The stability and thermodynamic functions of 4-amino-1,6-dihydro-1-methyl-2-methylthio-5-nitroso-6-oxo-pyrimidine complexes with Zn(II), Cd(II) and Hg(II)

The stability constants of the complexes formed by 4-amino-1,6-dihydro-1-methyl-2-methylthio-5-nitroso-6-oxo-pyrimidine with Zn(II), Cd(II) and Hg(II) ions, in aqueous media at different ionic strengths and temperatures, have been calculated by Bjerrum's method.From the data obtained, the thermodynamic functions of complexation processes are reported.     

Thermal studies on metal complexes of 5-nitrosopyrimidine derivatives

The following Zn(II), Cd(II), Hg(II) and Hg(I) complexes of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxopyrimidine (MTH) have been prepared and their thermal behaviour studied by TG and DSC techniques: Zn(MT)₂·3H₂O, Cd(MT)·H₂O. Cd(MTH)Cl₂, Hg(MTH)Cl₂ and Hg₂(MT)(NO₃). The dehydration and dehalogenation enthalpy values were calculated.     

Synthesis,characterization and the thermodynamic studies of some unsymmetrical tetradentate Schiff-base ligands and their Ni(II) and Cu(II) complexes

Some new unsymmetrical tetradentate Schiff-base ligands, (N-salicylidene-N′-pyrrolidene)-1,2-ethylenediamine(H₂salpyren) (H₂L¹), (H₂Mesalpyren) (H₂L²), (H₂phsalpyren) (H₂L³), (N-salicylidene-N′-pyrrolidene)-1,3-propylenediamine (H₂salpyrpd) (H₂L⁴), (H₂Mesalpyrpd) (H₂L⁵), (H₂phsalpyrpd) (H₂L⁶) and their Ni(II) and Cu(II) complexes were synthesized and characterized by elemental analyses, IR, UV-Vis, ¹H NMR and mass spectra and magnetic moments. Possible structures of these complexes have been proposed. The thermodynamic formation constants of the complexes were determined spectrophotometrically at constant ionic strength 0.1?M (NaClO₄), at 25°C in methanol.     

Complexation behaviour of benzilmono(Iepidyl)hydrazone (BLH) toward bivalent metal ions: A potentiometric study

Potentiometric investigations on metal complexes of various bivalent metal ions, viz. UO₂(II), Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Mn(II) with benzilmonol(lepidy!)hydrazone (BLH) have been carried out at different ionic strengths and at different temperatures in order to determine stability constants of the complexes. Thermodynamic parameters ΔC, ΔH and ΔS have also been evaluated from temperature coefficient data. The effect of varying the dielectric constant of the medium on the stability constants of complexes has also been investigated at 30±0.5°C and μ = 0.1MNaCl. Thermodynamic stability constants and thermodynamic stabilization energies for the first transition metals have also been 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.     

A study of complexation thermodynamic of humic acid with cadmium (II) and zinc (II) by Schubert's ion-exchange method

The complexation of humic acid from Azraq Oasis with two heavy metal ions Cd(II) and Zn(II) was investigated at pH 4 and 5 under constant ionic strength of 0.1 and at different temperatures (25, 35, 45, 55 and 65 °C). This investigation was done by using Schubert's ion-exchange equilibrium method, and its modified version.The derived conditional stability constants (log β_n) for these two metal-humate complexes were determined; they formed 1:1 and 1:2 complexes. It was found that the conditional stability constants (log β_n) increased by increasing pH and temperatures for all metal-humate complexes. It was found that the conditional stability constant log β₁ for Cd-humate is bigger than Zn-humate at all the desired temperatures and at pH 4 and 5.The derived constants and their temperature dependences have been used to calculate the corresponding thermodynamic parameters ΔG, ΔH, and ΔS, the results indicate that the stability of these complexes derives from very favorable entropy.     

Methylmercury(II) complexes with 2-mercaptopyridinecarboxylic acids

The stability constants of the complexes [MeHgL]^?(H₂L = 2-mercaptopyridine-3-carboxylic acid, 2-mercaptopyridine-4-carboxylic acid, 2-mercaptopyridine-5-carboxylic acid and 2-mercaptopyridine-6-carboxylic acid) have been obtained by differential pulse polarography. The values of log β₁ are in the range 14.14–14.96 at 20°C and ionic strength 0.1 mol dm^?3. The complexes MeHgHL have been isolated and characterized by chemical analysis and mass and IR spectrometry.     

