Studies on 1,2-Bis(O-Aminophenoxy)Ethane-N,N,N′,N′;-Tetraacetic Acid Chelates of the Tripositive Lanthanide Ions

The acid dissociation constants of 1,2-bis(cis-aminophenoxy)ethane-N,N,N′,N′;-tetraacetic acid (H₄BAPAT or H₄Z), and the stability constants of its chelates with tripositive rare-earth metal ions have been determined by the potentiometric titration and mercury indicator electrode methods at 15°, 25′ and 35°C and an ionic strength of 0.1 (KNO₃). The existence of a monohydrogen chelate species, LnHZ, and the normal chelate, LnZ^?, is illustrated. Enthalpy and entropy changes characterizing the formation of the normal chelates and the dissociation of the last two protons of chelating acid have been calculated at 25°C. These functions have been compared with corresponding values for related chelating agents.     

A novel methodology for evaluation of formation constants of complexes: example of lanthanide-Arsenazo III complexes

A novel method is proposed for the computation of formation constants of complexes. It makes use essentially of the data from the first stages of the titration and is based on the Taylor expansion of the concentration of the ligand as a function of the titrant concentration. The applicability of the methodology is examplified by the computation of the complexation constants of lanthanides (Ln) by 3,6-bis[(2-arsonophenyl)azo]-4,5-dihydroxy-2,7-naphtalenedisulphonic acid disodium salt (Arsenazo III). Arsenazo III is known to form stable complexes with a large variety of ions. The spectrophotometric study of these complexes in the visible domain is facilitated by the presence of chromophore groups in the ligand. In the present work, spectral deconvolution was used to improve the accuracy in the determination of formation constants of complexes between Arsenazo III and lanthanides. It turns out that all the 11 lanthanides studied here form the same type of complexes with this ligand. For each of them, the three formation constants correspond, respectively, to Ln to Ar ratios 1:1, 1:2 and 2:2. Their approximate values are in the ranges: K₁₁=10⁵; K₁₂=10¹⁰; K₂₂=10¹⁵. Accurate values are given in the text. The results are compared with those obtained with the classical iteration method which makes use of the whole titration curve. The two techniques give satisfactorily convergent results. The new methodology might be useful in the treatment of the competition of two ligands for the complexation of the same lanthanide, where the first stages of the titration of only one of the complexants is experimentally available.     

Determination of dissociation constants for coordination compounds of Cr(III) and Co(III) using potentiometric and spectrophotometric methods

The acid–base properties of analogous complex ions of chromium(III) and cobalt(III) in aqueous solution have been studied. The equilibrium constants for all metal complexes were determined by using potentiometric and spectrophotometric titration methods. First, dissociation constants for the studied complexes of Cr(III) and Co(III) were determined by means of the potentiometric titration method and using the STOICHIO computer programme. Then, pH-spectrophotometric titrations were performed and the OriginPro 7.5 computer programme was used to calculate the same constants. The measurements using both methods were carried out under the same conditions of temperature, T = 298.15 K, and over the same pH range 2.00–10.00, respectively. It turned out that the two methods used enabled us to obtain acidity constants in very good agreement.     

Stoichiometries and stability constants for the cerium(IV) carbonate complexes in dilute aqueous solution

Complexation between cerium(IV) and carbonate ions in aqueous solution has been studied by UV/Visible absorption spectroscopy, ¹⁷O NMR spectroscopy and potentiometric titration, and it is shown that in dilute solutions at pH 8.8 and 10, both 1?:?1 and 1?:?2 (metal?:?ligand) complexes are formed. This contrasts with the behaviour of the corresponding Th(IV) complex, where the dominant species is the pentacarbonato complex. From the NMR spectra, it is suggested that these species involve bidentate binding of carbonate ion by the metal, while potentiometric data provided accurate formation constants and indicated the dominant species to be the 1?:?2 complex.     

