2,2′-Bipyridylamine complexes with uranyl salts

Summary Coordination compounds formed by uranyl chloride, sulphate, nitrate and thiocyanate with 2,2-bipyridylamine have been prepared and characterized by i.r. spectral measurements down to 200 cm^–1 in the solid state. Possible coordination arrangement around the uranyl group in these complexes is discussed.Reprints of this paper are not available.     

Synthesis and structure of uranyl complexes with malonic acid dianions

The uranyl complexes with malonic acid dianions [UO₂(C₃H₂O₄)(CO(NH₂)₂)]·H₂O (1), [UO₂(C₃H₂O₄)(CONH₂NMe₂)]·H₂O (2), and [UO₂(C₃H₂O₄)(MeCONMe₂)] (3) were synthesized and characterized by X-ray crystallography. The structural units [UO₂(C₃H₂O₄)L] in the crystals of 1–3 refer to the AK²¹M¹ crystal chemical group (A = UO₂ ²⁺, K²¹ = C₃H₂O₄ ^2?, M¹ = L) of uranyl complexes; the crystals of 1 have a framework structure and 2 and 3 have a chain structure. Some structural features of the [UO₂(C₃H₂O₄)L] complex groups are discussed.     

Investigation of complexes of octaethyltetraamidepyrophosphate (OETAPP) with uranyl salts using infrared spectroscopy

The infrared spectra of the complexes UO₂ (NO₃)₂-octaethyltetraamidepyrophosphate (OETAPP) and UO₂ Cl₂-OETAPP were investigated to test their formation and structure. Under the experimental conditions used, a stoichiometry of 1∶1 was found for both complex types.     

Photocatalysis with visible-light-active uranyl complexes

Atomic energy is an important part of current energy resources.Production of nuclear weapons and applications of nuclear fuels in nuclear power plants have accumulated numerous spent fuels containing238U compounds,which are critical nuclear materials.How to reduce the nuclear wastes and to make use of the spent uranium are key scientific issues of environmental and nuclear science.We have reviewed here the physiochemical properties and photocatalytic mechanisms of homogeneous and heterogeneous uranium-containing materials.The current research efforts demonstrate that spent fuels can become promising new photocatalytic materials.     

Dimeric uranyl complexes with bridging perrhenates

The reaction between [UO2(ReO4)2.H(2)O] and two equivalents of either tri-n-butyl phosphine oxide (TBPO) or tri-iso-butyl phosphate (TiBP) results in the formation of [UO2(mu2-ReO4)(ReO4)(TBPO)2]2 (1) and [UO2(mu2-ReO4)(ReO4)(TiBP)2]2 (2) respectively. Both complexes crystallise as two structurally similar centrosymmetric dimers, the cores containing two uranyl moieties linked by bridging perrhenates. Two P=O donor ligands and one monodenatate perrhenate complete the pentagonal bipyramidal coordination sphere at each metal centre. Both complexes have also been characterised in the solid state by vibrational and absorption spectroscopy. Solution spectroscopic characterisation indicates that both perrhenate and phosphine oxide (1) or phosphate (2) remain coordinated, although it is not possible to state conclusively that the dimeric species remain intact. A low resolution structural study of a minor product from the reaction that yielded revealed a monomeric complex with only monodentate perrhenate coordination, [UO2(ReO4)2(H2O)(TiBP)2] (2'). These results represent the first structural evidence for the bridging coordination mode of perrhenate on coordination to an actinide and yields further insight into the possible solvent phase pertechnetate complexes that may exist in PUREX process phosphate rich solvent.     

Non-stoichiometric uranyl fluoride complexes with pyridine

Complexes of the type UO₂F₂·(x) pyridine, where x = 0.71 and 1.65, were prepared by the interaction of liquid pyridine on solid UO₂F₂ under similar conditions with the only reaction variable being temperature. These materials have been characterized by chemical reactivity, thermogravimetric analysis, IR spectral analysis and powder X-ray diffractometry. While the exact structure of these materials remains unknown, the possibility of their existence as intercalation compounds is explored.     

Stability and visible absorption of glutamic acid complexes with uranyl and neodymium ions

Summary The stability constants of the complexes of uranyl and neodymium ions with glutamic acid are determined pH-metrically in 0.1 M NaClO₄ solution at 25° C. In both cases protonated complexes are formed in significant concentrations. A new MA complex is found in the uranyl glutamic acid system. In accordance with this investigation a graphical treatment of the visible spectral data gives the molar absorption coefficients of both MA and MHA species.

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Untersuchung der Stabilität und der Absorption im Sichtbaren von Uranyl- und Neodymkomplexen von Glutaminsäure

Zusammenfassung Die Stabilitätskonstanten der Uranylund Neodymkomplexe von Glutaminsäure wurden pH-metrisch in 0,1 M NaClO₄-Lösung bei 25° C bestimmt. In beiden Fällen werden in beträchtlichen Konzentrationen protonierte Komplexe gebildet. Ein neuer MA-Komplex wurde im Uranyl-Glutaminsäure-System gefunden. Eine graphische Behandlung der spektralen Daten im sichtbaren Bereich ergab die molaren Absorptionskoeffizienten für die MA- und MHA-Komplexe.

