Solvent Effects on Complexation of Molybdenum（Ⅵ） with Nitrilotriacetic Acid in Different Aqueous Solutions of Propanol

By using spectrophotometric and potentiometric techniques the formation constants of the species formed in the systems H^＋＋ Mo（Ⅵ）＋nitrilotriacetic acid and H^＋ ＋ nitrilotriacetic acid have been determined in aqueous solutions of propanol at 25 ℃ and constant ionic strength 0.1 molodm^-3 sodium perchlorate. The composition of the complex was determined by the continuous variation method. It was shown that molybdenum（Ⅵ） forms a mononuclear 1 ： 1 complex with nitrilotriacetic acid of the type MoO3L^-3 at -lg[H^＋] =5.8. The formation constants in various media were analyzed in terms of Kamlet and Taft＇s parameters. Linear relationships were observed when lg Ks was plotted versusp. Finally, the results were discussed in terms of the effect of solvent on complexation.     

Ionic strength dependence of stability constants,complexation of W(VI) with iminodiacetic acid

The equilibria between tungsten(VI) and iminodiacetic acid (IDA) have been studied in aqueous solution. The stoichiometry and stability constants of the complexes formed are determined from a combination of potentiometric and Uv spectroscopic measurements. All measurements are carried out at 25°C, pH 7.5 and different ionic strengths ranging from (0.1 to 1.0) mol dm⁻³ (NaClO₄). According to these results, tungsten(VI) forms a mononuclear complex with IDA of the type (WO₃L²⁻). By introducing two empirical parameters C and D in the complex-formation reaction between tungsten(VI) and IDA, the dependence of the dissociation and stability constants on ionic strength is described by a modified Debye-Huckel-type equation. Finally, a pattern for the ionic strength dependence is obtained.     

Application of specific ion interaction theory and parabolic models for the molybdenum(VI) and tungsten(VI) complexes with NTA and IDA at different ionic strengths

The interaction of nitrilotriacetic acid (NTA) and iminodiacetic acid (IDA) with tungsten(VI) (pH 7.5) and molybdenum(VI) (pH 6.00) has been studied in aqueous solutions at 25 ℃, and different ionic strengths (0.1 相似文献   

Complexation of Molybdenum(VI) with GLDA at Different Ionic Strengths

The interaction of the biodegradable ligand, l-glutamic acid N,N-diacetic acid tetrasodium salt (GLDA) with molybdenum(VI) was studied by determining stability constants at pH 6.00, T?=?298.15 K, and ionic strength 0.0992?<?I/mol·dm^?3?<?2.5689 of sodium chloride. The ionic strength dependence of the stability constants was fitted to both extended Debye–Hückel and specific ion interaction models. Job’s method confirmed the formation of one species, MoO₃GLDA^4?. The values of the stability constants are in agreement with the other data in the literature for the complex formation of aminopolycarboxylic acids with molybdenum(VI). Experimental data were obtained by using UV spectrophotometric method. The formation constant in pure water is 18.96?±?0.08 on the molal concentration scale.     

Determination of the stability constants of the Mo(VI) complex with iminodiacetic acid in different sodium perchlorate aqueous solutions

The stability of molybdenum(VI) complex formed by iminodiacetic acid(IDA) has been studied at 25°C, pH = 6.0, and different ionic strengths ranging from (0.3 to 1.0) mol dm⁻³ of sodium perchlorate. A combination of potentiometric and spectrophotometric techniques have been used based on the continuous variations method. According to our investigations, the metal-to-ligand ratio is 1: 1. The Solver, Microsoft Excel 2000 powerful optimization package, has been used to perform non-linear least-squares curve fitting. In order to obtain better consistency between the experimental and calculated results, two empirical parameters have been introduced in a Debye-Huckel-type equation. This equation enables us to calculate the values of stability constants in the desired range of ionic strength. This article was submitted by the authors in English     

Comparison of the application of Debye-Huckel and specific ion interaction theories for the complexation of tungsten(VI) with ethylenediaminediacetic acid

