Composition and structure of complexes formed in the reaction of uranyl di(2-ethylhexyl)phosphate and tributyl phosphate or di-N-octyl sulfoxide in benzene solutions

This paper reprots of³¹P NMR and IR studies of the interaction of tributyl phosphate (TBP) and di-n-octyl sulfoxide (DOSO) with polymer molecules of uranyl di-2-ethylhexyl phosphate (UO₂X₂)_p (I) in C₆H₆ sulutions. Detailed interpretations of the³¹P NMR spectra and the v_as(POO) IR bands and determination of the fraction of nonequivalent phosphorus atoms of X⁻ anions and uranium (VI) atoms as well as the concentration of U(VI)-bonded TBP in I have shown that only a single TBP or DOSO molecule is coordinated to the uranium atoms of polymer I at C_TBP=0.1–2 M or C_DOSO=0.1–0.5 M. In the case of 100% TBP, two TBP molecules are coordinated to some U(VI) atoms. Distribution of TBP (DOSO) molecules along the polymer chain agrees with the mean statistical value. The portion of terminal chalate POO-groups of X⁻ anions is determined. The dependence of the degree of (UO₂X₂)_p·nL (L=TBP, DOSO) polymerization on C_L is obtained. Saturation of solutions with water only slightly affects the terminal POO-groups and has no effects on the distribution of L along the polymer chain of I. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 66–73, November–December, 1994. Translated by K. Shaposhnikova     

Heteroorganic betaines

The [Ph₃P⁺−CMe₂−SiMe₂−SEt]Br⁻ salt was prepared by the reaction of betaine Ph₃P⁺−CMe₂SiMeR−S⁻ (1a: R=Me) with EtBr. Acetylation of betaine1a or Et₃P⁺−CHMeSiMe₂−S⁻ (2a) afforded 2,2,6-trimethyl-1,3-dioxa-2-silacyclohex-5-ene-4-thione      

Ab initio study of the complexes of first-row transition-metal ions with CH, CH2, and CH3

The geometries and bonding characteristics of the complexes of the first-row transition-metal ions with CH, CH₂ and CH₃ were investigated byab initio molecular orbital theory. MCH⁺ and MCH₂ ⁺ are linear and coplanar, respectively. Both of them are with obvious treble or double bond characteristics, but these multiple bonds are mostly “imperfect”. The calculated bond dissociation energies of , and are mostly close to the experimental values, and appear in similar periodic trends from Sc to Zn. Project supported by the National Natural Science Foundation of China (Grant No. 29170070).     

The study of the speciation of uranyl–sulphate complexes by UV–Vis absorption spectra decomposition

Uranyl–sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO₂(NO₃)₂ + Na₂SO₄ solutions of different Φ _S = [SO₄²⁻]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO₂(NO₃)₂ + NaNO₃ solutions with different Φ _N = [NO₃⁻]/[U(VI)] ratio at pH = 2 were also measured. The effects of Φ _S and Φ _N ratios value were most pronounced in wavelength interval 380–500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO₂SO₄, UO₂(SO₄)₂²⁻, UO₂NO₃ ⁺ and UO₂(NO₃)₂ coincided well with published data, but those for UO₂(SO₄)₃⁴⁻ and UO₂(NO₃)₃⁻ were significantly lower.     

Extraction of actinides by quaternary amines from hydrochloric acid medium

The extraction of Np(IV), Pu(IV) and U(VI) from aqueous hydrochloric acid into quaternary amines has been studied. The dependence of the distribution coefficient on amine concentration suggests that the actinide ions extracted are NpCl ₆ ²⁻ PuCl ₆ ²⁻ and UO₂Cl ₄ ²⁻ . This is further supported by the absorption spectra of the amine extracts of these actinide ions. Based on the extraction data obtained, a simple method for the separation of typical metal ions such as Cs, lanthanides and Zr from U(VI) and Pu(IV) is suggested.     