Pb(II) and Bi(III) complexes involving a Schiff base ligand: syntheses,structures, physical,and antioxidant properties

Two new complexes, {[PbL(NO₃)₂H₂O]H₂O}_n (1) and [BiL₂(NO₃)₂]NO₃ (2), based on (E)-3-chloro-6-[2-(pyrazin-2-ylmethylene)hydrazinyl]pyridazine (L) were synthesized and characterized by IR spectra, single-crystal X-ray diffraction, and elemental analyzes. X-ray single crystal diffraction experiments of 1 and 2 display that extensive hydrogen bonds and π…π stacking interactions construct the 1-D infinite chain {[PbL(NO₃)₂H₂O]H₂O}_n and [BiL₂(NO₃)₂]NO₃ into two 3-D supramolecular frameworks. Interestingly, pure phase PbO nano-particles were synthesized by thermolysis of 1 and characterized by scanning electron microscopy and X-ray powder diffraction analyzes. Furthermore, antioxidant activities of L, 1, and 2 were also studied.     

Synthesis,structural, photophysical and thermal properties of some praseodymium(III) complexes

Some carboxylato-bridged praseodymium(III) complexes (1–5) having tp [hydrotris(pyrazol-1-yl)borate] and sodium p-X-benzoate (where X =?H, F, Cl, NO₂) have been synthesized and characterized by different techniques including X-ray crystallography. The X-ray studies demonstrated that 1, 3 and 5 crystallized in triclinic space group P 1 with cell dimensions a =?11.761(13) Å, b =?12.536(13) Å, c =?17.726(19) Å for 1, a =?9.309(8) Å, b =?12.667(11) Å, c =?14.421(12) Å for 3, a =?11.5688(9) Å, b =?12.0055(9) Å, c =?12.3005(10) Å for 5. In 1–4 the coordination number of praseodymium is seven, whereas in 5 it is eight. IR suggested that the benzoate groups in 1–5 are bidentate bridging. The photophysical properties of these complexes have been studied in solution at room temperature. Thermogravimetric analysis showed that these complexes undergo complete decomposition with formation of praseodymium oxide.     

Synthesis and characterization of dinuclear (Hedta)Ru(III) complexes with N-heterocyclic ligands: magnetic properties and DNA-binding studies

Two ruthenium(III) complexes containing ethylenediaminetetraacetate(edta), viz. [{Ru(Hedta)}₂L]·xH₂O L = 4,4′-bipyridine(bpy) (1) and 4,4′-azopyridine(Azpy) (2), have been synthesized by the reaction between K[Ru(Hedta)Cl]·1.5H₂O and the corresponding N-heterocycles. Complex 1 was determined by single-crystal X-ray diffraction. The products were characterized by IR, UV–vis, cyclic voltammetry, and magnetic techniques. Their DNA-binding activities were investigated using electronic absorption spectroscopic methods and ?uorescence quenching; the experimental results show that these two ruthenium complexes may bind to CT-DNA through intercalation modes.     

Dy(III) complexes of metformin Schiff-bases as glucose probe: synthesis,spectral, and thermal properties

Complexes of Dy³⁺ with metformin-Schiff-bases of salicylaldehyde (HL¹); 2,3-dihydroxybenzaldehyde (H₂L²); 2,4-dihydroxybenzaldehyde (H₂L³); 2,5-dihydroxybenzaldehyde (H₂L⁴); 3,4-dihydroxybenzaldehyde (H₂L⁵); and 2-hydroxynaphthaldehyde (HL⁶) were synthesized by template reactions. The new compounds were characterized through elemental analysis, conductivity and magnetic moment measurements, IR, UV–vis, fluorescence, GC–MS, and XRD spectroscopies. The complexes are seven coordinate with formulas [DyL^1–4,6(NO₃)₂(H₂O)₂]·nH₂O where n?=?2, 2½, 4, 2, 2 and [DyL⁵(NO₃)(H₂O)₄]·2H₂O. TGA, DTG, and DTA analyses confirmed the suggested stereochemistry and subsequently the proposed mechanism of thermal decomposition. Kinetic and thermodynamic parameters were calculated for the second decomposition step. Thus, we report the ability of using the prepared complexes in the detection of glucose at physiological conditions using UV–vis and fluorescence spectroscopy as well as viscosity measurements, where the association constants were calculated.

     

Equilibrium and spectral studies of putrescine complexes with copper(II)

Summary It has been found that in the putrescine-copper system several types of complex compounds (MHL,ML,ML ₂,ML ₂OH) are formed. In thepH range of 7–9, despite a multiple excess of ligand, a precipitation occurs. When adenosine is introduced to the system, the ability to observe the complexation reaction in solution is largely increased, because the additional ligand prevents precipitation. On the basis of computer analysis of potentiometric titration data the stability constants of the compounds have been determined. The coordination mode of the complexes is discussed.