Equilibrium of the reaction of tungsten(VI) with ethylenediaminediacetic acid (EDDA) has been investigated in aqueous solution of pH 7.5 and 25°C. All measurements have been carried out at different ionic strengths ranging from (0.1 to 1.0) mol dm⁻³ (NaClO₄). According to our results the metal to ligand ratio is 1: 1. Stability constants and stoichiometry of the complex have been determined from a combination of potentiometric and UV spectroscopic measurements. In this semi-empirical model, two parameters have been introduced in a Debye-Huckel type equation based on the Gauss—Newton nonlinear least-squares method and minimizing the sum of the squares of the errors. Comparison of the ionic strength effect on these complex formation reactions has been made using a Debye-Huckel type equation and Bronsted—Guggenheim—Scatchard specific ion interaction theory (SIT). Published in Russian in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 5, pp. 864–868. The article is published in the original     

Complexation of Tungsten(VI) with Methyliminodiacetic Acid at Different Ionic Strengths

The results of this research give ionic strength dependence patterns for the complexation of tungsten(VI) with methyliminodiacetic acid at T?=?298?K. The formation data reported in this work were obtained at different ionic strengths (0.1?<?I/mol·dm^?3?<?1.0) of sodium perchlorate on the basis of Job??s continuous variation method, which show that a 1:1 complex forms at pH?=?7.50. UV experimental data were collected for the calculation of the stability constants according to the extended Debye?CHückel theory, the specific ion interaction theory and the parabolic model. Finally, these three models have been compared.     

A study of solvent effects on complex formation of tungsten(VI) with ethylenediaminediacetic acid in aqueous solutions of propanol

By using spectrophotometric and potentiometric techniques, the formation constants of the species formed in the systems H⁺+W(VI) + ethylenediaminediacetic acid and H⁺ + ethylenediaminediacetic acid were determined in aqueous solutions of propanol at 25°C and a constant ionic strength of 0.1 mol dm⁻³ sodium perchlorate. The composition of the complex was determined by the continuous variation method. It was shown that tungsten(VI) formed a mononuclear 1: 1 complex with ethylenediaminediacetic acid of the type WO₃L³⁻ at −log[H⁺] = 5.8. The formation constants in various media were analyzed in terms of the Kamlet-Taft parameters. Solvents were parameterized by dipolarity/polarizability scales π*, hydrogen-bond donor (HBD) strength α, and hydrogen-bond acceptor strength β. Linear dependences (LSERs) on these solvent parameters were used to correlate and predict a wide variety of solvent effects and provide an analysis of them. Linear relationships were observed when log K_S values were plotted versus π*. Finally, the results are discussed in terms of the effect of solvents on complex formation. The article is published in the original.     

Ionic strength dependence of formation constants, complexation of nitrilotriacetic acid with tungsten(VI) ion

The dependence on ionic strength of protonation of nitrilotriacetic acid and its complexation with W(VI) is reported in sodium perchlorate, sodium nitrate and sodium chloride solutions as background salts. The measurements have been performed at 25°C and various ionic strengths in the range 0.1–1.0 mol dm⁻³, using a combination of potentiometric and spectrophotometric techniques. The overall analysis of the present and the previous data dealing with the determination of stability constants at different ionic strengths allowed us to obtain a general equation, by which a formation constant determined at a fixed ionic strength can be calculated, with a good approximation, at another ionic strength, if 0.1 ≤ ionic strength ≤ 1.0 mol dm⁻³ sodium perchlorate, sodium nitrate or sodium chloride.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Application of a ternary complex of tungsten(VI) with 4-nitrocatechol and thiazolyl blue for extraction-spectrophotometric determination of tungsten

A new ternary ion-association complex of tungsten(VI), 4-nitrocatechol (NC), and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (Thiazolyl Blue, MTT) was obtained and studied using an extraction-spectrophotometric method. The optimum pH, reagent concentrations, and extraction time were determined. The composition of the complex was found to be W(VI): NC: MTT = 1: 2: 2. The extraction process was investigated quantitatively and the key constants were calculated. The molar absorptivity of the chloroform extract at λ_max = 415 nm was 2.8 × 10⁴ dm³ mol⁻¹ cm⁻¹, and the Beer’s law was obeyed up to 8.8 μg cm⁻³ tungsten(IV). The limit of detection and limit of quantification were calculated to be 0.27 μg cm⁻³ and 0.92 μg cm⁻³, respectively. The effect of foreign ions and reagents was studied and a competitive method for determination of tungsten in products from ferrous metallurgy was developed. The residual standard deviation and the relative error were 0.53 % and 0.2 %, respectively.     

