A photometric study of the complexation reaction between Alizarin complexan and zinc(II), nickel(II), lead(II), cobalt(II) and copper(II)

The complexation reaction between Alizarin complexan ([3-N,N-di(carboxymethyl)aminomethyl]-1,2-dihydroxyanthraquinone; H(4)L) and zinc(II), nickel(II), lead(II), cobalt(II) and copper(II) has been studied by a spectrophotometric method. All these metal ions form 1:1 complexes with HL; 2:1 metal:ligand complex were found only for Pb(II) and Cu(II). The stability constants are (ionic strength I = 0.1, 20 degrees C): Zn(2+) + HL(3-) right harpoon over left harpoon ZnHL(-) log K +/- 3sigma(log K) = 12.19 +/- 0.09 (I = 0.5) Ni(2+) + HL(3-) right harpoon over left harpoon NiHL(-) log K +/- 3sigma(log K) = 12.23 +/- 0.21 Pb(2+) + HL(3-) right harpoon over left harpoon PbHL(-) log K +/- 3sigma(log K) = 11.69 +/- 0.06 PbHL(-) + Pb(2+) right harpoon over left harpoon Pb(2)L + H(+) log K approximately -0.8 Co(2+) + HL(3-) right harpoon over left harpoon CoHL(-) log K 3sigma(log K) = 12.25 + 0.13 Cu(2+) + HL(3-) right harpoon over left harpoon CuHL(-) log K 3sigma(log K) = 14.75 +/- 0.07 Cu(2+) + CuHL(-) right harpoon over left harpoon Cu(2)L + H(+) log K approximately 3.5 The solubility and stability of both the reagent and the complexes and the closenes of the values of the stability constants make this reagent suitable for the photometric detection of several metal ions in the eluate from an ion-exchange column.     

Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure

The reaction equilibria [H(4)L](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(H(2)L)](2+) + 2HOAc (K(1)) and [Zn(H(2)L)](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(2)L](2+) + 2HOAc (K(2)), involving zinc acetate and the perchlorate salts of the tetraiminodiphenol macrocycles [H(4)L(1)(-)(3)](ClO(4))(2), the lateral (CH(2))(n)() chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn(2)L(1)](ClO(4))(2), [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(2)(mu-O(2)CR)](ClO(4)) (R = CH(3), C(6)H(5), p-CH(3)C(6)H(4), p-OCH(3)C(6)H(4), p-ClC(6)H(4), p-NO(2)C(6)H(4)), and [Zn(2)L(3)(mu-OAc)](ClO(4)) have been investigated. The X-ray crystal structures of the complexes [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(3)(mu-OAc)](ClO(4)), and [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) have been determined. The complex [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) in which the coordinated water molecule is present as the hydronium ion (H(3)O(+)) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn(2)L(2)(mu-OBz)(2)].H(2)O. The equilibrium constants (K) for the reaction [Zn(2)L(2)(H(2)O)(2)](2+) + A(-) right harpoon over left harpoon [Zn(2)L(2)A](+) + 2H(2)O (K), where A(-) = acetate, benzoate, or the carboxylate moiety of the amino acids glycine, l-alanine, l-histidine, l-valine, and l-proline, have been determined spectrofluorimetrically in aqueous solution (pH 6-7) at room temperature. The binding constants (K) evaluated for these systems vary in the range (1-8) x 10(5).     

Interaction of palladium with sulphaguanidine

The formation constants of palladium with chloride ions have been determined by a new approach to the interpretation of the ultraviolet spectra. The interaction of PdCl(4)(2-) with sulphaguanidine (SG) has been interpreted and evaluated quantitatively. The formation constants of the mixed ligand complex Pd(SG)(2),Cl(2), were determined spectrophotometrically. The stability constants for the stepwise formation of the palladium chloride complexes are: log k(1) = 3.48; log k(2) = 2.79; log k(3) = 2.35; log k(4) = 1.1, and for the interaction of PdCl(4)(2-) with SG, log k(1) = 5.42; log k(2) = 4.38.     

