Mercaptokomplexe von Indium(III)

The complexes of In(III) with thioglycolate (HO? CH₂? CH₂? S^?) have been investigated by pH-metric methods. Only the mononuclear species In(SR)_n(3-n)+ (n = 1, 2, 3, 4) are formed (Fig. 1): It was difficult to obtain an accurate value for the first stability constant K₁ because of the high stability of the 1:1-complex and therefore mixtures of KCl-KNO₃ were used to keep up the ionic strength of μ = 0.1. In presence of chloride, the constants K_n are smaller because of the formation of chloro complexes and mixed complexes In(SR)_nCl_i(3-n-1)+ and the stability constants of these have also been determined. The constants for the complexes without coordinated chloride can finally be obtained by an extrapolation (Fig. 2). The problem of the influence of increasing charge on the stability of various complexes of the isoelectronic 4d¹⁰ cations is discussed (Fig. 3).     

Complexation Studies of Bidentate Heterocyclic N-Donor Ligands with Nd(III) and Am(III)

A new bidentate nitrogen donor complexing agent that combines pyridine and triazole functional groups, 2-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)pyridine (PTMP), has been synthesized. The strength of its complexes with trivalent americium (Am³⁺) and neodymium (Nd³⁺) in anhydrous methanol has been evaluated using spectrophotometric techniques. The purpose of this investigation is to assess this ligand (as representative of a class of similarly structured species) as a possible model compound for the challenging separation of trivalent actinides from lanthanides. This separation, important in the development of advanced nuclear fuel cycles, is best achieved through the agency of multidentate chelating agents containing some number of nitrogen or sulfur donor groups. To evaluate the relative strength of the bidentate complexes, the derived constants are compared to those of the same metal ions with 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2-pyridin-2-yl-1H-benzimidazole (PBIm). At issue is the relative affinity of the triazole moiety for trivalent f element ions. For all ligands, the derived stability constants are higher for Am³⁺ than Nd³⁺. In the case of Am³⁺ complexes with phen and PBIm, the presence of 1:2 (AmL₂) species is indicated. Possible separations are suggested based on the relative stability and stoichiometry of the Am³⁺ and Nd³⁺ complexes. It can be noted that the 1,2,3-triazolyl group imparts a potentially useful selectivity for trivalent actinides (An(III)) over trivalent lanthanides (Ln(III)), though the attainment of higher complex stoichiometries in actinide compared with lanthanide complexes may be an important driver for developing successful separations.     

The extraction of Yb(III) and Lu(III) with chloroform from aqueous solutions in the presence of cupferron

The equilibrium of distribution of Yb(III) and Lu(III) between chloroform and the aqueous phase in the presence of cupferron (the ammonium salt of N-nitrosophenylhydroxylamine) were studied as apH function of the aqueous phase and the concentration of N-nitrosophenylhydroxylamine (HL). The stability constants for theLnL _n ^3–n ) complexes (n=1÷3) being formed in the aqueous phase were established, as well as the equilibrium constants of the extraction reaction $$Ln(H_2 O)_m^{3 + } + 3HL_{(O)} \mathop \rightleftharpoons \limits^{K_{ex} } LnL_{3(O)} + 3H^ + + mH_2 O(Ln^{3 + } = Yb,Lu),$$ two-phase stability constants for theLnL ₃ complexes,pH _0.5 and the separation factor Lu(III) from Yb(III).     

Stability of bismuth(III), indium(III), lead(II), and cadmium(II) monocomplexes with selenourea and thiourea

The stability constants of the bismuth(III), indium(III), lead(II), and cadmium,(II) monocomplexes with selenourea (seu) and thiourea (tu) were determined spectrophotometrically at the ionic strength 1 (0.5 mol/L HClO₄ + NaClO₄) or 2 (1 mol/L HClO₄ + NaClO₄) and 276 and 298 K. For all metals, the stability constants (β₁) of the complexes with seu were higher than those of the complexes with tu and changed in the series Bi³⁺ > Cd²⁺ ≈ In³⁺ > Pb²⁺. A correlation between logβ₁(S) and logβ₁(Se) was established.     

