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   

Ionophoretic studies on mixed metal--nitrilotriacetate--penicillamine complexes

Paper ionophoresis is described for the study of equilibria in a mixed ligand complex system in solution. This method is based on the movement of a spot of metal ion in an electric field with the complexants added in the background electrolyte at pH 8.5. The concentration of the primary ligand (nitrilotriacetate) was kept constant, while that of the secondary ligand (penicillamine) was varied. The stability constants of the metal-nitrilotriacetate-penicillamine complexes have been found to be 6.26 +/- 0.09 and 6.68 +/- 0.13 (log K values) for Al3+ and Th4+ complexes, respectively, at 35 degrees C and ionic strength 0.1 M.     

Molecular switch triggered by solvent polarity: synthesis,Acid-base behavior,alkali metal ion complexation,and crystal structure

The synthesis and characterization of the new tetraazamacrocycle L, bearing two 1,1'-bis(2-phenol) groups as side-arms, is reported. The basicity behavior and the binding properties of L toward alkali metal ions were determined by means of potentiometric measurements in ethanol/water 50:50 (v/v) solution (298.1+/-0.1 K, I=0.15 mol dm(-3)). The anionic H(-1)L(-) species can be obtained in strong alkaline solution, indicating that not all of the acidic protons of L can be removed under the experimental conditions used. This species behaves as a tetraprotic base (log K(1)=11.22, log K(2)=9.45, log K(3)=7.07, log K(4)=5.08), and binds alkali metal ions to form neutral [MH(-1)L] complexes with the following stability constants: log K(Li)=3.92, log K(Na)=3.54, log K(K)=3.29, log K(Cs)=3.53. The arrangement of the acidic protons in the H(-1)L(-) species depends on the polarity of the solvents used, and at least one proton switches from the amine moiety to the aromatic part upon decreasing the polarity of the solvent. In this way two different binding areas, modulated by the polarity of solvents, are possible in L. One area is preferred by alkali metal ions in polar solvents, the second one is preferred in solvents with low polarity. Thus, the metal ion can switch from one location to the other in the ligand, modulated by the polarity of the environment. A strong hydrogen-bonding network should preorganize the ligand for coordination, as confirmed by MD simulations. The crystal structure of the [Na(H(-1)L)].CH(3)CN complex (space group P2(1)/c, a=12.805(1), b=20.205(3), c=14.170(2) A, beta=100.77(1) degrees, V=3601.6(8) A(3), Z=4, R=0.0430, wR2=0.1181), obtained using CH(2)Cl(2)/CH(3)CN as mixed solvent, supports this last aspect and shows one of the proposed binding areas.     

The thermodynamic model of inorganic arsenic species in aqueous solutions Potentiometric study of the hydrolitic equilibrium of arsenic acid

Protonation constants of arsenic acid were determined at different ionic strengths in NaClO(4) (0.1, 0.5, 1.0, 3.0 mol dm(-3)), NaCl (0.5 and 1.0 mol dm(-3)) and KCl (0.5, 1.0 and 3.0 mol dm(-3)) ionic media by means of a potentiometric study. The distribution of arsenate species was defined depending on two important variables in natural environments: pH and composition. All the experimentation was performed at 25 degrees C. The differences found in the protonation constants for different medium compositions, were explained by the different behaviour of the interaction parameters of the species considered in the different media and ionic strengths. These parameters were reported for all hydrolitic As(V) species and were calculated using the Modified Bromley's Methodology (MBM). The corresponding thermodynamic stepwise formation constants were also determined (log degrees K(1)=11.58+/-0.01, log degrees K(2)=7.06+/-0.01, log degrees K(3)=2.25+/-0.01). All the results obtained showed not only the importance of the ionic strength but also of the composition of the ionic medium on the distribution of the acid-base species of As(V) as a function of pH in natural waters.     