Analysis of variance applied to determinations of equilibrium constants

The statistical analysis of variance has been applied to the values of the equilibrium constants of the glycinate-proton and glycinate-nickel systems, determined in different laboratories by pH-titration in aqueous solution. The analysis shows how the main part of the error derives from the variability from one titration to another even in the same laboratory. Therefore the data for a single titration (k) must be processed separately, thus yielding a mean value for the equilibrium constant logbeta (pqr)(k) of the species M(p)H(q)L(r); from these mean values for different titrations in each laboratory l, a within-laboratory grand average, logbeta (pqr)(l), can be calculated; the variance of this grand average measures the experimental error. A further analysis of the data from the different participating laboratories shows that there were no significant differences between laboratories for the constants reported. From these results it can be inferred that all the values of the mean constants logbeta (pqr)(k) for one species, as determined separately for each titration in four laboratories, belong to the same population. A chi(2) analysis of these populations demonstrates that the stability constants of the species HL, H(2)L(+), NiL(+), NiL(2) (with L(-) = glycinate) are normally distributed, but not that for NiL(-)(3). Therefore, general mean values of the first four constants can be calculated and proposed as reliable standard values at 25 degrees and I = 1.0M Na(Cl): protonation of glycinate, log beta(011) = 9.651(12), log beta(021) = 12.071(26); nickel-glycinate complexes, log beta(101) = 5.615(35), log beta(102) = 10.363(62). These values indicate that the standard deviations are rather higher than those often reported in the literature.     

Highly selective and sensitized spectrophotometric determination of iron (III) following potentiometric study

A simple, selective and sensitized spectrophotometric method for determination of trace amounts of Fe3+ ion in tap and waste water solutions has been described. The spectrophotometric determination of Fe3+ ion using Ferron in the presence of N,N-Dodecytrimethylammonium bromide (DTAB) has been carried out. The Beer's law is obeyed over the concentration range of 0.05-2.6 microg mL(-1) of Fe3+ ion with the relative standard deviation (RSD %) <0.2% and the molar absorptivity of complexes in pH 3.5 is 3.8 x 10(3) L mol(-1) cm(-1). Potentiometric pH titration has been used for prediction of protonation constants of ferron, and evaluating its stoichiometry and respective stability constant with Fe3+ ion. As it is obvious the most likely species of ferron alone and its complexes are LH (log = 7.64), LH2 (logK = 10.52), LH3 (logK = 11.74) and ML2 (logbeta = 23.68), ML3 (logbeta = 23.68), ML3H (logbeta = 23.68), ML3H2 (logbta = 23.68) and ML(OH)2 (logbeta = 23.68) respectively.     

The chemistry of iron in biosystems-V Study of complex formation between iron(III) and tartaric acid in alkaline aqueous solutions

Complex formation between Fe(III) and tartaric acid (H(2)L) has been studied in O.5M NaNO(3) medium at 25 degrees by potentiometry at pH 4.5-11. The following complex species and corresponding values of the stability constants (charges omitted) are proposed: 2Fe + 2L + 5H(2)O --> Fe(2)(OH)(5)L(2) + 5H(+); log* beta(-522) = 4.95 Fe + L + 3H(2)O --> Fe(OH)(3)L + 3H(+); log* beta(-311) = -1.55 Fe + L + 5H(2)O --> Fe(OH)(5)L + 5H(+); log* beta(-511) = -21.2 These results are in good agreement with those reported for this system in acid. The results may be presented as the degeneration of the "core + link" mechanism observed in the acidic zone. Structures are suggested for the complex species formed.     

