Formation Of Mixed-ligand Complexes Research Articles

Mixed-ligand complex-formation of (2,2?,2?-terpyridine) copper(II) with monosubstituted phenolates

The copper(II)-phenolate oxygen interaction in several mixed-ligand complexes of copper(II) containing a 2,2′,2″-terpyridyl and a phenolate has been studied by i.r., electronic, e.p.r. spectroscopies and conductometric and polarographic measurements. Electronic spectral results demonstrate the dependence of such interaction on the nature of the phenol as well as the solvent. Partial dissociation of the phenolate from the complex was detected in methanol at low concentrations (≤1×10−4M). In dimethyl sulphoxide the complexes remain intact. The X-band e.p.r. spectral data obtained at ambient temperature and at 77 K are consistent with the results from the electronic spectral and conductometric study.

Thermodynamics of the homogeneous oxidation of L-ascorbic acid by molecular oxygen catalyzed by ruthenium ion and ruthenium chelates

The homogeneous oxidation of ascorbic acid by molecular oxygen catalyzed by RuCl 2(H 2O) 4 +, Ru(III)-IMDA and Ru(III)-EDTA has been investigated in the temperature range 278 – 308 K, μ = 0.1 M KNO 3. The rate of oxidation of ascorbic acid in the presence of RuCl 2(H 2O) 4 + was found to be first order in RuCl 2(H 2O) 4 + and ascorbate concentrations and one-half order in molecular oxygen concentration. Based on the kinetic parameters, a μ-peroxoruthenium(IV)-ascorbate complex was suggested as an active intermediate in the RuCl 2(H 2O) 4 +-catalyzed oxidation of ascorbic acid by molecular oxygen. The thermodynamic parameters corresponding to the formation of the μ-peroxoruthenium(IV)-ascorbate complex and the formation of various mixed ligand complexes with ascorbic acid were computed. The activation parameters for the oxidation steps corresponding to the rate constants were also calculated. The rate of oxidation of ascorbic acid in the presence of Ru(III) chelates was found to depend only on the metal chelate and ascorbate concentrations and was independent of the concentration of molecular oxygen. A mixed ligand complex of Ru(III)-EDTA and Ru(III)-IMDA with ascorbic acid is proposed as an active intermediate for electron transfer to the metal ion. The reduced metal ion is reoxidized in a fast step by molecular oxygen. As in the case of Fe(III) and Cu(II) aminopolycarboxylic acid chelate-catalyzed oxidation of ascorbic acid, the Ru(III)-IMDA and Ru(III)-EDTA chelates act as oxidase models in the oxidation of ascorbic acid by molecular oxygen. The thermodynamic parameters are discussed in terms of the oxidation potentials E 1 2 of the metal complexes.

TcNBr 4− pCl p] − ( p = 1–3) nitridotechnetate(VI) mixed-ligand complexes. An EPR study

The formation of mixed-ligand complexes of the type [TcNBr 4− p Cl p] − ( p = 1–3) during the reaction between TcNBr 4 − and TcNCl 4 − is reported. Evidence of the individual mixed-ligand compounds is given by their EPR spectral data. In liquid as well as in frozen solution, a strong dependence of the EPR quantities on the composition of the coordination sphere could be detected. This is shown by a nearly linear dependence of g 0, g∥, a 0 Tc and A∥ Tc on the spin-orbit coupling constants of the equatorial donors.

Mixed ligand complexes of lanthanides with macrocyclic and open-chained polyaminopolycarboxylic acids and acetylacetone