Equilibrium and formation/dissociation kinetics of some Ln(III)PCTA complexes

The protonation constants () of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine-containing macrocycle and several different metal ions have been determined in 1.0 M KCl at 25 degrees C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously, and a total of five protonation steps were detected (log = 11.36, 7.35, 3.83, 2.12, and 1.29). The stability constants of complexes formed between PCTA and Mg2+, Ca2+, Cu2+, and Zn2+ were also somewhat higher than those previously reported, but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln3+ series of ions and Y3+ were determined by using an "out-of-cell" potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the Ln series in proportion to decreasing Ln3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA) were followed by conventional UV-vis spectroscopy in the pH range 3.5-4.4. First-order rate constants (saturation kinetics) obtained for different ligand-to-metal ion ratios were consistent with the rapid formation of a diprotonated intermediate, Ln(H(2)PCTA)(2+). The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97, and 2.69 log K units for Ce(H(2)PCTA), Eu(H(2)PCTA), Y(H(2)PCTA), and Yb(H(2)PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate-determining step, and the rate constant (k(r)) for this process was found to be inversely proportional to the proton concentration. The formation rates (k(OH)) increased with a decrease in the lanthanide ion size [9.68 x 10(7), 1.74 x 10(8), 1.13 x 10(8), and 1.11 x 10(9) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively]. These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid-catalyzed dissociation rates (k1) varied with the cation from 9.61 x 10(-4), 5.08 x 10(-4), 1.07 x 10(-3), and 2.80 x 10(-4) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively.     

First fluorescence spectroscopic investigation of Am(III) complexation with an organic carboxylic ligand, pyromellitic acid

For the first time Am(III) complexation with a small organic ligand could be identified and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature and trace metal concentration. With pyromellitic acid (1,2,4,5-benzene-tetracarboxylic acid, BTC) as ligand spectroscopic characteristics for the Am-BTC complex system were determined at pH 5.0, an ionic strength of 0.1 M (NaClO4) and room temperature. The fluorescence lifetimes were determined to be 23.2±2.2 ns for Am3+(aq) and 27.2±1.2 ns for the Am-BTC 1:1 complex; the emission maximum for the 5D1-(7)F1 transition is 691 nm for both species. The complex stability constant for the Am-BTC 1:1 complex was calculated to be logβ110=5.42±0.16.     

配合物稳定性与配位体酸碱强度之间的直线自由能关系 IX: Cu(II)[或Ni(II)]-2,2'-联吡啶-N,N'-双(对位取代苯基)乙二胺三元配合物体系的研究

报导了以2,2'-联吡啶为第一配体, N,N'-双(对位取代苯基)乙二胺为第二配体的Cu(II)、Ni(II)三元配合物稳定性的研究, 发现三元配合物的稳定性与第二配体的碱性强度之间存在线性自由能关系.     

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be logbeta(210) = 7.33 +/- 0.10 at an ionic strength of 0.1 mol/l (NaClO(4)) and at 21 degrees C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.     

Solvent extraction of Cd(II) with N-cyclohexyl-N-nitrosohydroxylamine and 4-methylpyridine into methyl isobutyl ketone

The distribution equilibria of the complexes cadmium-cnha and cadmium-cnha-4-methylpyridine in the water-methyl isobutyl ketone system have been studied at 25 degrees , by using (109)Cd as a radiotracer to measure the metal distribution ratio. A very sensitive method for detection of (109)Cd, based on the use of a liquid scintillator, has been developed. From the graphical treatment of the equilibrium data, it has been deduced that CdL(2) is the complex extracted in the absence of 4-methylpyridine, and that the adduct CdL(2)B is extracted when the second ligand is present. This model has been checked by treating the data with the program LETAGROP-DISTR and the following equilibrium constants have been obtained: stability constants of CdL(2), log beta(1) = 2.82 +/- 0.14, log beta(2) = 5.981 +/- 0.004; distribution constant of CdL(2), log K(DC) = -0.49 +/- 0.01; adduct formation constant of CdL(2)B, log K(s) = 2.70 +/- 0.07.     