Kinetics of Formation and Dissociation of [Cr(3)O(O(2)CCH(3))(6)(urea)(3)](+): An Example of Statistically Controlled Kinetics and Equilibrium

Kinetics of the overall reaction [Cr(3)O(O(2)CCH(3))(6)(H(2)O)(3)](+) + 3 urea right harpoon over left harpoon [Cr(3)O(O(2)CCH(3))(6)(urea)(3)](+) + 3H(2)O have been studied spectrophotometrically. Monophasic kinetics were observed in both directions. The reverse steps, of urea dissociation, were monitored using an analytical technique which permits direct determination of the concentration of liberated urea and does not require knowledge of extinction coefficients of intermediate species. Results imply that consecutive steps occur with rate constants in close to the statistical ratios of k(1):k(2):k(3) = 3:2:1 and k(-)(1):k(-)(2):k(-)(3) = 1:2:3. Rates indicate strong labilization of urea, compared to the case of mononuclear complex [Cr(urea)(6)](3+).     

Dioxouranium(VI)-carboxylate complexes. Speciation of UO2(2+)-1,2,3-propanetricarboxylate system in NaCl(aq) at different ionic strengths and at t=25 degrees C

The formation constants of dioxouranium(VI)-1,2,3-propanetricarboxylate [tricarballylate (3-), TCA] complexes were determined in NaCl aqueous solutions at 0 < or = I/mol L(-1) < or = 1.0 and t=25 degrees C, by potentiometry, ISE-[H+] glass electrode. The speciation model obtained at each ionic strength includes the following species: ML-, MLH0, ML2(4-) and ML2H3- (M = UO2(2+) and L = TCA). The dependence on ionic strength of protonation constants of 1,2,3-propanetricarboxylate and of the metal-ligand complexes was modeled by the SIT (Specific ion Interaction Theory) approach and by the Pitzer equations. The formation constants at infinite dilution are [for the generic equilibrium p UO22+ + q (L3-) + r H+ = (UO2(2+))p(L)qHr(2p-3q+r); betapqr]: log beta110 = 6.222 +/- 0.030, log beta111 = 11.251 +/- 0.009, log beta121 = 7.75 +/- 0.02, log beta121 = 14.33 +/- 0.06. The sequestering ability of 1,2,3-propanetricarboxylate towards UO2(2+) was quantified by using a sigmoid Boltzman type equation.     

Synthesis of beta-P,N aminophosphines and coordination chemistry to Pd(II). X-ray structures of [PdCl2(Ph2PCH(Ph)NHPh-kappaP,kappaN)] and PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)

The reaction of the C=N bond in PhCH=NPh with the carbanionic species Ph2PCH2-, leading to the N-phenyl beta-aminophosphine Ph2PCH2CH(Ph)NHPh, L1, is described. This molecule reacts with different organic electrophiles to afford related compounds Ph2PCH2CH(Ph)NPhX (X = SiMe3, L2; COPh, L4), [Ph2MePCH2CH(Ph)NHPh]+(I-), L3, and [Ph2PCH2CH(Ph)N(Ph)CO]2, L5, containing two amido and two phosphino functions. The coordination properties of L1, L2, and L4 have been studied in palladium chemistry. The X-ray structure of [PdCl2(Ph2PCH2CH(Ph)NHPh-kappaP,kappaN)] shows the bidentate coordination mode for the L1 ligand with equatorial C(Ph)-N(Ph) phenyl groups. [PdCl2(Ph2PCH2CH(Ph)NHPh-kappaP,kappaN)] crystallizes at 298 K in the space group P2(1)/n with cell parameters a = 10.689(2) A, b = 21.345(3) A, c = 12.282(2) A, beta = 90.294(12) degrees, Z = 4, D(calcd) = 1.526. The reaction between 2 equiv of L1 and [PdCl(eta3-C3H5)]2 affords the [PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)] complex in which an unexpected N-H.Cl intramolecular interaction has been observed by an X-ray diffraction analysis. [PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)] crystallizes at 298 K in the monoclinic space group Cc with cell parameters a = 10.912(1) A, b = 17.194(2) A, c = 14.169(2) A, beta = 100.651(9) degrees, Z = 4, D(calcd) = 1.435. Neutral and cationic alkyl or allyl palladium chloride complexes containing L1 are also reported as well as a neutral allyl palladium chloride complex containing L4. Variable-temperature 31P[1H] NMR studies on the allyl complexes show that the eta3/eta1 allyl interconversion is enhanced by a positive charge and also by a N-H.Cl intramolecular interaction.     