Complexation of Am(III) and Nd(III) by 1,10-Phenanthroline-2,9-Dicarboxylic Acid

The complexant 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) is a planar tetradentate ligand that is more preorganized for metal complexation than its unconstrained analogue ethylendiiminodiacetic acid (EDDA). Furthermore, the backbone nitrogen atoms of PDA are aromatic, hence are softer than the aliphatic amines of EDDA. It has been hypothesized that PDA will selectively bond to trivalent actinides over lanthanides. In this report, the results of spectrophotometric studies of the complexation of Nd(III) and Am(III) by PDA are reported. Because the complexes are moderately stable, it was necessary to conduct these titrations using competitive equilibrium methods, competitive cation complexing between PDA and diethylenetriaminepentaacetic acid, and competition between ligand protonation and complex formation. Stability constants and ligand protonation constants were determined at 0.1 mol·L^?1 ionic strength and at 0.5 mol·L^?1 ionic strength nitrate media at 21 ± 1 °C. The stability constants are lower than those predicted from first principles and speciation calculations indicate that Am³⁺ selectivity over Nd³⁺ is less than that exhibited by 1,10-phenanthroline.     

Spectroscopic and Computational Characterization of Diethylenetriaminepentaacetic Acid/Transplutonium Chelates: Evidencing Heterogeneity in the Heavy Actinide(III) Series

The chemistry of trivalent transplutonium ions (Am³⁺, Cm³⁺, Bk³⁺, Cf³⁺, Es³⁺…) is usually perceived as monotonic and paralleling that of the trivalent lanthanide series. Herein, we present the first extended X‐ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to much shorter metal–oxygen nearest‐neighbor bond lengths in the case of Cf³⁺. Corroborating those results, density functional theory calculations, extended to Es³⁺, suggest that the shorter Cf?O and Es?O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [M^IIIDTPA(H₂O)]^2? (M=Am, Cm, Bk) complexes. Taken together, these experimental and theoretical results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years, and that may also be leveraged for future nuclear waste reprocessing technologies.     

Solution Properties of Azidokojatoiron(III) Complexes

The formation of iron(III) complexes with chelating azidokojate anions L⁻ was investigated in aqueous solutions as a function of the pH and the c(Fe³⁺):c(HL) molar ratio. Based on the stability constants, the distribution among the above complexes, [Fe(H₂O)₆]³⁺, and [Fe(H₂O)₅(OH)]²⁺ were calculated in solutions of various compositions. The complexes are redox stable in aqueous solutions both in the dark and in visible laboratory light. Properties of the investigated azidokojic acid and its iron(III) complexes are compared with those required for therapeutic applications as alternative iron chelators.     

Prediction and correlations between the stability constants of mono- and polynuclear chromium(III) and iron(III) complexes

Correlations between the experimentally determined stability constants of mono- and polynuclear chromium(III) and iron(III) complexes are discussed. An equation to evaluate the stability constants of mono- and polynuclear chromium(III) complexes is obtained: \(\log \beta [Cr_p^{3 + } (L_i )_{q_i } ] = 0.84\log \beta [Fe_p^{3 + } (L_i )_{q_i } ]\) .     

Studies on mixed ligand complexes of samarium(III), europium(III) and dysprosium(III) with 1-nitroso-2-naphthol and trioctylphosphine oxide

The extraction behavior of Sm(III), Eu(III) and Dy(III) with 1-nitroso-2-naphthol (HA) and trioctylphosphine oxide (TOPO) in methyl isobutyl ketone (MIBK) from aqueous NaClO₄ solutions in the pH range 4–9 at 0.1M ionic strength has been studied. The equilibrium concentrations of Sm and Dy were measured using their short-lived neutron activation products,¹⁵⁵Sm and^165mDy, respectively. In the case of Eu, the concentrations were assayed through the^152,154Eu radiotracer. The distribution ratios of these elements were determined as a function of pH, 1-nitroso-2-naphthol and TOPO concentrations. The extractions of Sm, Eu and Dy were found to be quantitative with MIBK solutions in the pH range 5.9–7.5, 5.6–7.5 and 5.8–7.5, respectively. Quantitative extraction of Eu was also obtained between pH 5.8 and 8.8 with chloroform solutions. The results show that these lanthanides (Ln) are extracted as LnA₃ chelates with 1-nitroso-2-naphthol alone, and in the presence of TOPO as LnA₃(TOPO) and LnA₃(TOPO)₂ adducts. The extraction constants and the adduct formation constants of these complexes have been calculated.     

Solvent extraction of Er(III) and Lu(III) with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester in presence of some reagents

The extraction of Er(III) and Lu(III) from thiocyanate media with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) and also with mixtures of EHEHPA and thenoltrifluoroacetone (HTTA) or tri-n-octylphosphine oxide (TOPO) or bis 2-ethylhexyl sulfoxide (B2EHSO) in benzene has been studied systematically. Synergistic effects have been observed with mixtures of EHEHPA+HTTA or TOPO. On the other hand, antagonistic effects have been observed with mixtures of EHEHPA+B2EHSO. These extraction data have been analyzed theoretically with the aid of a computer by taking into account complexation of the metal in the aqueous phase by SCN^– and plausible complexation in the organic phase. The extraction constants of the various product species have been deduced by non-linear regression analysis. The stability constants for the thiocyanate complexes of the metal ions have also been determined.     