Study of complex formation in the manganese(II)/azide system

The complex formation between Mn(II) cations and N(3)(-) anions was studied in aqueous medium at 25 degrees C and ionic strength 2.0 M (NaClO(4)). Data of average ligand number, n (Bjerrum's function), were obtained from pH measurements on the Mn(II)/N(3)(-)/HN(3) system followed by integration to obtain Leden's function, F(0)(L). Graphical treatment of data and a matrix solution of simultaneous equations have given the following overall formation constants of mononuclear stepwise complexes: beta(1)=4.15+/-0.02 M(-1), beta(2)=6.61+/-0.04 M(-2), beta(3)=3.33+/-0.02 M(-3), beta(4)=0.63+/-0.01 M(-4). A linear plot of log K(n) vs. (n-1) shows no change in the configuration during complex formation. Slow spontaneous oxidation of solutions to Mn(III) occurs when the N(3)(-) concentration is greater than 1.0 M.     

Spectral studies on the interaction between lanthanum ion and the ligand: N,N'-ethylenebis-[2-(o-hydroxyphenolic)glycine

The interaction between N,N'-ethylenebis-[2-(o-hydroxyphenolic)glycine] (EHPG) and lanthanum was studied by the difference UV spectra and fluorescence spectra. At pH 7.4, 0.01 M N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (Hepes), with the addition of 1.0 x 10(-3)M lanthanum, two new peaks were observed at 238 nm and 294 nm by absorptivity spectroscopy compared with blank solution EHPG suggesting the interaction of lanthanum and EHPG. At the same time, the reaction could be measured by fluorescence spectra. The fluorescence intensity of EHPG at 310 nm was significantly decreased in the presence of lanthanum. The 1:1 stoichiometric ratio of EHPG to lanthanum was confirmed by both fluorescence and UV titration curves. In addition, the molar absorptivity of La-EHPG at 238 nm is (1.23+/-0.01)x10(4)cm(-1)M(-1). The conditional binding constant was calculated to be log K(La-EHPG)=12.09+/-0.37 on the basis of the result of UV titration curves.     

Stoichiometry, stability constants and coordination geometry of Eu(III) 5-sulfosalicylate complex in aqueous system-A TRLIFS study

The complex formation between Eu(III) and 5-sulfosalicylate, (HSSA)(2-), has been investigated by means of TRLIFS (time resolved laser induced fluorescence spectroscopy). The concentration of free ligand in the solution was determined from the fluorescence emission of 5-sulfosalicylate by subtracting the dynamic quenching effect from the observed quenching of fluorescence emission by means of lifetime analysis, and the stoichiometry and the corresponding formation constants were obtained. A carboxylate coordinated complex, Eu(HSSA)(+), and also a chelate complex, Eu(SSA), were identified, and the formation constants of the complex Eu(HSSA)(2+) for the reaction, Eu(3+)+ HSSA(2-)[rightward arrow] Eu(HSSA)(+), and the deprotonation constant of the chelating reaction, Eu(HSSA)(+)--> Eu(SSA)+ H(+), were calculated at log beta(1,1)= 1.79 and log K'=-5.78, respectively. TRLIFS using the fluorescence emission from Eu(III) was performed in order to determine the number of coordination waters of the complex Eu(HSSA)(2+). The quenching of the Eu(III) fluorescence caused by (SSA)(3-) disturbed the lifetime analysis of the 'intrinsic lifetime' of Eu(III) in Eu(HSSA)(2+), however the problem was successfully solved by the analysis of emission intensity and lifetime, and the formulation of the complex was determined as [Eu(HSSA)8H(2)O](2+) with the explicit involvement of the coordinated waters.     

