UO2 Complexes Research Articles

Rates and mechanisms of water exchange of UO2(2+)(aq) and UO2(oxalate)F(H2O)2-: a variable-temperature 17O and 19F NMR study.

This study consists of two parts: The first part comprised an experimental determination of the kinetic parameters for the exchange of water between UO2(H2O)5(2+) and bulk water, including an ab initio study at the SCF and MP2 levels of the geometry of UO2(H2O)5(2+), UO2(H2O)4(2+), and UO2(H2O)6(2+) and the thermodynamics of their reactions with water. In the second part we made an experimental study of the rate of water exchange in uranyl complexes and investigated how this might depend on inter- and intramolecular hydrogen bond interactions. The experimental studies, made by using 17O NMR, with Tb3+ as a chemical shift reagent, gave the following kinetic parameters at 25 degrees C: kex = (1.30 +/- 0.05) x 10(6) s(-1); deltaH(not equal to) = 26.1 +/- 1.4 kJ/mol; deltaS(not equal to) = -40 +/- 5J J/(K mol). Additional mechanistic indicators were obtained from the known coordination geometry of U(VI) complexes with unidentate ligands and from the theoretical calculations. A survey of the literature shows that there are no known isolated complexes of UO2(2+) with unidentate ligands which have a coordination number larger than 5. This was corroborated by quantum chemical calculations which showed that the energy gains by binding an additional water to UO2(H2O)4(2+) and UO2(H2O)5(2+) are 29.8 and -2.4 kcal/mol, respectively. A comparison of the change in deltaU for the reactions UO2(H2O)5(2+)--> UO2(H2O)4(2+) + H2O and UO2(H2O)5(2+) + H2O --> UO2(H2O)6(2+) indicates that the thermodynamics favors the second (associative) reaction in gas phase at 0 K, while the thermodynamics of water transfer between the first and second coordination spheres, UO2(H2O)5(2+) --> UO2(H2O)4(H2O)2+ and UO2(H2O)5(H2O)2+ --> UO2(H2O)6(2+), favors the first (dissociative) reaction. The energy difference between the associative and dissociative reactions is small, and solvation has to be included in ab initio models in order to allow quantitative comparisons between experimental data and theory. Theoretical calculations of the activation energy were not possible because of the excessive computing time required. On the basis of theoretical and experimental studies, we suggest that the water exchange in UO2(H2O)5(2+) follows a dissociative interchange mechanism. The rates of exchange of water in UO2(oxalate)F(H2O)2- (and UO2(oxalate)F2(H2O)2- studied previously) are much slower than in the aqua ion, kex = 1.6 x 10(4) s(-1), an effect which we assign to hydrogen bonding involving coordinated water and fluoride. The kinetic parameters for the exchange of water in UO2(H2O)52+ and quenching of photo excited *UO2(H2O)5(2+) are very near the same, indicating similar mechanisms.

Synthesis and Characterization of Solid Coordination Complexes of Diamides for Uranium(VI) and Thorium(IV)

Five kinds of solid coordination complexes of uranium(VI) and thorium(IV) with the diamide (N,N,N′,N′-tetrabutylmalon-amide (TBMA), N,N,N′,N′-tetrabutylsuccinylamide (TBSA), N,N,N′,N′-tetrabutylglutaramide (TBGA), N,N,N′,N′-tetrabutyl-adipicamide (TBAA)) were synthesized. All these complexes of UO2(NO3)2·TBMA, UO2(NO3)2· TBSA, [UO2(NO3)2·(TBGA1/2)2] x , UO2(NO3)2·TBAA and Th(NO3)4·2TBMA were characterized by elemental analysis, UV spectra, IR spectra and 13C NMR spectra. The coordination form and proposed structures of the complexes are also discussed.

Removal of dissolved uranium by nanofiltration

A plate module membrane filtration equipment was operated to evaluate the uranium removal efficiency from drinking water of five different nanofiltration flat sheet membranes. Experiments were carried out using different model waters. Hydrochemical settings were chosen which allow uranium to form those complexes that are the most important for uranium mobilization in natural water: uranyl hydrogen carbonate complexes. Especially the divalent anion complex UO 2(CO 3) 2 2− and the four-valent anion complex UO 2(CO 3) 3 4− which mainly occur in natural water were rejected between 95% and 98% by four membranes and between 90% and 93% by one membrane.