Surface properties of hydrous manganite (gamma-MnOOH). A potentiometric, electroacoustic, and X-ray photoelectron spectroscopy study

The acid-base characteristics of the manganite (gamma-MnOOH) surface have been studied at pH above 6, where dissolution is negligible. Synthetic microcrystalline particles of manganite were used in the experiments. From potentiometric titrations, electrophoretic mobility measurements, and X-ray photoelectron spectroscopy (XPS), a one pK(a) model was constructed that describes the observed behavior. The data show no ionic strength effect at pH < 8.2, which is the pH at the isoelectric point (pH(iep)), but ionic strength effects were visible above this pH. To explain these observations, Na(+) ions were suggested to form a surface complex. The following equilibria were established: =MnOH(2)(+1/2) right harpoon over left harpoon =MnOH(-)(1/2) + H(+), log beta(0) (intr.) = -8.20; =MnOH(2)(+1/2) + Na(+) right harpoon over left harpoon =MnOHNa(+1/2) + H(+), log beta(0) (intr.) = -9.64. The excess of Na(+) at the surface was supported by XPS measurements of manganite suspensions containing 10 mM NaCl. The dielectric constant of synthetic manganite powder was also determined in this study.     

Complexation, extraction and determination of the H(3)CHg(+) ion with cadion [1-(p-nitrophenyl)-3-(p'-azobenzene)-triazene

The partition constants of Cadion, i.e., 1-(p-nitro-phenyl)-3-(p'-azobenzene)-triazene, of its complex with the methylmercuric ion, and of methylmercury chloride were determined in the system toluene/aqueous phase containing 40 vol.% methyl alcohol; they have the values of 4.3 x 10(3), 3.0 x 10(3), and 2.6 respectively. The reagent has an absorption maximum at 406 nm, whereas the methylmercury complex at 460 nm. The K(HR) value corresponding to the H(+) + R(-) right harpoon over left harpoon HR equilibrium is 10(10.85), HR being the reagent molecule and H belongs to the NH of the triazenic group (NNNH). The K(ext) value corresponding to the equilibrium H(3)CHg(+) + (HR)(o) right harpoon over left harpoon (H(3)CHgR)(o) + H(+) is 1.0, where the "o" indicates the species present in the organic phase. The reagent/H(3)CHg(+) combination ratio is 1/1. The formation constant of the methylmercury complex, K(H(3)CHgR), which corresponds to the equilibrium H(3)CHg(+) + R(-) right harpoon over left harpoon H(3)CHgR, has a value of 10(10.8) as estimated by means of two different methods. The IR spectra allowed some conclusions to be drawn concerning the formation of the complex. The complex is stable up to 180 degrees , and the reagent up to 140 degrees . The molar absorptivity is of 3.46 x 10(4) 1.mole(-1).cm(-1) and the H(3)CHg(+) can be determined in the range 0.025-4 ppm. The determination is highly selective.     

Studies on metal carbonate equilibria-part 21 Study of the U(VI)H(2)OCO(2)(g) system by thermal lensing spectrophotometry

Equilibria in the U(VI)H(2)OCO(2)(g) system in 0.5M sodium perchlorate medium at 25 degrees have been studied. By using thermal tensing spectrophotometry (TLS) and a very low total concentration of U(V1) (4 x 10(-6)M) information could be obtained on equilibria involving UO(2)(CO(3))(2-)(2) without complications due to formation of the trimer (UO(2))(3)(CO(3))(6-)(6). The experimental data allowed a precise determination of the equilibrium constant log K(3) = 6.35 +/- 0.05 for the reaction UO(2)(CO(3))(2-)(2) + CO(2-)(3) right harpoon over left harpoonright harpoon over left harpoon UO(2)(CO(3))(4-)(3). The interpretation of TLS data is briefly discussed, as well as the potential use of this technique for studies of the speciation of trace elements in natural water systems.     