---

Gleichgewichte und spektroskopische Untersuchungen an Putrescin-Komplexen mit Kupfer(II)

Zusammenfassung Es wurde festgestellt, daß sich im Putrescin-Kupfer System einige Typen von Komplexen bilden (MHL,ML,ML ₂ andML ₂OH). ImpH-Bereich von 7–9 tritt trotz eines mehrfachen Ligandenüberschusses ein Niederschlag auf. Bei Einführung von Adenosin in das System wird die Beobachtbarkeit der Komplexreaktion verbessert, da der zusätzliche Ligand die Niederschlagsbildung verhindert. Mittels Computeranalyse der potentiometrischen Titrationsdaten wurden die Stabilitätskonstanten der Verbindungen ermittelt. Die Art der Komplexierung wird ebenfalls diskutiert.

     

Synthesis,spectral and thermal properties of poly(2-hydroxy-4-methacryloyloxybenzaldehyde)-metal complexes

2-Hydroxy-4-methacryloyloxybenzaldehyde (2H4MBA), prepared from methacryloyl chloride and 2,4-dihydroxybenzaldehyde, was polymerized in methyl ethyl ketone at 70°C using benzoyl peroxide as a free radical initiator. Polychelates were obtained from N,N-dimethylformamide solutions of poly(2H4MBA) on addition of aqueous solutions of Cu(II)/Ni(II) ions. The polymers and polychelates were characterized by elemental analyses and spectral studies. The IR spectra of these polychelates suggest that metals are coordinated through the oxygen of the aldehyde group and oxygen of the phenolic—OH group. The electronic spectra, EPR, and magnetic moments of polychelates showed an octahedral and square planar structure for poly(2H4MBA)-Ni(II) and poly(2H4MBA)-Cu(II) complexes, respectively. X-ray diffraction studies reveal that the polychelates are highly crystalline. The thermal properties of polymer-metal complexes and their catalytic activity are discussed. © 1996 John Wiley & Sons, Inc.     

Synthesis,spectral and thermal properties of macrocyclic zinc(II) complexes

The new zinc ternary complexes [Zn(cyclen)NO₃]ClO4 (I), [Zn₂(cyclen)₂(m-nic)](ClO₄)₃ (II), [Zn₂(cyclen)₂(m-pic)](ClO₄)₃ (III) (cyclen=1,4,7,10-tetraazacyclododecane; nic=nicotinic acid; pic=picolinic acid) were synthesized and their spectral and thermal properties were investigated. The compounds were characterized by elemental analysis, IR spectroscopy and TG/DTG, DTA methods. Moreover, the way of coordination of pyridinecarboxylate anions was proposed on the basis of the spectral data and consequently proved with results of X-ray structure analysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reflections on the calculation and publication of potentiometrically-determined formation constants

Calculation and reporting procedures are described, which aim to improve the quality and comparability of published formation constant values obtained by glass-electrode potentiometry. Ways in which the processing of data by computer optimization programs can be standardized are the main concern, particularly in respect of improving the usefulness of equilibrium data through incorporation into large publically available databases. These recommendations may be particularly valuable to researchers beginning in this field as well as to those who determine formation constants only occasionally.     

Metal ions-purine interactions: Dichloro-gold(III) complexes of some theophylline derivatives

Complexes with the general formula AuLCl₂, whereL are the deprotonated forms of theophylline, 1,3,8-trimetylxanthine, 8-ethyl-theophylline, 8-isopropyl-theophylline and 8-pentyl-theophylline, have been synthesized and characterized by spectral (IR and¹H-NMR) and thermal methods (TG and DSC). Experimental data suggest that all of them present a polymeric structure, in which the corresponding theophylline derivative acts as a monoanion, bonding to contiguous Au(III) ions through both imidazole nitrogen atoms. The structure of the monomer seems be square-planar, with the chlorine atoms linked to metal ion intrans positions.

