Complexes of calcium(II), strontium(II) and barium(II) with heterocyclic ligands

The synthesis and characterization of new complexes of general formula ML_nX₂·mH₂O, where M = Ca(II), Sr(II), Ba(II); L = N-methylimidazole (N-Meim), 3-amino-5-methylisoxazole (3-AMI), 5-amino-3,4-dimethylisoxazole (5-ADI), 2,5-diphenyloxazole (PPO); n = 1–4, 6; X = Cl⁻, Br⁻, I⁻, SCN⁻ and m = 0–6, have been reported.All the derivatives are studied by chemical analysis, molar conductivity, i.r. spectra and X-ray powder diagrams in order to give information about the donor atoms' competitivity of the ligands and to elucidate the structure of the complexes.The ligands act as monodentate N-ring bonded, the compounds are generally distorted tetrahedral, only the [Ba(5-ADI)₆](SCN)₂, [Ca(N-Meim)₄Cl₂]·4H₂O and [Ca(3-AMI)₄Br₂]·3H₂O are octahedral.     

Thermodynamics of copper(II) 2,2′-dipyridyl complexes in aqueous solution

The thermodynamic parameters for the chelation of cupric ion with 2,2′-dipyridyl have been redetermined at 25°C and I=0.1 M. ΔG values were obtained by potentiometry with a selective ion electrode and ΔH values by direct calorimetry. Similar studies have been made on the relative hydroxocomplexes. The data obtained are compared with those in the literature and the chelate effect of the heterocyclic diimine is described.     

Thermodynamics of 2,2′,2′'-terpyridinecopper(II) complexes in aqueous solution

Summary The thermodynamic quantities relative to the protonation and the complexation of 2,2,2'-terpyridine with copper(II) ion have been determined at 25° and I=0.1 mol dm^–3 (NaNO₃). The G data was obtained by potentiometric measurements; a copper selective electrode was employed for the study of the complexation equilibria. The H values have been determined by direct calorimetry.The hydrolytic species, existing at pH>6 and their relative G and H values have also been obtained.From the thermodynamic data the importance of enthalpy and entropy terms in stabilizing the complexes is assessed.Moreover some considerations on the chelating effect are reported.Presented in part at 2 Congresso Nazionale di Chimica Analitica, Catania (1977).     

Complexation en solution aqueuse des ions magnesium(II), manganese(II), nickel(II), cuivre(II) et plomb(II) avec la s-carboxymethyl-l-cysteine: Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution

Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution.The complex formation between Mg(II), Mn(II), Ni(II). Cu(II), Pb(II) ions and S-carboxy-methyl-l-cysteine (H₂A) has been studied by measurement of pH at 25°C and constant ionic strength (1 M NaClO₄). Although no interaction occurs with Mg(II), this work provides evidence for a variety of complexes: MnA; CuHA⁺; CuA; CuA₂^2-; NiHA⁺; NiA; NiA₂^2-; PbHA⁺; PbA et PbA(OH)^-. The overall formation constants of all these species are computed and refined. The results allow the determination of the distribution of the complexes as a function of pH; some structural features of the metal complexes in solution are indicated.     

Thermodynamics of heteroligand mercury(II) complexes with nitrilotriacetic acid and ethylenediamine in aqueous solution

Formation of heteroligand complexes HgNtaEn⁻ and Hg(Nta)₂En⁴⁻, where Nta³⁻ is nitrilotriacetate ion and En is ethylenediamine, was studied by means of direct calorimetry, potentiometry, and NMR spectroscopy at 298.15 K and ionic strength I = 0.5 (KNO₃).     

Thermodynamics of the formation of nickel(II) complexes with L-histidine in aqueous solutions

The heat effects of the formation of Ni(II) complexes with L-histidine in an aqueous solution are determined via direct calorimetry at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃). The standard thermodynamic characteristics (Δ_r H ^○, Δ_r G ^○, Δ_r S ^○) of complex formation in the investigated system are calculated. It is concluded that the resulting values are consistent with the results from studying the structure of L-histidine complexes with Ni²⁺ ions by various spectral methods.     

Thermodynamics of complex formation of Cu(II) ethylenediaminetetraacetate with ethylenediamine in aqueous solution

The formation of mixed-ligand complexes in the system Cu²⁺-Edta^4?-En was studied by the calorimetric and pH-potentiometric methods at 298.15 K and I = 0.5(KNO₃). The thermodynamic characteristic of the CuEdtaEn^2? complex formation were determined.     

