Predicting the redox properties of uranyl complexes using electronic structure calculations

A plethora of chemical reactions is redox driven processes. The conversion of toxic and highly soluble U(VI) complexes to nontoxic and insoluble U(IV) form are carried out through proton coupled electron transfer by iron containing cytochromes and mineral surfaces such as machinawite. This redox process takes place through the formation of U(V) species which is unstable and immediately undergo the disproportionation reaction. Thus, theoretical methods are extremely useful to understand the reduction process of U(VI) to U(V) species. We here have carried out the structures and reduction properties of several U(VI) to U(V) complexes using a variety of electronic structure methods. Due to the lack of experimental ionization energies for uranyl (UO₂(V)‐UO₂(VI)) couple, we have benchmarked the current and popularly used density functionals and cost effective ab initio methods against the experimental electron detachment energies of [UO₂F₄]^1‐/2‐ and [UO₂Cl₄]^1‐/2‐. We find that electron detachment energy of U(VI) predicted by RI‐MP2 level on the BP86 geometries correlate nicely with the experimental and CCSD(T) data. Based on our benchmark studies, we have predicted the structures and electron detachment energies of U(V) to U(VI) species for a series of uranium complexes at the RI‐MP2//BP86 level which are experimentally inaccessible till date. We find that the redox active molecular orbital is ligand centered for the oxidation of U(VI) species, where it is metal centered (primarily f‐orbital) for the oxidation of U(V) species. Finally, we have also calculated the detachment energies of a known uranyl [UO₂]¹⁺ complex whose X‐ray crystal structures of both oxidation states are available. The large bulky nature of the ligand stabilizing the uncommon U(V) species which cannot be routinely studied by present day CCSD(T) methods as the system size are more than 20–30 atoms. The success of our efficient computational strategy can be experimentally verified in the near future for the complex as the structures are stable in gas phase which can undergo oxidation.     

Structural, spectroscopic and redox properties of uranyl complexes with a maleonitrile containing ligand

The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt((Et(2)N)(2))H(2)) in methanol produces [UO(2)(salmnt((Et2N)2))(H(2)O)] (1) where the uranyl equatorial coordination plane is completed by the N(2)O(2) tetradentate cavity of the (salmnt((Et(2)N)(2)))(2-) ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO(2)(salmnt((Et(2)N)(2)))(L)] complexes (L = py, DMSO, DMF, TPPO; 2-5, respectively). X-Ray crystallography of 1-5 show that the (salmnt((Et(2)N)(2)))(2-) ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt((Et(2)N)(2))H(2)). The Raman spectra of 1-5 only display extremely weak bands (819-828 cm(-1)) that can be assigned to the typically symmetric O=U=O stretch. This stretching mode is also observed in the infrared spectra for all complexes 1-5 (818-826 cm(-1)) predominantly caused by the distortion of the tetradentate (salmnt((Et(2)N)(2)))(2-) ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2-5 was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2-5 exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (< 5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO(2)}(2+)/{UO(2)}(+) couple are observed for complexes 2-5 (2: E(1/2) = -1.80 V; 3,5: E(1/2) = -1.78 V; 4: E(1/2) = -1.81 V : vs. ferrocenium/ferrocene {Fc(+)/Fc}, 0.1 M Bu(4)NPF(6)) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO(2)}(2+)/{UO(2)}(+) couple observed to date and indicate the strong electron donating nature of the (salmnt((Et(2)N)(2)))(2-) ligand. Multiple uranyl redox processes are clearly seen for [UO(2)(salmnt((Et(2)N)(2)))(L)] in L (L = py, DMSO, DMF; 2-4: 0.1 M Bu(4)NPF(6)) indicating the relative instability of these complexes when competing ligands are present, but the reversible {UO(2)}(2+)/{UO(2)}(+) couple for the intact complexes can still be assigned and shows the position of this couple can be modulated by the solvation environment. Several redox processes were also observed between +0.2 and +1.2 V (vs. Fc(+)/Fc) that prove the redox active nature of the maleonitrile-containing ligand.     