---

Wechselwirkungen zwischen Metall-Ionen und Purin: Dichlorgold(III)-Komplexe einiger Theophyllin-Derivate

Zusammenfassung Es wurden Komplexe der generellen Formel AuLCl₂ (wobeiL jeweils die deprotonierten Formen von Theophyllin, 1,3,8-Trimethylxanthin, 8-Ethyltheophyllin, 8-Isopropyltheophyllin und 8-Pentyltheophyllin sind) hergestellt und mittels spektroskopischer (IR,¹H-NMR) und thermischer Methoden (TG, DSC) charakterisiert. Die experimentellen Daten legen nahe, daß alle Komplexe eine polymere Struktur aufweisen, wobei die entsprechenden Theophyllin-Derivate als Monoanionen wirken, die an die benachbarten Au(III)-Ionen über beide Imidazol-Stickstoffatome gebunden sind. Die Struktur der Monomeren scheint quadratisch-planar zu sein, wobei die Chloratome intrans-Positionen an das Metall-Ion gebunden sind.

     

Synthesis and characterization of 3-amino-5-methylisoxazole Schiff bases and their complexes with copper(II), nickel(II) and cobalt(II)

Schiff bases obtained by condensing 3-amino-5-methylisoxazole with salicylaldehyde, 2,3-dihydroxybenzaldehyde, 2,4-dihydroxy-benzaldehyde, 2,5-dihydroxybenzaldehyde or o-hydroxynaphthaldehyde were obtained and characterized by C, H, N analysis, mass, NMR and IR spectra. Copper, nickel and cobalt complexes of the Schiff bases were prepared and characterized using elemental analysis, conductivity measurements, magnetic moments, IR, UV-VIS and ESR spectra, X-ray diffraction, TGA, DTA and DSC thermal analysis. All the complexes are non-electrolytes. ESR spectra show isotropic as well as axial symmetry for the copper complexes. Thermal studies support the formulation of these complexes and showed that they decompose in two or three steps depending on the metal used. Activation energy E _a and enthalpies ΔH associated with the decomposition process were calculated and correlated with the complexed metal used.     

Complex formation studies on Ho(III) and Lu(III) with 1-(2-pyridylazo)-2-naphthol (PAN) in alcohol-water solutions

The formation ofPAN complexes in the systemsLn(III)—PAN—alcohol-water (where:Ln(III)=Ho, Lu and alcohol=ethanol,n-propanol,iso-propanol) was investigated by a spectrophotometric method. Equilibrium constants for the reactionLn ³⁺ + HLLnL ²⁺ + H⁺ (HL=PAN) and stability constants of complexesLnL ²⁺ were calculated.

---

Untersuchungen zur Komplexbildung von Ho(III) und Lu(III) mit 1-(2-Pyridylazo)-2-naphthol (PAN) in alkoholisch-;wä\rigen Lösungen

Zusammenfassung Die Bildung der Komplexe vonPAN in den SystemenLn(III)—PAN—Alkohol-Wasser (Ln(III)=Ho, Lu; Alkohol=Ethanol,n-Propanol,iso-Propanol) wurde mit einer spektrophotometrischen Methode untersucht. Die Gleichgewichtskonstanten der ReaktionenLn ³⁺ + HLLnL ²⁺ + H⁺ (HL==PAN) und die Stabilitätskonstanten der KomplexeLnL ²⁺ wurden berechnet.

     

Synthesis,characterization and biological activity of triaminoxime and its metal complexes

Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes of multifunctional triaminoxime have been synthesized and characterized by elemental analyses, IR, UV–Vis spectra, magnetic moments, ¹H- and ¹³C-NMR spectra for ligand and its Ni(II) complex, mass spectra, molar conductances, thermal analyses (DTA, DTG and TG) and ESR measurements. The IR spectral data show that the ligand is bi-basic or tri-basic tetradentate towards the metals. Molar conductances in DMF indicate that the complexes are non-electrolytes. The ESR spectra of solid copper(II) complexes [(HL)(Cu)₂(Cl)₂] · 2H₂O (2) and [(L)(Cu)₃(OH)₃(H₂O)₆] · 7H₂O (6) show axial symmetry of a d _{x²???y ²} ground state; however, [(HL)(Co)] (4) shows an axial type with d _Z ² ground state and manganese(II) complex [(L)(Mn)₃(OH)₃(H₂O)6] · 4H₂O (10) shows an isotropic type. The biological activity of the ligand and its metal complexes are discussed.     