Complexation of UO2 2+ by the siderophore mycobactin S in ethanol

This paper reports preliminary results concerning the complexing affinity of the siderophore mycobactin S towards UO2 2+. Owing to the hydrophobic behaviour of the siderophore, all experiments are performed in ethanol as a solvent, involving specific pH-metry. The complexation is followed by UV-visible spectrophotometry and a model is developped in order to fit the data. This model takes into account ionic strength corrections in ethanol, by use of an adapted Davies equation. Although the fit is rather good, it is suggested that the hydrolysis of UO2 2+ while pH is increased should be taken into account.

Dioxouranium(Vi) Mixed Ligand Complexes Containing 8-Hydroxyquinoline and Some Amino Acids

The formation equilibria of binary and ternary complexes of UO2 (VI) with 8-hydroxyquinoline (HL) and some amino acids (HL') in 40% EtOH-H2O solution have been investigated by a potentiometric technique. The stepwise formation constants of the complexes formed in solution were calculated using the non-linear, least-squares computer program MINIQUAD. The concentration distribution of the complex species was resolved. Mixed ligand complexes of the general formula [UO2LL'-(H2O)n](NO3)m, where HL = 8-hydroxyquinoline; HL' = glycine, alanine, L-valine, proline, leucine, P-phenylalanine and H2L' = histidine or histamine, n = 0 or 2 and m = 0 or 1, have been synthesised and characterized by elemental analyses, electrolytic conductance, electronic spectra, IR, 1H NMR spectra and thermogravemetric studies. The uranium atom in these complexes is 6- or 8-coordinate. Both HL and HL' are bidentate, bonding through N or O atoms (phenolate or ionized COO− groups).

Interaction of uranium(VI) with silicic acid in aqueous solutions studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

We investigated for the first time the complex formation in the uranyl–silicate system by fluorescence spectroscopy. The interaction between soluble species of uranium(VI) with silicic acid was studied in 0.3 M NaClO 4 solution using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Tetramethylorthosilicate (TMOS) was used as source of silicic acid in order to minimize the formation of polymeric silicon species. Fluorescence lifetimes were obtained for (a) the free uranyl cation of 1.7±0.3 μs, and (b) the 1:1 silicato–uranyl complex of 19.0±4 μs. The main fluorescence bands of the complex UO 2OSi(OH) 3 + are centered at 500, 521, 544 and 570 nm. The stability constant of the complex UO 2OSi(OH) 3 + was determined at pH 3.9, as log β°=−(1.67±0.20) using an uranyl concentration of 2.3×10 −5 M, and a monosilicic acid concentration up to 5.4×10 −3 M.

ChemInform Abstract: Investigation of Aquo and Chloro Complexes of UO2+2, NpO+2, Np4+, and Pu3+ by X‐Ray Absorption Fine Structure Spectroscopy.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and Spectroscopic Studies of 2,2-Dipyridylamine Complexes of La(III), Ce(III), Pr(III), Th(IV), UO2(VI) and a Peroxo Derivative of UO2(VI)

Nitrato and isothiocyanato 2,2′-dipyridylamine (HDPA) complexes of La(III), Ce(III), Pr(III), Th(IV) and UO2(VI) have been synthesized. An acetato complex of UO2(VI) is also reported in addition to a peroxo complex of UO2(VI). The complexes have been characterized by elemental analyses, molar conductances, magnetic measurements, UV-Vis, IR and thermogravimetric methods. The lanthanide nitrato complexes are 1:1 electrolytes; chelated nitrato and ionic nitrate were established by IR measurements. The ambidentate thiocyanate binds through the hard donor N-site. The values of the bond stretching force constant (FU=0) and bond length (RU=0) of the uranyl complexes have been calculated. The peroxo content was determined by redox titration and the compound was found to be thermally stable. Referee I: P. R. Shukla Referee II: M. Athar

Synthesis and characterization of carbamoylphosphonate monomer and its copolymer with styrene. II

A monomer, diethyl α,α-dimethyl-m-isopropenylbenzyl carbamoylphosphonate, has been prepared by the base-catalyzed reaction of the isocyanate m-TMI (α,α-dimethyl-m-isopropenylbenzylisocyanate) with diethyl phosphite. The structure of the carbamoylphosphonate monomer and its styrene copolymer was confirmed spectroscopically, and the nature of the hydrogen bondings in the NHC(O)P(O)(OR)2 unit in the monomer and copolymer is discussed in detail. A bulk polymerization of the carbamoylphosphonate is very slow and tends to yield a crosslinked product, but a solution polymerization produced the soluble copolymers. The Tg(midpoint) of the homo-polymer is low, 67°C, and its capacity to complex UO2(NO3)2 is very high, 28 wt % (19 mol %). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 889–899, 1997

