Synthesis and reactivity of bis(imido) uranium(VI) cyclopentadienyl complexes

The bis(imido) uranium(VI)-C(5)H(5) and -C(5)Me(5) complexes (C(5)H(5))(2)U(N(t)Bu)(2), (C(5)Me(5))(2)U(N(t)Bu)(2), (C(5)H(5))U(N(t)Bu)(2)(I)(dmpe), and (C(5)H(5))(2)U(N(t)Bu)(2)(dmpe) can be synthesized from reactions between U(N(t)Bu)(2)(I)(2)(L)(x) (L=THF, x=2; L=dmpe, x=1) and Na(C(5)R(5)) (R=H, Me); these complexes represent the first structurally characterized C(5)H(5)-compounds of uranium(VI) and they further highlight the differences between UO(2)(2+) and the bis(imido) fragment.     

Thermal behaviour of uranium(VI) complexes

The solid-state syntheses of complexes of uranyl acetate dihydrate andN-phenylthiourea have been attempted by heating various stoichiometric mixtures of the reactants directly in a DSC and in a TA apparatus. Both the DSC and the TG results indicate that only the 1∶1 adduct is formed, independently of the molar ratios of the reactants. It appears that the reaction is complete only with a large excess ofN-phenylthiourea, in agreement with IR data.     

Polarographic study of uranium(VI)-succinate complexes

The polarographic behavior of uranium(VI)-succinate complexes was studied in 0.5M NaClO₄ medium at 30°C at a dropping mercury electrode. It was found that only the doubly charged succinate ion formed the complexes stable enough to be detected. The experimental evidence for this is discussed. The stability constant of uranium(V) (succinate)₂ complex was evaluated.     

Thermal decomposition of pentacoordinate uranium(VI) complexes

The thermal decomposition of some mixed uranyl complexes with Schiff bases and DMSO, EtOH or (Ph)₃PO as neutral ligand, were investigated and the corresponding activation energy, E*_a, and enthalpy of dissociation, ΔH_d, values were calculated.

The results obtained indicate that for the same neutral ligand, the thermal stability of the uranyl complexes is influenced by the Schiff base used; for the same Schiff base, the presence of (Ph)₃PO results in a greater thermal stability of the mixed complexes than when the other two neutral ligands are present.     

Polarography of uranium(VI) and lead(II) complexes with l-glutamine

The complexes of uranium(VI) and lead(II) with 1-glutamine were investigated polarographically. For uranium(VI), the complexes UO(2)G(+2), UO(2)G(2)(+2) and UO(2)(OH)Ga(2)(+) were identified at pH < 2.5, pH 2.5-4.1 and pH 4.1-5.2 respectively. With lead(II), complexes PbG(+2), Pb(OH)G(+) and Pb(OH)G(2)(+) were formed at pH 2.0-5.0, pH 5.0-7.0, and pH 7.0-8.5, respectively. The concentration dissociation constant of Pb(OH)G(2)(+) was found to be pK(c) = 10.16 +/- 0.04 at ionic strength 0.6.     

31P-NMR study of the organophosphorous complexes of uranium(VI)

The intermolecular ligand exchange in uranyl nitrate complexes with TBP and TOPO is studied by³¹P-NMR. The constant rates at 25°C in CCl₄ are: (8.47±1.86)·10³ s^?1 for U-TBP and (1.3±0.04)·10⁴M^?1·s^?1 for U-TOPO system. The very similar activation parameters values of the ligand exchange suggest the same mechanism for both systems, namely an one-step interchange mechanism. The differences between the systems regarding the rate equations and the extraction properties are discussed.     

Mechanistic investigation of the oxygen-atom-transfer reactivity of dioxo-molybdenum(VI) complexes

