Paper electrophoretic determination of the stability constants of binary and ternary complexes of copper(II) and cobalt(II) with nitrilotriacetate and cysteine

A paper ionophoretic method is described for the study of equilibria in mixed ligand (nitrilotriacetate-cysteine) complex system in solution. The proportion of ionic species of nitrilotriacetate (NTA) and cysteine were varied by changing the pH of background electrolyte. The stability constants of Cu(II)-NTA-cysteine and Co(II)-NTA-cysteine complexes were found to be 6.35+/-0.05 and 5.45+/-0.02 (logarithm stability constant values), respectively, at ionic strength 0.1 M and a temperature of 35 degrees C.     

Thermodynamic stability constants of beryllium(II) and p-substituted N-phenyl benzohydroxamic acid complexes

The thermodynamic stability constants of beryllium(II) complexes of p-substituted N-phenylbenzohydroxamic acids have been determined in 50% v v aqueous dioxan at 35 degrees. The effect of methoxy, methyl, chloro, bromo, and nitro groups as substituents is discussed. There is a linear relationship between log K(1) and pK(a) and the Hammett equation is applicable. The beryllium complexes have been compared with those of Cu, Zn, Ni and Mn.     

Polarographic determination of the stability constants of binary and ternary lead(II) complexes and different organic ligands

The stability constants of complexes of different stoichiometries, formed by Pb(II) with oxalate, maleate, tartrate and citrate anions, have been determined. The polarographic methods originally used by DeFord and Hume were used for the binary complexes and those of Schaap and McMasters for the mixed complexes. The reliability of the results obtained was verified by applying the POLAG program. Finally, different statistical considerations were undertaken which confirm the results.     

Determination of stability constants of metal(II)-methionine and metal(II)-methionine-cystiene (binary and mixed) complexes using the Paper Ionophoretic Technique

Mixed complexation reactions of methionine and cysteine with copper(II) and cobalt(II) have been studied in solution phase using the paper electrophoretic technique at ionic strength 0.1 M and temperature 35°C. The binary equilibria copper(II)-methionine and cobalt(II)-methionine have also been studied, since this is a prerequisite to the investigation of mixed complexes. The stability constants of copper(II)-methionine-cysteine and cobalt(II)-methionine-cysteine mixed complexes were found to be 2.80 ± 0.07 and 2.44 ± 0.11 (logarithm of stability constant values), respectively.     

Determination of stability constants of metal(II)-methylcysteine and metal(II)-nitrilotriacetate-methylcysteine complexes with using a paper electrophoretic method

A method involving the use of paper ionophoresis is described for the study of the equilibria in mixed ligand complex systems in solution. Present method is based on the movement of a spot of metal ion under the electric field with the complexants added in the background electrolyte at pH 8.5. The concentration of primary ligand nitrilotriacetate (NTA) was kept constant while that of the secondary ligand methylcysteine was varied. The plot of log [methylcysteine] versus mobility were used to obtain information on the formation of mixed complexes and to calculate its stability constants. The binary equilibria metal(II)-methylcysteine and metal(II)-NTA have also been studied, since this is a prerequisite for the investigation of mixed complexes. The stability constants of the complexes Pb(II)-NTA-methylcysteine and UO₂ (II)-NTA-methylcysteine were found to be 3.03 ± 0.05 and 3.42 ± 0.09 (log K values) at ionic strength 0.01 M and a temperature of 35°C. Original Russian Text ? B.B. Tewari, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 1, pp. 151–155.     

Spectrophotometric determination of stability constants of Ni(II) and Cu(II) complexes with N-substituted hydrazinedithiocarboxylic acids

The stability constants of Ni(II) complexes with 2-methylhydrazinedithio-carboxylic and 3,3-dimethylhydrazinedithiocarboxylic acids and Ni(II) and Cu(II) complexes with 3-methyl-3-phenylhydrazinedithiocarboxylic acid have been determined in aqueous solution at 25°C and I = 0.01 M. The Bjerrum method of corresponding solutions has been applied, revealing the simultaneous presence of 1:1 and 1:2 complexes in solution.     

