Showing papers on "Stability constants of complexes published in 1973"

Oxidation – Reduction Reactions of Tetrachloroaurate(III) Anion with Triphenyl Derivatives of Group V Elements

Abstract: The reduction of the tetrachloroaurate (III) anion by L (L = PPh3, AsPh3, SbPh3) is quantitative in non-aqueous solution. The products are the gold(I)-complexes AuClL (L = AsPh3, SbPh3) and Au(PPh3)+2 together with the corresponding oxidation product LCl2. Kinetic studies show that the reactions are first order in AuCl−1 and L. In addition a path independent of PPh3 was found in dichloromethane. These data are interpreted in terms of mechanisms which involve reduction of AuCl−4 to AuCl−2 followed by equilibrium formation of AuClL for L = AsPh3 and SbPh3. For PPh3, the data are consistent with a chloride replacement by PPh3 to give AuCl3 PPh3, which is followed by a rapid reduction by a second mole of PPh3. Equilibrium formation constants are reported for several Au(I) complexes.

Ternary Coordination Complexes Between Copper(II) and Amino Acids, and an Appraisal of the Enhancement of Ternary Complex Stability

Abstract: The equilibria involved in the ternary systems Cu(II)–A–B′ and Cu(II)–A–B″ (A = L-histidine, B′ = L-serine, B″ = L-glutamine) have been investigated by potentiometry in aqueous solution (0.15 M NaCl, 25°). In the ternary system Cu(II)–A–B′, three mixed complexes (MHAB′, MAB′, and MH−1AB′) were detected in addition to the binary complex species (MHA, MA, MH2A2, MHA2, MA2, MH−1A2, MB′, MB′2). The results observed in the Cu(II)–A–B″ system were quite similar to the system Cu(II)–A–B′ except that it did not show the presence of the species MH−1AB″. The stability constants were refined with a general least squares treatment. In the case of an equimolecular mixture of the constituents, a maximum of about 75% of Cu(II) is present as MAB′ at pH 5.5–9 and about 60% of Cu(II) as MAB″ at pH 5–10 when the concentration of each constituent is set equal to 10−2 M. A theoretical analysis and derivations of the expected stability constants of the complexes are presented on the basis of successive formation constants of t...

Stability of Fused Rings in Metal Chelates. X. Structures and Stability Constants of the Copper (II) Complexes of Tripeptides Composed of Glycine and/or β-Alanine

Abstract: On the basis of comparative studies of the equilibria involving copper(II) and triglycine (G·G·G), glycylglycyl-β-alanine (G·G·β-A), glycyl-β-alanylglycine (G·β-A·G), or β-alanylglycylglycine (β-A·G·G), the structures of the complexes formed at various pH values and the structure-stability relationship between the fusedring chelates have been discussed in reference to the equilibrium constants determined by potentiometric titration at 25°(μ=0.1 (KNO3)) and the properties of the copper(II) chelates isolated. For each tripeptide, the stability constant K1 for the 1: 1 complex and the constants for the deprotonation reactions Kc1 and Kc2 were calculated by the method of non-linear least-squares. For G·G·G, G·G·β–A, and G·β–A·G, the equilibrium indicating the formation of a protonated complex was detected at pH 3.5–4.5. The relatively small difference in the logK1 values (5.25–5.60) and the logKc1 values (5.23–5.36) and the larger difference in the −logKc2 values (5.54–6.73) have been interpreted in terms of ...

