Crystal structure of mixed-valent Np(IV)/Np(V) chloride, [Np(NpO2)6(H2O)8(OH)Cl9]·H2O

A new mixed-valent Np(IV)/Np(V) chloride, [Np(NpO₂)₆(H₂O)₈(OH)Cl₉]·H₂O, was synthesized, and its crystal structure was determined. The crystals consist of NpO ₂ ⁺ and Np⁴⁺ cations, of Cl^? and OH^? anions, of coordination-bonded water molecules, and of water molecules of crystallization. The Np(V) atom, Np(1), has pentagonal bipyramidal coordination surrounding with O atoms in the apical position and with the equatorial plane formed by three Cl^? anions, O atom of the adjacent NpO ₂ ⁺ cation, and O atom of water molecule. The mutual coordination of the neptunyl(V) ions, cation-cation (CC) interaction, links the Np(1) coordination polyhedra via common vertices into rings around sixfold axes, with the Np(V)?Np(V) distance in these fragments of 4.276 Å. The ring fragments are linked with each other via common equatorial edges of the bipyramids into layers perpendicular to c-axis. The Np(IV) atom, Np(2), has coordination surrounding in the form of tricapped trigonal prism (CN 9) with the tetragonal lateral faces formed by the O atoms of the NpO ₂ ⁺ cations and the capping positions occupied by the O atoms of two water molecules and one hydroxy group. The Np(2) atoms act in CC interactions as coordination center for six NpO ₂ ⁺ ions, with the Np(IV)?Np(V) distance of 4.183 Å. The Np(2) polyhedra are arranged in the crystal between layers of the Np(1) coordination polyhedra, linking them with each other.     

Effect of O2, H2O2, and HNO2 on the stability of Np(III–VII) in aqueous solutions

Published data on reactions of Np ions with O₂, H₂O₂, HNO₂, and HNO₃ in solutions of various compositions in a wide pH range are considered. O₂ oxidizes Np(III) in acid solution and Np(IV) and Np(V) in alkaline solutions. H₂O₂ exhibits dual behavior. In weakly acidic solutions, it converts Np(III) and (IV) to Np(V), in 0.75?C1 M NaHCO₃ it oxidizes Np(V) to Np(VI), whereas in dilute HClO₄ and HNO₃ and in carbonate and alkali solutions it reduces Np(VI), and in alkali solutions it reduces Np(VII). The first step of reduction in most cases is the formation of the Np(VI) peroxide complex, and the next step is the intramolecular charge transfer. In concentrated HNO₃ solutions, H₂O₂ converts Np(V) to Np(IV) and Np(VI) and then reduces Np(VI). Some radiation-, photo-, and sonochemical reactions occur via formation of excimers, i.e., of dimers arising from excited and unexcited Np ions. The excimer decomposes into two ions with higher and lower oxidation states. In reduction reactions, the excimer eliminates H₂O₂ (in addition to the H₂O₂ arising as primary product of water radiolysis). In HNO₃ solutions, oxidation of Np ions occurs only in the presence of HNO₂ arising as reaction product or upon radiolysis, photolysis, or sonolysis. The active species are NO ₂ ^? , NO₂, and NO⁺ present in equilibrium with HNO₂.     

X-ray powder diffraction and IR study of NaMg(H2O)2[BP2O8]·H2O and NH4Mg(H2O)2[BP2O8]·H2O

NaMg(H₂O)₂[BP₂O₈]·H₂O was prepared by hydrothermal synthesis and was characterized by X-ray powder difraction and IR method. The title compound was synthesized from MgCl₂·6H₂O, NaBO₃·4H₂O, and (NH₄)₂HPO₄ with variable molar ratios using hydrothermal method by heating at 165 °C for 3 days. The X-ray powder diffraction data was indexed in hexagonal system, the unit cell parameters were found to be as a = 9.428, c = 15.82 Å, Z = 4 and the space group is P6₁22. It is isostructural with M^lM^ll(H₂O)[BP₂O₈] type compounds where M^l = Na, K; M^ll = Mg, Mn, Fe, Co, Ni and Zn. In addition NH₄Mg(H₂O)₂[BP₂O₈]·H₂O was also synthesized the first time in this research. Its unit cell parameters and hkl values were in good agreement with the sodium magnesium compound. The unit cell parameters are a = 9.529, c = 15.736 Å. The indexed X-ray powder diffraction data of both compounds which were not reported in the literature is presented in this work. The IR data of NaMg(H₂O)₂[BP₂O₈]·H₂O is also reported.     