     

Reactions of uranyl(VI) complexes of acid dihydrazides with β-diketones

Summary Uranyl(VI) complexes of malonic acid dihydrazide (MDH₂) and phthalic acid dihydrazide (PDH₂) and the products of their reactions with four -diketones have been characterised by elemental analysis and by electrical conductance, and spectral (i.r. and electronic) measurements. The MDH₂ and PDH₂ complexes UO₂(L)₂(H₂O)₂ are eight coordinate whereas the macrocyclic UO₂(L)(H₂O)₂ complexes are six coordinate. In each complex MDH₂ and PDH₂ act as bidentate liglands having the coordination sites at secondary amide-nitrogen atoms.     

The first uranyl complexes with valerate ions

FT–IR spectroscopy and single‐crystal X‐ray structure analysis were used to characterize the discrete neutral compound diaquadioxidobis(n‐valerato‐κ²O,O′)uranium(VI), [UO₂(C₄H₉COO)₂(H₂O)₂], (I), and the ionic compound potassium dioxidotris(n‐valerato‐κ²O,O′)uranium(VI), K[UO₂(C₄H₉COO)₃], (II). The U^VI cation in neutral (I) is at a site of 2/m symmetry. Potassium salt (II) has two U centres and two K⁺ cations residing on twofold axes, while a third independent formula unit is on a general position. The ligands in both compounds were found to suffer severe disorder. The FT–IR spectroscopic results agree with the X‐ray data. The composition and structure of the ionic potassium uranyl valerate are similar to those of previously reported potassium uranyl complexes with acetate, propionate and butyrate ligands. Progressive lengthening of the alkyl groups in these otherwise similar compounds was found to have an impact on their structures, including on the number of independent U and K⁺ sites, on the coordination modes of some of the K⁺ centres and on the minimum distances between U atoms. The evolution of the KUO₆ frameworks in the four homologous compounds is analysed in detail, revealing a new example of three‐dimensional topological isomerism in coordination compounds of U^VI.     

Thermodynamics of uranyl complexes with threonine and hydroxyproline

The stability constants of uranyl complexes with threonine and hydroxyproline were studied in aqueous solution at 25 and 45°C by the Calvin-Bjerrum technique. Thermodynamic stability constants have been obtained by extrapolation of the values at various ionic strengths. The values of stepwise changes in ΔG, ΔH and ΔS have been reported.     

Preparation and characterization of uranyl complexes with phosphonate ligands

The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO₂ ²⁺, with phosphonate ligands, such as diphenylphosphonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP) are described. The complexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic solution. The ligands studied and their uranyl complexes were characterized using thermogravimetric and elemental analyses, ESI-MS, IR and UV–Vis absorption and luminescence spectroscopy as well as luminescence lifetime measurements. Compositions of the products obtained dependent on the ligands used: DPhP and DPhPO form UO₂L₂ type of complexes, whereas PhP forms UO₂L complex. Based on TG and DTG curves a thermal stability of the complexes was determined. The complexes UO₂PhP·2H₂O and UO₂(DPhPO)₂ undergo one-step decomposition, while UO₂PhP · 2H₂O is decomposed in a two-step process. The thermal stability of anhydrous uranyl complexes increases in the series: DPhPO < PhP < DPhP. Obtained IR spectra indicate bonding of P–OH groups with uranyl ion. The main fluorescence emission bands and the lifetimes of these complexes were determined. The complex of DPhP shows a green uranyl luminescence, while the uranyl emission of the UO₂PhP and UO₂(DPhPO)₂ complexes is considerably weaker.     

Polarographic studies of uranyl complexes with trans-and cis-butenedioic acids

The complexation of uranyl ion with fumaric and maleic acids was investigated by polarography and conductometry. The uranyl complexes of the two isomers differ: with fumaric acid, UO₂(HFum)₂ and UO₂Fum₂^2- were observed whereas with maleic acid, only one chelate, UO₂Mal₂^2-, was obtained. The dissociation constants obtained from the half-wave potential vs. pH plots were pK₁=3.05 and pK₂=4.55 for fumaric acid and pK₁=1.90 and pK₂=5.60 for maleic acid.     

On the precipitation of salts/complexes of trivalent cations with humic acid

It was found that some trivalent cations form precipitates with humic acid at pH 4.2. The precipitates contain less metal cations than suggested by the neutralization-charge model for soluble complexes based on the available anionic sites. It is suggested that cations, which can form inner-sphere complexes, may precipitate before they are completely neutralized, while those that do not form complexes precipitate only after complete neutralization. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conformation of diethylglyoxime in uranyl complexes

New complexes of uranyl with diethylglyoxime have been synthesized and studied. A feature of these complexes is the tetradentate bridging coordination of the ligand in both cis- and trans-conformations. The structure of organic ligand C₆H₁₂N₂O₂ and binuclear complex (CN₃H₆)₄[(UO₂)₂(C₆H₁₀N₂O₂)(CO₃)(C₂O₄)₂] ? H₂O have been determined by X-ray diffraction.     

Infrared spectroscopy of discrete uranyl anion complexes

The Free-Electron Laser for Infrared Experiments (FELIX) was used to study the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl (UO22+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0-3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands and are comparable to solution-phase values. This result was surprising because initial DFT calculations predicted values that were 30-40 cm(-1) higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO2AS]+ were in accord with trends in the data and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.