Potentiometric determination of stability constants of cyanoacetato complexes of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II)

Stability constants of cyanoacetato complexes of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II) were determined potentiometrically at 25.0 +/- 0.1 degrees and ionic strength 2M (sodium perchlorate). The stability constants were evaluated by a weighted least-squares method.     

Potentiometric determination of stability constants of inorganic cyclophosphate complexes with copper(II), cadmium(II) and lead(II) ions

The stability constants of the complexes of cyclophosphate anions and copper(II), cadmium(II) and lead(II) ions were determined by potentiometry with the use of ion-selective electrodes. For each metal ion, the stability constant of the 1:1 complex increases linearly with the charge on the phosphate ion. For the same cyclophosphate ion, the stability constants also increase with increase in the crystal radii of the cation, i.e. in the order: Cu²⁺ < Cd²⁺ < Pb²⁺. These results suggest that the complex formed is a typical outer-sphere type based on electrostatic forces.     

Temperature dependences of the formation constants of the cobalt(II) acetate complexes

The formation constant for the 1:1 complex between Co(II) and acetate ions (CoAc⁺) has been determined over the temperature range 25–75°C, both by spectrophotometry and by potentiometric titration. At an ionic strength of 1.0 M a near zero enthalpy of formation ws found.A spectrophotometer cell suitable for use up to ∼250°C is described and spectra of Co(II) acetate solutions are presented at temperatures up to 200°C. At elevated temperatures a tetrahedral species having the composition CoAc₂ is formed. The role of the complexation of Co(II) by acetate in the precipitation of Co₃O₄ from solutions of Co(II) acetate is briefly discussed.     

Palladium(II) halide complexes with dithioesters derived from sarcosine

Summary The compounds EtO₂CCH₂(Me)NCS₂R (R = Me, ESDTM; R = Et, ESDTE) were prepared from sarcosine ethyl ester hydrochloride, CS₂ and alkyl iodide in EtOH-H₂O. These ligands react with palladium halides in benzene to yield the benzene solvates [Pd(ESDTR)X₂]·nC₆H₆ (R = Me or Et; X = Cl or Br; n < 1), in which the dithioester molecule coordinates through both sulphur atoms. Ligands and complexes have been characterized by i.r. and ¹H n.m.r. spectroscopy and by thermal analysis (t.g., d.t.g. and d.t.a.). The low stability of the adducts in both solution and solid phase is discussed on the basis of proton n.m.r. spectra. Thermal degradation of the 1∶1 complexes has been examined up to 1000° C. The first decomposition step involves release of alkyl halide to form the [Pd(ESDT)X] _n (X = Cl or Br) intermediates, which successively decompose, finally giving palladium.     

Potentiometric determination of the dissociation constants of an asymmetric sorbent containing l-proline, and the stability constants of its Cu(II) complexes

The dissociation constants of the carboxyl groups (pK(a1) = 2.2, n = 1.8) and amino groups (pK(a2) = 9.5, n(2) = 1.6) of a sorbent prepared by reacting l-proline with a cross-linked chloromethylated styrene polymer have been determined by potentiometric titration. The potentiometrically measured stability constants of the Cu(II) complexes of the resin (logbeta(1) = 6.9 and log beta(2) = 12.4) were found to be close to the values for the Cu(II) complexes of N-benzyl-l-proline. For complexed resins of alpha-amino-acid type the pH-values of decomplexation do not appear to be directly correlated with the stability constants.     

Stability constants and molar absorptivities for complexes of chromium(III) and cobalt(II) with 2-pyridylmethanamine

The stability constants and molar absorptivities of complexes of Cr(3+) and Co(2+) with 2-pyridinemethanamine have been determined from spectrophotometric data of very dilute aqueous solutions.     

A spectrophotometric determination of the stability constants of the complexes of titanium(III) with acetylacetone

The stability constants of the consecutive complexes of titanium(III) with acetylacetone were determined by means of spectrophotometric methods. The values are log /gb₁ = 10.4, log β₂ = 18.8, and log β₃ = 24.9. Because of the fact that K₁K_a = 10^1.5 a high concentration of acetylacetone results in a considerable formation of TiL even at pH 0.     