Binuclear Uranium(VI) Complexes with a “Pacman” Expanded Porphyrin: Computational Evidence for Highly Unusual Bis‐Actinyl Structures

On the basis of uranyl complexes reacting with a polypyrrolic ligand (H₄L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO₂)₂(L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum‐energy structures. These complexes with cation–cation interactions (CCI) exhibit unusual coordination modes of uranyls: one is a T‐shaped ( T ) skeleton formed by two linear uranyls {O_exo?U₂?O_endo→U₁(?O_exo)₂}, and another is a butterfly‐like ( B ) unit with one linear uranyl coordinating side‐by‐side to a second cis‐uranyl. The CCI in T was confirmed by the calculated longest distance and lowest stretching vibrational frequency of U₂?O_endo among the four U?O bonds. Isomer B is more stable than T , for which experimental tetrameric analogues are known. The formation of B and T complexes from the mononuclear [(UO₂)(H₂L)(thf)] ( M ) was found to be endothermic. The further protonation and dehydration of B and T are thermodynamically favorable. As a possible product, we have found a trianglelike binuclear uranium(VI) complex having a O?U?O?U?O unit.     

X‐ray photoreduction of U(VI)‐bearing compounds

During XPS analysis, the soft X‐ray‐induced reduction of metals such as Cr(VI) and Ce(IV) in oxides has been reported in the literature and some mechanisms have been proposed to explain this phenomenon. The reduction of U(VI) by the beam during X‐ray Photoelectron Spectroscopy has been already reported in the literature but only for U(VI) sorbed or precipitated onto solids with reducing properties (as micas or pyrites) for whose Fe(II) can also induce the reduction of U(VI), or onto TiO₂ whose the photocatalytic properties are well known. The objective of this paper is to investigate the effects of X‐ray beam on U(VI) bulk compounds (UO₃, UO₂(OH)₂, (UO₂)₂SiO₄, UO₂(CH₃COO)₂ and UO₂C₂O₄). Successive U4f, U5f, C1s XPS spectra were recorded and compared as a function of the irradiation time. The XPS photoreduction of U(VI) into U(IV) is only observed for uranyl compounds containing organic matter (uranyl acetate and uranyl oxalate). Considering the evolution of the C1s signal during the X‐ray irradiation, a significant decrease of the C ? O component simultaneously to the U(VI) reduction is observed, which suggests a desorption of CO or other volatile organic products from the solid surface. All these results on U(VI) bulk compounds indicate the important role of organic carbon species in the photoreduction process and to explain these observations, a photoreduction mechanism has been suggested. Copyright © 2010 John Wiley & Sons, Ltd.     

Complexation of U(VI) with diphenyldithiophosphinic acid: spectroscopy,structure and DFT calculations

The complexation of U(VI) with diphenyldithiophosphinic acid (denoted as HL) in acetonitrile was studied by UV–Vis, FT-IR, crystallography and DFT calculations. UV–Vis absorption spectrophotometry implies that three successive complexes, UO₂L⁺, UO₂L₂, UO₂L₃^?, form in the solution. Significant ligand to metal charge transfer occurs from soft atom S to U(VI) in all the three complexes. A crystal of UO₂L₂ complex was successfully synthesized from the solution. In the crystal both the two ligands coordinate to U(VI) in bidentate form. DFT calculations confirm the formation of UO₂L₃^? complex and help illustrate the structures of all the U(VI) species in the solution.     

Heteronuclear complexes of oxorhenium(V) with Fe(III), Co(II), Ni(II), Cu(II), Cd(II) and UO2(VI) and their biological activities

