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.     

Spectrophotometric determination of cationic surfactants by formation of ternary complexes with Fe(III) and chrome azurol

An extraction-free spectrophotometric method for the determination of cationic surfactants, such as cetylpyridinium chloride, cetyltrimethylammonium bromide and zephiramine is proposed, which is based on the formation of ternary complexes with Fe(III) and chrome azurol S. The molar ratio of the complex is 2:1:1 (Fe(III):chrome azurol S: cationic surfactant). The method is simple, rapid and sensitive, giving an apparent molar absorptivity of 4.5×10⁴ L·mol^?1-cm^?1 and a linear range of 0.1–6.0 μmol/L cationic surfactants. The total cationic surfactant content can be determined directly in aqueous solutions by measuring the absorbance at 680 nm (pH 5.8). The method has been successfully applied to water samples.     

Complex formation constants and thermodynamic parameters for La(III) and Y(III)L-serine complexes

Summary The stoichiometric stability constants for La(III) and Y(III)L-serine complexes were determined by potentiometric methods at different ionic strengths adjusted with NaClO₄ and at different temperatures. The overall changes in free energy (G ^o), enthalpy (H ^o), and entropy (S ^o) during the protonation ofL-serine and that accompanying the complex formation with the metal ions have been evaluated.

---

Komplexbildungskonstanten und thermodynamische Parameter für La(III)- und Y(III)-L-Serin-Komplexe

Zusammenfassung Die stöchiometrischen Komplexbildungskonstanten für La(III)- und Y(III)-L-Serin-Komplexe wurden mittels potentiometrischer Methoden bei verschiedenen Ionenstärken (mit NaClO₄ adjustiert) und bei verschiedenen Temperaturen bestimmt. Die Änderungen in der freien Energie (G ^o), Enthalpie (H ^o) und Entropie (S ^o) während der Protonierung und der Komplexbildung mit den Metallionen wurden ermittelt.

     

Spectrophotometric study of etodolac complexes with copper (II) and iron (III)

A rapid, simple, and selective method was developed for the determination of etodolac. The method depends on complexation of etodolac with copper (II) acetate and iron (III) chloride followed by extraction of complexes with dichloromethane and then measuring the extracted complexes spectrophotometrically at 684 and 385 nm in case of Cu (II) or Fe (III), respectively. Different factors affecting the reaction, such as pH, reagent concentration, and time, were studied. By use of Job's method of continuous variation, the molar ratio method, and elemental analysis, the stoichiometry of the reaction was found to be in the ratio of 1:2 and 1:3, metal:drug in the case of Cu (II) and Fe (III), respectively. The method obeys Beer's law in a concentration range of 2.00-9.00 and 0.50-2.00 mg/mL in case of Cu (II) and Fe (III), respectively. The stability of the complexes formed was also studied, and the reaction products were isolated for further investigation. The complexes have apparent molar absorptivities of about 32.14 +/- 0.97 and 168.32 +/- 1.12 for Cu (II) and Fe (III), respectively. The suggested procedures were successfully applied to the analysis of pure etodolac and its pharmaceutical formulations. The validity of the procedures was further ascertained by the method of standard additions, and the results were compared with other reported spectrophotometric methods and showed no significant difference in accuracy and precision.     

Spectrophotometric determination of formation constants of 1:1 complexes of lanthanides with 4-(2-pyridylazo)resorcinol (par)

Complex formation (1:1) between lanthanides(III) and 4-(2-pyridylazo)resorcinol (PAR or H₂R) has been studied by spectrophotometry. The method is based on indirect estimation of the protonated (MHR) and the normal (MR) complexes by measuring the absorbance at the peak for the ligand, which decreases with increasing metal concentration at a constant pH. Similar experiments were made at various pH values. Both MHR and MR complexes were found to be formed in the pH range 5–6. Their formation constants, logK_MHR and logK_MR, determined by graphical analysis, ranged from 3.78 ± 0.02 (Ce) to 4.39 ± 0.02 (Lu), and from 9.61 ± 0.06 (Ce) to 10.70 ± 0.05 (Lu), respectively. The acidity of the MHR complexes parallels the order of stability of the MR complexes.     

