Metal chelates of phosphonate-containing ligands-I Stability of some N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid metal chelates

A potentiometric investigation of the acid dissociation constants of the octabasic ENTMP [N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid] is reported. The stability constants of protonated MH(n)L (n = 1, 2, 3 and 4) and unprotonated ML metal chelates of Mg, Ca, Ba and Cd with ENTMP have been measured. The stabilities are in the order Mg < Ca < Ba < Cd.     

Investigation of the extraction of some copper(II) chelates using isotope64Cu

The extraction of copper(II) 8-hydroxyquinolinate, 5,7-dichloro-8-hydroxyquinolinate and 2-thenoyltrifluoroacetonate was investigated and the stability constants and distribution constants of the complexes were determined. The dependence of thepH values for 50% extraction and of the distribution constants of the copper complexes on the dissociation constants and distribution constants of the corresponding agents are discussed.     

Modeling of equilibriums of formation of polynuclear chelates of nickel(ii) with histidine

Electronic absorption spectroscopy has been applied to study of protolytic and complex formation equilibriums in binary and tertiary systems containing nickel(II) salt, ethylenediaminetetraacetic acid and 2-amino-3-(imidazol-2-yl)propionic acid (ionic strength 0.1 mol/L aqueous NaClO₄, 20±2°C). Fitting of experimental spectral properties as function of pH and the components concentration requires dissociation constants of the ligands as well as stability constants of homoligand, heteroligand, and polynuclear complexes as parameters. These parameters have been estimated from the best fit model, and possible complexes structures have been suggested.     

Analysis of the kinetic stability of yttrium chelates by free-ion selective radiotracer extraction (FISRE)

Within this work the analysis of the kinetic stability of a series of yttrium complexes, i.e., Y-citrate, Y-NTA, Y-CDTA as well as Y-humic acid (Y-HA) has been successfully performed by the free-ion selective radiotracer extraction (FISRE) method. FISRE uses ⁹⁰Y with a high specific activity to perform CHELEX extractions in a buffered aqueous solution at pH 6 in two different modes by monitoring the dissociation and association reactions of the corresponding complexes. Whereas in the case of Y-citrate the dissociation profile could be successfully described in terms of (pseudo) first order kinetics, the other complexes tend to form two species with different kinetic properties, although only one species is predicted by speciation calculations. In the batch FISRE method, all (except Y-NTA) corresponding association rate constants were determined by monitoring the formation rate of the yttrium complexes.     

Thermodynamic stability and acidic properties of platinum(II) and palladium(II) bromide complexes

The instability constants of the platinum(II) and palladium(II) bromide complexes have been determined by potentiometry. The thermodynamic stability has been found to depend on the geometric structure of the complex and the nature of the central atom. The acid dissociation constants of the aqua complexes have been determined from pH measurements of the equilibrated solutions.     

邻苯二酚-3,6-二甲撑亚氨基二乙酸的酸离解平衡及其与碱土金属、锰(II)、镉(II)、锌(II)、钴(II)、镍(II)、铜(II)、铁(II)、钍(IV)及铀酰离子配合物稳定性的研究

本文报道用PH滴定法测得KNO3水溶液中邻苯二酚-3,6-二甲撑亚氨基二乙酸(CBMIDA, H6L)的六级酸解离常数及CBMIDA的镁(II)、钙(II)、锶(II)、钡(II)、镍(II)、锌(II)、钴(II)、镉(II)、锰(II)、铜(II)、铁(II)、钍(IV)和铀酰离子的配合物稳定常数及配合物的质子化常数. 讨论了CBMIDA的逐级酸离解的动态平衡机理以及金属离子与CBMIDA形成的各种配合物的配位形式.     