Heteronuclear complexes containing oxorhenium(V), with Fe(III), Co(II), Ni(II), Cu(II), Cd(II) and UO₂(VI) ions were prepared by the reaction of the complex ligands [ReO(HL¹)(PPh₃)(OH₂)Cl]Cl (a) and/or [ReO(H₂L²)(PPh₃)(OH₂)Cl]Cl (b), where H₂L¹?=?1-(2-hydroxyphenyl)butane-1,3-dione-3-(5,6-diphenyl-1,2,4-triazine-3-ylhydrazone) and H₃L²?=?1-(2-hydroxyphenyl)butane-1,3-dione-3-(1H-benzimidazol-2-ylhydrazone), with transition and actinide salts. Heterodinuclear complexes of ReO(V) with Fe(III), Co(II), Ni(II), Cu(II) and Cd(II) were obtained using a 1?:?1 mole ratio of the complex ligand and the metal salt. Heterotrinuclear complexes were obtained containing ReO(V) with UO₂(VI) and Cu(II) using 2?:?1 mole ratios of the complex ligand and the metal salts. The complex ligands a and b coordinate with the heterometal ion via a nitrogen of the heterocyclic ring and the nitrogen atom of the C=N⁷ group. All transition metal cations in the heteronuclear complexes have octahedral configurations, while UO₂(VI)?complexes have distorted dodecahedral geometry. The structures of the complexes were elucidated by IR, ESR, electronic and ¹H NMR spectra, magnetic moments, conductance and TG-DSC measurements. The antifungal activities of the complex ligands and their heteronuclear complexes towards Alternaria alternata and Aspergillus niger showed comparable behavior with some well-known antibiotics.     

Modulation of the unpaired spin localization in Pentavalent Uranyl Complexes

The electronic structure of various complexes of pentavalent uranyl species, namely UO₂⁺, is described, using DFT methods, with the aim of understanding how the structure of the ligands may influence the localisation of the unpaired 5f electron of uranium (V) and, finally, the stability of such complexes towards oxidation. Six complexes have been inspected: [UO₂py₅]⁺ (1), [(UO₂py₅)KI₂] (2), [UO₂(salan-^tBu₂)(py)K] (3), [UO₂(salophen-^tBu₂)(thf)K] (4), [UO₂(salen-^tBu₂)(py)K] (5), [and UO₂-cyclo[6]pyrrole]^1? (6), chosen to explore various ligands. In the five first complexes, the UO₂⁺ species is well identified with the unpaired electron localized on the 5f uranium orbital. Additionally, for the salan, salen and salophen ligands, some covalent interactions have been observed, resulting from the presence of both donor and acceptor binding sites. In contrast, the last complex is best described by a UO₂²⁺ uranyl (VI) coordinated by the anionic radical cyclopyrrole, the highly delocalized π orbitals set stabilizing the radical behaviour of this ligand.     

New uranyl(VI) complexes with ons ligand derived from aromatic acid hydrazides and phenyl isothiocyanate. part III

Summary The synthesis and characterization of some dioxouranium(VI) complexes containing potential ONS donor ligands derived from benzoyl,o-chloro-,o-methyl-,P-chloro-,p-nitro-,p-methoxy-,p-aminobenzoylhydrazines and isonicotinylhydrazine with phenyl isothiocyanate are reported. Two types of complexes with general formulae [UO₂(HL)₂(X)₂] and [[UO₂(HL)₂] have been identified and characterized. All the uranyl complexes are of the [UO₂(HL)₂(X)₂] type (HL=bidentate monoanionic ligand, X=H₂O and/or EtOH) and X bridges the uranyl ion and the thioketo groupvia hydrogen bonding. Upon heating to 140 °C, the complexes lose X giving a new complex of formula [UO₂(HL)₂] (HL=tridentate monoanionic ligand) in which the thioketo-group participates in bonding. The latter complexes take up X again on exposure to water and/or ethanol vapour.     

Infrared Spectroscopy of Dioxouranium(V) Complexes with Solvent Molecules: Effect of Reduction