Spectral luminescence studies of uranyl nitrate crystals with neutral ligands

UDC 535.372;41.426 Uranvl nitrates are usually considered to bc ore_" of the most convenient ob.iects for study of the interaction between the I..!O~ group and ligands in uranvl complexes. I'hc convenience prinl,:lrlly consists m the fact th;_ll these compounds provide broad variation of Neutral ligands (NI.~ in the equatorial crlvironmcnt of the ur/~n,,'l ion, becat]sc of which i! is possible 1o ~n,,esligi?~te cortlprehensi\'cly ilrld ttloroughly lht.: ['ilcLlns ~tnd ch~ractcr of lhc production of uranyl complexes, formation of their strctlturc, their physico-chemlc:~l, nnd. particlllarly, lumtnc~;ccrlcr propcrlles as functions of the physico-chcmtcal and empirical parameters of NL. Meanwhile, in spite Of a great rlumbcr of publications concerned with experimental studies of uran\'l nitrate complexes, their structurc is not known completely. For example, at present most of rcscarchcrs I l-4 I think that in the uranvl nitrate complexes with NL, the first coordination sphere of the uranyl ion contains only two rnolecules. However, some authors I1, 51 suggest that there may bc uranyl nitrate complexes with both one NL molecule [1 I and three molecules coordinated directly to the uranyl ion [,5 I. It should by also noted cas will bc shown later) that it is possible that solid nitrate complexes with NL are formed, and in these complexes nitrate groups are not coordinated directly to uranyl. Information that reflects the mechanisms of successive changes in the composition, struclure, and properties of uranyl nitrate compounds as functions of characteristics of NL is insufficient. The above-enumerated problems are considered and solved to some extent in the present work by analysis of tow-*emperature (T = 77 K) luminescence spectra of fine crystalline specimens of uranyl nitrate compounds grown from solutions with various proportions of uranyl and NL. An empirical parameter, the Gutman donor number (DN} [6, 71, was used as a quantitative characteristic of NL, as it reflects most completely specific and nonspecific interactions between electron donors and acceptors. In [8 } it is shown that this parameter is applicable to solutions. The specimens were produced using the complex UO2(NO3)2-6H20 and the following organic solvents: diethyl ether (DEE), tributylphosphat e (TBP), tripropyl phosphate CFPP), tetrahydrofuran cTHF), dimethyl formamide {DMFA), dimelhyl acetamide (DMAA), dimethvl sulfoxide (DMSO), hcxamethyl phosphortriamide (HMPTA), and others. Uranyl nitrate ctwstals with the indicated ligands were grown following procedures similar to those reported in [91. The uranyl-lo-ligand ratio was t:2 or 1:2.5. Most of the specimens were fine crystalline powders. It should be noted lhat some of the compounds studied were investigated earlier by different authors

The mechanism of the photoreaction of uranyl 1,3-diketonate complexes as thin films on silicon surfaces

The photolysis of the complexes UO 2(OH 2)(RCOCHCOR) 2 (R  Me or t-C 4H 9) on silicon surfaces leads to the production of uranium oxide. The quantum yields for this process are quite different for the two complexes. The methyl and the tert-butyl-substituted complexes decompose with quantum yields of 0.007 (±40%) and 0.015 (±30%) respectively. In spite of the similarity in chemical formula a detailed mechanistic investigation indicates that two distinct reaction pathways exist for these systems. In the case of the methyl derivative the reactivity is initiated by an excited state hydrogen abstraction through a six-member transition state. The tert-butyl-substituted complex cannot undergo hydrogen abstraction and so the excited state decays by a ligand fragmentation reaction.

Dioxouranium(VI) and thorium(IV) complexes with 2(2′-pyridyl)1-methylbenzimidazole and reaction of dioxouranium(VI) complex with mercury(II), cobalt(II) and nickel(II)

The biheterocyclic ligand 2(2′-pyridyl)-1-methylbenzimidazole (MePB) forms complexes of the type UO 2(MePB)X 2 (X  Cl, I, NO 3, CH 3COO, 0.5 SO 4), UO 2(MePB) 2(NCS) 2 and Th(MePB) 2X 4 (X  NO 3, NCS, I). Reaction of UO 2(MePB)Cl 2 with HgCl 2 resulted in the formation of the heterobinuclear complex UO 2(MePB)HgCl 4, whereas the reaction of UO 2(MePB) 2(NCS) 2 with M(NCS) 2 (M  Co II or Ni II) yield paramagnetic, octahedral complexes, M(MePB) 2(NCS) 2 (M  Co, Ni), with the displacement of UO 2 2+ ion. The electronic spectra and the effective magnetic moments of the complexes (4.77 and 2.79 μ B, respectively) confirmed their octahedral geometry. The complexes were characterized by combination of elemental analyses, conductivity measurements, thermogravimetric studies and IR, electronic, mass and NMR ( 1H and 13C) spectral studies. The 1H and 13C NMR signals of the free ligand undergo a downfield shift on complexation. The EIMS of the ligand and FABMS of the complex reveal the molecular mass of the ligand and its fragmentation pattern.

