Squarete complexes of uranyl ions in aqueous solution

The stability constants of UO ₂ ²⁺ -squarate complexes are measured at ionic strengths of 0.05M, 0.06M, 0.075M, 0.09M, 0.1M (squaric acid-perchloric acid) using a solvent extraction method at a pH of 1.1 and a temperature of 25 °C. The extractant used is dinonylnaphthalenesulfonic acid in n-heptane. The aqueous phase was made of a mixture of squaric and perchloric acid and²³³U radio tracer. The stability constants of squarate complexes of UO ₂ ²⁺ is seen to decrease linearly with the square root of the ionic strength.     

Complexation of managanese(II), cobalt(II), nickel(II), zink(II), and cadmium(II) cations with amoxicillin

The interaction of amoxicillin anions (Axn^?) with Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, and Cd²⁺ in aqueous solution at 20°C and an ionic strength of 0.1 (KNO₃) has been studied pH-metrically. In a neutral and weak alkaline solution, MAxn⁺ and M(OH)Axn complexes are formed. The formation constants and the pH ranges of existence of these complexes have been determined.     

Coordination properties of dehydroacetic acid – binary and ternary complexes

Complex formation equilibria of dehydroacetic acid with Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Mn²⁺ and the ternary complexes involving Cu²⁺, dehydroacetic acid and some amino acids containing different functional groups are investigated. Stoichiometry and stability constants for the complexes are estimated at 25°C and 0.1 M ionic strength in 25% dioxane-water mixtures. The concentration distribution diagrams of the complexes were evaluated. The effect of temperature and organic solvent on the acid dissociation constant of dehydroacetic acid and the formation constant of Cu²⁺ complex was studied and thermodynamic parameters calculated.     

Formation constants and composition of Ga3+ and In3+ complexes with iminodisuccinic acid in aqueous solutions according to potentiometric data

The complexation of Ga³⁺ and In³⁺ with iminodisuccinic acid (H₄L) at 25°C in 0.1, 0.4, 0.6, and 0.8 M KNO₃ supporting solutions was studied by potentiometry and mathematical modeling. The thermodynamic constants of formation of neutral, protonated, and hydroxo complexes were calculated by extrapolating the concentration constants to the zero ionic strength using an equation with one individual parameter.     

Complex formation reactions of palladium(II)-1,3-diaminopropane with various biologically relevant ligands. Kinetics of hydrolysis of glycine methyl ester through complex formation

The interaction of [Pd(DAP)(H₂O)₂]²⁺ (DAP = 1,3-diaminopropane) with some selected bio-relevant ligands, containing different functional groups, were investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA constituents. Stoichiometry and stability constants of the complexes formed are reported at 25°C and 0.1 M ionic strength. The results show the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants is examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. DNA constituents form 1:1 and 1:2 complexes. The effect of dioxane on the acid dissociation constants of CBDCA and the formation constant of its complex with Pd(DAP)²⁺ was reported. The kinetics of hydrolysis of glycine methyl ester bound to [Pd(DAP)(H₂O)₂]²⁺ was studied at 25°C and 0.1M ionic strength.      

Reaction of cefalexine with manganese(II), cobalt(II), nickel(II), zinc(II), and cadmium(II) ions

The reaction of cefalexine anions (Cpx^?) with Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, and Cd²⁺ ions in aqueous solution at 20°C and ionic strength 0.1 was studied by pH-metry. In weakly alkaline medium, unstable complexes MCpx⁺ and M(OH)Cpx are formed, in which Cpx^? behaves as a monodentate lidand coordinated through the amino group.     

Komplexone XLVII. The Stability of Palladium(II) Complexes with Aminopolycarboxylate Anions

The formation of Pd(II) complexes with aminopolycarboxylate anions has been investigated using pH and UV.-spectrophotometric measurements at ionic strength 1 M and 20°. In some cases bromide or thiocyanate ions have been used as auxiliary ligands. Pd²⁺ forms the strongest complexes of the hitherto investigated divalent metal ions. The stability constants are discussed in relation to the particular stereochemistry of Pd(II) complexes.     

The unusual extraction behavior of americium(III) and dioxouranium(VI) from picric acid medium using neutral oxodonors II. A thermodynamic study

The role of temperature on the distribution of Am³⁺ and UO₂ ²⁺ was investigated in the extraction systems involving TBP and DOSO as the neutral oxodonors and picrate as the organophilic counter anion. The inner-sphere water molecules and their substitution by the oxodonor molecules appeared to influence the extraction constants of these metal ions. The conditional extraction constants for Am³⁺ were found to be larger (about 3 order of magnitude) than those for UO₂ ²⁺. From the thermodynamics data it appeared that both TBP as well as DOSO bind Am³⁺ ion through outer-sphere coordination. In presence of 1M NaCl, though the interaction with TBP remains unaltered DOSO tend to form an inner-sphere complex. On the other hand, UO₂ ²⁺ forms inner-sphere complexes with DOSO and outer-sphere complex with TBP in the absence of salt. In the presence of 1M NaCl, both TBP and DOSO form inner-sphere complexes. The effect of ionic strength on metal ion extraction was also investigated. For Part I see Ref. 9.     