Application of capillary electrophoresis to the uranyl/citrate system in moderately acidic solutions

The capillary electrophoresis method has been applied to the speciation study of uranium(VI) at room temperature, in 0.02M citrate buffer solutions, at pH values between 2.5 and 5.5 and at citrate/U ratios between 20 and 40. No negatively charged species have been pointed out at pH values lower than 3. For a pH value higher than 5, the electropherograms are ill-defined and the signals cannot be analyzed simply (owing to a high and rough baseline). In the pH range 3–5, up to 4 peaks can be attributed to U(VI) species. Two of them are likely due to the expected monomer [(UO₂)(Cit)]⁻and dimer [(UO₂)₂(Cit)₂]²⁻ complex species and these species are shown to be in quasi-equilibrium with two other species possessing slightly lower migration velocities, [(UO₂)H(Cit)(OH)]⁻ and [(UO₂)₂H₂(Cit)₂(OH)₂]²⁻, respectively. Speciation diagrams calculated by an exact analytical approach are proposed in order to explain the experimental results. A complete agreement between theoretical and experimental results needs to take into account kinetic and hydrolysis effects.     

Synthesis,structural studies and biological activity of dioxomolybdenum(VI), dioxotungsten(VI), thorium(IV) and dioxouranium(VI) complexes with 2-hydroxy-5-methyl and 2-hydroxy-5-chloroacetophenone benzoylhydrazone

New complexes of MoO₂(VI), WO₂(VI), Th(IV) and UO₂(VI) with aroyl hydrazones have been prepared and characterized by various physicochemical methods. Elemental analysis suggested 1 : 1 metal : ligand stoichiometry for MoO₂(VI), WO₂(VI), and UO₂(VI) complexes whereas 1 : 2 for Th(VI) complexes. The physicochemical studies showed that MoO₂(VI), Th(IV) and UO₂(VI) complexes are octahedral. The electrical conductivity of these complexes lies in the range 1.00 × 10⁻⁷−3.37 × 10⁻¹¹Ω⁻¹ cm⁻¹ at 373 K. The complexes were found to be quite stable and decomposition of the complexes ended with respective metal oxide as a final product. The thermal dehydration and decomposition of these complexes were studied kinetically using both Coats-Redfern and Horowitz-Metzger methods. It was found that the thermal decomposition of the complexes follow first order kinetics. The thermodynamic parameters of the decomposition are also reported. The biological activities of ligands and their metal complexes were tested against various microorganisms.     

Kinetics of Complexation of Uranium with 2-(5-Bromo-2-Pyridylazo)-5-(Diethylamino) Phenol (Br-PADAP) in a 1:1 Water-Ethanol Medium

2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) forms a 1:1 complex with the uranyl ion in the presence of sulphosalicylic acid, which acts as stabilizer for this complex in the triethanol amine/perchloric acid buffer system. A change in the stoichiometry of the complex was seen at pH<5. Kinetic measurements were carried out using stopped-flow spectrophotometer in the presence of an excess concentration of U(VI) in the pH range 6.5 to 8. The dependence of the pseudo-first-order rate constant, k(obs), on the concentrations of U(VI), ligand and hydrogen ion showed that Br-PADAP reacts with UO₂(OH)⁺ to form an intermediate species (equilibrium constant = 1.28×10⁴mol.dm⁻³) that then rearranges (rate constant = 5.6×10⁻²s⁻¹) to form the product species. UO₂(OH)⁺ is present in equilibrium with the unreactive species UO₂(OH)₂, as well as with the unreactive sulfosalicylic acid complex.     

