Mischligandenkomplexe einiger Seltener Erden

Biligand complexes of the 1∶1Ln(III)-1,2-diaminocyclo-hexane-tetraacetic acid (CDTA) chelate with hydroxy acids [where hydroxy acids = salicylic acid (SA); Sulphosalicylic acid (SSA) and 8-hydroxyquinoline-5-sulphonic acid (HQSA)] have been investigated by potentiometric titration. Their formation constants have been calculated (μ=0.1M-KNO₃; andt=30±1°C) as 4.60±0.03, 5.46±0.03, 5.87±0.05; 3.12±0.04, 3.95±0.05, 4.42±0.07; 2.73±0.06, 3.45±0.05 and 3.90±0.08 forLn(III)-CDTA-SA,-SSA, and-HQSA respectively (whereLn=La, Pr or Nd). The value of logK _MAB follows the order: La(III)     

Potentiometrische Untersuchung von Lanthan(III)-Komplexen mit gemischten Liganden

Potentiometric studies of the 1∶1∶1, ternary systems, La(III)-aminopolycarboxylates-hydroxy acids [where amino-polycarboxylates=dipotassium nitrilotriacetate (NTA), N-hydroxyethylethylenediamine-N,N′,N′-dipotassiumtriacetate (HEDTA) and ethylenediamine-N,N,N′,N′-tripotassiumtetra-acetate (EDTA); hydroxy acids-5-sulfosalicylic acid (SSA) and dipotassium salt of 1.2-dihydroxybenzene-3.5-disulfonic acid (Tiron)], indicate the formation of 1∶1∶1, mixed ligand complexes.     

Ternary complexes of some rare earth metal ions with 1,2-diaminocyclohexanetetraacetic acid and hydroxy acids

1:1:1, Rare earth ions-CDTA-hydroxy acids ternary systems have been studied pH-metrically. The formation constants (log K_MLL′) and free energies of formation (ΔF°) of the resulting octa-coordinated metal ion mixed-ligand complexes have been calculated. The order of stability in terms of metal ions has been reported as: La < Pr < Nd < Gd < Dy and in terms of hydroxy acids as: TAR < MAL.     

Potentiometrische Untersuchungen an Cu(II)- und Ni(II)-Komplexen mit gemischten Liganden

Potentiometric evidences have been cited for the formation of 1∶1∶1 ternary complexes in the systems: Cu(II)/Ni(II)-glycine-diamines [where diamines = ethylenediamine (en), propylenediamine (pn), o-phenylenediamine (phenen) and 1.8-naphthalenediamine (naphen)].     

Solution Equilibria and Thermodynamic Studies of Complexation of Divalent Transition Metal Ions with Some Triazoles and Biologically Important Aliphatic Dicarboxylic Acids in Aqueous Media

The formation of binary and ternary complexes of the divalent transition metal ions Cu^II, Ni^II, Zn^II, and Co^II with some triazoles [1,2,4-triazole (TRZ), 3-mercapto-1,2,4-triazole, and 3-amino-1,2,4-triazole], and the biologically important aliphatic dicarboxylic acids adipic, succinic, malic, malonic, maleic, tartaric, and oxalic acid, was investigated in aqueous solutions using the potentiometric technique at 25 °C and I = 0.10 mol·dm^?3 NaNO₃. The formation of 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes was inferred from the corresponding titration curves. The formation of ternary complexes occurs in a stepwise manner with the carboxylic acids acting as primary ligands. The ionization constants (pK _a) of the investigated ligands were redetermined and used for determining the stability constants of the binary and ternary complexes formed in solution. The order of stability of the ternary complexes was investigated in terms of the nature of the triazole, carboxylic acid and metal ion used. The ?log₁₀ K values, percent relative stabilization, and log₁₀ X for the ternary complexes have been evaluated and discussed. The concentration distributions of the various species formed in solution were evaluated. The ionization constants of TRZ and malic acid and stability constants of their binary and ternary complexes with Cu^II, Ni^II, and Co^II metal ions were studied at four different temperatures (15, 25, 35, and 45 °C) and the corresponding thermodynamic parameters have been evaluated and discussed. The complexation behavior of ternary complexes was ascertained using conductivity measurements. In addition, the formation of ternary complexes in solution has been confirmed by using UV–visible spectrophotometry.     

Binary and ternary phenylboronic acid complexes with saccharides and Lewis bases

Cumulative formation constants for the association of three boronic acids (phenylboronic acid and its ortho-anilinomethyl and ortho-benzylaminomethyl derivatives) with four saccharides (fructose, glucose, mannitol, and sorbitol) were determined by potentiometric titration. Similarly, the constants for the formation binary complexes of the three boronic acids with (hydrogen) phosphate, (hydrogen) citrate, or imidazole were determined. Finally, the formation of ternary complexes of the boronic acids, phosphate, citrate or imidazole, and the saccharides were determined based on the determined values of the binary complexes. The previously unrecognized ternary complexes are significant in all systems investigated, and under some solution compositions, they can be the dominant species in solution over a wide pH range. A value of 15-25 kJ mol⁻¹ was determined for the energy of the B-N interaction in the benzylmethyl derivative based on the relative stabilities of the ternary phosphate complexes of the three boronic acids. The data are used to rationalize the medium dependence of stepwise formation constants and the apparent acidity constants of previous literature reports.     

