Synthesis and crystal structure of K3[NpO4(OH)2]

Attempts were made to isolate anhydrous compounds of [NpO₄(OH)₂]^3? anions with heavy alkali metal cations (K, Rb, Cs) by crystallization at elevated temperatures, and the salt K₃[NpO₄(OH)₂] was isolated and studied. Crystals of K₃[NpO₄(OH)₂] consist of tetragonal bipyramidal [NpO₄(OH)₂]^3? anions and K⁺ cations. The [NpO₄(OH)₂]^3? anion occupies the position in the symmetry center. The Np-O distances in this anion are 1.8992(7) and 1.9100(7) Å in the equatorial plane of the bipyramid and 2.3231(8) Å with OH groups. The OH hydrogen atoms participate in weak H bonds [O?O 3.0250(11) Å] linking the anions in layers [NpO₄(OH)₂] _n ^3n? parallel to the (010) plane. In the interlayer space, there are two crystallographically different K atoms. Their coordination number (CN) can be considered to be equal to 7 and 8. Comparison with the structures of the known compounds Na₃[NpO₄(OH)₂] and K₃[NpO₄(OH)₂]·2H₂O was made. The structure of the latter compound was redetermined with higher accuracy. The failure of attempts to prepare the anhydrous rubidium and cesium compounds is probably due to large ionic radius of these cations, requiring high coordination number.     

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 NpO ₂ ⁺ 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)] ₂ ^2? . 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.     

Molybdate Complexes of Np(V) with Outer-Sphere Cs+ Cations

Radiochemistry - Structure of two new molybdate complexes of Np(V) with composition of Cs2[(NpO2)2(MoO4)2(H2O)]·H2O (I) and Cs3[(NpO2)(MoO4)2] (II) has been studied. In structure I, two...     

Synthesis and crystal structure of new Np(VI) and Pu(VI) phthalates, Na4{AnO2[(OOC)2C6H4]3} · n H2O

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. Original Russian Text ? I.A. Charushnikova, N.N. Krot, I.N. Polyakova, Z.A. Starikova, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 2, pp. 106–110.     

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.     

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.     

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),...     

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.     

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

Mixed-cation salts of the general composition NaM₂[NpO₄(OH)₂]·4H₂O, where M = Rb (I, II) and Cs (III), were synthesized and structurally characterized. The compounds differ from each other in the structural organization. The Np central atom in [NpO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with the O atoms of hydroxide ions in the 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, and in the structures of II and III the framework of large cations is built of 12-vertex Rb and Cs polyhedra. The coordination polyhedra of the Np and Na atoms, sharing a common edge (I, III), or chains of the coordination polyhedra of the Np and Na atoms, sharing common vertices (II), are accommodated in the channels of the frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [NpO₄(OH)₂]^3– anions.     

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.