Synthesis, characterisation and chemical reactivity of some new dioxouranium(VI) complexes of 2-aminobenzoylhydrazone of butane-2,3-dione

A new series of dioxouranium(VI) complexes of a potential ONNO tetradentate donor 2-aminobenzoylhydrazone of butane-2,3-dione (L₁H₂) have been synthesized. At pH 2·5–4·0, the donor (L₁H₂) reacts in the keto form and complexes of the type [UO₂(L₁H₂)(X)₂] (X⁻=Cl⁻, Br⁻, NO ₃ ⁻ , NCS⁻, ClO ₄ ⁻ , CH₃COO⁻, 1/2SO ₄ ²⁻ ) are obtained. At higher pH (6·5–7), the complex of the enol form having the formula [UO₂(L₁)(H₂O)] has been isolated. On reaction with a monodentate lewis base (B), both types of complexes yield adducts of the type [UO₂(L₁)(B)]. All these complexes have been characterised adequately by elemental analyses and other standard physicochemical techniques. Location of the bonding sites of the donor molecule around the uranyl ion, status of the uranium-oxygen bond and the probable structure of the complexes have also been discussed.     

Heteroorganic betaines

Photolysis and thermal decomposition of betaines R₃P−CR¹R²−SiR³R⁴−S⁻ (1) follows two main pathways: (a) a Corey—Chaykovsky type reaction with elimination of Ph₃P and generation of silathiirane (2) and (b) a retro-Wittig type reaction accompanied by elimination of R₃P=CR¹R² and generation of silanethione R³R⁴Si=S (3). Highly reactive compounds2 and3 undergo subsequent transformations to give derivatives of tetrahydro-1,4-dithia-2,5-disilin, 1,3-dithia-2,4-disilolane, and phosphonium salts ofsymm-tetraorganodisilthiane dithiolates [Ph₃P⁺CHR¹R²]₂[(R³R⁴SiS⁻)₂S]. The structures of the compounds obtained were established by X-ray diffraction analysis and multinuclear NMR spectroscopy. For part 3, see Ref. 1. The betaines Et₃P⁺CHMeSiMe₂S⁻ and Et₃P⁺CHMeSiPh₂S⁻ with alkyl groups at the phosphorus atom are distinguished by high thermal stability; their spectral characteristics do not change during storage of solutions of these compounds in pyridine-d₅ or metastable solutions in benzene-d₆ for 1–2 years at −20°C in sealed evacuated tubes or on heating (150°C) for 15 h. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1594–1603, September, 2000.     

BEAMGAA with photons — the axial gradient

The extraction of uranyl nitrate by the novel extractant N,N’-dimethyl-N,N’-dioctylsuccinylamide (DMDOSA) from aqueous nitric/nitrate solutions was investigated. The effects of concentration of HNO₃ and DMDOSA on the U(VI) extraction distribution was studied. The extraction mechanism was established and the stoichiometry of the main extracted species was confirmed to be UO₂(NO₃)₂·2DMDOSA. The value of ΔH of the extraction is −23.9±1.7 kJ·mol⁻¹. A IR spectral study of the U(VI) extracted species was also made.     

Study of kinetics,equilibrium and isotope exchange in ion exchange systems. II

The kinetics of isotope exchange in the²³⁸U(VI)-²³³U(VI)-strongly acidic cation exchanger Ostion KS system was studied in the temperature range 275–307K and for total uranium concentration 2.94·10⁻⁴–1.75·10⁻² mol·l⁻¹ in UO₂(NO₃)₂ solution. The experimental results were evaluated by means of the “two-film mass-transfer model” and by the use of Fick's diffusion equations which have been proved more suitable for the system studied than McKay's equation. The influence of the temperature was evaluated using the Arrhenius equation. The diffusion character of the process follows also from the value of the activation energy (15.12 kJ·mol⁻¹). In comparison with the UO ₂ ²⁺ ↔H⁺ ion exchange⁶ the isotope exchange studied is faster and less dependent on temperature (the activation energy is substantially lower).     