Thermodynamic study of the complexation processes between 6,7-dihydro-3(H)-6-methyl-5-methoxy-7-oxo-vic-triazolo (4,5-d) pyrimidine and Cu(II), Zn(II), Cd(II) and Hg(II)

The compound 6,7-dihydro-3(H)-6-methyl-5-methoxy-7-oxo-vic-triazolo (4,5-d) pyrimidine (LH) has been characterized by IR, ¹H-NMR and UV-visible spectroscopy. Furthermore, its acid behaviour in aqueous solutions at variable temperatures and ionic strengths have been studied.The stability constants of the complexes formed by LH with Cu(II), Zn(II), Cd(II) and Hg(II) metal ions at different ionic strengths and temperatures have been calculated by the method of Chabereck and Martell. From these data, the thermodynamic functions for the corresponding complexation processes have been obtained.     

Some new unsymmetrical diimino tetradentate schiff base derived from 3,4-Diaminobenzophenone: Synthesis, characterization and the formation constant of Ni(II) and Cu(II) complexes

Some new unsymmetrical diimino tetradentate Schiff bases derived from 3,4-diaminobenzophenone, (N-salicyliden-N′-5- OMe.salycyliden)-3,4-diaminobenzophenone (H₂sal-5-OMe.sal.dabp) (H₂L¹), (H₂sal-5-Br.sal.dabp) (H₂L²), (H₂sal-5-Cl.sal.dabp) (H₂L³) and (H₂sal-5-NO₂.sal.dabp) (H₂L⁴) and their Ni(II) and Cu(II) complexes were synthesized and characterized by elemental analysis, IR, ¹H NMR, UV-Vis spectra and mass spectra. The thermodynamic formation constants of the complexes were determined spectrophotometrically at constant ionic strength (0.1 M NaClO₄) at 25 °C in DMF and their free energies of formation were calculated at 25 °C.     

Physico-chemical studies of Ni(II), Co(II), Zn(II), and Cd(II) ions with p-fluorobenzoylacetone

Incorporation of pH correction, in data obtained from the potentiometric titration of p-fluorobenzoylacetone with NaOH solution in dioxane-water (31,V/V) at 30±0.1°C in a medium of constant ionic strength, =0.1M (NaClO₄) gave the value of thermodynamic dissociation constant (pk _D ) as 12.06±0.02. Under similar conditions of solvent composition, temperature and ionic strength the thermodynamic stepwise formation constants of the complexes formed between Ni(II), Co(II), Zn(II) and Cd(II) ions and the above ligand, using method of least squares, gave log ₂ as 19.50±0.05, 18.89±0.05, 18.61±0.04 and 16.16±0.08 resp. This order is in accordance with theIrving-Williams series. Derivatives of the above metals have also been synthesised and characterised.With 2 Figures     

Polarographic study of the complexes of cadmium(II) and lead(II) with methoxyacetate ions

Reduction of the complexes of cadmium(II) and lead(II) atdme in aqueous and aqueous-methanol media at μ = 1.0 M(NaClO₄) at 15 ±0.1 and 25 ±0.1°C is reversible and diffusion-controlled. Four complex species are formed in either case. The overall stability constants of 1:1,1:2, 1:3 and 1:4 complexes have been determined. Lead(II) complexes are much stronger than the corresponding cadmium(II) complexes.     

Paper electrophoretic determination of the stability constants of biologically significant binary complexes of beryllium(II) and cobalt(II) with sarcosine

Quantitative indication of the process of forming a complex comes from the evaluation of the stability constants or formation constant, which characterize the equilibria corresponding to the successive addition of ligands. Paper electrophoretic technique is described for the study of beryllium(II) and cobalt(II) biologically significant binary complexes with sarcosine. The stability constants of ML and ML₂ complex species of Be(II)/Co(II)—sarcosine have been found to be (6.17 ± 0.09, 4.06 ± 0.04) and (4.27 ± 0.07, 2.98 ± 0.11) (log-arithm stability constant values), respectively at ionic strength 0.1 Mol L⁻¹ and a temperature of 35°C.     

