Uranyl complexes of n-alkanediaminotetra-acetic acids

The uranyl complexes of n-propanediaminetetra-acetic acid, n-butanediaminetetra-acetic acid and n-hexanediaminetetra-acetic acid have been studied by potentiometry, with computer evaluation of the titration data by the MINIQUAD program. Stability constants of the 1:1 and 2:1 metal:ligand chelates have been determined as well as the respective hydrolysis and polymerization constants at 25 degrees in 0.10M and 1.00M KNO(3). The influence of the length of the alkane chain of the ligands on the complexes formed is discussed.     

Uranyl aquahydroxylaminate complexes

Uranylaqua complexes with N-methyl-, N-ethyl-, N-isopropyl-, and N,N-dimethylhydroxylamines were studied. The structure of [UO₂{(CH₃)₂NO}₂(H₂O)₂] was determined by X-ray crystallography. The N, N -dimethylhydroxylaminate ion is coordinated to uranyl through the nitrogen and oxygen atoms with the formation of a three-membered chelate ring.     

Uranyl complexes with ethylmethylglyoxime

Uranyl complexes with ethylmethylglyoxime were studied. The structure of (CN₃H₆)₄[(UO₂)₂(CO₃)(C₂O₄)₂(C₅H₈N₂O₂)] · 1.5H₂O was determined by X-ray crystallography. The structure of the complex is binuclear with a double carbonate dioximate bridging fragment.     

Uranyl complexes with acetophenone oxime

The interaction of uranyl compounds with acetophenone oxime has been studied. Mixed-ligand uranyl acetophenone oximates have been synthesized. X-ray crystallography shows that, in single crystals of [UO₂(C₈H₈NO)₂{(CH₃)₂SO}₂] and [UO₂(C₈H₈NO)(NO₃){(CH₃)₂SO}₂], acetophenone oxime is coordinated to uranyl as a bidentate chelating ligand.     

Uranyl complexes with 1,2-cycloheptanedione dioxime

Uranyl compounds with 1,2-cycloheptanedione dioxime (heptoxime) have been studied. Partial isomerization of the ligand takes place upon the formation of aqua complexes. The coordination modes of heptoxime in uranyl complexes were established by X-ray crystallography on [(UO₂)₂(C₇H₁₀N₂O₂)₂{(CH₃)₂SO}₃] single crystals: cis-(E,E)tetradentate chelating bridging and cis-(E,Z)pentadentate chelating bridging.     

Studies on uranyl complexes-III Uranyl complexes of edta

The uranyl complexes of EDTA have been studied by potentiometry ; stability constants of the 1:1 and 2:1 (metal to ligand) chelates have been determined, as well as the respective hydrolysis and polymerization constants. Possible structures for these species are discussed. To account for the abnormally high stability of UO(2)(H(2)O)HL-, hydrogen bonding between a protonated nitrogen atom of the ligand and one oxygen atom of UO(2)(2+) is suggested.     

Uranyl complexes with methyl derivatives of alicyclic dioximes

A reaction of uranyl dioxalate complexes with methyl derivatives of alicyclic ??-dioximes, 3-methyl-1,2-cyclohexanedione dioxime and 3-methyl-1,2-cyclopentanedione dioxime, was studied. The structure of (CN₃H₆)₄[(UO₂)₂(C₆H₈N₂O₂)(CO₃)(C₂O₄)₂] · (C₆H₁₀N₂O₂) · 2H₂O and NH₄(CN₃H₆)₃[(UO₂)₂(C₇H₁₀N₂O₂)(CO₃)(C₂O₄)₂] · 2H₂O based on binuclear complex anions with carbonate-dioximate fragment was studied by X-ray diffraction.     