Coordinating ability of rhodium(III) porphyrins toward organic bases

Reactions of hydroxo(2,3,7,8,12,13,17,18-octaethylporphyrinato)rhodium(III) and acetylacetato-(5,10,15,20-tetraphenylporphyrinato)rhodium(III) with nitrogen-containing substrates were studied by spectrophotometry. The stability constants and compositions of the resulting molecular complexes were determined, and the effects of the macrocycle nature and substrate basicity on the stability constants were estimated. The structures of the isolated rhodium porphyrin molecules and their complexes with organic bases were optimized by the PM3 quantum chemical method. The degree of macrocycle deformation was found to change in the course of metal–substrate coordination. A correlation between the metal–substrate bond energy and equilibrium constant was revealed.

     

A pH- and Redox-Potentiometric Study of Equilibria between Fe(II), Fe(III), and N-(Carboxymethyl)Aspartic Acid

Complexation in the Fe²⁺–Fe³⁺–N-(carboxymethyl)aspartic acid (H₃L) system in aqueous solutions was studied by pH- and redox-potentiometric titration at 25°C and at an ionic strength of 0.1 (KCl). Depending on the H₃L concentration and pH, neutral, protonated, and hydroxo complexes of iron(III) can be formed in the solutions. The stability constants for all the detected complexes were calculated, and the distribution plots for the fractions of complexes vs. the solution pH were constructed.     

Multiply charged ions of ruthenium(II), rhodium(III) and cobalt(III) complexes in electrospray ionization mass spectrometry

Multiply charged ions from electrospray ionization (ESI) were observed for ruthenium-bidentate ligand complexes, such as [RuL₂B]X₂ and [(RuL₂)₂B]X₄, where L is 2,2′-bipyridine, B are tetradentate ligands of 2,2′-bis(2′-pyridyl)bibenzimidazole and 2,6-bis(2′-pyridyl)benzodiimidazole, bidentate ligand of 2-(2′-pyridyl)benzimidazole and related compounds and X is CIO₄^- or CI^-. ESI mass spectra showed a simple mass pattern for easy structural assignment and detecting impurities. The mass spectra for binuclear complexes provide a charge state distribution ranging from 4+ to 2+ for Ru(II)—Ru(II) compounds and 5+ to 2+ for Ru(II)—Rh(III) compounds. It was found that different multiply charged ions are generated by loss of counterions and by protonation/deprotonation at the proton site of ligands B. The abundances of these ions are qualitatively explained in terms of the acidity of metal complexes depending on the bridging ligand structures and the charge of the metal ions. Ions produced by removal of ligands were hardly observed.     

Spectrophotometric and Potentiometric Studies on the Binding Abilities of Two Novel Tripodal Imine-Phenol Ligands Towards Al(III) and Ga(III)

The aqueous coordination behavior of two novel tripodal imine-phenol ligands, cis,cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L¹) and cis,cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me₃- TMACHSAL, L²) with Al³⁺ and Ga³⁺ has been investigated at an ionic strength of 0.1 mol⋅dm⁻³ KCl and 25±1 °C by potentiometric and spectrophotometric methods. Both ligands formed various monomeric metal complex species MLH₃, MLH₂, MLH, ML and MLH₋₁ with Ga(III); and MLH₃, ML and MLH₋₁ with Al(III). The Ga(III) complexes showed higher thermodynamic stability than the Al(III) complexes. Semi-empirical PM6 calculations along with TDDFT/B3LYP/3-21G calculations have been performed to complement the experimental measurements. The calculated structure of the metal complexes predicted a distorted octahedral geometry where favorable ring-flipping from the equatorial conformation in uncomplexed ligands to the axial conformation was observed upon chelation.     

Modeling of metal-humate complexation based on the mean molecular weight and charge of humic substances: Application to Eu(III) humate complexes using ion exchange

A general model, the so called Mean Molecular Weight Model (MMWM), of complexation of metal cations (Me^z+) with macromolecular polyanions of humic acid (HA^p-) is proposed. The model is based on the results of previous studies of the electrophoretic mobility of humate complexes and assumes that the complexation proceeds by consecutive neutralization of the dissociated carboxyl groups of the central polyanion HA^p- with Me^z+ cations. It reflects the macromolecular character of humic acid, applies molar concentrations of reacting components with equations for stability constants and incorporates also the mean charge of humic macromolecules. The model has been verified with experimental data obtained in the study of complexation of Eu(III) with Aldrich humic acid using ion exchange (Amberlite IR-120), over a broad range of [Eu] to [HA] ratio, at pH 4 and 7.     