Ternary Cu(II) complexes involving N-(1-naphthyl)ethylenediamine, ethylenediamine (N-N donors) and a series of amino acids (N-O? donors)

The dissociation constants for N-(l-naphthyl)ethylenediamine (NEN) and the formation constants for binary (ML) and ternary metal complexes (MLA), where M = Cu(II), L = alanine, phenylalanine, tryptophan, lysine, arginine, serine, threonine, aspartic acid or histidine and A = NEN or ethylenediamine (EN) have been determined by pH titrations and are reported at 35°C (gm = 0.2 M KNO₃). The relative stability of the ternary complexes are discussed in terms of statistical effects and the nature of ligands in the coordination sphere of the metal ion.     

Spectrophotometric studies on 5,7-dibromo-8-aminoquinoline chelates of some bivalent transition metals

The acid dissociation constant of 5,7-dibromo-8-amino-quinoline and the stability constant of 1:1 chelates of some bivalent transition metals were determined spectrophotometrically in 50% v v dioxan-water medium at an ionic strength of 0.50 at 25.0 +/- 0.1 degrees and compared with those of 8-aminoquinoline. The dissociation constant was found to be 7.54 x 10(-2) and the stability constants (log K(1)) were 2.3 (copper), 1.8 (nickel), 1.8 (zinc), 2.2 (cobalt) and 1.6 (cadmium), respectively. The dissociation constants are greater and the stability constants smaller than the corresponding values for 8-aminoquinoline and 8-quinolinol.     

Study of acidic and complexing properties of tetraphenylporphyrazine and octa(4-bromophenyl)porphyrazine in DMSO at 298 K

The acid dissociation of tetraphenylporphyrazine (H₂PA(Ph)₄) and octa(4-bromophenyl)porphyrazine (H₂PA(4-BrPh)₈) and their reactions with Cd²⁺ ions were studied in DMSO at 298 K. The equilibrium formation constants of the complexes and the acid dissociation constants of porphyrins were calculated; their relationship with the stability constants of the complexes was analyzed. The acidity sequence for porphyrazine derivatives was established.     

Electroanalytical studies of complexes of tetracyclines with Cd(II), Pb(II) and Cu(II) in aqueous medium

The dissociation constants of protonated tetracycline, chlorotetracycline and desmethylchlorotetracycline and the overall stability constants of the complexes of Cd, Pb and Cu(II) with these tetracyclines have been determined.     

Metal complexes of 4-(2'-thiazolylazo)-resorcinol A comparative study with 4-(2'-pyridylazo)-resorcinol

The acid dissociation constants of 4-(2'-thiazolylazo)-resorcinol (TAR) and the formation constants of the metal complexes formed by this reagent with Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) have been determined potentiometrically at 25° in 50% v/v mixtures of dioxane and water. The values obtained for TAR and the metal complexes are contrasted with similar values for the reagent 4-(2'-pyridylazo)-resorcinol (PAR). Differences and similarities between the co-ordinating tendencies of these two reagents are revealed in terms of the proton displacement constant and the acid dissociation constants of the metal complexes. Evidence is presented which suggests that both TAR and PAR may act as terdentate ligands toward some bivalent metal ions.     

Enthalpy and entropy changes associated with mixed ligand chelates of Cu(II) and Ni(II) with 4-methoxy picolinic acid N-oxide and some amino acids in aqueous medium

The stability constants of mixed complexes of Cu(II) and Ni(II) with 4-methoxy picolinic acid N-oxide, and glycine, α-alanine, proline and hydroxy-proline have been determined at various temperatures by the potentiometric method in 0·1 M ionic strength. The formation constants of the mixed complexes have been evaluated and are in good agreement with statistically expected values. The enthalpy and entropy values have been calculated from 1∶1∶1 stability constants temperature coefficient data. From the enthalpy values of the mixed complexes it may be concluded that the bond strengths are not equal to the average of the bond strengths inMA ₂ andMB ₂ type parent complexes. The entropy values have been found to be favourable for ternary complex formation.     

