Cation–Cation Interaction in Complexes of Np(V) Benzoate and Salicylate with N-Containing Molecular Ligands

Radiochemistry - The hydrothermal method was used to obtain two new compounds of Np(V): benzoate [(NpO2)3(py) (C7H5O2)3(H2O)2] (1) and salicylate [(NpO2)(phen)(HOC7H4O2)] (2), where py = pyridine...     

Synthesis and crystal structure of a new Np(V) oxalate, Na4(NpO2)2(C2O4)3·6H2O

A new oxalate complex, Na₄(NpO₂)₂(C₂O₄)₃·6H₂O, with the Np:C₂O₄ ratio of 2:3 was synthesized and studied by single crystal X-ray diffraction. In the crystal, the NpO ₂ ⁺ cations and oxalate anions are bound in open networks [(NpO₂)₂(C₂O₄)₃] _n ^4n- parallel to the bc plane. The Na(1) cations are accommodated in large voids of the neptunyl oxalate networks with the formation of crimped mixed-cation layers of the composition [Na₂(NpO₂)₂(C₂O₄)₃] _n ^2n- . The negative charge of the layers is compensated by the Na(2) cations arranged between the layers. The Np atoms have a pentagonal bipyramidal coordination surrounding with the equatorial plane formed by the oxygen atoms of three oxalate anions. The structure contains tridentate-bridging and tetradentate-bridging oxalate anions.     

Synthesis and Structure of Mixed-Cation Salts with [PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.     

Crystal Structure of a Double Neptunium(V) Lanthanum Nitrate,La(NpO<Subscript>2</Subscript>)<Subscript>3</Subscript>(NO<Subscript>3</Subscript>)<Subscript>6</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The structure of a double neptunium(V) lanthanum nitrate, La(NpO₂)₃(NO₃)₆·nH₂O, was studied by single crystal X-ray diffraction. Each neptunyl(V) ion in the structure of the compound is bonded to four other neptunyl(V) ions, acting simultaneously as a bidentate ligand and as a coordination center for two other dioxocations. The cation-cation interaction of the neptunyl(V) ions results in formation of trigonal-hexagonal cationic networks. The surrounding of each Np atom also includes two bidentate nitrate ions. The CN of the Np atom is 8, and the coordination polyhedron is a distorted hexagonal bipyramid. The La³⁺ cations are surrounded only by water molecules.     

Reaction of ozone with Np(IV) and Pu(IV) oxalates in water

The reaction of the ozone–oxygen mixture with aqueous suspensions of Np(IV) and Pu(IV) oxalates was studied. Both metal cations and oxalate anions are oxidized in the process. The final products are Np(VI) and Pu(VI) hydroxides. The composition of Np(VI) hydroxide was confirmed by X-ray diffraction analysis. Oxidation of Np(IV) oxalate with oxygen leads to the accumulation of Np(V) oxalate and oxalic acid in the solution. At incomplete oxidation of Np(IV) oxalate with ozone in water, Np(V) is also accumulated. Heating considerably accelerates the ozonation. The possible reaction mechanism is briefly discussed. The Np(V) and Np(VI) ions participate in the catalytic cycle of the decomposition of oxalate ions with ozone.     

Complexes of An(VI) with Cyclobutanecarboxylic Acid Anions and Outer-Sphere Alkali Metal Cations

New complexes of hexavalent actinides with cyclobutanecarboxylic acid (Hcbc) anions, Na₄[NpO₂· (cbc)₃]₄·H₂O (I), K[NpO₂(cbc)₃] (II), Cs[NpO₂(cbc)₃] (III), and Cs[PuO₂(cbc)₃] (IV), cbc = C₄H₇(COO)^–, were synthesized and studied by single crystal X-ray diffraction. The structures of I–IV are based on the anionic complexes [AnO₂(cbc)₃]^– surrounded by alkali metal cations. The AnO ₂ ²⁺ cation in the anionic complex is bonded with three chelating C₄H₇COO^– anions, and the coordination polyhedron (CP) of An is a hexagonal bipyramid with the O atoms of the AnO ₂ ²⁺ cations in apical positions. The coordination number (CN) of the alkali metal cations in the structures of II–IV is the same and equal to 6; the coordination surrounding of the K⁺ and Cs⁺ cations is constituted by the O atoms of six C₄H₇COO^– anions. The crystal structures of II–IV are examples of cubic 3-connected networks (10,3) built of alkali metal and actinide cations. In the structure of I, there are four kinds of crystallographically different NpO ₂ ²⁺ and Na⁺ cations. The coordination surrounding of the NpO ₂ ²⁺ cations differs only in the conformational characteristics of the C₄H₇COO^– ligands. Four independent Na⁺ cations differ from each other in the structure of the coordination surrounding. The CPs of the Na(1) and Na(4) atoms can be described as distorted octahedra (CN 6); that of Na(3), as a trigonal prism (CN 6); and that of Na(2), as a tetragonal pyramid (CN 5) with one of the basal vertices occupied by the Ow(1) atom of a water molecule. In the structure of I, the configuration of the network formed by the Na and Np cations differs from the cubic 3-connected network found in the structures of II–IV.     