Cation-cation interaction in mixed-valent An(IV)/Np(V) tribromoacetates [An(NpO2)(H2O)3(CBr3COO)5]·CBr3COOH·nH2O,An = Th(IV), Np(IV)

The structure of new mixed-valent An(IV)/Np(V) compounds [An(NpO₂)(H₂O)₃(CBr₃COO)₅]·CBr₃COOH·nH₂O, where An(IV) = Th and Np, was studied. Two independent Np(V) atoms have the coordination surrounding in the form of pentagonal bipyramids with the O atoms of NpO ₂ ⁺ dioxocations in apical positions; the equatorial planes of the bipyramids are constituted by the O atoms of five CBr₃COO^? ions. Two independent An(IV) atoms have the oxygen surrounding in the form of distorted tricapped trigonal prisms (CN = 9) constituted by the O atoms of four CBr₃COO^? ions, two NpO ₂ ⁺ cations, and three water molecules. Eight of ten independent CBr₃COO^? anions link the An⁴⁺ and NpO ₂ ⁺ cations in the bidentate bridging fashion into electrically neutral chains [An(NpO₂)(H₂O)₃(CBr₃COO)₅]n, and two CBr₃COO^? anions interact with two independent NpO ₂ ⁺ dioxocations in the monodentate fashion. CBr₃COOH and water molecules are located between the layers. In the [An(NpO₂)(H₂O)₃(CBr₃COO)₅]n chains, NpO ₂ ⁺ cations alternate with An⁴⁺ cations, and mixed-valent An(IV)/Np(V) cation-cation interaction arises, in which each NpO ₂ ⁺ cation acts as a bidentate ligand and An⁴⁺ acts as coordination center for two dioxocations. [Th(NpO₂)(H₂O)₃(CBr₃COO)₅]·CBr₃COOH·2H₂O is the first example of a Th(IV) compound in which cation-cation bonds with the NpO ₂ ⁺ ions are present.     

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 crystal structure of An(VI) complexes with cyclobutanecarboxylic acid anions and 2,2′-bipyridine [An(VI) = U,Np, Pu]

New complexes of hexavalent U, Np, and Pu of the composition [UO₂(bipy)(cbc)₂] (I) and [AnO₂(bipy)(cbc)₂]·0.5(bipy) [An = Np (II) and Pu (III)] with cyclobutanecarboxylic acid anions C₄H₇COO^– and 2,2′-bipyridine (bipy) were synthesized, and their structures were studied. The An atoms in I–III have the coordination surrounding in the form of distorted hexagonal bipyramids with the О atoms of AnO₂²⁺ cations in the apical positions. The equatorial plane of the bipyramids is constituted by the O atoms of two C₄H₇COO^– anions and N atoms of bipy.     

Reaction of Cd(NO3)2·4H2O with 4,4'–bipyridine (bpy) in MeOH solvent: synthesis and characterization of T-shaped [Cd(bpy)1.5(NO3)2]·3H2O,square grid [Cd(bpy)2(H2O)2](NO3)2·4H2O and linear polymeric [Cd(bpy)(H2O)2(NO3)2]

The influence of concentration of water and metal salt in the reaction between Cd(NO₃)₂·4H₂O and 4,4′–bipyridine in MeOH has been studied and three compounds namely, T-shaped [Cd(bpy)_1.5(NO₃)₂]·3H₂O, 1 square grid [Cd(bpy)₂(H₂O)₂](NO₃)₂ 4H₂O, 2 and one dimensional linear polymer, [Cd(bpy)(H₂O)₂(NO₃)₂], 3 were isolated quantitatively in this process. Compound 1 forms in MeOH at high dilution of the metal salt (5.0 mg/mL or less) and for the metal-to-ligand ratio 1:(1.5–2.0). Compound 2 forms exclusively in the concentration range, 17–33% for water in MeOH by volume and 12–28 mg/mL for the metal salt of the solution. Outside these limits, mixtures of 2 and 3 were isolated. For 1:1 ratio of metal salt to bpy, the linear polymer, 3 was obtained in major quantity and its formation was found to be independent of concentration of water or the metal salt. Compounds 1 and 2 have been characterized by X-ray crystallography. On heating all the compounds decompose through a common intermediate [Cd(bpy)(NO₃)₂] and finally to CdO as monitored by TG.     