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.     

Spectrophotometric studies of ruthenium(III)and rhodium(III)-oximidobenzotetronic acid complexes and the simultaneous determination of the two metals

Ruthenium(III) and rhodium(III) form stable coloured complexes in ethanolic solution with oximidobenzotetronic acid (OBTA). Ruthenium forms a purple-violet Ru(OBTA)(3) complex at pH 1.1-3.5, which is stable over the pH range 1.1-11.3. Rhodium(III) forms a yellowish-brown complex, RhCl(2)(OBTA)(2), at pH 2-8; at higher pH (11.5 and above) the complex is reddish-brown, but has the same Rh:OBTA ratio. A method for the simultaneous determination of these two metals is proposed, and the interference by commonly occurring ions has been investigated.     

Apparent formation constants of dithiooxamide and substituted dithiooxamide complexes of cobalt(II,III), nickel(II) and copper(II) in strongly acidic media

The apparent stability constants of the complex species formed between cobalt(II, III), nickel(II) or copper(II) and dithiooxamide or some N,N′- and tetra-substituted dithiooxamides have been determined in strongly acidic media at 25 ° C. The configuration of the complexes in solution is discussed on the basis of the electronic spectra.     

Spectrophotometric study of the complexes of hydroxyethylethylenediaminetriacetic acid with bismuth(III), copper(II) and lead(II)

The bismuth(III), copper(II) and lead(II) hydroxyethylethylenediaminetriacetic acid systems were investigated in detail. Evidence for the formation of species BiX, Bi(OH)X⁻, CuHX, CuX⁻, PbHX and PbX⁻ is presented and their stability constants given.     

Spectrophotometric determination of formation constants of various types of complexes by use of another competing ligand

A method has been developed for determining the formation constants of various colored complexes, ML and ML₂, and their protonated forms, spectrophotometrically, by measuring the absorbance of all forms of the colored complexes in the absence and presence of another ligand, Y, which forms the colorless complex MY, with a known formation constant. This method is based on the competition between the two ligands, L and Y, for the metal ion. An experimental test has been done for the Zn(II)-4-(2-pyridylazo)resorcinol (PAR) (H₂L) system by using nitrilotriacetic acid (NTA) as another ligand, Y. The results showed that the concentrations of PAR used were suitable for the study of 1:2 complexes, ZnL₂, ZnL(HL) and Zn(HL)₂, but were too high to study the 1:1 complexes. With the aid of the formation constants of ZnL and ZnHL determined previously, the experimental data gave an approximate value for the formation constant of ZnY (Y = NTA) which agreed with the published value.     

Spectrophotometric determination of the protonation constants of o-cresolphthalexone and the formation constants of its alkaline-earth-metal comple

The first three protonation constants of o-cresolphthalexone and the two constants of phenolphthalein and o-cresolphthalein, and also the forma.     

Polarographic determination of iron(II) and iron(III) complexes with edta

The iron(II) and iron(III) complexes with EDTA can be determined separately and in mixtures in acetate-buffered medium at pH 4.0. The E_{$\text{1}\text{2}$}values are in the range ?0.105 to ?0.112 V vs. SCE. Linear calibration plots are obtained over the range 0–1.0 mM for each oxidation state. A sample-handling procedure for avoiding oxidation of iron(II) species is described. It is shown that the acetate buffer system does not affect the stability of the iron-EDTA complexes.     

Stability constants of iron(III) borate complexes

The ultraviolet absorbance data from experiments conducted at constant pH and total iron concentration but variable B(OH)₃ concentration were used to determined the stability constants of FeB(OH) ₄ ²⁺ and Fe[B(OH)_{4 2} ⁺ at 25°C and an ionic strength of 0.68. The estimates obtained were *₁ = 1.0 ± 0.2 × 10^–2 and *₂ = 2 ± 1 × 10^–5, respectively (uncertainties are two times the standard error of the estimates). A calculation of the extent of iron(III) borate formation in ocean water at pH 8.2 shows that iron(III) borates are not a significantly large component of iron(III) speciation in seawater.     

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.     