Determination of formation constants of hydroxo and carbonate complexes of Pr(3+) in 2 M NaCl at 303 K

The hydrolysis of praseodymium III in 2 M sodium chloride at 303 K was studied. Two methods were used: pH titration followed by a computational refinement and solvent extraction in the presence of a competitive ligand. The hydrolysis constants obtained by pH titration were: logbeta(1,H)=-7.68+/-0.07, logbeta(1,2H)=-15.10+/-0.03, and beta(1,3H)=-23.80+/-0.04. The stability constants of praseodymium carbonate complexes were determined by pH titration as well and were: logbeta(1,CO(2-)(3))=5.94+/-0.08 and logbeta(1,2CO(2-)(3))=11.15+/-0.15. Praseodymium carbonate species were taken into consideration for calculating the first hydrolysis constants by the solvent extraction method and the value obtained was: logbeta(1,H)=-7.69+/-0.27. The values for logbeta(1,H) attained by both methods are the same. The species-distribution diagram was obtained from the stability constants of praseodymium carbonate complexes and hydrolysis products in the conditions of the present work.     

Sequestering ability of polycarboxylic ligands towards dioxouranium(VI)

In this paper we report a comparison on the sequestering ability of some polycarboxylic ligands towards dioxouranium(VI) (UO(2)(2+), uranyl). Ligands taken into account are mono- (acetate), di- (oxalate, malonate, succinate and azelate), tri- (1,2,3-propanetricarboxylate) and hexa-carboxylate (1,2,3,4,5,6-benzenehexacarboxylate). The sequestering ability of polycarboxylic ligands towards UO(2)(2+) was quantified by a new approach expressed by means of a sigmoid Boltzman type equation and of a empirical parameters (pL(50)) which defines the amount of ligand necessary to sequester 50% of the total UO(2)(2+) concentration. A fairly linear correlation was obtained between pL(50) or log K(110) (log K(110) refers to the equilibrium: UO(2)(2+)+L(z-)=UO(2)L((2-z)); L=generic ligand) and the polyanion charges. In order to complete the picture, a tetra-carboxylate ligand (1,2,3,4-butanetetracarboxylate) was studied in NaCl aqueous solutions at 0相似文献   

Complexation of Pu(IV) with the natural siderophore desferrioxamine B and the redox properties of Pu(IV)(siderophore) complexes

The bioavailability and mobility of Pu species can be profoundly affected by siderophores and other oxygen-rich organic ligands. Pu(IV)(siderophore) complexes are generally soluble and may constitute with other soluble organo-Pu(IV) complexes the main fraction of soluble Pu(IV) in the environment. In order to understand the impact of siderophores on the behavior of Pu species, it is important to characterize the formation and redox behavior of Pu(siderophore) complexes. In this work, desferrioxamine B (DFO-B) was investigated for its capacity to bind Pu(IV) as a model siderophore and the properties of the complexes formed were characterized by optical spectroscopy measurements. In a 1:1 Pu(IV)/DFO-B ratio, the complexes Pu(IV)(H2DFO-B)4+, Pu(IV)(H1DFO-B)3+, Pu(IV)(DFO-B)2+, and Pu(IV)(DFO-B)(OH)+ form with corresponding thermodynamic stability constants log beta1,1,2 = 35.48, log beta1,1,1 = 34.87, log beta1,1,0 = 33.98, and log beta1,1,-1 = 27.33, respectively. In the presence of excess DFO-B, the complex Pu(IV)H2(DFO-B)22+ forms with the formation constant log beta2,1,2 = 62.30. The redox potential of the complex Pu(IV)H2(DFO-B)22+ was determined by cyclic voltammetry to be E1/2 = -0.509 V, and the redox potential of the complex Pu(IV)(DFO-B)2+ was estimated to be E1/2 = -0.269 V. The redox properties of Pu(IV)(DFO-B)2+ complexes indicate that Pu(III)(siderophore) complexes are more than 20 orders of magnitude less stable than their Pu(IV) analogues. This indicates that under reducing conditions, stable Pu(siderophore) complexes are unlikely to persist.     

