNa2[(NpVO2)(NpVIO2)2(MoO4)4(H2O)]·4H2O (5) have been synthesized and structurally characterized. The coordination polyhedra of the NpV and AnVI atoms in compounds 1-5 are pentagonal bipyramids. The basis of structures 1-3 is anionic layers of the composition [(NpVO2)(AnVIO2)(MoO4)3(H2O)]n3n-. Three crystallographically independent molybdate ions are tridentate-bridging ligands. The water molecule, which is a part of the anion layer, is coordinated to the NpV atom. The anionic layers in complexes 2 and 3 have the same structure, different from 1. The basis of structure 4 is anionic layers of the composition [(NpVO2)2(UVIO2)(MoO4)5]n6n-, the structure of which differs from the structure of anionic layers in 1-3. Complex 5 has a three-dimensional (3D) structure. The spectra of all compounds in the UV-visible and IR ranges were measured and analyzed.

Secondary Role of Aliphatic and Heterocyclic Amines in the Formation of Low-Temperature Amine-Bearing U, Np, and Pu(VI) Chromates.

Uranyl compounds with tetrahedral oxoanions demonstrate a significant structural and topological diversity. Complexes of transuranium elements with such anions are not equally well-represented in the literature. To answer the question about the structural similarity in a series of An6+ complexes with XO42- anions, we synthesized and studied 10 new U, Np, and Pu chromates with outer-sphere organic cations. The structural analysis and comparison with the literature data shows that the Np and Pu complexes are generally based on the same structural blocks as the uranyl compounds. Moreover, the chromate anion does not show any unique structural role as compared to the sulfate and selenate ions. As a result, the neptunium and plutonium chromates contain 1D and 2D structural units similar to those found in the uranyl sulfates and selenates. The templating role of the outer-sphere cations in the actinyl complexes with tetrahedral oxoanions is also not evident, and there is no clear correlation between the nature of the outer-sphere cations and the topology of the structural units.

Neptunium(V) Isothiocyanate Complexes with 4'-Aryl-Substituted 2,2':6',2″-Terpyridines and N,N-Dimethylacetamide as Molecular Ligands.

New complexes of neptunyl(V) isothiocyanate with 4'-aryl-substituted 2,2':6',2″-terpyridines (Terpy) and N,N-dimethylacetamide (DMA) were obtained: [(NpO2)(4'-Ph-Terpy)(DMA)(NCS)]·DMA, [(NpO2)(4'-(4-(CF3)C6H4)-Terpy)(DMA)(NCS)]·2H2O·DMA, [(NpO2)(4'-(3-BrC6H4)-Terpy)(DMA)(NCS)]·DMA, and [(NpO2)(4'-(2-(COOH)C6H4)-Terpy)(DMA)(NCS)]·DMA. The structures of the compounds were determined with X-ray diffraction analysis. The neptunium coordination polyhedra were found to be pentagonal bipyramids with O atoms of the NpO2 groups in the apical positions and the equatorial planes formed by three N atoms of the terpyridine ligand, a N atom of the isothiocyanate anion, and an O atom of DMA. The influence of the substituents of the Ar group on the crystal structure is discussed. The IR spectra contain well-resolved bands of characteristic vibrations of all groups in the complex. The electronic absorption spectra are typical for neptunium(V) complexes and contain an intense narrow absorption band belonging to an f-f transition with a maximum of 988 nm and several long-wave satellites of lower intensity. The substituted terpyridines were shown to be efficient for the extraction of various valence forms of neptunium from the isothiocyanate solutions.

Interaction with Simple Monopyridinecarboxylic Ligands Revealing Unexpected Structural Types of Uranyl Halides.

The inclusion of monopyridinecarboxylic acids into the structures of uranyl halides results in the formation of unexpected structural units. Molecules of picolinic and nicotinic acids acting as bridging ligands favor the formation of unprecedented dinuclear units in two uranyl bromide complexes, which comprise two metal centers in different, tetragonal- and pentagonal-bipyramidal, coordination geometries. Moreover, the different positions of the nitrogen atom in the molecule of nicotinic acid induce significant bending of the heterodimer. The uranyl chloride complex with isonicotinic acid also exhibits a structure containing metal atoms in two unique geometries. The structure consists of cationic and anionic isolated fragments. The anionic part is unprecedented and represents the first example of a 1:3 uranyl halide unit with a tetragonal bipyramid surrounding the central atom.

Perrhenate and Pertechnetate Complexes of U(IV), Np(IV), and Pu(IV) with Dimethyl Sulfoxide as an O-Donor Ligand.

A series of new dimethyl-sulfoxide-containing pertechnetates and perrhenates of tetravalent U, Np, and Pu were synthesized and structurally characterized by the X-ray diffractometry. In all the synthesized compounds, the actinide atoms were coordinated by eight DMSO molecules with or without an extra XO4- anion in the coordination sphere. This resulted in the square antiprismatic or capped square antiprismatic coordination of An atoms. Three or four XO4- anions play the role of outer-sphere anions. The electron and IR spectra of the compounds correlated with their crystal structure.

Peculiarities of the Supramolecular Assembly of Tetraethylammonium and 3-Bromopropionate Ions in Uranyl, Neptunyl, and Plutonyl Coordination Compounds.