The effect of ligand donor atoms on ternary complex stability

Formation constants of mixed ligand complexes of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺,with cyadine-5′-monophosphoric acid (CMP) and various primary ligands such as 1,10-phenanthroline(phen), glycylglycine(glygly) and salicylic acid (sal) have been determined in aqueous solution at 35°C and 0.1 M (KNO₃) by potentiomeric measurements. The acid dissociation constants of all the above mentioned ligands together with their 1 : 1 binary metal complex formation constants were also measured at 35°C. In general all the 1 : 1 binary complexes follow the Irving-Williams order of stability. Further the binary metal complexes of primary ligands are more stable than their ternary complexes with CMP. For ternary complexes, Δ(log K) values seem to change from positive to highly negative as the coordinating atoms of the primary ligands were varied from N,N to N,O^? to O^?O^?. The higher stability of ternary complexes involving phen is due to its Π-bonding interaction with the above metal ions and the relative decrease in the stability of other ternary systems is due to the coulombic repulsion of donor oxygen atoms of primary and secondary ligands. Thus for ternary complexes the stabilities follow a decreasing order of M-phen-CMP > M-glygly-CMP > M-sal-CMP.     

Studies of Size-Based Selectivity in Aqueous Ternary Complexes of Americium(III) or Lanthanide(III) Cations

Spectrophotometric and calorimetric titrations were used to determine the equilibrium constants (log₁₀ K ₁₁₁) and enthalpies of formation (ΔH ₁₁₁) for aqueous ternary complexes of the form M(L^a)(L^b) (M = Nd³⁺, Sm³⁺, Tb³⁺, Ho³⁺, Er³⁺, or Am³⁺; L^a = DTPA^5?, DO3A^3?, or CDTA^4?; L^b = oxalate (Ox), malonate (Mal), or iminodiacetate (IDA)). Inner-sphere ternary complexes were readily formed with the septadentate DO3A (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) and hexadentate CDTA (trans-1,2-diaminocyclohexanetetraacetic acid) ligands, whose binary complexes have residual metal-coordinated water molecules that are readily displaced by the smaller secondary ligands. The stability constants for the formation of lanthanide–CDTA complexes with Ox, Mal, and IDA generally increase with decreasing ionic radius when steric hindrance is minimal, with the trend in the M(CDTA)^? formation constants overshadowing any size-based reversal in the stepwise ternary complexation constants. Similar ternary complexes with DO3A showed little increase in thermodynamic stability compared to analogous CDTA complexes and no preference for larger Ln cations. The octadentate DTPA (diethylenetriaminepentaacetic acid) ligand proved too large to form ternary complexes to a measurable extent with any of the secondary ligands investigated, despite the presence of one residual inner sphere water molecule.     

Studies on Complexation of Resorcinol with Some Divalent Transition Metal Ions and Aliphatic Dicarboxylic Acids in Aqueous Media

The binary and ternary complexes of Cu²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions with resorcinol (R) as primary ligand and some biologically important aliphatic dicarboxylic acids (adipic, succinic, malic, malonic, maleic, tartaric and oxalic acids) as secondary ligands were studied in aqueous solution at 25 °C and I=0.1 mol⋅dm⁻³ NaNO₃ using the potentiometric technique. The formation of different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes is inferred from the corresponding potentiometric pH-titration curves. The ternary complex formation was found to take place in a stepwise manner. The protonation constants of the ligands were determined and used for determining the stability constants of the different complexes formed in aqueous solutions. The lower stability of the 1:2 binary complexes compared to the corresponding 1:1 systems of all ligands studied were in accordance with statistical considerations. The order of stability of the complexes formed in solution was investigated in terms of the nature of the resorcinol, carboxylic acid, and metal ion used. The values of Δlog ₁₀ K, percentage of relative stabilization (% R.S.), and log ₁₀ X for mixed-ligand complexes studied have been evaluated and discussed. The concentration distribution of the various species formed in solution was evaluated. The mode of chelation of the ternary complexes was ascertained by conductivity measurements.     