Complexation of metal ions, including alkali-earth and lanthanide(III) ions, in aqueous solution by the ligand 2,2',6',2'-terpyridyl

Some metal-ion-complexing properties of the ligand 2,2',6',2'-terpyridyl (terpy) in aqueous solution are determined by following the π-π* transitions of 2 × 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH ～5, in the presence of electrolytes such as NaClO(4) or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at the ionic strength (μ) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K(1) values were determined for terpy with alkali-earth metal ions Mg(II), Ca(II), Sr(II), and Ba(II) and Ln(III) (Ln = lanthanide) ions La(III), Gd(III), and Lu(III) by titration of 2 × 10(-5) M free terpy at pH >5.0 with solutions of the metal ion. Log K(1)(terpy) was determined for Zn(II), Cd(II), and Pb(II) by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad π-π* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the π-π* transitions and thus broaden them. It is shown that log K(1)(terpy) for a wide variety of metal ions correlates well with log K(1)(NH(3)) values for the metal ions. The latter include both experimental log K(1)(NH(3)) values and log K(1)(NH(3)) values predicted previously by density functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]·CH(3)CH(2)OH·H(2)O (1) is reported as follows: triclinic, P1, a = 8.644(3) ?, b = 9.840(3) ?, c = 20.162(6) ?, α = 97.355(5)°, β = 97.100(5)°, γ = 98.606(5)°, V = 1663.8(9) ?(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) ?, while the four peripheral Ni-N bonds average 2.107(10) ?. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed.     

EDTA and mixed-ligand complexes of tetravalent and trivalent plutonium

EDTA forms stable complexes with plutonium that are integral to nuclear material processing, radionuclide decontamination, and the potentially enhanced transport of environmental contamination. To characterize the aqueous Pu(4+/3+)EDTA species formed under the wide range of conditions of these processes, potentiometry, spectrophotometry, and cyclic voltammetry were used to measure solution equilibria. The results reveal new EDTA and mixed-ligand complexes and provide more accurate stability constants for previously identified species. In acidic solution (pH < 4) and at 1:1 ligand to metal ratio, PuY (where Y4- is the tetra-anion of EDTA) is the predominant species, with an overall formation constant of log beta110 = 26.44. At higher pH, the hydrolysis species, PuY(OH)- and PuY(OH)(2)2-, form with the corresponding overall stability constants log beta(11 - 1) = 21.95 and log beta(11 - 2) = 15.29. The redox potential of the complex PuY at pH = 2.3 was determined to be E(1/2) = 342 mV. The correlation between redox potential, pH, and the protonation state of PuY- was derived to estimate the redox potential of the Pu(4+/3+)Y complex as a function of pH. Under conditions of neutral pH and excess EDTA relative to Pu4+, PuY(2)4- forms with an overall formation constant of log beta120 = 35.39. In the presence of ancillary ligands, mixed-ligand complexes form, as exemplified by the citrate and carbonate complexes PuY(citrate)3- (log beta1101 = 33.45) and PuY(carbonate)2- (log beta1101 = 35.51). Cyclic voltammetry shows irreversible electrochemical behavior for these coordinatively saturated Pu4+ complexes: The reduction wave is shifted approximately -400 mV from the reduction wave of the complex PuY, while the oxidation wave is invariant.     

A new zinc(II) fluorophore 2-(9-anthrylmethylamino)ethyl-appended 1,4,7,10-tetraazacyclododecane