Thermodynamics of Ni(II) Complexation with L-Asparagine in Aqueous Solution

Complexation of the Ni²⁺ ion with L-asparagine (HAsn^±) is studied by potentiometric titration at 298.15 K and at the 0.3, 0.5 and 1.0 ionic strength of the solution (KNO₃). The formation of the NiAsn⁺ and NiAsn₂ complexes was established and their stability constants were determined. The thermodynamic stability constants of the mono- and bis(L-asparagine)nickel(II) complexes were obtained by extrapolation to zero ionic strength. The direct calorimetry method was used to measure the heat effect of the L-asparagine reaction with the Ni(II) nitrate solution in different pH intervals at 298.15 K and at the 0.5, 1.0, and 1.5 ionic strength (KNO₃). The standard enthalpies of the NiAsn⁺ and NiAsn₂ formation were found using extrapolation and the equation with one individual parameter. The enthalpies of the formation of the Ni(II) complexes with L-asparagine in aqueous solution were calculated in the standard hypothetically undissociated state.     

Thermodynamics of reactions of complex formation for Ce<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> ions with glycine in an aqueous solution

Enthalpies of complex formation for glycine (HL^±) with Ce³⁺ and Er³⁺ ions at 298.15 K and the value of the ionic strength of 0.5 (KNO₃) are determined by calorimetric means using two independent procedures. Thermodynamic characteristics of the reactions of formation for complexes of glycine with Ce³⁺ and Er³⁺ ions at various [metal]: [ligand] molar ratios are calculated.     

Standard thermodynamic functions and constants of complex formation of Nd<Superscript>3+</Superscript> and La<Superscript>3+</Superscript> with L-asparagine in aqueous solutions at 298 K

The enthalpies of complex formation of L-asparagine (HAsn^±) with Nd³⁺ and La³⁺ ions are determined calorimetrically at 298.15 K and an ionic strength of 0.5 (KNO₃). The thermodynamic characteristics of the formation of the NdAsn²⁺, NdAsn²⁺, LaAsn₂⁺, and LaAsn₂⁺ complexes are calculated.     

Environmental Coordination Chemistry: Binary Systems Comprising Some Bivalent Cations and Monocarboxylates in Aqueous Solution. Ionic Medium Effects on Equilibrium Constants

Abstract

The molar single activity coefficients associated with propionate ion (Pr) have been determined at 25°C and ionic strengths comprised between 0.300 and 3.00 M, adjusted with NaClO₄, as background electrolyte. The investigation was carried out potentiometrically by using a second class Hg/Hg₂Pr₂ electrode. It was found that the dependence of propionate activity coefficients as a function of ionic strength (I) can be assessed through the following empirical equation: log y_pr = –0.185 J^3/2 + 0.104 I². Next, simple equations relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous solution, at 25°C, as a function of ionic strength were derived, allowing the interconversion of parameters from one ionic strength to another, up to I = 3.00 M. In addition, thermodynamic formation constants as well as parameters associated with activity coefficients of the complex species in the equilibria are estimated. The body of results shows that the proposed calculation procedure is very consistent with critically selected experimental data.     

Stability quotients of neodymium acetate complexes from 20 to 70‡C by laser-induced photoacoustic spectroscopy

The formation of Nd(III) acetate complexes in aqueous solution is studied by laser-induced photoacoustic spectroscopy and spectrophotometry. Stability quotients for the complexes Nd(CH₃COO)²⁺ and Nd(CH₃COO)² and dissociation quotients for acetic acid are determined at 20, 35, 50 and 70‡C in NaClO₄ medium of ionic strength 2.2m (2.0M at 20‡C). The 20‡C results are consistent with previous values determined by potentiometry and energy transfer from Tb(III). The temperature dependence of the stability quotients is consistent with the measured enthalpies of reaction at 25‡C.     

Thermodynamics of Complex Formation of Ce<Superscript>3+</Superscript> and La<Superscript>3+</Superscript> Ions with Glycylglycine in Aqueous Solution

Enthalpy of the complex formation between diglycine (HL^±) and Ce³⁺ or La³⁺ at 308.15 K and ionic strength of 0.5 mol/L (KNO₃) has been determined by means of calorimetry. Thermodynamic parameters of the diglycine complexes formation with Ce³⁺ and La³⁺ at different metal to ligand molar ratios have been determined.     