Metal chelates in adsorption polarography I: Mo(VI) and derivatives of oxine

The formation of complexes between Mo(VI) and 8-hydroxy-quinoline (oxine) and four oxine derivatives were investigated by multiwavelength molecular absorption spectrometry, potentiometry, and polarography. The following pK_OH- and pK_NH- values of the ligands and logK ₂₁₁-values of the complexes MoO₂(OH)₂L ^x– (x=1 or 2) were obtained at 25° C and an ionic strength of 1M(NaClO₄): 5,7-dinitro8-hydroxyquinoline 4.59, <0, 14.50; 7-nitro-8-hydroxyquinoline-5-sulfonic acid 5.34, 0.41, 15.70; 7-iodo-8-hydroxyquinoline-5-sulfonic acid 6.98, 2.62, 17.65; 8-hydroxyquinoline-5-sulfonic acid 8.33, 4.13, 18.71; and 8-hydroxyquinoline 9.62, 5.28, 19.69. A good linearity was found between logK ₂₁₁ and the sum of the pK-values of the OH- and NH⁺-groups. The dependence of the peak current of Mo(VI)-determinations by adsorption polarography of the 7-nitro-8-hydroxyquinoline-5-sulfonate complex of Mo(VI) MoO(OH)₃L^– can quantitatively be described at pH 0.8–2 using the corresponding pK-values and the log K₃₁₁ of 18.54±0.03, determined by polarography.     

Complexation of tungsten(VI) with ethylenediaminetetraacetic acid and iminodiacetic acid at different ionic strengths using the Debye-Hückel and specific ion interaction theories

The equilibria in systems ethylenediaminetetraacetic acid-W^VI and iminodiacetic acid-W^VI were studied by a combination of UV-Vis spectrophotometric and potentiometric techniques at different ionic strengths ranging from 0.1 to 1.0 mol L^s-1 (NaC1O₄, 25 °C, pH = 7.5). The ionic strength effect on these complex formation reactions was studied using a Debye-Hückel-type equation and the Brønsted-Guggenheim-Scatchard specific ion interaction theory.     

Interaction of Molybdenum(VI) with Methyliminodiacetic Acid at Different Ionic Strengths by Using Parabolic,Extended Debye-Hückel and Specific Ion Interaction Models

The main aim of this research is to study the complexation of molybdenum(VI) with methyliminodiacetic acid in NaClO₄ aqueous solutions at pH = 6.00 and ionic strengths (0.1<I/mol⋅dm⁻³<1.0) at 25 °C by using potentiometric and UV spectrophotometric measurements in order to obtain thermodynamic stability constants at I=0 mol⋅dm⁻³. A comparison with previous literature data was made for the stability constants, though few data were available. The stability constants data have been analyzed and interpreted by using extended Debye-Hückel theory, specific ion interaction theory and parabolic model. Finally it might be concluded that parabolic model applies better for this complexation reaction.     

Complexes of pyrimidine DNA bases with thallium(I)

The stability constants of complexes of a thallium(I) ion with cytosine and thymine were determined in aqueous solution at 25°C and 0.1 mol dm⁻³ ionic media, using a combination of potentiometric and spectrophotometric techniques. Sodium perchlorate was used to maintain the ionic strength. The composition of the formed complexes was determined and it was shown that thallium(I) forms two mononuclear 1:1 species with cytosine of the type TIHL⁺ and TIL, and a mononuclear 1:1 complex species with thymine in the form TIHL, in the pH range of study (1–11), where L represents the fully dissociated ligand. The cumulative stability constants, β _xyz, of the complexes, [(thallium)_x(H)_y(ligand)_z], were calculated by a nonlinear fitting method and their distributions were presented as a function of-log[H⁺]. This text was submitted by the authors in English.     

Solvent extraction studies of cobalt(II) by capric acid from sodium sulfate solution

The extraction of cobalt(II) from sulfate medium of ionic strength 0.33?mol dm^?3 by capric acid dissolved in chloroform has been carried out at 25°C. By using the slope analysis method, the stoichiometry of the organometallic complex extracted was determined. Cobalt(II) complex exists as a mononuclear species CoL₂.2HL in the lower concentration region of capric acid and a binuclear ones (CoL₂.2HL)₂ in the higher concentration region. Extraction constants for each species were given. UV–visible and FTIR spectroscopy have also been used for the investigation of the extractant and their complexes. Electronic spectrum of cobalt(II) caprate species indicates the octahedral structure.     