Stabilities of the Ternary Complexes of Copper(II) with Substituted 1,10-Phenanthrolines and Some Amino Acids in Aqueous Solution

In this study the binary and ternary complexes of copper(II) with substituted 1,10-phenanthrolines [s-phen: 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (dmphen) and 5-nitro-1,10-phenanthroline (nphen)] and l-amino acids [aa: l-phenylalanine (phe), l-tyrosine (tyr) and l-tryptophan (trp)] have been investigated using potentiometric methods in 0.1 mol·L^?1 KCl aqueous ionic media at 298.2 K. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the “BEST” software package. It was inferred that the aromatic 1,10-phenanthrolines act as a primary ligand in the ternary complexes, while the oxygen and nitrogen donor-containing amino acids are secondary ligands. The observed values of Δlog₁₀ K indicate that the ternary complexes are more stable than the binary ones, suggesting no interaction takes place between the ligands in the ternary complexes. The magnitudes of the measured stability constants of all of the ternary complexes are in the order [Cu(s-phen)(trp)]⁺ > [Cu(s-phen)(tyr)]⁺ > [Cu(s-phen)(phe)]⁺, which is identical to the sequence found for the binary complexes of Cu(II) with the amino acids. When the substituted 1,10-phenanthroline is changed, the stability constants of the ternary complexes decrease in the following order: [Cu(dmphen)(aa)]⁺ > [Cu(phen)(aa)]⁺ > [Cu(nphen)(aa)]⁺.     

Complexation Equilibria of Zn(II), Pb(II) and Cd(II) with Reduced Glutathione (GSH) and Biologically Important Zwitterionic Buffers

The interaction of zinc(II), lead(II), and cadmium(II) with Glutathione (S‐L‐glutamyl‐Lcysteinylglycine) as primary ligand and zwitterionic buffers (N‐[2‐Hydroxyethyl]piperazine‐N′‐[2‐ethanesulfonic acid]) (HEPES) and (N‐Hydroxyethyl]piperazine‐N′‐[2‐hydroxy‐propanesulfonic acid]) (HEPPSO) as secondary ligands were studied by potentiometric‐pH titration in 1:1:1 ratio at 25.0 °C and I = 0.1 mol.dm^?3 (KNO₃). The formation constants of different normal and protonated binary and ternary complex species were calculated. Formation constants for the monohydroxy, and dihydroxy complexes for the binary systems M(II) + HEPES and M(II) + HEPPSO have been evaluated. The distribution curves for the various complex species as a function of pH were constructed.     

Complexation Equilibria and Determination of Stability Constants of Binary and Ternary Nickel(II) Complexes with Amino Acids (Glycine, α-Alanine, β-Alanine and Proline) and Dipicolinic Acid as Ligands

In this paper we report the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H₂Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ?-alanine (H?-Ala), ??-alanine (H??-Ala) and proline (HPro)} as secondary ligands. These complexes were studied at 25?°C by means of electromotive force measurements, emf(H), using 1.0?mol?dm^?3 NaCl as the ionic medium. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the nickel(II) cation and the acid/base reactions of the ligands whose equilibrium constants were kept fixed during the analysis. In the study of the binary nickel(II)?Camino acids systems the species [NiL]⁺, NiL₂ and [NiL₃]^? were observed, and in the case of the ternary nickel(II)?Cdipicolinic acid?Camino acids systems the complexes Ni(Dipic)HL, [Ni(Dipic)L] ^? and [Ni(Dipic)L(OH)]^2? were observed. The respective stability constants were determined, and the species distribution diagrams, as a function of pH, are briefly discussed.     

Synthesis, Solution Equilibria and Antibacterial Activity of Co(II) with 2-(Aminomethyl)-Benzimidazole and Dicarboxylic Acids

Formation equilibria of cobalt(II) complexes of 2-(aminomethyl)-benzimidazole (AMBI) and the ternary complexes Co(AMBI)L (L = aliphatic or aromatic dicarboxylic acids) were investigated in aqueous solutions at 25?°C and 0.1 mol?dm^?3 ionic strength. Stoichiometry and stability constants are reported for the complexes formed. The speciation of the complexes was resolved. Values of $\log_{10}\ (K_{\mathrm{Co(AMBI)L}}^{\mathrm{Co(AMBI)}})$ and Δlog?₁₀ K are calculated and discussed. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. The effect of temperature on the dissociation constant of AMBI, CBDCA, and the formation constant of Co(AMBI) and Co(AMBI)-CBDCA complexes was studied and the thermodynamic parameters were calculated. Formation of the metal complexes has been found to be spontaneous, exothermic and entropically favorable. The solid complexes of [Co(AMBI)L] (L = oxalic acid, 1,1-cyclobutanedicarboxylic acid (CBDCAH₂) and malonic acid) have been synthesized and characterized by elemental analysis, infrared, spectra, magnetic and conductance measurements. Electronic spectra and μ _eff values suggest a tetrahedral geometry for Co(II)-complexes. The isolated metal chelates have been screened for their antibacterial activities and the complexes show a significant antibacterial activity against Pseudomonas fluorescence (Gram ?ve) and Bacillus subtilis (Gram +ve). The activity increases at higher concentration of the compounds.     