Thermodynamics of copper(II) dicarboxylate coordination in aqueous solution

Summary The association of H⁺ and Cu²⁺ with malonate, maleate, succinate and phthalate ions has been investigated both potentiometrically and calorimetrically at 25° and I = 0.1 mol dm^–3 (NaClO₄).The structures of the complexes existing in aqueous solution are proposed on the basis of thermodynamic data.     

Thermodynamics of mixed-ligand complex formation of copper (II) ethylenediaminetetraacetate with hexamethylenediamine in an aqueous solution

The mixed-ligand complex formation in the system Cu²⁺−Edta⁴⁻−(CH₂)₆(NH₂)₂ (L), where L is hexamethylenediamine has been calorimetrically, pH-potentiometrically and spectrophotometrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of the CuEdtaL²⁻, CuEdtaHL⁻ (CuEdta)₂L⁴⁻ and (CuEdta)₂En⁴⁻ complexes have been determined. The most probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed.     

Thermodynamics of formation of urea complexes with manganese(II), nickel(II) and zinc(II) ions in N,N-dimethylformamide

The complexation of urea (ur) with manganese(II), nickel(II) and zinc(II) ions has been studied by titration calorimetry in N,N-dimethylformamide (DMF) containing 0.4M (C(2)H(5))(4) NBF(4) as a constant ionic medium at 25 degrees C. The calorimetric data were well explained in terms of the formation of [Mn(ur)](2+), [Mn(ur)(2)](2+) and [Mn(ur)(4)](2+) for manganese(II), [Ni(ur)](2+) for nickel(II) and [Zn(ur)](2+) and [Zn(ur)(2)](2+) for zinc(II), and their formation constants, reaction enthalpies and entropies were determined. The complexation of the nickel(II)-urea system in DMF has also been studied by means of spectrophotometric titration and electronic spectra of individual nickel(II) complexes were determined. On the basis of the stepwise thermodynamic quantities and the individual electronic spectra of the complexes, it is revealed that the [Mn(ur)](2+), [Mn(ur)(2)](2+), [Ni(ur)](2+), [Zn(ur)](2+) and [Zn(ur)(2)](2+) complexes have a six-coordinate octahedral structure, while the [Mn(ur)(4)](2+) complex has a four-coordinate tetrahedral structure.     

Copper(II) complexes of diaminodiamides in aqueous solution

The basicity constants of N,N′-bis(β-carbamoylethyl)ethylenediamine, N,N′-bis(β-carbamoylethyl)trimethylenediamine, N,N′-bis(β-carbamoylethyl)-1,2-propylenediamine, and N,N′-bis-(β-carbamoylethyl)-2-hydroxyltrimethylenediamine were determined potentiometrically in 0.10 mol dm^?3 NaNO₃ at 25.0°C. The formation of Cu(II) complexes of these ligands and the CuO to CuN bond rearrangements at the two amide sites of these complexes were investigated quantitatively by potentiometric and spectrophotometric techniques under the same conditions. Electronic spectra of the Cu(II) complexes of these ligands and their deprotonated species formed in aqueous solution were measured and discussed.     

The formation of protonated copper(II)-8-oxyquinoline complexes in aqueous solution

The constants of formation of copper-8-oxyquinoline complexes in aqueous solution (logβ) were determined using pH-metric titration combined with mathematical simulation for the following complexes: CuHOx²⁺ (14.39 ± 0.20), CuHOx ₂ ⁺ (25.25 ± 0.16), CuOx⁺ (10.07 ± 0.21), and CuOx₂ (20.92 ± 0.29); 293 K, I = 0.01. It was shown by UV spectrophotometry that, in protonated complexes, the metal atom is probably bound to the ligand through oxygen.     

Mixed metal complexes in solution. Thermodynamic and spectrophotometric study of copper(II)-citrate heterobinuclear complexes with nickel(II), zinc(II) or cadmium(II) in aqueous solution

Summary A thermodynamic study of Cu^II–M^II-citrate (M^II=Ni^II, Zn^II or Cd^II) ternary systems has been performed by means of potentiometric measurements of hydrogen ion concentration at different temperatures (10, 25, 35 and 45°C) and at I=0.1 mol dm^–3 (KNO₃).The different binary and ternary systems involved have been further characterized by visible spectra and by calculating the spectra ( versus ) of all the Cu^II complexes.The thermodynamic data suggest strong entropic stabilization for the species under discussion. As regards the visible spectral characteristics of Cu^II(d-d transitions), the substitution of one Cu^II ion in the dimer [Cu₂(cit)₂H_–2]^4– by Ni^II or Zn^II to form heterobinuclear [CuM(cit)₂H_–2]^4– complexes, gives rise to a change in the visible spectrum.     