THE DETERMINATION OF A STABILITY CONSTANT FOR THE AQUEOUS COMPLEX Zn(OH)20 USING ANODIC STRIPPING VOLTAMMETRY1

Abstract: The shift in the potential of the zinc stripping current maximmn observed in anodic stripping voltammetry is related to the free energy of the reaction between ionic zinc and a complexing anion. The model was tested using the zinc hydroxyl system; the agreement with experimental results was excellent. The findings suggest the existence of the aqueous complex, Zn( OH ):, which has been reported only once beEore. The stability constant calculated here is in good agreement with the single published value. Anodic stripping voltammetry from thin layers and hanging drops of mercury was developed and used for determining the concentrations and the extent of organic chelation of some trace metals in natural waters (e.g. Matson 1968; Fitzgerald 1970; Seitz 1970; Zirino and Healy 1972; Bradford 1972). A phenomenon associated with the technique that has received scant attention is the shift in the potential of the stripping current maximum (the so-called stripping peak potential, EP) with changes in the activity oE a complexing anion in the test solution. The phenomenon is implied by the equations of Roe and Toni ( 1965) and was discussed by Matson (1968) who noted that it might be useful for detecting chelating reactions in natural waters. Zirino and Healy (1970) observed a 35-55 mV shift anodic in the EE, of zinc in seawater when the pI1 was lowered from 8.3 to 5.5, suggesting the existence of zinc carbonate or zinc hydroxide associations. Bradford ( 1972) found that shifts in the E, of zinc could not be caused either by adding organic ligands (e.g. EDTA, adenine) to test solutions or by irradiating estuarine water samples wjth ’ Contribution from the Chesapeake Bay Institute. This research was sponsored by U.S. Atomic Energy Commission Contract AT ( 30-l ) -3497 and AT( 11-1)-3292. 2 Present address : URS Research Co., 155, Bovet Rd., San Mateo, California 94402. high intensity ultraviolet light (Armstrong and Tibbitts 1968) to break up the naturally occurring chelators, and thus suggested that shifts in E, could be caused only by inorganic ligands. Nicholson and Shain ( 1964) showed that in stationary polarography a shift in the potential of the peak oxidation current with varying complexing anion activity requires that the reaction between the metal cation and the complexing anion be fast relative to the rate at which the metal cation is oxidized from the mercury electrode. Bradford ( 1972) estimated the first order rate constant to be of the order of lo” set-I. My thanks to J. H. Carpenter for many helpful comments and for careful criticism of the experimental results. MATHEMATICAL TREATMENT The Rot-Toni equation predicting the potential at the stripping current peak is WV E,=E”‘+ylogy 0 where E, is the potential where the maximum stripping current for a given metal occurs; E”’ is the thermodynamic equilibrium potential for the reaction couple metal /metal ion species/test solution/reference reaction;

Synthesis and Structural Studies of the Metal(II) Mercury Tetrathiocyanate Complexes with Lewis Bases

Abstract: Complexes of the type MHg(SCN)4•2L, where M = Mn2+ to Zn2+ and Cd2+ and L = THF or Py, have been synthesized and characterized by spectroscopic methods. The thiocyanato groups are bridging between M2+ and Hg2+ whereas the donor atom of the ligand is coordinated to M2+ which now attains octahedral configuration. Definite shifts in certain absorption bands of the ligands upon coordination to M2+ are correlated to the formation constant of the metal atom involved in coordination. Electronic spectral data as well as magnetic measurements show that the M2+ is a high spin species in an octahedral environment. The X-ray powder photographs indicate that Co2+ and Zn2+ complexes are isostructural and also most probably are Mn2+ and Fe2+. Tentative assignments for metal–NCS, M–ligand, Hg—S, and L—M—L absorption bands are discussed.

NMR Study of Amino Acids and Their Derivatives. V. Structures and Formation Constants of Zinc-L-Aspartic Acid Complexes in Aqueous Solution

Abstract: NMR spectra of L-aspartic acid coordinated with Zn ions were measured in aqueous solution at various pH values. Three species of zinc-L-aspartic acid complexes were identified i.e., 1 : 1 zinc–L-aspartic acid(zwitter ionic form) complex (MAH), and 1 : 1 and 1 : 2 zinc–aspartic acid(anionic form) complexes (designated as MA and MA2, respectively). It is shown that, in MAH, the amino acid coordinates with Zn as a monodentate ligand, whereas in MA and MA2, approximately 65% of the molecules of amino acid coordinate as a tridentate ligand. From the chemical shift data, the equilibrium constants for these complexes are determined as follows: pKa-(MAH)=5.3±0.2 and logK2=4.5±0.2 where Ka(MAH)=[MA][H+]/[MAH] and K2=[MA2]/[MA][A].