UO₂⁺–solvent complexes having the general formula [UO₂(ROH)]⁺ (R=H, CH₃, C₂H₅, and n‐C₃H₇) are formed using electrospray ionization and stored in a Fourier transform ion cyclotron resonance mass spectrometer, where they are isolated by mass‐to‐charge ratio, and then photofragmented using a free‐electron laser scanning through the 10 μm region of the infrared spectrum. Asymmetric O=U=O stretching frequencies (ν₃) are measured over a very small range [from ～953 cm^?1 for H₂O to ～944 cm^?1 for n‐propanol (n‐PrOH)] for all four complexes, indicating that the nature of the alkyl group does not greatly affect the metal centre. The ν₃ values generally decrease with increasing nucleophilicity of the solvent, except for the methanol (MeOH)‐containing complex, which has a measured ν₃ value equal to that of the n‐PrOH‐containing complex. The ν₃ frequency values for these U(V) complexes are about 20 cm^?1 lower than those measured for isoelectronic U(VI) ion‐pair species containing analogous alkoxides. ν₃ values for the U(V) complexes are comparable to those for the anionic [UO₂(NO₃)₃]^? complex, and 40–70 cm^?1 lower than previously reported values for ligated uranyl(VI) dication complexes. The lower frequency is attributed to weakening of the O?U?O bonds by repulsion related to reduction of the U metal centre, which increases electron density in the antibonding π* orbitals of the uranyl moiety. Computational modelling of the ν₃ frequencies using the B3LYP and PBE functionals is in good agreement with the IRMPD measurements, in that the calculated values fall in a very small range and are within a few cm^?1 of measurements. The values generated using the LDA functional are slightly higher and substantially overestimate the trends. Subtleties in the trend in ν₃ frequencies for the H₂O–MeOH–EtOH–n‐PrOH series are not reproduced by the calculations, specifically for the MeOH complex, which has a lower than expected value.     

Synthesis and characterization of mononuclear cadmium(II) and dinuclear uranyl(VI) complexes with <Emphasis Type="Italic">vic</Emphasis>-dioximes

In this study, the mononuclear complexes of cadmium(II) and dinuclear complexes of uranyl(VI) with five vic-dioximes have been obtained. Cadmium(II) forms, with ligands, complexes [(L ^xH)(Cl)(H₂O)(Cd)] with x=1–5. Mononuclear complexes with a metal: ligand ratio of 1:1 were obtained for cadmium(II) with the ligands, and a chloride ion and a water molecule are also coordinated to the cadmium(II) ions. Uranyl(VI) complexes of these ligands are a dinuclear structure with μ-hydroxo-bridges. Uranyl(VI) forms, with ligands, complexes [(L^xH)₂(OH)₂(UO₂)₂] with x=1–5, which have a 2:2 metal:ligand ratio. The structures of the complexes were identified by elemental analysis, i.r., and ¹H-n.m.r. spectra, u.v.–vis. spectroscopy, magnetic susceptibility measurements, conductivity measurements and thermogravimetric analysis (t.g.a.).     

一系列水合和非水合铀酰卤族(F,Cl,Br)配合物在水溶液中的结构和紫外吸收光谱性质的密度泛函理论研究

本文考虑相对论效应并应用密度泛函理论(DFT)研究水溶液中UO2Xn(H2O)5-n(X=F,Cl,Br;n=1～4)和UO2Xn(X=F,Cl,Br;n=1～6)一系列水合和非水合铀酰化合物的结构和紫外吸收光谱性质。将这一系列物质命名为Xnm(X为F,Cl,和Br;n为卤素配体个数,m为水分子配体的个数)。在水溶液中,溶剂化效应采用类导体屏蔽模型(COSMO)并采用SAS溶剂接触曲面构造空穴模拟水溶剂对配合物的作用。配合物的紫外光谱性质采用考虑旋-轨耦合相对论效应的含时密度泛函(SO-TD-DFT)进行计算。U=O键随着F配体数目的增加而明显伸长,然而随Cl和Br配体数目的增加变化较小。随X配体数目的增加和水分子参与配位,铀与X的结合能逐渐减弱。配合物的紫外光谱计算表明铀酰氟的各种配合物并不出现特征吸收峰,而铀酰氯和铀酰溴的各种配合物均有特征吸收光谱。通过分子轨道分析可以很好解释光谱所体现的特征。     

Synthesis and spectral characterization of dioxouranium (VI) complexes of salicylhydrazine and acetone salicylhydrazone