The oxygen-atom-transfer (OAT) reactivity of [LiPrMoO2(OPh)] (1, LiPr=hydrotris(3-isopropylpyrazol-1-yl)borate) with the tertiary phosphines PEt3 and PPh2Me in acetonitrile was investigated. The first step, [LiPrMoO2(OPh)]+PR3-->[LiPrMoO(OPh)(OPR3)], follows a second-order rate law with an associative transition state (PEt3, DeltaH not equal=48.4 (+/-1.9) kJ mol-1, DeltaS not equal=-149.2 (+/-6.4) J mol-1 K-1, DeltaG not equal=92.9 kJ mol-1; PPh2Me, DeltaH not equal=73.4 (+/-3.7) kJ mol-1, DeltaS not equal=-71.9 (+/-2.3) J mol-1 K-1, DeltaG not equal=94.8 kJ mol-1). With PMe3 as a model substrate, the geometry and the free energy of the transition state (TS) for the formation of the phosphine oxide-coordinated intermediate were calculated. The latter, 95 kJ mol-1, is in good agreement with the experimental values. An unexpectedly large O-P-C angle calculated for the TS suggests that there is significant O-nucleophilic attack on the P--C sigma* in addition to the expected nucleophilic attack of the P on the Mo==O pi*. The second step of the reaction, that is, the exchange of the coordinated phosphine oxide with acetonitrile, [LiPrMoO(OPh)(OPR3)]+MeCN-->[LiPrMoO(OPh)(MeCN)]+OPR3, follows a first-order rate law in MeCN. A dissociative interchange (Id) mechanism, with activation parameters of DeltaH not equal=93.5 (+/-0.9) kJ mol-1, DeltaS not equal=18.2 (+/-3.3) J mol-1 K-1, DeltaG not equal=88.1 kJ mol-1 and DeltaH not equal=97.9 (+/-3.4) kJ mol-1, DeltaS not equal=47.3 (+/-11.8) J mol-1 K-1, DeltaG not equal=83.8 kJ mol-1, for [LiPrMoO(OPh)(OPEt3)] (2 a) and [LiPrMoO(OPh)(OPPh2Me)] (2 b), respectively, is consistent with the experimental data. Although gas-phase calculations indicate that the Mo--OPMe3 bond is stronger than the Mo--NCMe bond, solvation provides the driving force for the release of the phosphine oxide and formation of [LiPrMoO(OPh)(MeCN)] (3).     

Synthesis and characterization of peroxo complexes of uranium(VI) with aroylhydrazone ligands

The uranium(VI) peroxo complexes containing aroylhydrazones ligands having composition [UO(O₂)L-L(NO₃)₂]·H₂O (where L-L = Benzoic acid[1-(Furan-2-yl)methylene] hydrazide, Benzoic acid[(thiophene-2-yl)methylene] hydrazide, Benzoic acid[1-(thiophene-2-yl)ethylidene] hydrazide, Benzoic acid(phenylmethylene) hydrazide, Benzoic acid[1-(anisol-3-yl)methylene] hydrazide and Benzoic acid[(p-chlorobenzyl)methylene] hydrazide are reported. The complexes were characterized by various physico-chemical techniques, viz. elemental analysis, molar conductivity, magnetic susceptibility measurements, infra red, electronic, mass spectral and TGA/DTA studies. These studies revealed that complexes are non-electrolytes and diamagnetic in nature. The ligands are bound to metal in a bidentate mode. Thermal analysis results provide conclusive evidence for the presence of water molecules in the complexes. Mass spectra confirm the molecular mass of the complexes. Antifungal activity of complexes revealed enhanced activity of complexes as compared to the corresponding ligands.     

Photoelectron spectra of uranium(IV), (V) and (VI) complexes

Satellites were observed on 4f photoelectron spectra of uranium (IV) complexes, while none was seen for diamagnetic uranyl complexes. Photoelectron lines of oxygen 1s coordinated to the uranium ion were broad for NaUO₃ and uranyl complexes.     

Interaction of uranium(VI) with lipopolysaccharide

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Lipopolysaccharides form the main part of the outer membrane of Gram-negative bacteria. We investigated the interaction of the uranyl cation (UO2(2+)) with lipopolysaccharide (LPS) from Pseudomonas aeruginosa by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH and concentration range. Generally, LPS consists of a high density of different functionalities for metal binding such as carboxyl, phosphoryl, amino and hydroxyl groups. The dissociation constants and corresponding site densities of these functional groups were determined using potentiometric titration. The combination of both methods, potentiometry and TRLFS, show that at an excess of LPS uranyl phosphoryl coordination dominates, whereas at a slight deficit on LPS compared to uranyl, carboxyl groups also become important for uranyl coordination. The stability constants of one uranyl carboxyl complex and three different uranyl phosphoryl complexes and the luminescence properties of the phosphoryl complexes are reported.     

Microdetermination of uranium (VI)

Summary A new method has been evolved for the separation and estimation of UO₂ ²⁺ from Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺, Ga³⁺, In³⁺, Tl³⁺, La³⁺, Ti⁴⁺, Zr⁴⁺ and Th⁴⁺ with the sodium salt of benzilic acid as precipitating and chelating agent andn-butanol as solvent for solvent extraction. All these cations except UO₂ ²⁺ are precipitated by benzilic acid; UO₂ ²⁺ forms a deep yellow complex extractable byn-butanol. The uranium can be determined in the organic phase spectrophotometrically at 430 nm. The pH range over which the separation can be carried out is 2.6–4.0. Few anions and cations interfere.

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Zusammenfassung Eine neue Methode der Trennung und Bestimmung von UO₂ ²⁺ neben Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺, Ga³⁺, In³⁺, Tl²⁺, La³⁺, Ti⁴⁺, Zr⁴⁺ und Th⁴⁺ wurde ausgearbeitet. Das Natriumsalz der Benzilsäure dient als Färbungs- und Komplexbildungsmittel und n-Butanol zur Extraktion. Alle angeführten Kationen mit Ausnahme von UO₂ ²⁺ werden von Benzilsäure gefällt; UO^{2 2+} bildet einen tiefgelben, mit n-Butanol extrahierbaren Komplex und kann in der organischen Phase spektrophotometrisch bei 430 nm bestimmt werden. Die Trennung kann bei pH 2,6 bis 4,0 durchgeführt werden. Nur wenige Anionen und Kationen stören.