Spectrophotometric determination of molybdenum(vi) with benzoylacetanilide

Abstract

The complex formed between molybdenum(VI) and benzoylacetanilide in the pH range 0.6 and 1.9 has been extracted into methyl isobutyl ketone and the absorbance has been measured at 410 mμ. Quantities of 0.15 to 2.10 mg of molybdenum have been determined with a standard deviation of 0.6%. The color is stable up to 2 hours. The presence of Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Be²⁺, Al³⁺, Cr³⁺, Ce⁴⁺, Th⁴⁺ or UO²⁺ ₂ up to 100 μg causes no interference. Ordinarily, Fe³⁺ interferes with the determination, but when masked with 1 ml of 0.5% solution of ascorbic acid the tolerance limit is 10 mg. Thus, molybdenum can be determined in steel when present in amounts as low as 0.26%.     

Kinetics of Complexation of Uranium with 2-(5-Bromo-2-Pyridylazo)-5-(Diethylamino) Phenol (Br-PADAP) in a 1:1 Water-Ethanol Medium

2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) forms a 1:1 complex with the uranyl ion in the presence of sulphosalicylic acid, which acts as stabilizer for this complex in the triethanol amine/perchloric acid buffer system. A change in the stoichiometry of the complex was seen at pH<5. Kinetic measurements were carried out using stopped-flow spectrophotometer in the presence of an excess concentration of U(VI) in the pH range 6.5 to 8. The dependence of the pseudo-first-order rate constant, k(obs), on the concentrations of U(VI), ligand and hydrogen ion showed that Br-PADAP reacts with UO₂(OH)⁺ to form an intermediate species (equilibrium constant = 1.28×10⁴mol.dm⁻³) that then rearranges (rate constant = 5.6×10⁻²s⁻¹) to form the product species. UO₂(OH)⁺ is present in equilibrium with the unreactive species UO₂(OH)₂, as well as with the unreactive sulfosalicylic acid complex.     

Chemical Modified Carbon Paste Electrode for Potentiometric Determination of Mo(VI) and its Application in Food Analysis and Agriculture Fertilizers

Since to the best of our knowledge, there is no potentiometric sensors based on carbon paste electrodes were proposed for the potentiometric determination of molybdenum(VI) ion. In this study, 2,2′-(propane-1,3-diylbis(oxy))dibenzoic acid (PBODBA) was synthesized and used as modifier in the fabrication of carbon paste electrode (CPE) for the quantification of molybdenum(VI). The developed electrodes I and II showed hexavalent Nernstian response of 9.80±0.05 and 9.90±0.08 mV decade⁻¹ over the concentration ranges of 1.0×10⁻⁷–1.0×10⁻³ and 1.0×10⁻⁸–1.0×10⁻³ mol L⁻¹, respectively. The electrodes showed good selectivity for Mo(VI). The modified electrodes were applied for the determination of Mo(VI) concentration in masscuaje agricultural fertilizer and spiked juice extractions containing several metals.     

Synthesis,structure and properties of eight novel molybdenum(VI) complexes of the types: [MoO2LD] and [{MoO2L}2D] (L = thiosemicarbazonato ligand,D = N-donor molecule)

Eight new molybdenum(VI) complexes with 4-(diethylamino)salicylaldehyde and 2-hydroxy-3-methoxybenzaldehyde thiosemicarbazones have been prepared. They were characterized as mononuclear [MoO₂LD] or dinuclear [{MoO₂L}₂D] complexes. In all the compounds the MoO₂²⁺ core is coordinated by a tridentate ONS thiosemicarbazonato ligand and by the N-donor molecule (imidazole, pyridine or γ-picoline). All the complexes were characterized by chemical analysis, IR spectroscopy and thermogravimetry. Three of the mononuclear complexes, dioxo[(2-hydroxy-3-methoxybenzaldehyde thiosemicarbazonato)(pyridine)]molybdenum(VI), dioxo[(2-hydroxy-3-methoxybenzaldehyde thiosemicarbazonato)(γ-picoline)]molybdenum(VI) and dioxo[(2-hydroxy-3-methoxybenzaldehyde thiosemicarbazonato)(imidazole)]molybdenum(VI) were also characterized by single-crystal X-ray structural analysis. A spectrophotometric method for the determination of molybdenum based on extraction of ion-pairs formed by the cationic surfactant and the [MoO(SCN)₄]⁻ anion is described.