Uranyl and lanthanide complexes of the 1,2-dipyridylethylene isomers

Several new complexes of lanthanide(III) and uranyl cations with 1,2-di-(4-pyridyl)ethylene and 1-(3-pyridyl)-2-(4-pyridyl)ethylene have been prepared and characterized by elemental and thermal analyses, conductivity measurements and IR spectra. IR spectra show that the diimine acts generally as a bidentate bridging ligand; however, there is some evidence that complexes with the diimine monodentate to the cation are also formed. Enthalpy change and “activation energy” values for the thermal dissociation reaction of the lanthanide nitrate complexes show a periodic trend along the lanthanide series.     

Uranyl complexes with di-2-pyridyl ketone and di-2-pyridyl sulphide

Uranyl complexes of the type UO₂L_nX₂, where L is di-2-pyridyl ketone or di-2-pyridyl sulphide and n = 2 (X = Cl, NCS, ClO₄) or n = 1 (X = NO₃), have been prepared and characterized by elemental analyses, molar conductivity and thermoanalytical measurements.IR spectral data suggest that both ligands in all complexes act as bidentate chelating agents through the two nitrogen atoms. Alcoholation of the carbonyl group occurs in the complexes of di-2-pyridyl ketone obtained from alcoholic media.Conductivity measurements indicate that the thiocyanate and nitrate complexes are non electrolytes in MeNO₂ solution whereas the perchlorate complexes are 1:2 electrolytes.     

Uranyl ion complexation by citric and citramalic acids in the presence of diamines

Uranyl nitrate reacts with citric (H4cit) or d-(-)-citramalic (H3citml) acids under mild hydrothermal conditions and in the presence of diamines to give different complexes which are all characterized by the presence of 2:2 uranyl/polycarboxylate dianionic dimers or of polymeric chains based on the same dimeric motif. Each uranium ion is chelated by the two ligands through the alkoxide and the alpha- or beta-carboxylate groups, the second beta-carboxylic group in citrate being uncoordinated. The uranium coordination sphere is completed by either a water molecule or the beta-carboxylate group of a neighboring unit, thus giving zero- or one-dimensional assemblages, respectively. The evidence for [UO2(Hcit)]2 dimers in the solid state confirms previous results from potentiometric and EXAFS measurements on solutions. Depending on the diamine used (DABCO, 2,2'- and 4,4'-bipyridine, [2.2.2]cryptand) and its ability to form divergent hydrogen bonds or not, different uranyl/polycarboxylate topologies are obtained, thus evidencing template effects, and extended hydrogen bonding gives two- or three-dimensional assemblages. These results, together with those previously obtained with NaOH as a base, add to the knowledge of the uranyl/citrate system, which is much investigated for its environmental relevance.     

Uranyl compounds and complexes: Electronic structure,chemical bonding and spectral properties

The electronic structure of solid compounds -UO₃, Cs₂UO₂CL₄, UO₂F₄ and complexes UO ₂ ²⁺ and UO₂(NO₃)₂ · 2H₂O has been studied by the cluster discrete variational DV X method in Dirac-Slater and Hartree-Fock-Slater approximation. The analysis of relativistic effects in the electronic structure of uranyl compounds was based on the comparison of non-relativistic and relativistic DV results. The interpretation of X-ray photoelectron spectra of -UO₃ and Cs₂UO₂Cl₄ basing on the MO model is given. The various electronic states contributions to the chemical bonding in uranyl compounds are investigated.     

Thermal decomposition of metal complexes: III. Uranyl nitrate adducts with N-donor ligands

The thermal decomposition of some uranyl nitrate adducts with neutral N-donor ligands was investigated in order to correlate the “activation energy” , E^*₂, of the first step, whose shape depends on the kind of the neutral ligand, with the anti-symmetric stretching vibration ν₃ of the O—U—O group. The linear relationship

was found.Some considerations about the identification of the symmetric stretching band ν₁ have been drawn.     