Studies of mixed ligand complex formation stabilities and dissociation kinetics have been performed on lanthanide ions with macrocyclic and open- chained polyaminopolycarboxylic acids ( i.e. DAPDA, DACDA, EDDA, and EDTA) and acetylacetone (acac). From UV spectroscopic evidence, it was found that Ln(DACDA) + and Ln(EDTA) − complexes do not form mixed ligand complexes with acac under the set conditions, i.e. pH = 7.2 and complex concentration of 1 x 10 −4 M. On the other hand, formation of Ln(DAPDA)(acac) and Ln(EDDA)(acac) 2 − complexes were readily detectable. The mixed complex forma- tion constants,β 1, for the equilibrium Ln(L) + + acac − ⇌ Ln(L)(acac), and β 2, for the equilibrium Ln(L) + + 2 acac − ⇌ Ln(L)(acac) 2 − were determined by potentiometric titration technique where possible. It was found that β 1 values were in general greater for Ln(EDDA) + complexes than for Ln(DAPDA) + complexes indicating the resulting reduced charge density at the lanthanide ion of Ln(DAPDA) + and that less space is available for the acetylacetone moiety to coordinate to the Ln(DAPDA) + complexes due to the large size and the greater number of coordination atoms of DAPDA. The hydrolysis constants of Ln(EDDA)(H 2O) n + species were also determined and were found to be increasing with increasing atomic number of Ln. Attempts to measure the acid assisted mixed ligand complex dissociation rates by a stopped-flow spectrophotometer were not fruitful due to the much faster rates.

Potentiometric studies on complexes in Cr(III)-l-aspartic acid-dl-methionine or dl-ethionine systems

Simple and mixed-ligand complexes of Cr(III) with l-aspartic acid and dl-methionine or dl-ethionine have been investigated by potentiometric measurements at 25°C and 0.1 M (NaClO4) ionic strength. The stability constants of the complexes and tendency toward mixed-ligand complex formation have been determined.

Potentiometric studies on mixed-ligand complexes of Cr(III) with dl-methionine, dl-ethionine and other amino acids

Binary and ternary complexes of Cr(III) with amino acids have been investigated by the potentiometric method using a glass electrode in the Cr(III)-A-B-H2O systems, where A  dl-methionine or dl-ethionine, and B  l-glutamic acid, dl-α-amino-n-butyric acid, l-serine or l-threonine. The stability constants of the complexes and a tendency toward mixed-ligand complex formation have been determined.

Potentiometric study of mixed ligand complex formation in the copper(II)-salicylate-mono, DI-, and triethanolamine systems

Etude de la formation. Evaluation des constantes de stabilite. Les ethanolamines agissent comme coordinats multidentes par les groupes amino et OH

Effects of mixed-ligand complex formation on deprotonation of amide groups in acid amides and peptides

The stability constants of the parent complexes of the A ligands glycinamide, glycylglycinamide, and N-acetylhistidine with copper(II), and of the mixed complexes formed with the B ligands glycine, 2,3-diaminopropionic acid, tiron, histamine, L-histidine, and 2,2′-bipyridyl, have been determined from pH-metric measurements. It has been found that glycinamide forms mixed-ligand complexes of composition [CuAB] and [CuABH–1](charges omitted), and most favourably with histamine, L-histidine, or 2,2′-bipyridyl. In the glycylglycinamide complexes of type [CuABH–1] the B ligand is co-ordinated to a considerable extent via two equatorial sites, while the bonding in the complex [CuABH–2], similarly to the other dipeptides, is mainly axial–equatorial. In the parent complexes of copper(II) with N-acetylhistidine and with N-acetylhistamine, deprotonation and co-ordination of the amide group could not be detected. It has been found, however, that the presence of B ligands containing an aromatic N donor permits deprotonation of the amide groups in both N-acetylhistidine and N-acetylhistamine.

Mixed-ligand complex formation of (2,2?,2?-terpyridine)copper(I) and (2,2?2?-terpyridine)copper(II) with some sulfur-containing amino acids

Mixed-ligand complex formation of copper(I) with 2,2′,2″-terpyridine (terpy) and various biologically significant sulfurcontaining amino acids, L′ [L′ = cysteine, penicillamine,N-acetylcysteine andN-acetylpenicillamine] was investigated. WithN-acetylcysteine andN-acetylpenicillamine, copper(I) complexes [Cu(terpy)L′]HCl have been isolated and characterised. The amino acid in each case bonds to the copper(I) through the sulfur atom only. These complexes are readily oxidised to the corresponding copper(II) complexes which contain a CuII-S(mercaptide) bond as demonstrated by the π(S)→CuII LMCT at 420 nm. The e.p.r. and electronic spectroscopic results are consistent with a distorted octahedral structure. Reactions of copper(I) with terpy and cysteine/ penicillamine in weakly acidic medium produce complexes containing two different copper(II) centres. From a strongly acidic medium, a binary copper(I) terpyridine complex is obtained instead and is shown from i.r. spectral absorptions to contain a protonated pyridyl ring.