Diazabutadiene cobalt(II) complexes

Summary Studies on the chelates of cobalt(II) with the bidentate ligands 1,4-diphenyl(2,3-dimethyl-1,4-diazabutadiene) (PMB) and 1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene (MPMB) have been carried out. On the basis of elemental analyses, the complexes are [Co(PMB)Cl₂], [Co(PMB)₂(C1O₄)₂], [Co(MPMB)Cl₂] and [Co(MPMB)₂(ClO₄)₂].Both ligands are bidentatevia nitrogen atoms in all the complexes. The magnetic susceptibility and i.r. and u.v.-visible spectra are reported and discussed. The chloro-compounds involving two chlorine ligands and, in the perchlorate compounds, the ClO ₄ ^– groups are bound to the cobalt(II) centre.     

Determination of the composition and the stability constants of complexes of mercury (II) with amino acids

The execution of a titration rarely performed, or of one with a reagent of limited stability, may be facilitated by applying multiparametric curve-fitting to titration-curve data in such a way that the amount of the substance titrated and the concentration of the reagent are evaluated simultaneously; the necessity for prior standardization of the reagent is thereby eliminated. In the potentiometric titration of acetate ion, a very weak base, with unstandardized hydrochloric acid, the accuracy and precision of the concentration of acetate thus obtained are approximately five times better than those which can be secured by titration with standardized acid and location of the point of maximum slope. The accuracy and precision of the concentration of acid are comparable to those that can be secured in very careful standardizations against a primary standard that gives a titration curve of far more favorable shape.     

Capillary electrophoretic separation of mono- and dimaltosyl-β-cyclodextrins and determination of the stability constants of their benzoate complexes

Summary Capillary zone electrophoresis method has been developed for the separation (and determination) of monoand dimaltosyl-β-cyclodextrins using indirect UV absorbance detection. The separation is based on inclusion complex formation with benzoate ion which is used as background electrolyte and absorbance provider simultaneously. Good resolution of cyclodextrin mixtures can be achieved optimizing the pH and the benzoic acid concentration in the background electrolyte. Capillary zone electrophoresis method has also been developed for the determination of formation constants of inclusion complexes.     

Polarographic determination of stability constants and thermodynamic parameters of lead(II) propanoate and 2-hydroxypropanoate complexes with a computer-controlled system

A computer-controlled electrometric system is described. It is used for d.c. polarographic determinations of the stability constants of lead(II) propanoate and 2-hydroxypropanoate complexes at four temperatures. From the values of the monoligand complex stability constants obtained at different temperatures, standard thermodynamic functions (ΔH_j and ΔS_j) for the first and second steps of complex formation were obtained. Closed-loop interaction between the minicomputer and electrometric instrument was achieved through computer control of the potentiostat, drop-life timer, burette and valve for nitrogen purging. Computer programs are outlined for numerical and statistical evaluation of the experimental data giving E_{$\text{1}\text{2}$}i_d and slope of logarithmic presentation of polarograms, F_o functions and cumulative stability constants, β_j as well as for calculation of the standard thermodynamic functions.     

Potentiometric determination of stability constants of Lanthanon(III) complexes with some Schiff bases and benzothiazolines

The protonation constants of five Schiff base and two benzothiazoline type ligands and stability constants of their complexes with six lanthanide ions were determined by potentiometrically in ethanol-water solution (1:1, v/v) at 25 +/- 0.1 degrees C. The Schiff base-type ligands were salicylidene 2-iminopyridine (SAPy), salicylidene-5-methyl-2-iminopyridine (SAPyMe), salicylidene-5-chloro-2-iminopyridine (SAPyCl), 2-(2-pyridylmethyleneamino) phenol (PyOH), 2-(2-quinolylmethyleneamino) phenol (QuOH) and the benzothiazoline-type ligands were pyridine-2-car-bozaldehydebenzothiazoline (PyS) and quinoline-2-carboxaldehydebenzothiazoline (QuS). The order of stability constants was found to be for metal ions La(III) < Pr(III) < Nd(III) < Eu(III) < Ho(III) < Yb(III), and for ligands SAPyCl < SAPy < QuS < QuOH < PyS < PyOH < SAPyMe. The FORTRAN programs PKAS and BEST were used for the calculation of protonation constants and stability constants, respectively.