Flotation of Uranium from Seawater with Phosphate Esters of C-Undecylcalix[4]resorcinarene

Abstract Table-type chelating surfactants ([4]ArmX-R12, mX means the number of phosphates (P), carboxylic acid (Ac), and hydroxamic acid (Hx), respectively) have been derived from the calix[4]resorcinarene bearing tetradodecyl side chains ([4]Ar-R12), and applied to a collector of uranium flotation. The surface tension of the aqueous solution was 35 mN m−1 for [4]Ar5.6P-R6 (Rn means the alkyl chain length), 52 mN m−1 for [4]Ar5.9P-R12, 42 mN m−1 for [4]Ar8.0Ac-R12, and 48 mN m−1 for [4]Ar5.1Hx-R12. They formed UO2 complexes and floated the UO22+ from an aqueous solution by air-bubbling. Furthermore, [4]Ar5.9P-R12 and [4]Ar6.3P-R12 had competence to float the uranium from seawater. A trace amount of uranium in 450 cm3 of seawater was floated at 68—94% using 1—10 mg of [4]Ar5.9P-R12 or [4]Ar6.3P-R12. On the other hand, [4]Ar5.1Hx-R12 and [4]Ar8.0Ac-R12 brought about lower floatabilities. [4]ArmP-R12 could be recycled several times by dissolving the scum (uranium complex) in 5 mol dm−3 H2SO4.

Effect of Alkyl Substituents on the Hydrogen Bonding and Molecular Structure of Benzophenylhydroxamic Acids Crystal structure of UO2 Complex of p-Isopropylbenzophenylhydroxamic Acid

The effect of alkyl substituents on the C-phenyl and/or the N-Phenyl ring of benzophenylhydroxamic acid on their molecular structure and hydrogen bonding has been investigated. The predominant configuration in CHCl3 is determined by steric and electronic effects. Substituents on the C-phenyl ring favor the cis configuration, while substituents in the N-phenyl ring favor a trans configuration. These can be rationalized on the basis of electronic effects. Bulky substituents in the C-phenyl ring give rise to a mixture of cis and trans forms due to steric factors. When substituents are present on the C-phenyl ring and N-phenyl ring the trans configuration is preferred. The crystal and molecular structures of complex of p-isopropylbenzophenylhydroxamic acid have been determined from a single crystal of this complex to elucidate the effect of complexation on the structure of this ligand which exists as a cistrans mixture. Complexation occurs exclusively from the cis configuration.

Synthesis of Neutral and Anionic Uranyl Aryloxide Complexes from Uranyl Amide Precursors: X-ray Crystal Structures of UO2(O-2,6-i-Pr2C6H3)2(py)3 and [Na(THF)3]2[UO2(O-2,6-Me2C6H3)4

Reaction of anhydrous UO{sub 2}Cl{sub 2} with 2 equiv of KN(SiMe{sub 3})2 in THF leads to formation of the neutral bis(amido) complex UO{sub 2}[N(SiMe{sub 3})2]2 (1), whereas the use of 2, 3, or 4 equiv of NaN(SiMe{sub 3})2 in an analogous reaction produces the tetrakis (amido) salt [Na(THF){sub 2}]2[UO{sub 2}[N(SiMe{sub 3})2]4] (2). Alcoholysis of 1 with 2 equiv of HO-2,6-i-Pr{sub 2}C{sub 6}H{sub 3} in the presence of pyridine gives the bis(aryloxide) complex UO{sub 2}(O-2,6-i-Pr{sub 2}C{sub 6}H{sub 3})2(py){sub 3} (3) (py=C{sub 5}H{sub 5}N), whereas alcoholysis of 2 with 4 equiv of HO-2,6-Me{sub 2}C{sub 6}H{sub 3} in THF produces the tetrakis (aryloxide)salt [Na(THF){sub 3}]2[UO{sub 2}(O-2,6-Me{sub 2}C{sub 6}H{sub 3})4] (4) The molecular structures of 3 and 4 have been determined by means of single-crystal X-ray diffraction studies. Compound 3 exhibits pentagonal bipyramidal geometry, with the uranyl oxygen atoms occupying the axial positions and the aryloxide atoms and 2.197 (9) {Angstrom} for the aryloxide ligands, while U-N distances to the pyridine ligands average 2.616 (7) {Angstrom}. Compound 4 is comprised of a uranium metal center coordinated in a pseudo-octahedral fashion by six oxygen atoms, with two sodium cations each coordinated to one uranyl oxygen atom and one oxygen atom of an aryloxide ligand. U-Omore » bond distances to the uranyl oxygens average 1.814(5) {Angstrom}, while distances to the aryloxide ligands average 2.204(8) {Angstrom} for the two aryloxide ligands not involved in coordination to the sodium cations and 2.288(5) {Angstrom} for the aryloxide ligands forming U-O-Na interactions.« less