Comparative study of hydroxo-fluoro and hydroxo-sulphido mixed ligand complexes of aluminum(III) and gallium(III)

The mixed ligand complex formation had been studied in the aluminate-fluoride, gallate-fluoride, aluminate-sulphide and gallate-sulphide systems by spectrophotometric as well as potentiometric methods using glass and sulphide selective electrodes. The formation of the species Al(OH) 3F − and Ga(OH) 2S − has been demonstrated and the equilibrium constants have been determined. Similar interaction could not be detected in the aluminate-sulphide and gallate-fluoride systems. The differences in behaviour of the metal ions to the characteristically hard fluoride and soft sulphide ligands can be interpreted in that the Ga 3+ ion may form complexes with charged soft ligands too, its behaviour then differing from that of the typically hard Al 3+ ion.

Simple and mixed ligand complexes of copper(II) with polyfunctional phenolic compounds as models of natural substances

In order to analyse metal complexation with polyfunctional phenolic compounds as ligand models of natural substances, a detailed examination is described for five simple binary complexes and three ternary mixed ligand complexes at 25°C (μ = 0.1 M NaClO 4). The ligands are tyrosine, 4,5-dihydroxy-1,3-benzene disulfonic acid, disodium salt (tiron), 3,4-dihydroxycinnamic acid (caffeic acid), 3,4,5-trihydroxy-1 -cyclohexene-1 -carboxylic acid (shikimic acid) and 1,3,4,5-tetrahydroxycyclohexanecarboxylic acid 3-(3,4-dihydroxycinnamate) (chlorogenic acid). The ternary systems are Cu(II)/H qA/tiron, where H qA is tyrosine, caffeic or chlorogenic acids. Potentiometric data were used successively to evaluate the protonation of each individual ligand, to detect simple and mixed complexes (including protonated species) and to determine their stability constants (a set of 33 values of constants with several original data is provided). The calculated distribution (speciation) of each species as a function of pH is indicated. Mixed coordination enhances the stability of complexes and the stabilization is expressed in terms of various parameters. The results emphasize that mixed ligand complex formation is essential to studies of multiple equilibria.

Mixed-ligand complex formation in the copper(II)-salicylate-ammonia and in the copper(II)-salicylate-pyridine systems

Mixed ligand complexation between Cu(ll) ion, salicylate ion (sal) and a nitrogen base which acts as unidentate ligand, pyridine (py) or ammonia, is studied potentiometrically at 25 °C and in 1.0 mole dm-3 ionic media (KN03 or NH4 N03 respectively). Experimental data are analysed using both Miniquad and Letagrop programs ; the performances of these programs are compared. Analysis of variance in the case of copper-ammonia complexation is performed. All the species present in solution in both systems are identified and their formation constants are evaluated. Distribution plots of the mixed complexes at several concentration ratios of their constituents are obtained. Stabilization of these mixed-ligand complexes. Cu(sal)(py)2 and Cu(sal)(NH3 )2 , is estimated and different stabilizing factors are discussed.

Equilibrium studies on the formation of mixed-ligand complexes in solution—Part IV

Formation of ternary complexes of copper(II) with thiodiglycolic acid as primary ligand(A) and glycine, α-alanine, β-alanine, serine, ethylenediamine or malonic acid as secondary ligand(B) have been investigated in aqueous solution at 30°C employing pH-metric and spectrophotometric methods. The overall formation constants of the mixed-ligand complexes have been evaluated and the relative stabilities of the complexes are compared and discussed in terms of statistical considerations, nature of the donor atoms, steric effects and charge neutralisation as also the distribution of the different complex species present in the solution as a function of pH.