Dioxouranium(VI) complexes of the types UO₂LSO₄ and UO₂L₂SO₄ (where L=SH, ASH) have been prepared from reaction of uranyl sulphate with salicylhydrazine (SH) and acetone salicylhydrazone (ASH) and characterized by conventional chemical and physical measurements. Infrared and Raman spectra indicate thatmono- andbis-complexes contain six-and seven-coordinate uranium atom respectively with all the ligand atoms arranged in an equatorial plane around the linear uranyl group. The infrared spectra (4000-200 cm⁻¹) reveal that both SH and ASH act as neutral bidentate ligands coordinating through a carbonyl oxygen and primary amine/azomethine nitrogen atoms. The sulphato group coordinates to the uranyl ion as bidentate chelating ligand and terminal monodentate ligand in mono- and bis-complexes respectively.     

IR spectroelectrochemical study on UVO2+ complex: first evidence for weakening of U[double bond]O bond strength in uranyl moiety with reduction from U(VI) to U(V)

We have obtained the first evidence that the U[double bond]O bond strength in uranyl moiety is weakened with the reduction from U(VI)O(2)(2+) to U(V)O(2)(+) from the IR spectroelectrochemical study on U(VI)O(2)(saloph)DMSO and [U(V)O(2)(saloph)DMSO](-) (saloph = N,N'-disalicylidene-o-phenylenediaminate, DMSO = dimethyl sulfoxide) complexes with the thin layer electrode cell for IR measurements.     

Polymer complexes: XLX. Novel supramolecular coordination modes of structure and bonding in polymeric hydrazone sulphadrugs uranyl complexes

Novel five binuclear polymeric dioxouranium(VI) of azosulphadrugs [(azodrug substances) azobenzene sulphonamides] were prepared for the first time. The infrared spectra of the samples were recorded and their fundamental vibration wave number was obtained. The resulting polymeric uranyl complexes were characterized on the basis of their elemental analyses, conductance and spectral (IR, NMR, and electronic spectra) data. The ligation modes of the azosulphadrugs ligands towards uranyl(II) ions were critically assigned and addressed properly on the basis of their IR and their uranyl(II) complexes. The theoretical aspects are described in terms of the well-known theory of 5d–4f transitions. The coordination geometries and electronic structures are determined from a framework for the modeling of novel polymer complexes. The values of ν₃ of the prepared complexes containing UO₂²⁺ were successfully used to calculate the force constant, F_UO (1n 10^?8 N/Å) and the bond length R_UO of the U–O bond. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the U–O bond distances from the values of the stretching and interaction force constants. The most probable correlations between U–O force constant to U–O bond distance were satisfactorily discussed in terms of “Badger's rule”, “Jones” and “El-Sonbati equations”.     

Dioxouranium Complexes with Acetylpyridine Benzoylhydrazones and Related Ligands

Acetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air‐stable complexes. Reactions with 2, 6‐diacetylpyridinebis(benzoylhydrazone) (H₂L^1a) or 2, 6‐diacetylpyridinebis(salicylhydrazone) (H₂L^1b) give yellow products of the composition [UO₂(L¹)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonal‐bipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep‐red complexes have hexagonal‐bipyramidal coordination environments with the oxo ligands in axial positions. The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2, 6‐diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL²) and bis(2‐pyridyl)ketone benzoylhydrazone (HL³) deprotonate and form neutral, red [UO₂(L)₂] complexes. The equatorial coordination spheres of these complexes are puckered hexagons. X‐ray diffraction studies on [UO₂(L^1a)(pyridine)], [UO₂(L^1b)(DMSO)], [UO₂(L²)₂] and [UO₂(L³)₂] show relatively short U—O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U—N bond lengths: 2.588(7)—2.701(6) Å ).     