Complex formation reactions of lanthanum(III), cerium(III), thorium(IV), dioxouranyl(IV) complexes with tricine

Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules.     

Equilibrium study of the systems of aluminium(III), gallium(III) and indium(III) with mercaptoacetate, 3-mercaptopropionate and 2-mercaptobenzoate

Equilibrium studies were carried out by pH-potentiometry on the systems of aluminium(III), gallium(III) and indium(III) with mercaptoacetate (MerAc^2?), 3-mercaptopropionate (MerPr^2?) and 2-mercaptobenzoate (MerBe^2?). It was found that the complex-forming properties of the Al³⁺ ion towards these mercaptocarboxylic acid ligands differ from those of Ga³⁺ and Al³⁺. Under the conditions of the study, Al³⁺ forms only hydroxo complexes, while Ga³⁺ and In³⁺ form relatively stable complexes involving the simultaneous coordination of the carboxylate and the deprotonated mercapto group. In all cases the equilibrium systems can be described without the assumption of polynuclear complexes. The complexes Ga(MerAc)₂ and Ga(MerBe)₂ show marked stability; this was interpreted in terms of back-coordination and of interaction between the d¹⁰ electrons of the Ga³⁺ ion and the empty d orbitals of the S donor atom. Complexes of composition ML_i are not formed in the Ga³⁺-MerPr^2? system; this points to the importan roles of the number of atoms in the chelate ring and the higher stability of the Ga(III)-hydroxo complexes.     

Prediction of Stability Constants for Cr(III) and Cr(II) Complexes

Regression analysis was used to derive equations for estimaing thermodynamic stability constants for complexes of Cr²⁺ (log^° ₁[Cr²⁺L] = 0.53log^° _n [H _n L]) and Cr³⁺ (log^° ₁[Cr³⁺L] = 0.88log^° _n [H _n L]) from the known protonation constants of H _n L ligands and for determining stability constants of Cr²⁺ and Cr³⁺ complexes from the available stability constants of Cu²⁺ complexes (log^° ₁[Cr²⁺L] = 0.76log^° ₁[Cu²⁺L] and log^° ₁[Cr²⁺L] = 0.60log^° ₁[Cr³⁺L], respectively). Parameters of the Panteleon–Ecka equation for calculating stability constants of Cr²⁺ complexes ( = 0.57) and Cr³⁺ complexes ( = 0.69) with two and three bidentate ligands were also determined. The ratio of logarithmic stability constants for complexes with the same metals but with different metal ionic charges was found to be approximately equal to the ratio of charges on the central ions. The stability constant of Cr(II) sulfate complex was calculated.     

A Direct Carbon-13 and Nitrogen-15 NMR Study of Praseodymium(III)- and Neodymium(III)-Isothiocyanate Complex Formation in Aqueous Solvent Mixtures

Multinuclear magnetic resonance spectroscopic studies of the trivalent lanthanide complexes with isothiocyanate have been completed for the praseodymium(III) and neodymium(III) ions. In water–acetone–Freon mixtures, at temperatures low enough to slow ligand exchange, usually –85 to –125°C for isothiocyanate, separate carbon-13 and nitrogen-15 NMR signals can be observed for free anion and NCS^- in each metal–ion complex. For both metal ions, ¹⁵N NMR signals are observed for four complexes, displaced about +1500 ppm downfield from free NCS^- for Pr³⁺ and about +2000 ppm for Nd³⁺. In the ¹³C NMR spectra, only three peaks are observed for the complexes of both metal anions, with signal overlap obscuring the resonance for the fourth complex. However, the metal ion coordination numbers, obtained by integration of the resonance signals, are comparable in the ¹⁵N and ¹³C spectra, approaching a maximum value of about 3. These spectral data indicate the formation of Ln(NCS)²⁺ through Ln(NCS) ₄ ^1- occurs for both lanthanides in these solvent systems, a result also observed previously for Ce³⁺, Sm³⁺, and Eu³⁺ in our laboratory. Attempts to study these complexes in water–methanol were unsuccessful, due to the inability to achieve low enough temperatures to slow ligand exchange sufficiently. Results for NCS^- and Cl^- competitive-binding studies by ³⁵Cl NMR for both metal ions will also be described.     

Potentiometric determination of Pu(III) complexes formed by citric acid,EDTA, DHTP and DTPP

A computer method of direct analysis of potentiometric (pH) curves of equimolar M^z++HnL alkali titrated systems has been used for the determination of composition and stability constants of complexes of Pu(III) with some weak organic acids.