Synthesis and X-ray diffraction studies of {N(C2H5)4}[AnO2(C2H4BrCOO)3] [An = U (I), Np (II), or Pu (III)] and C2H4BrCOOH (IV), where C2H4BrCOO- is an anion of the 3-bromopropionic acid, are reported. The isostructural coordination compounds I-III contain mononuclear anionic complexes [AnO2(C2H4BrCOO)3]- belonging to the crystal chemical group AB013 (A = AnO22+; B01 = C2H4BrCOO-). In the crystal structure of IV, the C2H4BrCOOH molecules are hydrogen bonded into centrosymmetric dimers R22(8). Using the method of molecular Voronoi-Dirichlet (VD) polyhedra, the features of intermolecular interactions in crystals of I-IV are discussed in support of the results of IR and UV spectroscopy experiments. Actinide contraction in I-III manifests itself in a regular reduction of the average length of the axial and equatorial bonds in hexagonal bipyramids AnO8, in an increase in νas(AnO22+) wavenumbers, and in a simultaneous decrease in the volume and sphericity degree of VD polyhedra of An atoms in the U-Np-Pu series. The title compounds represent an interesting architecture, where 3-bromopropionate ions penetrate through the square 44 net of tetraethylammonium ions and thus bind adjacent nets via the "locking effect".

Structural Role of Isonicotinic Acid in U(VI), Np(VI), and Pu(VI) Complexes with TcO4-, ReO4-, and ClO4- Ions.

A series of new pertechnetate, perrhenate, and perchlorate compounds of hexavalent U, Np, and Pu containing isonicotinic acid were synthesized. Their crystal structures were determined by X-ray diffractometry. In all compounds, actinide atoms are found in pentagonal bipyramidal surroundings. They are coordinated by 2 to 4 isonicotinic acid molecules which exist in zwitterionic form as a result of N atom protonation. If only 2 or 3 isonicotinic acid molecules are present in the surroundings of an actinide (An) atom, TcO4- or ReO4- anions act as monodentate ligands. Otherwise, XO4- play the role of outer sphere anions. Electron and IR spectra of the compounds correlate with their crystal structure.

Polymeric structure of oxalato-bridged complexes of tetravalent actinides Th, U, Np and Pu.

A series of isostructural oxalates of Th, U, Np, and Pu have been synthesized. The crystal structure of {C(NH(2))(3)}(4)[An(C(2)O(4))(4)]·2H(2)O comprises infinite [An(C(2)O(4))(4)](4n-) chains, guanidinium cations and water molecules. Each An atom is connected to five oxalate anions, two of which act as bridging tetradentate ligands, while the other three function as terminating bidentate ligands. Electron and IR spectra of the compounds as well as the results of thermal analysis correlate with their structure. An actinide contraction effect is demonstrated by a decrease in the An-O interatomic distances and the volumes of An atom coordination polyhedra and Voronoi-Dirichlet polyhedra. Ten-coordinate An oxalates are discussed in terms of continuous shape measures approach.

Synthesis and structural examination of complexes of Am(IV) and other tetravalent actinides with lacunary heteropolyanion alpha2-P2W17O61(10-).

This study concerns the formation of complexes with actinides at oxidation state +IV, from Th to Am, through a lacunary heteropolyanion ligand P(2)W(17)O(61)(10-). The preparation of original single crystals of complexes with 1:2 stoichiometry provided structural data through single-crystal X-ray diffraction for the entire An(IV) series. An(IV) atoms in these complexes have a coordination number of 8, and their coordination polyhedron is a distorted square antiprism. The data were used to compute a mean (An-O) interatomic distance for each actinide. When the interatomic distance is plotted versus the inverse ionic radius of these tetravalent actinides, it appears that the simple electrostatic model is not suitable for Am(IV) and Pu(IV), although this trend must be confirmed by further investigation with other examples from the An(IV) series.

Interaction of transuranium elements with biologically important ligands: structural and spectroscopic evidence for nucleotide coordination to plutonium.

The first complex of a transuranium element (tetravalent plutonium) with nucleotide (deoxycytidinemonophosphate, dCMP) was synthesized and structurally characterized. The crystal structure of [Pu(4)(NO(3))(8)(HdCMP)(4)(H(2)O)(8)](NO(3))(4).2H(2)O consists of complex cations [Pu(4)(NO(3))(8)(HdCMP)(4)(H(2)O)(8)](4+), NO(3)(-) anions, and water molecules. There are two crystallographically independent Pu atoms in the structure, both having similar surroundings. Each of the Pu atoms is coordinated by three O atoms of phosphate groups belonging to three different (HdCMP)(-) anions, two bidentate nitrate anions, and two water molecules. The crystal structure is confirmed by IR and UV/vis/near-IR spectroscopic data.

Interaction of transuranium elements with biologically important molecules: structural and spectroscopic study of NP(V) complexes with imidazole.

New Np(V) complexes with imidazole, [NpO(2)(CH(3)COO)(Im)(2)(H(2)O)], [(NpO(2))(2)(C(2)O(4))(Im)(6)] x 5 Im x H(2)O, and [NpO(2)(NO(2))(Im)(4)], were synthesized. Their crystal structures were determined using X-ray single-crystal diffractometry. The crystal structures are confirmed by IR and UV-vis spectroscopic data. In all three complexes, neptunium coordinates the imidazole molecule through the nitrogen atom. These complexes are the first example of direct bonding of the imidazole molecule to the actinide atom. These results suggest that coordination of histidine residue in proteins or other imidazole-containing biologically important molecules could occur under usual biological conditions.

First structural evidence of actinide-nitrite coordination.

The first nitrite complex of actinide metal, {C(NH 2)3}2[NpO 2(NO 2)(Pic)2], was synthesized, and its crystal structure was determined using X-ray diffractometry and confirmed by NIR and IR spectroscopies. Main crystallographic data: space group P1, triclinic, a = 8.9329(1) A, b = 11.6669(2) A, c = 11.6698(2) A, alpha = 68.080(1) degrees, beta = 88.213(1) degrees, gamma = 73.254(1) degrees, V = 1076.45(3) A (3), and Z = 2.