Dioxouranium (II) Chelates with Nitrogen Donor Ligands

The chelates formed by the reaction of dioxouranium (II) with (α-benzoylmethyl-benzylideneimino)benzene sulphonic acid (H₂BB), (α-benzoylmethyl-benzylideneimino) ethane sulphonic acid (H₂BE), 3-(α-benzomethyl-benzylideneimino) propanoic acid (H₂BPA) & 0-(α-benzoylmethyl-benzylideneimino) benzoic acid (H₂BBA) have been prepared and studied potentiometrically using Calvin's extension of Bjerrum's method in aqueous medium at different ionic strengths (0.01, 0.05 and 0.1 M NaClO₄) at 25°, 35° and 45°. The thermodynamic parameters for all the chelates have been evaluated. These compounds have also been isolated as crystalline solids and are characterised by analytical data, electrical conductance, magnetic moment and IR studies.     

Interaction of manganese(II) with methyl salicylate ethyl salicylate and phenyl salicylate

The proton ligand stability constants of methyl salicylate, ethyl salicylate and phenyl salicylate and the stepwise stability constants of manganese(II) complexes with these have been determined potentiometrically in aqueous ethanol system 50/50 (v/v) at 25°C at different ionic strengths, viz. 0.050 M, 0.075 M, 0.100 M and at 35 and 45°C at an ionic strength of 0.05 M. The thermodynamic stability constants of the complexes have been evaluated from the various values by extrapolating to zero ionic strength at 25°C. The thermodynamic parameters such as free energy changes (ΔG), enthalpy changes (ΔH) and entropy changes (ΔS) involved have been calculated.     

The reactivity of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine towards copper(II) ions

The acid–base properties of the N-substituted amino acid HL [HL = N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine] and its reactivity towards the Cu^II ion have been measured by potentiometric and spectrophotometric techniques in aqueous solution at 25 °C and 0.1 M KCl ionic strength. These studies show that the neutral HL compound is present in aqueous solution (3–7 pH range) in the zwitterionic form with the diprotonated imidazolic residue. Studies of HL/Cu^II mixtures reveal the existence of complex species with the neutral ligand, HL and containing the deprotonated L ligand. By controlling the reaction conditions, four solid phases of stoichiometry: CuLCl(H₂O)₆, Cu₂LCl₃(H₂O)₈, CuL₂(H₂O)₆ and Cu(HL)₂Cl₂(H₂O)₆ were isolated and characterised by i.r. and electronic spectroscopy, thermal techniques and magnetic measurements.     

Equilibrium studies of Mn(II), Mg(II), Ca(II), Sr(II) and Ba(II) withp-fluoro-,p-chloro-,p-bromo-,p-methyl-benzoylacetones and 1-(4-fluorophenyl)-1,3-pentanedione

The rawpH-data, obtained from the potentiometric titrations of the titled ligands with NaOH in 75% (v/v) dioxane-water mixture performed at 20, 30 and 40°C at constant ionic strength (=0.1M-NaClO₄), have been adequately corrected for dilution, and solvent effects in order to evaluate thermodynamic dissociation constants. Variance of the latter as a function of temperature has also been accounted for. The differing magnitudes of thermodynamic dissociation constants of the titled ligands have been explained on the basis of the non coplanar orientation of the phenyl ring in the ligands and a comparison has been made with those of unsubstituted benzoylacetone, dibenzoylmethane and acetylacetone.Following similar technique, thermodynamic stepwise and overall formation constants of the titled metal-ligand systems have been obtained and the results correlated with ligand basicity inverse metal crystal radii and second potentials of metals. Decrease in the free enthalpy (–G) of complexation reaction has also been evaluated.

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Untersuchung der Gleichgewichte von Mn(II), Mg(II), Ca(II), Sr(II) und Ba(II) mit p-Fluor-, p.-Chlor-, p-Brom-, p-Methyl-benzoylaceton und 1-(4-Fluorphenyl)-1,3-pentanedion

Zusammenfassung Aus der potenitometrischen Titration der Titelverbindungen mit NaOH in 75 (v/v) Dioxan—Wasser bei, 20, 30 und 40°C bei konstanter Ionenstärke (=0,1M-NaClO₄) wurden die thermodynamischen Dissoziationskonstanten ermittelt. Verdünnungs-, Lösungsmittel-und Temperatureffekte wurden berücksichtigt. Die unterschiedlichen Dissoziationskonstanten werden mit der Nichtplanarität des Phenylrings in den Liganden erklärt. Außerdem wurden die Komplexbildungskonstanten bestimmt; sie sind in die Diskussion miteinbezogen.