Sequestering Ability of Dicarboxylic Ligands Towards Dioxouranium(VI) in NaCl and KNO<Subscript>3</Subscript> Aqueous Solutions at <Emphasis Type="Italic">T</Emphasis>=298.15 K

The formation constants of dioxouranium(VI)-2,2′-oxydiacetic acid (diglycolic acid, ODA) and 3,6,9-trioxaundecanedioic acid (diethylenetrioxydiacetic acid, TODA) complexes were determined in NaCl (0.1≤I≤1.0 mol⋅L⁻¹) and KNO₃ (I=0.1 mol⋅L⁻¹) aqueous solutions at T=298.15 K by ISE-[H⁺] glass electrode potentiometry and visible spectrophotometry. Quite different speciation models were obtained for the systems investigated, namely: ML⁰, MLOH⁻, ML₂²⁻, M₂L₂(OH)⁻, and M₂L₂(OH)₂²⁻, for the dioxouranium(VI)–ODA system, and ML⁰, MLH⁺, and MLOH⁻ for the dioxouranium(VI)–TODA system (M=UO₂²⁺ and L = ODA or TODA), respectively. The dependence on ionic strength of the protonation constants of ODA and TODA and of both metal-ligand complexes was investigated using the SIT (Specific Ion Interaction Theory) approach. Formation constants at infinite dilution are [for the generic equilibrium pUO₂²⁺+q(L²⁻)+rH⁺ ⇌(UO₂²⁺) _p (L) _q H _r ^(2p−2q+r);β _pqr ]: log ₁₀ β ₁₁₀=6.146, log ₁₀ β ₁₁₋₁=0.196, log ₁₀ β ₁₂₀=8.360, log ₁₀ β ₂₂₋₁=8.966, log ₁₀ β ₂₂₋₂=3.529, for the dioxouranium(VI)–ODA system and log β ₁₁₀=3.636, log ₁₀ β ₁₁₁=6.650, log ₁₀ β ₁₁₋₁=−1.242 for dioxouranium(VI)–TODA system. The influence of etheric oxygen(s) on the interaction towards the metal ion was discussed, and this effect was quantified by means of a sigmoid Boltzman type equation that allows definition of a quantitative parameter (pL ₅₀) that expresses the sequestering capacity of ODA and TODA towards UO₂²⁺; a comparison with other dicarboxylates was made. A visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO₃ medium) has been calculated to better characterize the compounds found by pH-metric refinement.     

Extraction of U(VI) and Th(IV) from nitric acid medium using tri(butoxyethyl) phosphate (TBEP) in <Emphasis Type="Italic">n</Emphasis>-paraffin

Extraction behavior of U(VI) and Th(IV) from nitric acid medium is investigated using organo-phosphorous extractant, tri(butoxyethyl) phosphate in n-paraffin at room temperature (27 ± 1 °C). The effect of diluents, nitric acid concentration as well as extractant concentration on extraction of U(VI) and Th(IV) are evaluated. Extraction of U(VI) and Th(IV) from nitric acid medium proceeds via solvation mechanism. Slope analysis technique showed the formation of neutral complexes of the type of UO₂(NO₃)₂·2TBEP and Th(NO₃)₄·3TBEP with U(VI) and Th(IV) respectively in the organic phase. The FTIR data showed shifting of P=O stretching frequency from 1,282 to 1,217 cm⁻¹ indicating the strong complexation of P=O group with UO₂ ²⁺ ions in the organic phase. Effect of stripping agents, other metal ions and their separation with respect to U(VI) extraction has also been investigated.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP)

Except for conditions of low acidity and low ratios of di(2-ethylhexyl)phosphoric acid (HDEHP) to U(VI) the data obtained for the distribution of U(VI) between sulfuric acid solutions and polyurethane foams loaded with solutions of HDEHP in nitrobenzene could be analyzed by the equation: log (4.36 D_u)=log K+1.43 log (C_d–4C_u)/(C_H)^1.4+log f_u where the polymerization number of HDEHP is about 2.8, D_u is the distribution ratio, and f_u=[UO ₂ ²⁺ ]_(aq)/[UO₂]_(aq) indicating that the extraction proceeds via the formation of a 14 UO₂:HDEHP complex. At both low acidity and HDEHP/U(VI) ratio a UO₂-HDEHP polymer is formed.     