Diastereoselective formation of metallamacrocyclic (arene)Ru(II) and CpRh(III) complexes

The reaction of [(arene)RuCl(2)](2) (arene = cymene, 1,3,5-C(6)H(3)Me(3)) and [CpRhCl(2)](2) half-sandwich complexes with tridentate heterocyclic ligands in the presence of base has been investigated. In all cases, the chloro-ligands were substituted to give metallacyclic products with ring sizes between 4 and 18 atoms. The cyclization occurs in a highly diastereoselective fashion with chiral recognition between the different metal fragments. The complexes were comprehensively characterized by elemental analysis, NMR spectroscopy, and single crystal X-ray crystallography. For 2-hydroxy-nicotinic acid and 2-amino-nicotinic acid, dinuclear structures were obtained (15-17) whereas for 2,3-dihydroxyquinoline, 2,3-dihydroxyquinoxaline, and 6-methyl-2,3-phenazinediol, trimeric assemblies were found (19-22), and for 4-imidazolecarboxylic acid, a tetrameric assembly (18) was found.     

Spectrophotometric determination of iron(III) dimethyldithiocarbamate (ferbam)

A spectrophotometric method was developed for the determination of ferbam (iron(III) dimethyldithiocarbamate) by converting it into an iron-phenanthroline complex, which was then absorbed on microcystalline naphthalene in the presence of tetraphenylborate, and the absorbance was measured at 515 nm against a reagent blank. The molar absorptivity of the complex was 1.2 x 10(4)l mol(-1)cm(-1). Ten replicate analyses of a sample solution containing 150 mug of ferbam gave a relative standard deviation of 0.84%. Beer's law was obeyed over the concentration range 22.4-372.9 mug of ferbam. The effects of various factors such as reagent concentration and naphthalene, shaking time and diverse ions were studied in detail. The method is sensitive and selective and can be applied to the direct determination of ferbam in commercial samples and in mixtures containing various other dithiocarbamates (e.g. ziram, zineb and maneb) in foodstuffs.     

Calculations of microconstants and equilibrium formation constants for platinum(II) and palladium(II) halide complexes in solution

Distribution diagrams and formation functions for halide complexes [M(H₂O)_{4 ? n} Cl _n ]^{2 ? n} (M = Pt(II) or Pd(II)) and [PdCl_{4 ? n} Br _n ]^2? (n = 0?C4) in solution are analyzed in terms of the matrix model. Equilibrium constants for binding the first ligand $\left( {\bar K} \right)$ and corrections for the mutual influence between ligands (??) in the course of complex formation in solution are calculated. In examples analyzed, the substitution of chloride ion for water in the coordination sphere of platinum(II) and palladium(II) is an anti-cooperative process. The substitution of bromide ion for chloride ion in the coordination sphere of [PdCl₄]^2? is weakly cooperative. Quantum-chemical calculations show that platinum(II) and palladium(II) cis-bisaquadichloro complexes in the gas phase are thermodynamically less stable than trans-isomers. The cis-trans isomerization constants in the gas phase calculated by the DFT method and those found for solutions using the matrix model have the same order of magnitude.     

Spectrophotometric determination of ruthenium(III) using diphenylcarbazone

Summary The purple violet ruthenium(III)-diphenylcarbazone complex which is formed at p _h 5–7, and has an absorption maximum at 530 nm with molar absorption coefficient 16.2·10⁴l.cm^–1.mole^–1 is suggested for the estimation of 20–125g ruthenium(III) spectrophotometrically in 30–60% ethanol. The complex is stable over p _h range 3.2–8.4. The limits of interference due to foreign ions have been studied.

---

Zusammenfassung Der bei p _h 5 bis7 entstehende Ruthenium(III)-Diphenylcarbazon-Komplex hat ein Absorptionsmaximum bei 530 nm und einen Absorptionskoeffizienten von 16,2·10⁴ l.cm^–1.Mol^–1. Die spektrophotometrische Bestimmung von 20 bis 125g Ruthenium(III) in 30 bis 60%igem Äthanol mit Hilfe dieses zwischen p _h 3,2 und 8,4 beständigen Komplexes wurde vorgeschlagen. Die Störung durch Fremdionen wurde geprüft.