     

Studies on mixed ligand complexes of samarium(III), europium(III) and dysprosium(III) with 1-nitroso-2-naphthol and trioctylphosphine oxide

The extraction behavior of Sm(III), Eu(III) and Dy(III) with 1-nitroso-2-naphthol (HA) and trioctylphosphine oxide (TOPO) in methyl isobutyl ketone (MIBK) from aqueous NaClO₄ solutions in the pH range 4–9 at 0.1M ionic strength has been studied. The equilibrium concentrations of Sm and Dy were measured using their short-lived neutron activation products,¹⁵⁵Sm and^165mDy, respectively. In the case of Eu, the concentrations were assayed through the^152,154Eu radiotracer. The distribution ratios of these elements were determined as a function of pH, 1-nitroso-2-naphthol and TOPO concentrations. The extractions of Sm, Eu and Dy were found to be quantitative with MIBK solutions in the pH range 5.9–7.5, 5.6–7.5 and 5.8–7.5, respectively. Quantitative extraction of Eu was also obtained between pH 5.8 and 8.8 with chloroform solutions. The results show that these lanthanides (Ln) are extracted as LnA₃ chelates with 1-nitroso-2-naphthol alone, and in the presence of TOPO as LnA₃(TOPO) and LnA₃(TOPO)₂ adducts. The extraction constants and the adduct formation constants of these complexes have been calculated.     

The reactivity of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxo-pyrimidinyl)-L-histidine towards silver(I) and zinc(II) ions

Reactions of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine with Ag^I and Zn^II ions in 1/1 and 4/1 ligand-to-metal molar ratios, in aqueous media at 25 °C and 0.1 M KNO₃ and KCl ionic strength, respectively, were followed by potentiometric techniques in order to determine formation equilibria for the complex species. The spectral curves, as a function of ligand-to-metal molar ratio at established pH values, were studied and four solid phases of stoichiometry: AgL·4H₂O, Ag(HL)NO₃·1.5H₂O, AgL(OH)₂K₂·H₂O and Zn(HL)₂Cl₂·7H₂O were isolated and characterised by analytical, spectroscopic and thermal measurements.     

THE INTERACTION OF 2-AMINO-2-HYDROXYMETHYL-1,3-PROPANEDIOL WITH COBALT(II) AND MANGANESE(II) IONS

Abstract

The stepwise complex formation between 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) with Co(II) and Mn(II) was studied by potentiometry at constant ionic strength 2.0 M (NaClO₄) and T = (25.0 ± 0.1)°C, from pH measurements. Data of average ligand number (Bjerrum's function) were obtained from such measurements followed by integration to obtain Leden's function, F ₀(L). Graphical treatment and matrix solution of simultaneous equations have shown two overall stability constants of mononuclear stepwise complexes for the Mn(II)/TRIS system (β₁ = (5.04 ± 0.02) M^?1 and β₂ = (5.4 ± 0.5) M^?2) and three for the Co(II)/TRIS system (β₁ = (1.67 ± 0.02) × 10² M^?1, β₂ = (7.01 ± 0.05) × 10³ M^?2 and β₃ = (2.4 ± 0.4) × 10⁴ M^?3). Slow spontaneous oxidation of Co(II) solutions by dissolved oxygen, accelerated by S(IV), occurs in a buffer solution TRIS/HTRIS⁺ 0.010/0.030 M, with a synergistic effect of Mn(II).     

Complex formation of copper(II) with chrome azurol s

The complex formation of copper(II) with chrome azurol S (CAS) was studied by spectrophotometric and potentiometric methods. In the pH range 5–7, two complexes with the composition Cu(H₂O)₂HCAS- and (Cu(H₂O)₂)₂CAS were detected; the stability constants were calculated to be log K = 4.02 ±0.05 and log K = 13.7±0.1, respectively (at 25° and ionic strength 0.1 (KCl)). A comparison is made between the copper(II)-CAS and iron(III)-CAS systems.