Potentiometric, spectroscopic and thermal studies on the metal chelates of 1-(2-thiazolylazo)-2-naphthalenol

The synthesis and characterization of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pd(II) and UO2(II) chelates of 1-(2-thiazolylazo)-2-naphthalenol (TAN) were reported. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 degrees C and 0.1 M ionic strength. The solid complexes were characterized by elemental and thermal analyses, molar conductance, IR, magnetic and diffuse reflectance spectra. The complexes were found to have the formulae [M(L)2] for M = Mn(II), Co(II), Ni(II), Zn(II) and Cd(II); [M(L)X].nH2O for M = Cu(II) (X = AcO, n = 3), Pd(II) (X = Cl, n = 0) and UO2(II) (X = NO3, n = 0), and [Fe(L)Cl2(H2O)].2H2O. The molar conductance data reveal that the chelates are non-electrolytes. IR spectra show that the ligand is coordinated to the metal ions in a terdentate manner with ONN donor sites of the naphthyl OH, azo N and thiazole N. An octahedral structure is proposed for Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II) and UO2(II) complexes and a square planar structure for Cu(II) and Pd(II) complexes. The thermal behaviour of these chelates shows that water molecules (coordinated and hydrated) and anions are removed in two successive steps followed immediately by decomposition of the ligand molecule in the subsequent steps. The relative thermal stability of the chelates is evaluated. The final decomposition products are found to be the corresponding metal oxides. The thermodynamic activation parameters, such as E*, delta H*, delta S* and delta G* are calculated from the TG curves.     

Formation and dissociation kinetics of triaza-crown-alkanoic acid complexes of transition metal(II) and lanthanide (III)

The formation and dissociation rates of some transition metal(II) and lanthanide(III) complexes of the 1,7,13-triaza-4,10,16-trioxacyclooctadecane N',N',N'-triacetic acid (1) and 1,7,13-triaza-4,10,16-trioxacyclooctadecane-N',N',N'- trimethylacetic acid (2) have been measured by the use of stopped-flow and conventional spectrophotometry. Experimental observations were made at 25.0 +/- 0.1 degrees C and at an ionic strength of 0.10 M KCl. The complexation of Zn(2+) and Cu(2+) ions with 1 and 2 proceeds through the formation of an intermediate complex (MH(3)L(+) *) in which the metal ion is incompletely coordinated. This may then lead to a final product in the rate-determining step. Between pH 4.68 and 5.55, the diprotonated (H(2)L(-)) form is revealed to be a kinetically active species despite its low concentration. The stability constants (log K (MH (3)L (+) *)) and specific base-catalyzed rate constants (k(OH)) of intermediate complexes have been determined from the kinetic data. The dissociation reactions of 1 and 2 complexes of Co(2+), Ni(2+), Zn(2+), Ce(3+), Eu(3+) and Yb(3+) were investigated with Cu(2+) ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The buffer and Cu(2+) concentration dependence on the dissociation rate has also been investigated. The metal and ligand effects on the dissociation rate of some transition metal(II) and lanthanide(III) complexes are discussed in terms of the ionic radius of the metal ions, the side-pendant arms and the rigidity of the ligands.     

State and Stability of Erbium(III) and Dysprosium(III) Complexes of Octaphenyltetraazaporphine in Proton-Donor Media

The acid-base interaction of chloro(octaphenyltetraazaporphinato)erbium(III), (acetylacetonato)(octaphenyltetraazaporphinato)erbium(III), and (acetylacetonato)(octaphenyltetraazaporphinato)dysprosium(III) in AcOH and in AcOH-benzene and AcOH-H₂SO₄ systems involves one meso-nitrogen atom of the complexes; the stability constants of the resulting acid forms were estimated. The solvoprotolytic dissociation of the complexes in the AcOH-H₂SO₄ system was studied, its kinetic parameters were determined, and some suggestions as to the dissociation mechanism were made.     