Diphosphines possessing electronically different donor groups: synthesis and coordination chemistry of the unsymmetrical Di(N-pyrrolyl)phosphino-functionalized dppm analogue Ph2PCH2P(NC4H4)2

The unsymmetrical diphosphinomethane ligand Ph(2)PCH(2)P(NC(4)H(4))(2) L has been prepared from the reaction of Ph(2)PCH(2)Li with PCl(NC(4)H(4))(2). The diphenylphosphino group can be selectively oxidized with sulfur to give Ph(2)P(S)CH(2)P(NC(4)H(4))(2) 1. The reaction of L with [MCl(2)(cod)] (M = Pd, Pt) gives the chelate complexes [MCl(2)(L-kappa(2)P,P')] (2, M = Pd; 3, M = Pt) in which the M-P bond to the di(N-pyrrolyl)phosphino group is shorter than that to the corresponding diphenylphosphino group. However, the shorter Pd-P bond is cleaved on reaction of 2 with an additional 1 equiv of L to give [PdCl(2)(L-kappa(1)P)(2)] 4. Complex 4 reacts with [PdCl(2)(cod)] to regenerate 2, and with [Pd(2)(dba)(3)].CHCl(3) to give the palladium(I) dimer [Pd(2)Cl(2)(mu-L)(2)] 5, which exists in solution and the solid state as a 1:1 mixture of head-to-head (HH) and head-to-tail (HT) isomers. The palladium(II) dimer [Pd(2)Cl(2)(CH(3))(2)(mu-L)(2)] 6, formed by the reaction of [PdCl(CH(3))(cod)] with L, also exists in solution as a mixture of HH and HT isomers, although in this case the HT isomer prevails at low temperature and crystallizes preferentially. Complex 6 reacts with TlPF(6) to give the A-frame complex [Pd(2)(CH(3))(2)(mu-Cl)(mu-L)(2)]PF(6) 7. The reaction of L with [RuCp*(mu(3)-Cl)](4) leads to the dimer [Ru(2)Cp*(2)(mu-Cl)(2)(mu-L)] 8, for which the enthalpy of reaction has been measured. The reaction of L with [Rh(mu-Cl)(cod)](2) gives a mixture of compounds from which the dimer [Rh(2)(mu-Cl)(cod)(2)(mu-L)]PF(6) 9 can be isolated. The crystal structures of 2.CHCl(3), 3.CH(2)Cl(2), 4, 5.(1)/(4)CH(2)Cl(2), 6, 7.2CH(2)Cl(2), 8, and 9.CH(2)Cl(2) are reported.     

Hydrolysis of uranium(VI) at variable temperatures (10-85 degrees C)

The hydrolysis of uranium(VI) in tetraethylammonium perchlorate (0.10 mol dm(-3) at 25 degrees C) was studied at variable temperatures (10-85 degrees C). The hydrolysis constants (*beta(n,m)) and enthalpy of hydrolysis (Delta H(n,m)) for the reaction mUO(2)(2+) + nH(2)O = (UO(2))(m)(OH)(n)((2m-n))+) + nH(+) were determined by titration potentiometry and calorimetry. The hydrolysis constants, *beta(1,1), *beta(2,2), and *beta(5,3), increased by 2-5 orders of magnitude as the temperature was increased from 10 to 85 degrees C. The enthalpies of hydrolysis, Delta H(2,2) and Delta H(5,3), also varied: Delta H(2,2) became more endothermic while Delta H(5,3) became less endothermic as the temperature was increased. The heat capacities of hydrolysis, Delta C(p(2,2)) and Delta C(p(5,3)), were calculated to be (152 +/- 43) J K(-1) mol(-1) and -(229 +/- 34) J K(-1) mol(-1), respectively. UV/Vis absorption spectra supported the trend that hydrolysis of U(VI) was enhanced at elevated temperatures. Time-resolved laser-induced fluorescence spectroscopy provided additional information on the hydrolyzed species at different temperatures. Approximation approaches to predict the effect of temperature were tested with the data from this study.     