A study of polyamine complex formation with H+, Cu(II), Zn(II), Pb(II), and Mg(II) in aqueous solution

Summary The composition and stability of the following biogenic amine complexes have been investigated: 1,4-diaminobutane(Put), 4-azaoctane-1,8-diamine(Spd), 4,9-diazadodecan-1, 12-diamine(Spm) as well as homologues such as 1,3-diaminopropane(Put3), 4-azaheptane-1, 7-diamine(Spd3,3) and 4,8-diazaundecan-1,11-diamine(Spm3,3,3) with H⁺, Cu(II), Zn(II), Pb(II) and Mg(II). A potentiometric method was used. The VIS technique enabled the determination of coordination mode in copper/amine systems. It was found that Mg(II) does not form coordination compounds with any of the studied polyamines in solution. An increase in the concentration of ligand and metal was found to result in a stronger tendency towards the formation of protonated compounds accompanied by a decrease in the concentration of hydroxocomplexes. At physiologicalpH (7.4) an increase in the concentration of protonated compounds by approximately 15% was observed within the ligand concentration range from 0.001 mol dm^–3 to 0.0001 mol dm^–3 at a Cu(II) concentration of 0.000177 mol dm^–3.

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Untersuchungen zur Komplexbildung von Polyaminen mit H⁺, Cu(II), Zn(II), Pb(II) und Mg(II) in wäßriger Lösung

Zusammenfassung Anhand einer Analyse von potentiometrischen Daten wurden Zusammensetzung und Beständigkeit folgender biogener Aminkomplexe untersucht: 1,4-Diaminobutan(Put), 4-Azaoktan-1,8-diamin(Spd), 4,9-Diazadodekan-1,12-diamin(Spm), sowie auch deren Homologen 1,3-Diaminopropan(Put3), 4-Azaheptan-1,7-diamin(Spd3,3) und 4,8-Diazaundekan-1,11-diamin(Spm3,3,3) mit H⁺, Cu(II), Zn(II), Pb(II) und Mg(II). Mit Hilfe der VIS-Technik wurde die Koordinationsweise in Kupfer/Amin-Systemen bestimmt. Es wurde festgestellt, daß Mg(II) keine Koordinationsverbindungen mit den untersuchten Polyaminen bildet. Eine höhere Konzentration von Ligand und Metall führte zu stärkerer Tendenz der Bildung protonierter Verbindungen, wobei die Konzentration von Hydroxokomplexen kleiner wurde. Bei physiologischempH (7.4) wurde im Bereich der Ligand-Konzentration von 0.001 mol dm^–3 bis 0.0001 mol dm^–3 bei einer Cu(II)-Konzentration von 0.000177 mol dm^–3 ein Anstieg der Konzentration protonierter Verbindungen um etwa 15% beobachtet.

     

Cyclo(L-histidyl-L-histidyl)copper(II) complexes in aqueous solution

Summary The structure of the copper(II) complex cation with HISH₂ [HISH₂ = cyclo(L-histidyl-L-histidyl)] was determined from molecular weight data and n.m.r. and c.d. spectra in aqueous solution. Two HISH₂ moieties ligate to coppervia two nitrogen atoms of the imidazole rings giving rise to two 13-membered chelate rings in solution, a situation seen previously in the crystal.     

Mercury(II) cysteine complexes in alkaline aqueous solution

Mercury(II) complexes with l-cysteine (H(2)Cys) in alkaline aqueous solutions have been structurally characterized by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. The distribution of [Hg(Cys)(n)] (n = 2, 3, and 4) species in approximately 0.09 mol dm(-3) mercury(II) solutions with H(2)Cys/Hg(II) ratios varying from 2.2 to 10.1 has been evaluated by fitting linear combinations of simulated EXAFS functions for the separate complexes to the experimental EXAFS data, aided by (199)Hg NMR and Raman results. For the [Hg(Cys)(2)](2-) and [Hg(Cys)(3)](4-) complexes and the novel four-coordinated Hg(Cys)(4) species that dominates in solutions with excess of cysteine (H(2)Cys/Hg(II) > 5), the mean Hg-S bond distances were found to be 2.35(2), 2.44(2), and 2.52(2) Angstroms, respectively. The minor amount of the linear [Hg(Cys)(2)](2-) complex that can still be discerned in solutions with ratios up to H(2)Cys/Hg(II) = 5 was derived from the distinct S-Hg-S symmetric stretching Raman band at 334 cm(-1). From (199)Hg NMR spectra, the chemical shift of the Hg(Cys)(4) species was estimated to -340 ppm with an amount exceeding 85% in the highest excess of cysteine, consistent with the EXAFS data.     