An X-ray diffraction study of Rb[UO2(SeO4)F]·H2O

An X-ray diffraction study of Rb[UO₂(SeO₄)F]·H₂O (I) was performed. The compound crystallizes in the rhombic system with the following unit cell parameters: a = 8.4753(6), b = 13.5234(9), c = 13.5296(9) Å, space group Pnma, Z = 8, V = 1550.7(2) ų; R = 0.0248. The principal structural units of crystals of I are [UO₂(SeO₄)F]^? layers belonging to crystal-chemical group AT³M² (A = UO ₂ ²⁺ , T³ = SeO ₄ ^2? , M² = F^?) of uranyl complexes. The uranium-containing layered units are combined via electrostatic interaction with Rb cations and via a system of hydrogen bonds involving outer-sphere water molecules.     

Complexation of hexavalent U,Np, and Pu with cyclopropanecarboxylate anions. Crystal structure of the uranyl complexes {[UO2(bipy)(cpc)]2O2} and [UO2(cpc)2(H2O)2] (bipy = 2,2′-Bipyridine,cpc− = cyclopropanecarboxylate anion)

The complexation of hexavalent U, Np, and Pu with cyclopropanecarboxylate anions, cpc^?, in aqueous solutions was studied. The stepwise concentration stability constants of the complexes PuO₂(cpc) _i ^2?i (i = 1, 2, 3) are as follows: logK _1,2,3 = 2.63 ± 0.20, 1.61 ± 0.20, 1.43 ± 0.20, respectively; the overall concentration stability constant of the complex PuO₂(cpc) ₃ ^? is logβ₃ = 5.67 ± 0.60. The complexing properties of the cpc^? anion are very close to those of butyrate and isobutyrate anions. Two crystalline uranyl compounds were synthesized: {[UO₂(bipy)(cpc)]₂O₂} (bipy = 2,2′-bipyridine) and [UO₂(cpc)₂(H₂O)₂]. The specific feature of the first complex is that it contains peroxide ion. Its appearance may be due to the formation of the cationic moiety via hydrolytic uranyl dimer. The second compound forms a 3D structure, with the complexes linked via hydrogen bonds.     

Crystal structure of a double Np(V) ammonium propionate, NH4[(NpO2)3(C2H5COO)4(H2O)]·3H2O

The structure of NH₄[(NpO₂)₃(C₂H₅COO)₄(H₂O)]·3H₂O was studied by single crystal X-ray diffraction. The single crystals were prepared by hydrothermal synthesis. In the structure, there are three crystallographically independent Np atoms with different equatorial surrounding. All of them have CN 7; the coordination polyhedron is a distorted pentagonal bipyramid. Each NpO ₂ ⁺ cation is bonded to four other cations, acting simultaneously as a bidentate ligand and a coordination center for two other dioxocations. The cation-cation interactions result in formation of trigonal-hexagonal cationic networks.     

Complexes with substituted 2,5-dihydroxy-p-benzoquinones: The inclusion compounds [Y(H2O)3]2 (C6Cl2O4)3·6.6H2O and [Y(H2O)3]2 (C6Br2O4)3·6H2O

Single crystal of [Y(H₂O)₃]₂ (C₆Br₂O₄)₃·6H₂O and [Y(H₂O)₃]₂ (C₆Cl₂O₄)₃·6.6H₂O were grown in aqueous silicagel. The compounds are in principle isostructural. In Y chloranilate one additional water site is occupied as verified by X-ray single crystal structure analysis. Y³⁺ is nine-coordinated by three water molecules and six oxygen atoms of the bischelating (C₆X₂O₄)²⁻ ions (XCl, Br). The coordination polyhedron is an only slightly distorted tri-capped trigonal prism. The connection of Y³⁺ with the dianions leads to infinite, corrugated layers. The layer stacking yields cage-like cavities in which water molecules are accomodated. Hydrogen bonds interlink adjacent layers. Further hydrogen bonds involve the entrapped water molecules. DSC measurements indicated a complicated dehydration process which caused right at the start destruction of the single crystals.     