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Résumé On développe une nouvelle méthode pour la séparation et l'évaluation de UO₂ ²⁺ dans Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺, Ga³⁺, In³⁺, Tl³⁺, La³⁺, Ti⁴⁺, Zr⁴⁺ et Th⁴⁺, par le sel de sodium de l'acide benzilique comme agent précipitant et chélatant et le N-butanol comme solvant pour l'extraction par solvant. Tous ces cations, sauf UO₂ ²⁺, précipitent par l'acide benzilique; UO₂ ²⁺ forme un complexe jaune intense que l'on peut extraire par le N-butanol. On peut doser l'uranium en phase organique par spectrophotométrie à 430 nm. La séparation peut s'effectuer dans le domaine de pH de 2,6 à 4,0. Peu d'anions et de cations interfèrent.

     

Extraction of uranium(VI) with octyldodecylsulfoxide (ODoSO)

Complexes of Hf with polyaminopolycarboxylic acids viz. diethylene-triamine-penta-acetic acid (DTPA) and its dimethoxy derivative DMDTPA have been studied using paper chromatography at different acidities. Kinetic stabilities of the complexes have also been looked at. Behaviors of these two ligands in complexing with Hf(IV) have been found to be similar. The extent of complexation reduces slowly with acidity and increase with time and reaches a maximum around 70-80% after about 24 hours.     

Peroxo complexes of uranium(VI) containing nitrogen and oxygen donor ligands

The uranium(VI) peroxo complexes containing Mannich base ligands having composition [UO(O₂)L-L(NO₃)₂] {where L-L = morpholinobenzyl acetamide (MBA), piperidinobenzyl acetamide (PBA), morpholinobenzyl benzamide (MBB), piperidinobenzyl benzamide (PBB), morpholinomethyl benzamide (MMB), piperidinomethyl benzamide (PMB), morpholinobenzyl formamide (MBF)}, piperidinobenzyl formamide (PBF) are reported. In a typical reaction UO₂(NO₃)₂ · 6H₂O (1 mmol, 0.502 g) was dissolved in methanol. An equimolar (1 mmol) methanolic solution (30 mL) of the ligand (Mannich bases) was added to a solution of uranyl nitrate followed by addition of potassium hydroxide (KOH) (2 mmol, 0.1122 g). The solution was refluxed for 15 min and then 10 mL of 30% hydrogen peroxide (H₂O₂) was added dropwise and was refluxed for an additional 1 h. The synthesized complexes have been characterized by various physico-chemical techniques, viz. elemental analysis, molar conductivity, magnetic susceptibility measurements, infra red, electronic, mass spectral and TGA/DTA studies. These studies revealed that the synthesized complexes are non-electrolytic and diamagnetic in nature. The ligands are bound to metal in a bidentate mode through carbonyl oxygen and the ring nitrogen. Thermal analysis result provides conclusive evidence for the absence of water molecule in the complexes. Mass spectra confirm the molecular mass of the complexes. Antibacterial activity of complexes revealed enhanced activity of complexes as compared to corresponding free ligands. Molecular modeling suggests pentagonal bipyramidal structure for complexes.     

A density functional theory study of uranium(VI) nitrate monoamide complexes

Density functional theory calculations were performed on uranyl complexed with nitrate and monoamide ligands (L) [UO(2)(NO(3))(2)·2L]. The obtained results show that the complex stability is mainly governed by two factors: (i) the maximization of the polarizability of the coordinating ligand and (ii) the minimization of the steric hindrance effects. Furthermore, the electrostatic interaction between ligands and uranium(vi) was found to be a crucial parameter for the complex stability. These results pave the way to the definition of (quantitative) property/structure relationships for the in silico screening of monoamide ligands with improved extraction efficiency of uranium(vi) in nitrate acidic solution.     

Thorium(IV) and uranium(VI) complexes with some heterocyclic azo dyes in absolute ethanol

Thorium(IV) and uranium(VI) chelate complexes with PAN, PAR, TAN and TAR have been studied in absolute ethanol. The uranyl ion forms complexes with PAN, PAR, TAN and TAR in the metal to ligand molar ratio of 1:1. Thorium(IV) forms complexes with PAR, TAR and TAN in the molar ratio of 1:2. In case of Th(IV)-PAN complexes the molar ratio is 1:2.4. The stability constants for all the above complexes have been worked out using the mole ratio method. The kinetics of aquation of Th(IV)-PAN complexes indicate that PAN acts as a tridentate ligand.