Ternary complexes in solution: Complex formation between copper(II), zinc(II), cadmium(II) and ligands of biological importance

The stability constants of ternary complexes of theMAL type have been determined for Cu(II), Zn(II) and Cd(II). The ligands chosen for this study belong to the biologically important ones viz. Bipyridyl (A) and Nitrilotriacetic acid (L). LogK _MAL values for Cu(II), Zn(II) and Cd(II) are 11.42, 10.67 and 9.72, respectively, at temp.=25°C and =0.1M (KNO₃); the order is discussed.

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Ternäre Komplexe in Lösung: Die Komplexibildung zwischen Kupfer(II), Zink(II) und Kadmium(II) mit Liganden von biologischem Interesse

Zusammenfassung Die Stabilitätskonstanten für Cu(II)-, Zn(II)- und Cd(II)-Komplexe vom TypMAL wurden bestimmt. Die biologisch relevanten Liganden, die für diese Untersuchung ausgewählt wurden, waren Bipyridyl (A) und Nitrilotriessigsäure (L). Bei einer Temperatur von 25°C und =0,1M (KNO₃) sind die entsprechenden logK _MAL -Werte für Cu(II), Zn(II) und Cd(II) 11,42, 10,67 und 9,72; diese Reihenfolge wird ebenfalls diskutiert.

     

Complex formation between glycine and magnesium (II), calcium(II), and iron(II) at 25 °C in 3.00M NaClO4

Equilibria occurring between glycine (L) and magnesium(II) and calcium(II) were studied by measuring at 25 °C the electromotive force (e.m.f.) of the cell: (–) Pt, H₂/SolutionS/R.E. (+) where R.E. is the reference electrode described in the text.Equilibria taking place in solutions containing iron(II) and glycine were investigated by means of the cell: (–) R.E./SolutionS/G.E. (+) where G.E. is the glass electrode. The general composition of solutionS was in both cases the following: B M inM ²⁺;H M in H⁺;A M inL; 3.00M in ClO ₄ ^– ; (3-H-2B)M in Na⁺.Experimental data were explained by assuming the existence of the species:: MgL(log _1,0,1=1.53±0.05); MgL ₂(log _2,0,1=2.26±0.05); CaL(log _1,0,1==0.75±0.03); FeL(log _1,0,1=4.20±0.04).Protonation constants of aminoacetate, not known in the experimental conditions selected, were determined by means of e.m.f. measurements carried out with a H₂ electrode.

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Komplexbildung zwischen Glycin und Magnesium(II), Calcium(II), bzw. Eisen(II) bei 25 °C in 3,00M NaClO₄

Zusammenfassung Die Gleichgewichte zwischen Glycin (L) und Magnesium(II) bzw. Calcium(II) wurden bei 25 °C durch E.M.K. Messungen der folgenden Meßkette untersucht: (–) Pt, H₂/ProbenlösungS/R.E. (+) wobei R.E. Referenz-Elektrode bedeutet (siehe Text).Zum Studium der Reaktion zwischen Eisen(II) und Glycin bei 25 °C wurde folgende Meßkette benutzt: (–) R.E./ProbenlösungS/G.E. (+) wobei G.E. Glas-Elektrode bedeutet.Alle Meßproben hatten die folgende allgemeine Zusammensetzung:B M inM ²⁺;H M in H⁺;A M inL; 3,00M in ClO ₄ ^– ; (3-H-2B)M in Na⁺.Die experimentellen Daten konnten unter Annahme folgender Komplexe erklärt werden: MgL(log _1,0,1=1,53±0,05); MgL ₂(log _2,0,1=2,26±0,05); CaL(log _1,0,1=0,75±0,03); FeL(log _1,0,1=4,20±0,04). Die Protonierungskonstanten von Aminoacetat, die bei den gewählten experimentellen Bedingungen nicht bekannt sind, wurden mittels E.M.K. Messungen (mit Wasserstoff-Elektrode) bestimmt.