A new 2-(9-anthrylmethylamino)ethyl-appended cyclen, L(3) (1-(2-(9-anthrylmethylamino)ethyl)-1,4,7,10-tetraazacyclododecane) (cyclen = 1,4,7,10-tetraazacyclododecane), was synthesized and characterized for a new Zn(2+) chelation-enhanced fluorophore, in comparison with previously reported 9-anthrylmethylcyclen L(1) (1-(9-anthrylmethyl)-1,4,7,10-tetraazacyclododecane) and dansylamide cyclen L(2). L(3) showed protonation constants log K(a)(i)() of 10.57 +/- 0.02, 9.10 +/- 0.02, 7.15 +/- 0.02, <2, and <2. The log K(a3) value of 7.15 was assigned to the pendant 2-(9-anthrylmethylamino)ethyl on the basis of the pH-dependent (1)H NMR and fluorescence spectroscopic measurements. The potentiometric pH titration study indicated extremely stable 1:1 Zn(2+)-L(3) complexation with a stability constant log K(s)(ZnL(3)) (where K(s)(ZnL(3)) = [ZnL(3)]/[Zn(2+)][L(3)] (M(-)(1))) of 17.6 at 25 degrees C with I = 0.1 (NaNO(3)), which is translated into the much smaller apparent dissociation constant K(d) (=[Zn(2+)](free)[L(3)](free)/[ZnL(3)]) of 2 x 10(-)(11) M with respect to 5 x 10(-)(8) M for L(1) at pH 7.4. The quantum yield (Phi = 0.14) in the fluorescent emission of L(3) increased to Phi = 0.44 upon complexation with zinc(II) ion at pH 7.4 (excitation at 368 nm). The fluorescence of 5 microM L(3) at pH 7.4 linearly increased with a 0.1-5 microM concentration of zinc(II). By comparison, the fluorescent emission of the free ligand L(1) decreased upon binding to Zn(2+) (from Phi = 0.27 to Phi = 0.19) at pH 7.4 (excitation at 368 nm). The Zn(2+) complexation with L(3) occurred more rapidly (the second-order rate constant k(2) is 4.6 x 10(2) M(-)(1) s(-)(1)) at pH 7.4 than that with L(1) (k(2) = 5.6 x 10 M(-)(1) s(-)(1)) and L(2) (k(2) = 1.4 x 10(2) M(-)(1) s(-)(1)). With an additionally inserted ethylamine in the pendant group, the macrocyclic ligand L(3) is a more effective and practical zinc(II) fluorophore than L(1).     

Unusual metal ion selectivities of the highly preorganized tetradentrate ligand 1,10-phenanthroline-2,9-dicarboxamide: a thermodynamic and fluorescence study

Some metal ion complexing properties of the ligand PDAM (1,10-phenanthroline-2,9-dicarboxamide) in aqueous solution are reported. Using UV-visible spectroscopy to follow the intense π-π* transitions of PDAM as a function of metal ion concentration, log K(1) values in 0.1 M NaClO(4) and at 25 °C are, for Cu(II), 3.56(5); Ni(II), 3.06(5); Zn(II), 3.77(5); Co(II), 3.8(1); Mg(II), 0.1(1); Ca(II), 1.94(4); and Ba(II), 0.7(1). For more strongly bound metal ions, competition reactions between PDAM and EDTA (ethylenedinitrilo-tetraacetic acid) or tetren (1,4,7,10,13-pentaazatridecane), monitored following the UV spectrum of PDAM, gave the following log K(1) values in 0.1 M NaClO(4) and at 25 °C: Cd(II), 7.1(1); Pb(II), 5.82(5); In(III), 9.4(1); and Bi(III), 9.4(1). The very low log K(1)(PDAM) values for small metal ions such as Cu(II) or Zn(II) are unprecedented for a phen-based ligand (phen = 1,10-phenanthroline), which is rationalized in terms of the low basicity of the N donors of the ligand (pK(a) = 0.6) and the fact that PDAM has a best-fit size corresponding to large metal ions of ionic radius ~1.0 ?. Large metal ions with ionic radius ≥1.0 ? show large increases in log K(1) relative to their phen complexes, which in turn produces unparalleled selectivities, such as a 3.5 log units greater log K(1)(PDAM) for Cd(II) than for Cu(II). PDAM shows strong fluorescence in aqueous solution, suggesting that its carboxamide groups do not produce a fluorescence-quenching photon-induced electron transfer (PET) effect. Only Ca(II) produces a weak CHEF (chelation enhanced fluorescence) effect with PDAM, while all other metal ions tested produce a decrease in fluorescence, a CHEQ (chelation enhanced quenching effect). The production of the CHEQ effect is rationalized in terms of the idea that coordination of metal ions to PDAM stabilizes a canonical form of the carboxamide groups that promotes a PET effect.     