Synthesis and characterization of thorium and uranium cyanoacetates and their coordination compounds

Tetracyanoacetates of thorium and uranium, M(NCCH₂COO)₄ (where M = Th or U) and dioxouranium (VI) dicyanoacetate [UO₂(NCCH₂COO)₂H₂O] and their coordination complexes with dimethyl sulphoxide (DMSO), dimethyl formamide (DMF), 1,10 phenanthroline (Phen) and 2,2′-bipyridyl (Bipy) have been synthesised and characterised by elemental analysis, molecular weight determination, molar conductance measurements, X-ray diffraction and infrared spectroscopic studies (4000–200cm⁻¹). Structural aspects of the compounds and the sites of bonding of the ligands to the central metal atom have been discussed in the light of shifts in thev(C ≡ N),v(COO),v(UO₂) and the metal-ligand stretching vibrations. Thermogravimetric analysis of the compounds have been carried out to study thermal decomposition modes.     

Complexes of dioxouranium(VI) with zwitter-ionic forms of Bi- and tetra-dentateSchiff bases

Potentially bi- and tetra-dentateSchiff bases derived from salicylaldehyde react with hydrated uranyl salts to give complexes: UO₂H₂ LX ₂, UO₂H₂ LX ₂ and UO₂(HL)₂ X ₂ [H₂ L=N,N-propane-1,3-diylbis(salicylideneimine), H₂ L=N,N-ethylenebis(salicylideneimine) and HL=N-phenylsalicylideneimine;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^–, and NCS^–]. Because of marked spectral similrities with the structurally known Ca(H₂ L) (NO₃)₂, theSchiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups which carry the protons transferred from phenolic groups on coordination. Halide, nitrate, perchlorate and thiocyanate groups are covalently bonded to the uranyl ion, resulting a 6-coordinated uranium ion in the halo and thiocyanato complexes and 8-coordinated in nitrato and perchlorato complexes.

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Komplexe von Dioxouranyl(VI) mit zwitterionischen Formen von zwei- und vierzähnigen Schiff-Basen

Zusammenfassung Von Salizylaldehyd abgeleitete zwei- und vierzähnigeSchiff-Basen reagieren mit hydratisierten Uranylsalzen zu Komplexen folgenden Typs: UO₂H₂ LX ₂, UO₂H₂ LX ₂ und UO₂(HL)₂ X ₂ [H₂ L=N,N-Propan-1,3-diylbis(salicylidenimin), H₂ L=N,N-Ethylen-bis(salicylidenimin) und HL=N-Phenylsalicylidenimin;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^– und NCS^–]. Auf Grund eindeutiger spektraler Ähnlichkeiten mit dem bekannten Ca(H₂ L) (NO₃)₂ wird auf Koordination über die negativ geladenen phenolischen Sauerstoffatome (und nicht über die Azomethin-Stickstoffe) geschlossen. Die AnionenX ^– sind kovalent an das Uranyl-Ion gebunden; damit ergibt sich ein hexakoordiniertes Uranyl-Ion für die Halogen- und Thiocyanat-Komplexe und Oktakoordination für die Nitrat- und Perchlorat-Komplexe.