On the formation of iron(III) hydroxo acetate complexes

The formation of hydroxo acetate complexes of iron (III) ion has been studied at 25 degrees C in 3 M (Na)ClO4 ionic medium by measuring with a glass electrode the hydrogen ion concentration in Fe(ClO4)3-HClO4-NaAc mixtures (Ac = acetate ion). The acetate/metal ratio ranged from 0 to 6, the metal concentration varied from 0.005 to 0.06 M, whereas [H+] was stepwise decreased from 0.1 M to initial precipitation of hydroxo-acetates. This occurred, depending on the acetate/metal ratio, in the -log[H+] range 1.85-2.7. The potentiometric data are consistent with the presence of Fe3(OH)3Ac3(3+), Fe2(OH)2(4+), Fe3(OH)4(5+), Fe3(OH)5(4+) and, as minor species, of Fe3(OH)2Ac6+, FeAc2+, FeAc2+, FeOH2+ and Fe(OH)2+. Previously published EMF measurements with redox and glass half-cells were recalculated to refine the stability constants of FeAc2+, FeAc2+ and Fe3(OH)2Ac6+. Formation constants *beta pqr for pFe(3+)+(q-r)H2O + rHAc reversible Fep(OH)(q-r)(Ac)r3p-q + qH+ (in parenthesis the infinite dilution value): log*beta 111 = -1.85 +/- 0.02 (-0.67 +/- 0.15), log*beta 122 = -3.43 +/- 0.02 (-1.45 +/- 0.15); log*beta 363 = -5.66 +/- 0.03 (-2.85 +/- 0.40), log*beta 386 = -8.016 +/- 0.006 (-4.06 +/- 0.15), log*beta 220 = -2.88 +/- 0.02 (-2.84 +/- 0.05), log*beta 340 = -6.14 +/- 0.18 (-6.9 +/- 0.4), log*beta 350 = -8.44 +/- 0.09 (-7.65 +/- 0.15).     

Use of electrospray mass spectrometry (ESI-MS) for the study of europium(III) complexation with bis(dialkyltriazinyl)pyridines and its implications in the design of new extracting agents

ESI mass spectrometry was used to investigate the europium complexation by tridentate ligands L identical with 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridines (DATP) that have shown unique separation properties of actinides(III) from lanthanides(III) in nitric acid solutions. Complexes of three ligands, namely methyl (DMTP), n-propyl (DnPTP), and iso-propyl (DiPTP), have been investigated in acidic solutions to check the aqueous-phase stability of Eu(L)(3)(3+) ions identified previously in the solid state. The data obtained show, first, the presence of stable Eu(L)(3)(3+) ions with DnPTP (log beta(3)(app) = 12.0 +/- 0.5) and DiPTP (log beta(3)(app) = 14.0 +/- 0.6) in methanol/water (1:1 v/v) solutions under pH range 2.8-4.6 and, second, a mechanism whereby alkyl moieties contribute to a self-assembling process leading to the formation of Eu(L)(3)(3+) ions. Other complexes such as Eu(L)(2)(3+) ions are only observed for DnPTP (log beta(2)(app) = 6.7 +/- 0.5) and DMTP (log beta(2)(app) = 6.3 +/- 0.1) and Eu(L)(3+) only for DMTP (log beta(1)(app) = 2.9 +/- 0.2). The log beta(n)(app) values for the Eu(L)(n)(3+) (n = 1-3) complexes were determined at pH 2.8. Better insight was given in this study concerning the role of the hydrophobic exterior of the ligands for the design of a new range of extracting agents.