Copper (II) Ion Binding in Polyacrylic Acid

Abstract: The complexing of Cu(II) by polyacrylic acid has been investigated. Potentiometric measurements have been employed to facilitate the experimental program. The stability constant of CuA2, the dominant species observed, has been determined to be approximately 6.5 × 103, a value in good agreement with the formation constant of 4.25 × 103 reported for Cu(acetate)2. The quantitative evaluation of this stability constant is made possible by (1) correcting for complication arising from the large and variable electric field at the surface of the polyelectrolyte in the polymer domain and by (2) expressing the concentration of polymer species in terms of the polymer domain volume.

Potentiometric Titration of Weak Acids

Abstract: A desk-calculator program has been developed for determination of the equivalence point when a weak acid is titrated with a strong base. The stability constant (KH HA) of the acid can be computed simultaneously. When data from a potentiometric titration of boric acid with sodium hydroxide have been processed with the program the equivalence point has been determined with an accuracy of 0.3–0.4 per cent. The computed value of the stability constant of boric acid (log KH HA = 9.11) is in good agreement with the values given in literature.

Ionic Equilibria in Mixed Solvents. X. Hydrolysis of Nickel(II) Ion in Dioxane-Water Mixtures

Abstract: The hydrolytic reactions of nickel(II) ion were studied at 25 °C in water and dioxane-water mixtures containing 3 M (Li)ClO4 as an ionic medium. Emf measurements were carried out in the range of the total nickel(II) ion concentration of 0.02469–0.7891 M in water, 0.02488–0.7996 M in a 0.1 mole fraction (35.21% w/w) dioxane-water mixture and 0.05170–0.9016 M in a 0.2 mole fraction (55.01% w/w) dioxane-water mixture, respectively. Some supplementary measurements were performed in a 0.5 mole fraction (83.02% w/w) dioxane-water mixture. Only the Ni4(OH)44+ complex was found in all solvent systems and its formation constant in log*β44 was −27.32±0.08 (in water), −27.11±0.08 (in a 0.1 mole fraction dioxane-water mixture), and −27.04±0.05 (in a 0.2 mole fraction dioxane-water mixture). In order to test the relative change of the formation consatnt of the Ni4(OH)44+ complex over the whole solvent composition examined, the variation of the formation constant was measured with the continual change of solvent compos...

Spectrophotometric studies of the metavanadate system. I. Solution equilibria

Abstract: Spectrophotometric absorbance measurements on sodium metavanadate solutions in the region 240-300 nm were made at 10°, 25°, and 40°C on: (1) a series of solutions 2.46 x 10-5M in vanadium and covering the pH range 7-9; and (2) a series of solutions at constant pH and covering the concentration range from 4x10-5 to 1.2x10-2M. All solutions contained 3.0M NaClO4 and 0.10M Tris buffer. From these data were computed the extinction coefficients of HVO42-, H2VO4-, and (VO3-), as well as the pKa of H2VO4- (7.62±0.07). Metavanadate is probably a mixture of V3O93- and V4O124- under the conditions of the experiment. Upper limits on the formation constants at 25° are K3 = 10.8±0.5x106 12 mol-2 and K4 = 73±7x 10913 mol-3. The temperature dependence of the data gives for the enthalpy of polymerization, ΔH° = -21±2 kJ mol-1 H2VO4-.

The conductance of lanthanide (III) sulfate solutions in D2O

Abstract: The formation constants of the LnSO4+ complexes are reported for La3+, Pr3+, Sm3+, Dy3+, Yb3+, and Lu3+ in D2O and for Sm3+ and Lu3+ in water at 25°C. Formation constants which were calculated from conductance data are identical with those obtained in H2O within the limits of the assumptions made in the mathematical analysis.