Oxo–Group‐14‐Element Bond Formation in Binuclear Uranium(V) Pacman Complexes

Simple and versatile routes to the functionalization of uranyl‐derived U^V–oxo groups are presented. The oxo‐lithiated, binuclear uranium(V)–oxo complexes [{(py)₃LiOUO}₂(L)] and [{(py)₃LiOUO}(OUOSiMe₃)(L)] were prepared by the direct combination of the uranyl(VI) silylamide “ate” complex [Li(py)₂][(OUO)(N”)₃] (N”=N(SiMe₃)₂) with the polypyrrolic macrocycle H₄L or the mononuclear uranyl (VI) Pacman complex [UO₂(py)(H₂L)], respectively. These oxo‐metalated complexes display distinct U? O single and multiple bonding patterns and an axial/equatorial arrangement of oxo ligands. Their ready availability allows the direct functionalization of the uranyl oxo group leading to the binuclear uranium(V) oxo–stannylated complexes [{(R₃Sn)OUO}₂(L)] (R=nBu, Ph), which represent rare examples of mixed uranium/tin complexes. Also, uranium–oxo‐group exchange occurred in reactions with [TiCl(OiPr)₃] to form U‐O? C bonds [{(py)₃LiOUO}(OUOiPr)(L)] and [(iPrOUO)₂(L)]. Overall, these represent the first family of uranium(V) complexes that are oxo‐functionalised by Group 14 elements.     

The preparation and electrochemistry of manganese(II) complexes of an unsaturated pentadentate macrocyclic ligand

The preparation of a series of six and seven coordinate manganese(II) complexes [Mn^(II)(L)X]⁺, and [Mn^(II)(L)X₂]^2? (X = halide, water, triphenylphosphine oxide, imidazole, 1-methyl imidazole and pyridine) incorporating the pentadentate planar macrocylic ligand L is described. Cyclic voltammetry of these complexes in acetonitrile each shows a reversible one-electron reduction wave near - 1.4 V vs a Ag/AgNO₃ reference electrode. Quantitative reduction of these complexes by controlled potential electrolysis at a platinum gauze at - 1.4 V yields the corresponding one-electron reduction products which have been shown by ESR spectroscopy to be manganese(II)-ligand radical species, the electron being thought to reside on the di-imino pyridine moiety of the macrocyclic ligand. No metal reduced species could be isolated even in the presence of π-acceptor ligands such as CO or phosphines.     

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.     

Spectrophotometric study of the complexation equilibria of uranium(VI) with 1,4-bis(4′-methylanilino)anthraquinone and determination of uranium(VI)

The reaction of U(VI) with 1,4-bis(4′-methylanilino)anthraquinone (quinizarin green) in water-dimethylformamide medium was investigated spectrophotometrically. The complexation equilibria in solution were demonstrated. The study of the reaction in presence of equimolar concentrations or in solutions containing metal or ligand excess gave evidence for the formation of complexes with stoichiometric ratios of UO₂:L = 1:1 and 1:2 in dependence on the pH of the medium. Their thermodynamic stabilities and the values of their molar absorption coefficients were determined. The optimum conditions for spectrophotometric determination of U(VI) with this reagent were found.     

Synthesis and electrochemistry of cis-dioxomolybdenum(VI) complexes with tridentate Schiff base ligands containing O,N and S donor atoms

The synthesis and characterization of a number of cis-dioxomolybdenum(VI) coordination complexes involving tridentate (ONS) ligands is described. The Schiff base ligands were obtained by condensation of 5-substituted salicylaldehydes with o-aminobenzenethiol or 2-aminoethanethiol. The chemical properties of these molybdenum complexes are compared with those having tridentate ligands with the ONO donor atom set. Cyclic voltammetry was used to obtain cathodic reduction potentials (E_pc) for the irreversible reduction of the Mo(VI) complexes. Although the reductions are irreversible, trends are observed in E_pc both within each series and when different series are compared. Cathodic reduction potentials for the four series examined span the range from ?1.53 to ?1.05 V versus NHE. There are three ligand features whose effect systematically alters the Mo(VI) cathodic reduction potentials. These include (1) the X-substituent on the salicylaldehyde portion of each ligand; (2) the degree of ligand delocalization; and (3) the substitution of a sulphur donor atom for an oxygen donor atom. Each of these effects is considered separately with regard to the Mo(VI) cathodic reduction potentials and then their cumulative effect is described.