Potentiometric and spectral studies of complex formation of La(III), Pr(III) and Lu(III) with aspartic acid and asparagine

The composition and stability of La³⁺, Pr³⁺ and Lu³⁺ complexes with aspartic acid and asparagine were analysed. The formation of complexes of the typeML andMHL was determined for La³⁺ and Pr³⁺ with aspartic acid, and of the typeMHL for Lu³⁺ with aspartic acid. For La³⁺, Pr³⁺ and Lu³⁺ with asparagine the formation ofML(OH) complexes was observed. By means of¹H NMR and¹³C NMR studies the participation in the coordination of both -COOH groups was determined for aspartic acid, whereas for asparagine the participation of the -COOH group was determined in complexes with La³⁺, Pr³⁺, and of the -COOH and the -NH₂ groups in the complex with Lu³⁺.

---

Potentiometrische und spektroskopische Untersuchungen an La(III), Pr(III) und Lu(III)-Komplexen von Asparaginsäure und Asparagin

Zusammenfassung Die Zusammensetzung und die Stabilität von La³⁺, Pr³⁺ und Lu³⁺-Komplexen mit Asparaginsäure und Asparagin wurden untersucht. Es wurde die Bildung von La³⁺ und Pr³⁺-Komplexen des TypsML undMHL, und ein Lu³⁺-Komplex des TypsMHL mit Asparaginsäure festgestellt. Für diese drei Lanthaniden wurde auch die Bildung von Komplexen des TypsML(OH) mit Asparagin beobachtet. Mit Hilfe von¹H-NMR und¹³C-NMR-Untersuchungen wurde für Asparaginsäure die Teilnahme der beiden -COOH-Gruppen, für Asparagin die Teilnahme der -COOH-Gruppe in den Komplexen mit La³⁺, Pr³⁺ und der-COOH und -NH₂-Gruppen in dem Komplex mit Lu³⁺ an der Koordinierung festgestellt.

     

Influence of poly (ethylene glycol) on the thermal, mechanical, morphological, physical-chemical and biodegradation properties of poly (3-hydroxybutyrate)

Blends of poly (3-hydroxybutyrate) (PHB) with poly (ethylene glycol) (PEG), (PHB/PEG), in different proportions of 100/0, 98/2, 95/5, 90/10, 80/20 and 60/40 wt%, respectively, were investigated for their thermal properties (using differential scanning calorimetry and thermogravimetric analysis), tensile properties, water vapor transmission rate, enzymatic biodegradation (using light microscopy) and mass retention. The addition of plasticizer did not alter the thermal stability of the blends, although an increase in the PEG content reduced the tensile strength and increased the elongation at break of pure PHB.     

Kinetics of thermal decomposition of iron(III) dicarboxylate complexes

Summary Tris(dicarboxylate) complexes of iron(III) with oxalate, maleate, malonate and phthalate viz. K₃[Fe(C₂O₄)₃]×3H₂O (1), K₃[Fe(OOCCH₂COO)₃]×3H₂O (2), K₃[Fe(OOCCH=CHCOO)₃]×3H₂O (3), K₃[Fe(OOC-1,2-(C₆H₄)-COO)₃]×3H₂O (4) have been synthesized and characterized using a combination of physicochemical techniques. The thermal decomposition behaviour of these complexes have been investigated under dynamic air atmosphere upto 800 K. All these complexes undergo a three-step dehydration/decomposition process for which the kinetic parameters have been calculated using Freeman-Carrol model as well as using different mechanistic models of the solid-state reactions. The trisoxalato and trismalonato ferrate(III) complexes undergo rapid dehydration at lower temperature below 470 K. At moderately higher temperatures (i.e. >600 and 500 K, respectively) they formed bis chelate iron(III) complexes. The trismalonato and trismaleato complexes dehydrate with almost equal ease but the latter is much less stable to decomposition and yields FeCO₃ below 760 K. The cis-dicarboxylate complexes particularly with maleate(2-) and phthalate(2-) ligands are highly prone to the loss of cyclic anhydrides at moderately raised temperatures. The thermal decomposition of the tris(dicarboxylato)iron(II) to iron oxide was not observed in the investigated temperature range up to 800 K. The dehydration processes generally followed the first or second order mechanism while the third decomposition steps followed either three-dimensional diffusion or contracting volume mechanism.