Determination of the thermodynamic parameters and stability constants of UO2(2+), Th4+, and Ce3+ complexes with some azo-benzene-N-malonic acid derivatives

Proton-ligand dissociation and metal-ligand formation constants of azobenzene-N-malonic acid (I), p-Cl-azobenzene-N-malonic acid (II), p-Br-azobenzene-N-malonic acid (III) and p-COOH- azobenzene-N-malonic acid (IV) with UO2(2+), Th4+ and Ce3+ were evaluated potentiometrically using Bjerrum's method at 25, 35 and 45 +/- 0.5 degrees C and ionic strength 0.1 M in 40% v/v ethanol-water medium. The order of stability constants was found to be Ce3+ > Th4+ > UO2(2+). The effect of temperature on the dissociation and stability constants of the formed complexes was studied and the corresponding thermodynamic functions were derived and discussed. The ratio of metal-ligand was determined conductometrically. The structure of the ligands under investigation as well as their metal complexes has been elucidated by elemental analysis, IR and 1HNMR spectroscopy.     

Composition and stability of copper(II), nickel(II), and cobalt(II) complexes with mono- and bis(2-carboxy)-2-pycolylamine

Complexation of N-(2-pyridyl)methyl-3-aminopropionic (HL¹) and N-(2-pyridyl)methyliminodipropionic (H₂L²) acids with copper(II), nickel(II), and cobalt(II) ions is studied. The composition of complexes is determined using the Starik–Barbanel relative yield method. The acid dissociation constants of HL¹ and H₂L² are determined potentiometrically; the stability constants of HL¹ and H₂L² complexes with metal ions are calculated.     

Metal chelates of phosphonate-containing ligands-II: stability constants of some beta-styrylphosphonic acid metal chelates

The synthesis and properties of beta-styrylphosphonic acid (SPA) are reported. The values of the protonation constants of the ligand were determined potentiometrically at different ionic strengths and in the temperature range 0-65 degrees. The enthalpy and entropy of protonation have been calculated by using the van't Hoff isochore. The protonation process is endothermic and is stabilized by a relatively large positive entropy change. The stability constants of the complexes formed between SPA and the bivalent Mg, Ca, Ba, Co, Ni and Pd ions at 25 degrees and ionic strength of 0.12M KNO(3) were also determined. All measurements were carried out in 18% dimethylformamide-water mixture.     

Equilibrium study on Cd(II) and Zn(II) chelates of mercapto carboxylic acids

Cadmium(II) and zinc(II) complexes with the chelating agents meso-2,3-dimercapto succinic acid, meso-monomethyl dimercapto succinate, meso-dimethyl dimercapto succinate and the related methylmercapto acetate and mercapto succinic acid were studied potentiometrically in 0.1 M KCl at 25 °C. Models and hypotheses of coordination for the solution complexes are proposed. IR characterisation and stoichiometry of the solid state compounds evaluated by elemental analysis are presented. The obtained formation constants, together with the previously measured ionisation constants of the ligands, were used to compute pCd and pZn values and then to evaluate the effectiveness of the studied chelating agents in binding Cd(II) and Zn(II) in intoxication treatments.     

Binuclear chelates of diethylenetriamine-Pentaacetic acid with chromium(III) and oxovanadium(IV) ions

The reactions of diethylenetriaminepentaacetic acid (DTPA=H₅L) or chromium(III)-DTPA, a ‘chelating agent’, with oxovanadium(IV) were investigated in aqueous solution by potentiometric methods. Homo- and hetero-binuclear species were evidenced as well as mixed complexes with hydrogen or hydroxide ions. The stability constants for these equilibria were calculated in 1.0 mol 1^?1 NaClO₄ solution at 20?C. The mononuclear (VO)H₃L·H₂O and the heterobinuclear (VO)CrL·5H₂O complexes were also obtained as solid compounds and were characterized by IR spectroscopy and thermoanalytical techniques (TG and DSC).