Polarographic study of simple and mixed-ligand complex formation

Theoretical, experimental and statistical aspects of the polarographic method applied to simple and mixed-ligand complex formation have been studied. Some misunderstandings and erroneous interpretations have been clarified according to experimental results obtained with several systems. A criterion for establishing the number of complex species present in a simple system is proposed. For the first time the polarographic method has been applied to a mixed-ligand complex system where fourteen species co-exist.

Potentiometric investigation mixed ligand complexes of Ni(II) with DL-methionine and Dl-ethionine in aqueous solution

The formation of mixed ligand complexes of Ni(II) with DL-methionine in aqueous solution was investigated. The composition and stability constants of the complexes were determined by the potentiometric method.

Formation of mixed-ligand complexes of cadmium(II) with chloride and substituted pyridines in 1,2-dichloroethane as solvent

Formation of mixed-ligand complexes of cadmium(II) with chloride and substituted pyridines in 1,2-dichloroethane as solvent

ChemInform Abstract: STUDIES ON TRANSITION METAL‐PEPTIDE COMPLEXES. PART 8. PARENT AND MIXED‐LIGAND COMPLEXES OF HISTIDINE‐CONTAINING DIPEPTIDES

AbstractSpektrophotometrische, pH‐metri ‐ sche und teilweise 13C‐NMR‐spektroskopische Untersuchungen der Komplexe von Co(II), Ni(Il) und Zn(II) mit Gly‐L‐His, L‐His‐Gly und L‐Camosin zeigen die unterschiedliche Art der Koordination und die dadurch bedingte Bildung verschiedener Gemischt‐ligand‐Komplexe mit Gly, Gly‐Gly, His und 2,2′‐Bipyridyl als zweitem Liganden.

Polarographic studies on ternary complexes of copper(II) involving amino acids

Polarographic investigations have been carried out on the mixed-ligand complex formation of copper(II) with oxalate/ethylenediamine and one of the amino acids glycine, α-alanine, β-alanine and valine at 303 K and ionic strength of 0.3 M (KNO 3). Diffusion controlled reversible waves are obtained in each case. The values of stability constants for mixed ligand complexes and the reproportionation constant (log X) for the reactions Cu(Ox/En) 2 + Cu(Aa) 2 ⇌ 2 Cu(Ox/En)(Aa) have been evaluated and discussed in terms of statistical, electrostatic and steric effects.

Polarographic Study of Mixed Ligand (o-Mercaptobenzoate–Citrate) Complexes of Cadmium(II), Lead(II), and Thallium(I)

Abstract The mixed ligand complex formation of o-mercaptobenzoic acid and citric acid with Cd(II), Pb(II), and Tl(I) in aqueous KNO3 (μ=1.0 mol dm−3) solutions containing Triton X-100 (0.001%) has been investigated by polarography. It was shown that only one mixed ligand entity MAiXj is formed, where i is two for Cd (II) and one for Tl(I) j is one for all complexes and A and X are the o-mercaptobenzoate and citrate ligands respectively. The stability constants have been evaluated.

COORDINATION OF 8-QUINOLINOL-5-SULFONIC ACID TO ALUMINIUM(III) COMPLEXES OF 8-HYDROXY-7- [(6 ' -SULFO-2 ' -NAPHTHYL)AZO]-QUINOLINE-5-SULFONATE. EVIDENCE FOR MIXED LIGAND COMPLEX FORMATION

Abstract Studies have been made on the coordination behaviour of the aluminium(III) 8-quinolinol-5-sulfonate (hqs)1 and aluminium(III) nqs1 complexes2 with hqs in 0.1 mol dm−2 aqueous sodium chloride solution at 25°. Mixed-ligand complex formation was evidenced by electronic absorption spectral and other spectrophotometric equilibrium studies. Stopped-flow kinetic studies revealed that mixed-ligand complex formation with a mono-nqs complex proceeds via its reaction with Hhqs− and hqs2- whereas formation of the tris-hqs complex proceeds via the reaction of [Al(H2O)6]3+ with Hhqs− and hqs2- and also of [Al(OH)(H2O)5]2+ with H2 hqs and Hhqs−. Coordination mechanisms and structures for the mixed-ligand and the tris-hqs complexes are also discussed.