Solvent extraction of zinc with 5,7-dichloro-2-methyl-8-hydroxyquinoline into chloroform

The distribution equilibria of the zinc complex with 5,7-dichloro-2-methyl-8-hydroxyquinoline in the water-chloroform system have been studied at 25 degrees . The influence of pH, reagent and metal concentrations, and the presence of sodium perchlorate in the aqueous phase has been determined. From quantitative evaluation of the extraction equilibrium data, it has been deduced that the complex extracted is the simple 1:2 chelate, ZnR(2), although at ligand concentrations higher than 0.3M, the self-adduct complex seems to begin to form. The extraction constant of the ZnR(2) species, refined by means of the program Letagrop-Distribution, has the value log K(ex) = - 6.15 +/- 0.07.     

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.     

Stoichiometries and thermodynamic stabilities for aqueous sulfate complexes of U(VI)

The formation constants of UO2SO4 (aq), UO2(SO4)2(2-), and UO2(SO4)3(4-) were measured in aqueous solutions from 10 to 75 degrees C by time-resolved laser-induced fluorescence spectroscopy (TRLFS). A constant enthalpy of reaction approach was satisfactorily used to fit the thermodynamic parameters of stepwise complex formation reactions in a 0.1 M Na(+) ionic medium: log 10 K 1(25 degrees C) = 2.45 +/- 0.05, Delta r H1 = 29.1 +/- 4.0 kJ x mol(-1), log10 K2(25 degrees C) = 1.03 +/- 0.04, and Delta r H2 = 16.6 +/- 4.5 kJ x mol(-1). While the enthalpy of the UO2(SO4)2(2-) formation reaction is in good agreement with calorimetric data, that for UO2SO4 (aq) is higher than other values by a few kilojoules per mole. Incomplete knowledge of the speciation may have led to an underestimation of Delta r H1 in previous calorimetric studies. In fact, one of the published calorimetric determinations of Delta r H1 is here supported by the TRLFS results only when reinterpreted with a more correct equilibrium constant value, which shifts the fitted Delta r H1 value up by 9 kJ x mol(-1). UO2(SO 4) 3 (4-) was evidenced in a 3 M Na (+) ionic medium: log10 K3(25 degrees C) = 0.76 +/- 0.20 and Delta r H3 = 11 +/- 8 kJ x mol(-1) were obtained. The fluorescence features of the sulfate complexes were observed to depend on the ionic conditions. Changes in the coordination mode (mono- and bidentate) of the sulfate ligands may explain these observations, in line with recent structural data.     

Precise investigation of the axial ligand substitution mechanism on a hydrogenphosphato-bridged lantern-type platinum(III) binuclear complex in acidic aqueous solution

Detailed equilibrium and kinetic studies on axial water ligand substitution reactions of the "lantern-type" platinum(III) binuclear complex, [Pt(2)(mu-HPO(4))(4)(H(2)O)(2)](2)(-), with halide and pseudo-halide ions (X(-) = Cl(-), Br(-), and SCN(-)) were carried out in acidic aqueous solution at 25 degrees C with I = 1.0 M. The diaqua Pt(III) dimer complex is in acid dissociation equilibrium in aqueous solution with -log K(h1) = 2.69 +/- 0.04. The consecutive formation constants of the aquahalo complex () and the dihalo complex () were determined spectrophotometrically to be log = 2.36 +/- 0.01 and log = 1.47 +/- 0.01 for the reaction with Cl(-) and log = 2.90 +/- 0.04 and log = 2.28 +/- 0.01 for the reaction with Br(-), respectively. In the kinetic measurements carried out under the pseudo-first-order conditions with a large excess concentration of halide ion compared to that of Pt(III) dimer (C(X)()- > C(Pt)), all of the reactions proceeded via a one-step first-order reaction, which is a contrast to the consecutive two-step reaction for the amidato-bridged platinum(III) binuclear complexes. The conditional first-order rate constant (k(obs)) depended on C(X)()- as well as the acidity of the solution. From kinetic analyses, the rate-limiting step was determined to be the first substitution process that forms the monohalo species, which is in rapid equilibrium with the dihalo complex. The reaction with 4-penten-1-ol was also kinetically investigated to examine the reactivity of the lantern complex with olefin compounds.