1,4,7トリアザシクロノナンおよび直鎖状トリアミンの2価金属キレートの安定度定数

Abstract: Acid formation constants, and stability constants fer divalent metal chelates of 1, 4, 7-triazacyclononane (2, 2, 2), 2, 2 diaminodiethylamine (2, 2), N (2-aminoethyl) 1, 3-propanediamine (2, 3), and 3, 3 diaminodipropylamine (3, 3) were determined by the pH titration at 25. OCC and ionic strength of O.1. A (2, 2, 2) coordinates with most metal ions alone in the facial configuration and forms three combined chelate rings. This restriction on freedom should contribute to the stabilities of its metal chelates as shown in Table 2. Besides, nickel, cobalt, zinc and cadmium chelates of (2, 2, 2) have the highest stabilities among triamine chelates ever reported. However, copper (2, 2, 2) chelate has slightly lower value than that of (2, 2) chelate, becau e copper(II)can only be coordinated with two nitrogen atoms of (2, 2, 2). On the other hand, the formation rates of (2, 2, 2) chelates are generally very slow, perhaps due to the comformational effect. Systematic comparison of the fermation constants with straight-chain triamine chelates has also been done in Table 1 and 2. Among three acid formatien constants of each triamine, Ka3 is mostly af ected by the Iigand size, K vaules of(2, 2)and(2, 3)chelates are nearly comparable and that of (3, 3) chelate falls respecting each metal, but KML, values are simply decreased in the order of (2, 2), (2, 3), and (3, 3), except copper and zinc chelates.

Thermodynamics of metal-ligand bond formation. VIII. Pyridine adducts of zinc(II) β-diketonates

Abstract: Equilibrium constants and enthalpies in benzene solution are reported for the formation of 1 : 1-adducts of pyridine with four zinc(II) complexes of β-diketones, determined by calorimetric titration. Adduct formation constants at 30°C fall in the range 300-2000 and enthalpies of formation lie between -15 and - 34 kJ mol-1. Though the enthalpies of formation differ little from those of corresponding copper(II) complexes, the adducts are about a hundred times more stable. The pyridine adduct of bis(2,2,6,6-tetramethylheptane-3,5-dionato)zinc(II) is entropy-stabilized relative to those of other complexes. No evidence was obtained for the addition of a second molecule of pyridine under the experimental conditions used.

The Coordination Bonding and Stability of the 1 : 1 Complexes of Copper(II) with Various Bidentate Ligands in Aqueous-methanolic Solutions

Abstract: ESR and spectrophotometric studies have been made of a number of 1 : 1 complexes of copper (II) with ethylenediamine, its analogues, and amino acids in aqueous-methanolic solutions. It has been shown that the complexes in the solutions are characteristic of copper(II) ions with a normal tetragonal environment and that their metal-ligand bondings are intermediate in the degree of covalency between those of hydrated cupric ions and the corresponding 1 : 2 complexes. The disproportionation constants and their temperature dependences, determined for the 1 : 1 complexes by the ESR and spectrophotometric methods, have been discussed, with particular empahsis on the fact that those values are in fair agreement with those derived from the step-by-step formation constants and the thermodynamic data obtained in aqueous solutions in the literature.

Potentiometric Studies of Cadmium- and Zinc-Halide Complexes in Acetonitrile

Abstract: The overall formation constants of cadmium- and zinc-halide complexes in acetonitrile were determined by potentiometric titration using a saturated metal amalgam indicator electrode. The effect of ion-pair formation was taken into consideration to elucidate the free halide ion concentration in the experiments. The values of logβ3 and logβ4 for cadmium-halide complex were found to be: I−, 22.4 and 26.5; Br−, 25.3 and 29.8; Cl−, 29.2 and 34.0. The values for zinc-chloride complex were 20.1 and 23.4.