Metal complexes of cyclic tetra-azatetra-acetic acids

The cyclic tetra-aza complexones cDOTA ([12]ane N(4).4ac), cTRITA ([13]ane N(4).4ac) and cTETA ([14]ane N(4).4ac) have been synthesized and characterized by elemental analysis, titration, melting-point determination and NMR (and infrared) spectroscopy. The ionization constants and the stability constants of the MH(2)L, MHL and ML complexes formed with alkali, alkaline-earth and some transition metals were determined at 25.0 +/- 0.1 degrees and ionic strength 0.10M [KNO(3) and (CH(3))(4)NNO(3)]. It was confirmed that cDOTA forms the most stable Ca(2+) and Sr(2+) complexes but the reported inversion of the order of stability of the complexes of these two ions with cTRITA was not confirmed. Also, the values of the stability constants determined in this work differ substantially from those previously reported for ML species. cDOTA is an interesting alternative to classical non-cyclic complex-ones for the complexometric determination of Ca(2+) and Mg(2+) but neither this ligand nor the other two offer advantages over EDTA or DCTA for the complexometric titration of transition metals.     

Uranyl sequestration: synthesis and structural characterization of uranyl complexes with a tetradentate methylterephthalamide ligand

Uranyl complexes of a bis(methylterephthalamide) ligand (LH(4)) have been synthesized and characterized by X-ray crystallography. The structure is an unexpected [Me(4)N](8)[L(UO(2))](4) tetramer, formed via coordination of the two MeTAM units of L to two uranyl moieties. Addition of KOH to the tetramer gave the corresponding monomeric uranyl methoxide species [Me(4)N]K(2)[LUO(2)(OMe)].     

Metal complexes of carbazic acids,part 2. Copper(II) complexes ofN-substituted carbazic acids

Summary Copper(II) complexes of N-substituted carhazic acids have been prepared and characterised by analytical, magnetic. electronic and i.r. spectral measurements. The complexes, which are of two types, CuL₂(H₂O), (where L = carhazic acid. methy1carbazic acid and phenylcarbazic acid) and CuL, (where L = 2,3-dimethylcarbazic acid, 3.3-dimethvlcarbazic acid and 3.3-methylphenylcarbazic acid), have distorted octahedral structures, bonded through one of the nitrogen atoms and carboxylate group.     

Reactions of Pd-PEPPSI complexes with protic acids

The Pd-PEPPSI complexes widely used to catalyze numerous reactions eliminate the pyridine ligand on treatment with protic acids to give binuclear complexes [Pd(NHC)X₂]₂ with the Pd–X–Pd (X = Cl, Br, I) bridging bonds. The reaction proceeds with high yields (78–98%) and can be regarded as a preparative approach to binuclear complexes. A prolonged heat treatment of either Pd-PEPPSI complexes or binuclear [Pd(NHC)X₂]₂ complexes in the presence of strong protic acids results in the Pd–NHC bond cleavage to give azolium salts (proligands) and palladium salts.     

Utilization of heterobimetallic complexes as Lewis acids

The lithium-containing multifunctional heterobimetallic catalysts such as LaLi₃tris((R)-6,6′-dibromobinaphthoxide) showed moderate Lewis acidity in non-polar solvents. Asymmetric Diels–Alder reactions proceeded efficiently in the presence of the heterobimetallic catalyst. This is the first application of heterobimetallic asymmetric catalysts solely as Lewis acids.     

Thermal behaviour of Uranium(VI) complexes. Uranyl acetate dihydrate-thiourea system: Synthesis and decomposition

The solid-state syntheses of uranyl acetate adducts with thiourea were attempted directly in a DSC apparatus according to the scheme: UO₂Ac₂·2 H₂O_(s)+n thiourea_(s) → → UO₂Ac₂·thiourea_n(s)+2 H₂O_(v) (n=1–6), and the correspondingδH values were evaluated. At all stoichiometric ratios the same UO₂Ac₂·thÌourea product was obtained, to which a pentagonal bipyramidal structure was attributed. Thermoanalytical (TG and DTG) and infrared spectra measurements were also performed and agree with the DSC results.