     

Effective complex formation in the interaction of 1,2-dimethyl-3-hydroxypyrid-4-one (Deferiprone or L1) with uranium(VI)

In an effort to develop new chelating agents for the decorporation of uranium and other actinides, the interaction of the clinically used 1,2-dimethyl-3-hydroxypyrid-4-one (Deferiprone or L1) with hexavalent uranium was investigated by using UV-VIS spectroscopy and solubility measurements. The complex stoichiometry estimation carried out by the Job plot method indicated that under normal conditions up to pH 8.0 a 1[U(VI)]∶1[L1] complex is formed. The stability constant of the UO₂L1⁺ complex was determined by spectroscopic and solubility experiments and found to be log β₁₁=9.1±0.3. The molar extinction coefficient at pH 7.6 for the complex at 500 nm was estimated to be 650 l·mol⁻¹·cm⁻¹. At ligand concentrations higher than 6·10⁻⁴ mol·l⁻¹ the formation of a precipitate was observed. The stoichiometry UO₂(L1)₂ was identified following FTIR measurements of the red precipitate and UV/VIS spectroscopy after dissolution.     

Spectroscopic investigation of uranium sorption on soil surface using X-ray photoelectron spectroscopy

A study was carried out to understand the sorption of uranium (U) onto soil surface and identify the species of U on soil surface using X-Ray Photoelectron Spectroscopy (XPS). For the study soil was amended with uranyl nitrate and surface speciation study was carried out by investigating the energy region for U in spectrum. Analysis of spectrum revealed that U is present in U(VI) state. Deconvolution of XPS spectrum of U(VI) sorbed on soil surface revealed that U(VI) species such as, UO₂ ²⁺ and (UO₂)_x(OH) _y ^(2x?y)+ form complex with silanol, aluminol and goethite sites. The possible surface complexation is: ≡Al(OH)₂UO₂ ²⁺, ≡SiO₂UO₂, ≡SiO₂(UO₂)₃(OH)₅ and ≡Fe(OH)₂UO₂.     

On the Hydrolysis of the Tetravalent Uranium Ion U4+

The formation of the hydrolytic complexes of U(IV) has been investigated at 25.00°C by measuring the Emf of a cell containing inert metal sponge and glass electrodes, in 3 mol·dm^?3 aqueous NaClO₄ solutions containing both U(VI) and U(IV) at acidities ranging between 10^?0.5 and 10^?1.8 mol·dm^?3. The lower limit of acidity is imposed by the precipitation of the sparingly soluble oxides of U(IV) whereas the upper limit has been chosen in order to avoid large corrections for the liquid junction potential. The experimental data have been treated using classical graphical methods (Rossotti, F.J.C., Rossotti, H.: The Determination of Stability Constants. McGraw Hill Book Company, Inc. New York (1961)) and by the computerized least-squares program LETAGROP-ETITR (Sillen, L.G., Warnqvist, B.: Arkiv för Kemi. 31, 315–39 (1969)). The results can be explained by assuming the formation of two mononuclear complexes, U(OH)³⁺ and $\mathop {{\rm U(OH)}}\nolimits_4^0The formation of the hydrolytic complexes of U(IV) has been investigated at 25.00°C by measuring the Emf of a cell containing inert metal sponge and glass electrodes, in 3 mol·dm⁻³ aqueous NaClO₄ solutions containing both U(VI) and U(IV) at acidities ranging between 10^−0.5 and 10^−1.8 mol·dm⁻³. The lower limit of acidity is imposed by the precipitation of the sparingly soluble oxides of U(IV) whereas the upper limit has been chosen in order to avoid large corrections for the liquid junction potential. The experimental data have been treated using classical graphical methods (Rossotti, F.J.C., Rossotti, H.: The Determination of Stability Constants. McGraw Hill Book Company, Inc. New York (1961)) and by the computerized least-squares program LETAGROP-ETITR (Sillen, L.G., Warnqvist, B.: Arkiv f?r Kemi. 31, 315–39 (1969)). The results can be explained by assuming the formation of two mononuclear complexes, U(OH)³⁺ and . The obtained formation constants in the 3 mol·dm⁻³ NaClO₄ ionic medium are: and . The formal standard potential ^* E _6,4 for the couple UO₂ ^{2 +}/U^{4 +} at the same conditions is 335.7± 0.5 mV.