Thermodynamique des complexes metalliques ternaires des amino acides: Etude du systeme Ni(II)—Glycine—DL-α-alanine

Standard enthalpies and entropies of formation for binary and ternary Ni(II) complexes with glycine and DL-α-alanine were calorimetrically determined at 25°C in aqueous solution (I = 1 M NaClO₄). The evolution of these values from binary to ternary complexes is discussed on the basis of the stabilization characterizing the stability constants of the ternary species which have been previously calculated under the same experimental conditions.     

Different-ligand coordination compounds of nickel(II) with 1,3-dicarboxypropane-1-iminodiacetic acid and dicarboxylic acids in aqueous solutions

The equilibria in the ternary systems containing a nickel(II) salt and 1,3-dicarboxypropane-1-iminodiacetic acid and dicarboxylic acids (oxalic, malonic and succinic) were studied by spectrophotometry with supporting perchlorate (NaClO₄) for I = 0.1 at T = 20 ± 2°C. The stoichiometry and pH regions of existence of different-ligand complexes were determined; the stability constants of these complexes were calculated. The accumulation fractions of the complexes as functions of acidity were found. The experimental data were treated with mathematical models that estimate the possibility of existence of a broad range of complex species in solution and distinguish those of them that are sufficient to reproduce the observed picture.     

Equilibrium Study of the Mixed Complexes of Copper(II) with Adenine and Amino Acids in Aqueous Solution

Solution equilibria of the systems Cu(II)-adenine (A)-amino acids (L) have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been calculated at 25 °C and ionic strength 0.1 mol⋅dm⁻³ NaNO₃. Ternary complexes are formed by simultaneous reactions. The relative stability of each ternary complex was compared with that of the corresponding binary complexes in terms of Δlog ₁₀ K values. The concentration distribution of the complexes in solution was evaluated.     

Potentiometric studies on mixed-ligand complexes of copper(II) and zinc(II) with some amino acids (glycine,DL-α-alanine and DL-valine) as primary ligands and imidazole as a secondary ligand

Summary Mixed-ligand complexes of Cu^II and Zn^II with glycine(GL), DL--alanine (AL) and DL-valine (VL) as primary ligands and imidazole (IM) as secondary ligand have been studied potentiometrically under physiological conditions (t=37° C and I=0.15 M KNO₃). The experimental pH-titration data were analysed with aid of the SUPERQUAD computer program in order to evaluate formation constants of binary and ternary systems involying amino acids (AA) and IM. The relative stability of each of the ternary complexes was compared with that of corresponding binary complexes in terms of log K and log X values.     

Complex formation of mono-and binuclear dimeric cyclophane zinc diphenylporphyrinates with pyridine

The formation of host-guest complexes between zinc diphenylporphyrinates of dimeric diphenylporphyrins and pyridine in toluene has been studied by the spectrophotometric titration method and ¹H NMR spectroscopy. The zinc porphyrinates with pyridine form “internal” or “external” 1: 1 or 1: 2 complexes, depending on the length of binding ether O(CH₂)_nO bridges (n = 2, 3) of the cyclophane dimers and the reactant concentration. The stability constants of the porphyrinate-ligand complexes and concentration ranges of their formation have been determined.     

Mixed Ligand Complex Formation Reactions and Equilibrium Studies of Cu(II) with Bidentate Heterocyclic Alcohol (N,O) and Some Bio-Relevant Ligands

The formation equilibria of copper(II) complexes and the ternary complexes Cu(HMI)L (HMI=4-Hydroxymethyl-imidazole, L=amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(HMI)L and Cu(HMI,H₋₁)(L) complexes. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog ₁₀ K and log ₁₀ X. The effect of the side chains of amino acid ligands (Δ_R) on complex formation was discussed. The concentration distributions of various species formed in solution were also evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants are investigated. The effects of dioxane as a solvent, on the protonation constant of HMI and the formation constants of Cu^II–HMI complexes, were discussed.     

Mixed ligand complex formation of copper(II) and zinc(II) ions with 3-hydroxynaphthoate and picolinate ions as ligands in dioxane-water mixtures

Cu(II)-hydroxynaphthoate-picolinate and Zn(II)-hydroxynaphthoate-picolinate ternary systems were studied in dioxane-water (1 : 1, ν/ν) solutions at a 0.2 mol dm⁻³ ionic strength and 25°C. From EMF data the mixed ligand complexes M(hna)(pic) for M = Cu(II) and Zn(II) and M(hna)(pic)₂ for M = Zn(II) were detected and their formation constants evaluated (log K_f = 18.94± 0.03, 18.09±0.08 and 23.4±0.07, respectively). Factors contributing to the stabilization of these complexes are discussed and optimum experimental conditions for their predominance established.