Synthesis and Structure of the Np(VII) Complex with Guanidinium,Li[C(NH<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>[NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]·6H<Subscript>2</Subscript>O

The previously unknown Np(VII) compound Li[C(NH₂)₃]₂[NpO₄(OH)₂]·6H₂O (I), containing organic cations, was synthesized and studied by single crystal X-ray diffraction. In contrast to the relatively numerous structurally characterized salts of [NpO₄(OH)₂]^3– anions with Na⁺, K⁺, Rb⁺, and Cs⁺ cations, which were prepared only from strongly alkaline media, crystals of I were isolated from solutions with a very low concentration of OH^– ions (about 0.1 M). The compound is relatively stable in storage in the dry form, but is strongly hygroscopic. In the structure of I, there are two independent Np(VII) atoms with the oxygen surrounding in the form of tetragonal bipyramids. In contrast to the other salts of the [NpO₄(OH)₂]^3– anions with singlecharged alkali metal cations, the C(NH₂) ₃ ⁺ ions and hydrated Li⁺ ions in I interact with the oxygen surrounding of Np(VII) only via hydrogen bonds of types O_w–H···O and N–H···O with the formation of a three-dimensional H-bond network.     

Synthesis,Crystal Structure,and Spectral Characteristics of the Np(V) Complex with Triphenylphosphine Oxide [NpO2(PO(C6H5)3)4]ClO4

Single crystals of [NpO₂(PO(C₆H₅)₃)₄]ClO₄ were grown and the structure of this compound was studied (CAD4 diffractometer, MoK ; triclinic unit cell: a = 9.140(2), b = 13.528(3), c = 13.918(3) Å, = 97.14(3)°, = 108.17(3)°, = 91.75(3)°, space group P-1, Z = 1, V = 1618.0 ų, d _{c a l c} = 1.521 g cm^-3; R ₁ = 0.0245 for 5342 observed reflections with F ₀ > 4(F ₀), wR ₂ = 0.0677 for 5601 unique reflections, 419 refined parameters). [NpO₂(PO(C₆H₅)₃)₄]ClO₄ consists of complex cations [NpO₂(PO(C₆H₅)₃)₄]⁺ and disordered ClO_4- anions. The Np(V) atom has tetragonal-bipyramidal oxygen surrounding with coordination number (CN) 6. The NpO₂ group is linear, the O = Np = O bond angle is 180.0°, and the Np = O bond length is 1.797(2) Å. The equatorial coordination plane of the bipyramid is formed by oxygen atoms of four triphenylphosphine oxide (TPPO) molecules. The Np-O_eq bond lengths vary from 2.434(2) to 2.442(2) Å (average 2.438 Å). The O_eq-Np-O_eq bond angle is close to the right angle (88.98°). The average bond lengths in TPPO ligands are P-O 1.498, P-C 1.798, and C-C 1.376 Å; the average bond angles are O-P-O 111.12°, C-P-C 107.78°, P-C-C 120.2, and C-C-C 120.0°. The electronic absorption spectra (Shimadzu UV-3100, 900-1050 nm) and IR spectra (Specord-M80, 400-4000 cm^{- 1}) of crystalline [NpO₂(PO(C₆H₅)₃)₄] were measured in an NaCl matrix. The absence of the main characteristic absorption band of the NpO₂ ⁺ dioxocation (980 nm) in the electronic absorption spectrum suggests centrosymmetrical equatorial surrounding of the Np(V) atom. The narrow absorption band ta_{a s}(NpO₂ ⁺) in the IR spectra in the region of 860 cm^-1 suggests the absence of cation-cation interaction, and its position is consistent with a short Np-O bond length in neptunyl(V) groups.     

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) ?, ?? = 91.0930(11)° for I and a = 12.1254(3), b = 10.9506(2), c = 7.7699(2) ?, ?? = 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.     

Nitrate Complexes of Neptunium(V) with Alkali Metal Cations in the Outer Sphere

Radiochemistry - Nitrate complexes of pentavalent neptunium with alkali cations in the outer sphere, with composition Li[NpO2(NO3)2]·2H2O (I), Na[NpO2(NO3)2]·2H2O (II),...