Synthesis and coordination chemistry of 2,6-bis(diethoxyphosphino)pyridine P, P-dioxide. Crystal and molecular structure of UO 2(NO 3) 2{[EtO) 2P(O)] 2C 5H 3N}

A Michaelis-Becker reaction of excess Na(EtO) 2P(O) with 2,6-dichloropyridine N-oxide results in the formation of 2,6-bis(diethoxyphosphino)pyridine P, P-dioxide [(EtO) 2P(O)] 2C 5H 3N. Attempts to N-oxidize the pyridine were unsuccessful. The ligand in 1:1 combination with UO 2(NO 3) 2 · 6H 2O gives a complex UO 2(NO 3) 2{[(EtO) 2P(O)] 2C 5H 3N} whose molecular structure was determined by single crystal X-ray diffraction techniques. The compound crystallizes in the monoclinic space group C2/ c with a = 24.909(6), b = 6.819(1), c = 23.213(6) A ̊ , β = 141.26(1)° and Z = 4 . The structure consists of infinite chains formed by trans coordination of phosphoryl groups from two ligands on each UO 2 2+ unit. The pyridine nitrogen atom is not involved in the coordination chemistry.

Uranium Speciation in Solution by Time-Resolved Laser-Induced Fluorescence

Complexation studies of radionuclides (such as uranium) are important to perform in order to predict their migration behavior in natural systems. Time-resolved laser-induced fluorescence, which is a very selective and sensitive method for actinide and lanthanide analysis, is used to study the interactions between uranyl cation and hydroxide ions at low uranium concentration (0.4 [mu]M). The principle of the study is based on time resolution and spectral convolution since free uranyl ion (UO[sub 2][sup 2+]) and first hydroxide complex give specific fluorescence spectra characterized by their spectral shift and fluorescence lifetime. Spectroscopic data (main fluorescence wavelengths, half-bandwidth, lifetime) for the first hydrolyzed complex UO[sub 2]OH[sup +] are obtained. From experimental spectra and time-resolved spectral convolution, the proportion of each species (free uranyl, complexed uranyl) can be estimated at different pH. 33 refs., 5 figs., 3 tabs.

ChemInform Abstract: Complex Fluorouranates(VI). Synthesis, Characterization and Structural Assessment of New Mixed‐Fluoro Complexes of UO2+ 2 Containing Phosphate, Nitrate or Hydrazine as the co‐Ligands.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Squarete complexes of uranyl ions in aqueous solution

The stability constants of UO 2 2+ -squarate complexes are measured at ionic strengths of 0.05M, 0.06M, 0.075M, 0.09M, 0.1M (squaric acid-perchloric acid) using a solvent extraction method at a pH of 1.1 and a temperature of 25 °C. The extractant used is dinonylnaphthalenesulfonic acid in n-heptane. The aqueous phase was made of a mixture of squaric and perchloric acid and233U radio tracer. The stability constants of squarate complexes of UO 2 2+ is seen to decrease linearly with the square root of the ionic strength.

EXAFS analysis of aqueous and acetonitrile solutions of UO 2-trilate with crown-ethers and aza-crowns. Crystals structures of the inclusion complexes UO 2(18-crown-6)(CF 3SO 3) 2 and UO 2(dicyclohexyl-18-crown-6)(CF 3SO 3) 2

Aqueous and acetonitrile solutions of uranyltriflatecrown systems have been studied by EXAFS and compared to the corresponding solids. In aqueous solution the uranyl moeity is surrounded by five water molecules. In acetonitrile solution, uranyl inclusion compounds are formed when the crown has six donor atoms. If the macrocycle has a different size, a direct uranyltriflate bond is observed, acetonitrile molecules complete the uranyl coordination. UO 2(18-crown-6)(CF 3SO 3) 2 and UO 2(dicyclohexyl-18-crown-6)(CF 3SO 3) 2 inclusion complexes have been structurally characterized by single-crystal X-ray diffraction: in both complexes, the uranyl is bonded to the six O atoms of the crown ether in an hexagonal bipyramidal coordination.