Effect of ionic strength on the stabilities of ciprofloxacin – Metal complexes

Proton–ligand dissociation constant of 1-cyclopropyl-1,4-dihydro-4-oxo-7-(1-piperazinyl) quinolone-3-carboxylic acid is ciprofloxacin and metal–ligand stability constants of its complexes with some metal ions have been determined potentiometrically in the presence of (0.01, 0.02 and 0.03 mol/dm³) NaClO₄. The order of the stability constants of the formed complexes increases in the sequence Cu²⁺, Fe³⁺, Ni²⁺ and Zn²⁺ and decreases with increase in the concentration of ionic strength.     

Potentiometric study of binary complexes of 3-[(1R)-1-hydroxy-2-(methylamino)ethyl]phenol hydrochloride with some lanthanide ions in aqueous and mixed solutions

The complexation of lanthanide ions (Y³⁺, La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Gd³⁺, Tb³⁺, and Dy³⁺) with 3-[(1R)-1-hydroxy-2-(methylamino)ethyl]phenol hydrochloride was studied at different temperatures and different ionic strengths in aqueous solutions by Irving-Rossotti pH titration technique. Stepwise calculation, PKAS and BEST Fortran IV computer programs were used for determination of proton-ligand and metal-ligand stability constants. The formation of species like MA, MA₂, and MA(OH) is considered in SPEPLOT. Thermodynamic parameters of complex formation (ΔG, ΔH, and ΔS) are also evaluated. Negative ΔG and ΔH values indicate that complex formation is favourable in these experimental conditions. The stability of complexes is also studied at in different solvent-aqueous (vol/vol). The stability series of lanthanide complexes has shown to have the “gadolinium break.” Stability of complexes decreases with increase in ionic strength and temperature. Effect of systematic errors like effect of dissolved carbon dioxide, concentration of alkali, concentration of acid, concentration of ligand and concentration of metal have also been explained.     

Competitive Complexation of Lanthanide Cations by Xylitol and Nitrate Anion in Aqueous Solution: A Microcalorimetric Investigation

The apparent equilibrium constants and enthalpies of complexation of Nd³⁺, Sm³⁺, Eu³⁺, and Gd³⁺ by xylitol in aqueous solutions containing NaNO₃ at an ionic strength of 2.0 mol-kg^–1 have been determined by microcalorimetry at 25°C. Since nitrate anion weakly complexes the lanthanide cations, these values are analyzed in terms of competition between xylitol and NO ₃ ^- The method leads to the apparent equilibrium constants and enthalpies of complexation of the lanthanide cations by NO ₃ ^- at this particular ionic strength. Despite the difficulties encountered in characterizing rather weak associations, the results are, whenever comparison is possible, in good agreement with those obtained by direct microcalorimetry. The advantage of this competition method is that it can be used when the enthalpic effects are too weak and insufficiently concentration dependent for direct microcalorimetric determination. In the present case, it allows us to thermodynamically characterize the formation of SmNO ₃ ²⁺ and EuNO ₃ ²⁺ , processes we have not been able to study directly.     

Plutonium(IV) mononitrate and dinitrate complex formation in acid solutions as a function of ionic strength

Titrations of Pu(IV) with HNO₃ in a series of aqueous HClO₄ solutions ranging in ionic strength from 2 to 19 molal were followed using visible and near-infrared absorption spectrophotometry. The Pu 5f-5f spectra in the visible and near IR range change with complex formation. At each ionic strength, a series of spectra were obtained by varying nitrate concentration. Each series was deconvoluted into spectra of Pu⁴⁺ (aq), Pu(NO₃)³⁻ and Pu(NO₃)₂ ²⁺ complexes, and simultaneously their formation constants were determined. When corrected for the incomplete dissociation of nitric acid, the ionic strength dependence of each formation constant can be described by two parameters, β⁰ and Δε using the formulae of specific ion interaction theory.     

Stability constants of zinc(II), cadmium(II), and cobalt(II) complexes of trimethylenediamine-<Emphasis Type="Italic">N,N,N′,N′</Emphasis>-tetraacetic acid

Stability constants of Zn²⁺, Cd²⁺, and Co²⁺ complexes of trimethylenediamine-N,N,N′,N′-tetraacetic acid were determined at 298.15 K and ionic strengths of 0.1, 0.5, and 1.0 by potentiometric titration. Potassium nitrate and chloride were used as supporting electrolytes. The results obtained were extrapolated to the zeroth ionic strength using an equation with one individual parameter, and the thermodynamic stability constants of the complexes were calculated. The results are compared with the corresponding data on related compounds.     

Stability Constants of Zinc and Cadmium Complexes of 2-Hydroxypropene-1,3-Diamine-N,N,N",N"-Tetraacetic Acid

Stability constants of complexes of 2-hydroxypropene-1,3-diamine-N,N,N",N"-tetraacetic acid with Zn²⁺ and Cd²⁺ ions have been determined by potentiometric titration in a KNO₃ supporting electrolyte at 298.15 K and ionic strengths of 0.1, 0.5, and 1.0. The results obtained were extrapolated to the zero ionic strength of the solution using a one-parameter equation.