Synthesis and Study of Sr[HSiUO6]2·2H2O and Ba[HSiUO6]2·2H2O

Uranosilicates of the general formula M^{I I}[HSiUO₆]₂·2H₂O (M^{I I} = Sr, Ba) were prepared by hydrothermal synthesis. Previously unknown intermediate crystal hydrates were separated and studied by X-ray diffraction (XRD), IR spectroscopy, and thermal analysis. Polymorphic transitions -Sr[HSiUO₆]₂ -Sr[HSiUO₆]₂ and -Ba[HSiUO₆]₂ -Ba[HSiUO₆]₂ were revealed at 700 and 780°C, respectively.     

Framework materials containing polyoxovanadates as building units: synthesis and characterization of (N2H5)2[M3(H2O)12V18O42(EO4)]·24H2O (M = Mg,Ca) and Li6[Mn3(H2O)12V18O42(EO4)]·24H2O (E = V,S)

The reaction of an aqueous solution of lithium vanadate with hydrazinium sulfate results in a dark-colored solution that reacts with magnesium sulfate heptahydrate, calcium sulfate dihydrate, and manganese(II) chloride tetrahydrate to yield single crystals of (N₂H₅)₂[M₃(H₂O)₁₂V₁₈O₄₂(EO₄)]·24H₂O (M = Mg, Ca) and Li₆[Mn₃(H₂O)₁₂V₁₈O₄₂(EO₄)]·24H₂O (E = V, S), respectively. The crystal structures of the new solids consist of interpenetrating three-dimensional networks of {V₁₈O₄₂(EO₄)} clusters interlinked via bridging {M(H₂O)₄} (M = Mg, Ca, Mn) groups. The voids in these structures are occupied by lattice water and ion exchangeable cations.     

Crystallization of salts M3[NpO4(OH)2]·nH2O (M = Na, K, Rb, Cs) from concentrated alkali solutions at low temperatures. Synthesis and structure of a new Np(VII) compound, Na3[NpO4(OH)2]·6H2O

Precipitation of salts M₃[NpO₄(OH)₂]·nH₂O (M = Na, K, Rb, Cs) from concentrated alkali solutions at low temperatures (about ?10°C) was studied. From solutions with [OH^?] > 9.5 M, these compounds are isolated as coarse black crystals in high yield without impurity of other phases. The K, Rb, and Cs salts crystallize in the form of the previously studied compounds K₃[NpO₄(OH)₂]·2H₂O and M₃[NpO₄(OH)₂]·3H₂O (M = Rb, Cs). In the case of Na, a new hydrate Na₃[NpO₄(OH)₂]·6H₂O was obtained, and its crystal structure was determined. Crystals of the hexahydrate consist of centrosymmetrical tetragonal-bipyramidal anions [NpO₄(OH)₂]^3?, crystallographically independent Na(1) and Na(2) cations, and water molecules. The coordination surrounding of the Np atom is characterized by noticeable difference (Δ = 0.0203 Å) in the Np-O bond lengths in the equatorial plane of the bipyramid. The [NpO₄(OH)₂]^3? anions are combined with the Na(2) cations to form infinite chains [Na(2)NpO₄(OH)₂(H₂O)₂]^2? in such a manner that the lateral edges of the anion are simultaneously the lateral edges of the Na(2) coordination polyhedron. Incorporation of one of the two crystallographically independent O atoms of the NpO₄ group into the Na(2) coordination surrounding is responsible for a noticeable difference in the Np-O bond lengths in the equator of the [NpO₄(OH)₂]^3? anion. The types of hydrogen bonding in the structures of Na3[NpO₄(OH)₂]·nH₂O (n = 0, 2, 4, 6) are compared.     

Synthesis, Physicochemical Properties, and Electrode Behavior of Ni2[Ni(OH)6W6O18 ] · 8H2O

Nickel(II) hexatungstonickelate(II) was synthesized and characterized by elemental analysis, x-ray diffraction, thermal analysis, IR spectroscopy, and ¹H nuclear magnetic resonance. The results demonstrate that constitutional water is present in the form of OH groups, which can be removed by heating to 230–370°C. The chemical formula of the compound is Ni₂[Ni(OH)₆W₆O₁₈] · 8H₂O. Nickel(II) hexatungstonickelate(II), a poorly soluble compound, was tested as an electrode for Ni(II) determination in solution. Its electrode properties and selectivity for other ions suggest that it is a promising material for such applications. At pH 5, the ion-selective electrode we fabricated has a Nernstian response to Ni(II) (10^–5 to 10^–1 mol/l) which is close to that predicted theoretically.     

Synthesis and structure of Cs3[UO2(CH3COO)3]2(NCS)·H2O

The compound Cs₃[UO₂(CH₃COO)₃]₂(NCS)·H₂O (I) was synthesized and studied by IR spectroscopy and single crystal X-ray diffraction. Compound I crystallizes in the monoclinic system with the following unit cell parameters: a = 7.8286(9), b = 19.892(2), c = 20.050(2) Å, β = 94.527(2)°, space group P2₁/c, Z = 4, R = 0.0387. The uranium-containing structural units in crystals of I are mononuclear complexes [UO₂(CH₃COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?) of uranyl complexes.     

Novel self-assembled decavanadate clusters forming 1D molecular chains and 2D molecular arrays: [HMTA-H···H2O][HMTA-CH2OH][H3V10O28{Na(H2O)4}]·4H2O and [Na2(H2O)10] [H3V10O28 {Na(H2O)2}]·3H2O

Two novel materials, [HMTA-H··H₂O] [HMTA-CH₂OH] [H₃V₁₀O₂₈[Na(H₂O)₄}]·4H₂O, 1 and [Na₂(H₂O)₁₀][H₃V₁₀O₂₈[Na(H₂O)₂}]·3H₂O, 2 containing decavanadate clusters interconnected through hydrated sodium cations forming 1D molecular chains and 2D molecular arrays have been self-assembled from acidified, aqueous vanadate solution in the presence of organic bases, hexamethylenetetramine and 1,3,5-triazine respectively.     

Synthesis and crystal structure of americium(V) dichromate, Cs3AmO2(Cr2O7)2·H2O

A new Am(V) chromate complex with outer-sphere cesium cation, Cs₃AmO₂(Cr₂O₇)₂·H₂O, was prepared from aqueous solution. Its composition and structure were determined by single crystal X-ray diffraction. The Am(V) atom has coordination surrounding in the form of a distorted pentagonal bipyramid with the O atoms of the AmO ₂ ⁺ group in apical positions. The equator of the bipyramid is formed by the O atoms of four dichromate groups and of the water molecule. The mean bond lengths (Å) are as follows: Am=O 1.802(5), Am-O(Cr₂O₇) 2.443(6), and Am-O_w 2.519(6). The Am(V) pentagonal bipyramids are combined via bidentate bridging Cr₂O ₇ ^2? anions into infinite chains [AmO₂(Cr₂O₇)₂H₂O] _n ^3? arranged in layers parallel to the series of diagonal planes (111). A system of hydrogen bonds links the chains in a layer and the layers with each other. The Cs cations are arranged between the layers, forming cationic interlayers.     

Cobalt-mediated synthesis of 2-(4-pyridyl)benzimidazole. x-ray structures of Co[2-(4-pyridyl)benzimidazole]2(H2O)2(NO3)2 and [Co(isonicotinate)(4-pyridiniumcarboxylate)(H2O)(NO3)]∞

We have observed an unusual example of cobalt-mediated cyclization of 4-pyridinecarboxaldehyde and 2-nitroaniline to afford 2-(4-pyridyl)benzimidazole under hydro(solvo)thermal conditions. Reaction of Co(NO₃)₂·6H₂O with 4-pyridinecarboxaldehyde and 2-nitroaniline in ethanol at 120°C gave a cobalt(II) coordination compound, Co[2-(4-pyridyl)benzimidazole]₂(H₂O)₂(NO₃)₂, 1. In contrast, when the hydro(solvo)thermal reaction was carried out between Co(NO₃)₂·6H₂O and isonicotinic acid in the presence of 2-nitroaniline at 110°C, a one-dimensional Co(II) coordination polymer with the formula of [Co(isonicotinate)(4-pyridiniumcarboxylate)(H₂O)(NO₃)]_∞, 2, resulted. The X-ray single crystal structures of both 1 and 2 are described. Interestingly, the isonicotinic acid in 2 exists as a 4-pyridiniumcarboxylate tautomer, and the pyridinium hydrogen atom forms a very strong hydrogen bond to the carboxylate oxygen of the 4-pyridiniumcarboxylate on an adjacent metal center. 1 forms a three-dimensional polymeric network through hydrogen bonding interactions, while 2 exists as a 2-D bilayer polymeric network through hydrogen bonding interactions.