Stability Of Mixed-ligand Complexes Research Articles

Synthesis, structure and thermal behavior of volatile mononuclear mixed ligand complexes of rare-earth dipivaloylmethanates with diethylenetriamine

Highly volatile and stable complexes of rare-earth elements with mononuclear structure are of great importance for gas phase deposition of functional thin film materials. Mixed ligand complexes with β-diketonate anions (e.g. thd− = 2,2,6,6-tetrametylheptane-3,5-dionate) and ancillary neutral donor ligands demonstrate mononuclear structure and sufficient volatility, however, they are unstable to neutral ligand elimination especially in case of light rare earth elements. Here diethylenetriamine (deta) has been applied as tridentate neutral ligand to improve the stability of mixed ligand complexes due to macrochelate effect and additional weak intramolecular interactions, e.g. hydrogen bonds. Synthesis of a series of mixed-ligand [Ln(thd)3(deta)], Ln = La (1L), Pr (2L), Nd (3L), Sm (4L) and Gd (5L) complexes, their X-ray single crystal structure characterization, DFT calculations, and thermal behavior study have been performed. Compounds 1L-5L demonstrate similar mononuclear molecular structure, but different molecular packing of three types, which may undergo mutual transformation. Compounds 1L-4L sublime intact in temperature range of 140–160 °C in vacuum without decomposition. 1L was successfully applied as volatile precursors for MOCVD preparation of epitaxial complex oxide thin films, (0 0 l) LaMnO3 and (0 0 l) LaAlO3, on (0 0 l) MgO and (0 0 l) SrTiO3 substrates.

Potentiometric, Thermodynamics and Coordination Properties for Binary and Mixed Ligand Complexes of Copper(II) with Imidazole-4-acetic Acid and Tryptophan or Phenylalanine Aromatic Amino Acids

Binary and ternary complex formation equilibria of copper(II) with imidazole-4-acetic acid (IMA) and some aromatic amino acids such as tryptophan and phenylalanine have been studied from 15 to 45 °C by potentiometric titration. The pH-titrations of the reaction mixtures have shown 1:1:1 (Cu:IMA:amino acid) ternary complex formation. The stability of mixed-ligand complexes was quantitatively compared with the stability of the binary complexes as Δlog10 K, Δlog10 β and log10 X parameters. The speciation of different species in solution has been evaluated as a function of pH. The effect of temperature on protonation of the ligands and formation of mixed ligand complexes was investigated. Thermodynamic parameters were calculated and are discussed. The effect of solvent of the protonation of IMA and Cu–IMA complex formation was also investigated and discussed. Additionally, the stoichiometric protonation constants (log10 β) of imidazole-4-acetic acid and its binary Cu(II)–IMA complexes were determined potentiometrically over a wide range of solvent composition.

Geometry optimization and thermodynamic stabilities of mixed ligand complexes [Co(β-diketone)(L)(H2O)2

Geometry optimization and thermodynamic stabilities of mixed ligand complexes [Co(β-diketone)(L)(H2O)2

Morphological and pharmacological investigation on some biopotent materials derived from substituted pyrimidine and imidazole enzyme constituents

Coordinating behavior of novel N2O type mixed ligand complexes (1–6) have been synthesized from substituted fluoropyrimidine [5-Fluorouracil (5-FU; A)] with biopotent imidazole enzyme constituents (B) viz., imidazole(him) and benzimidazole(bim) in the presence of Ni(II), Cu(II) and Zn(II) ions. Synthesized complexes were characterized by chemical analysis, spectral studies, magnetic moment and conductivity measurements. The results of chemical analysis and the observed low molar conductance values propose their stoichiometry to be 1:1:1 (M:A:B) with non-electrolytic nature. From the spectral data, it is inferred that the ligands A & B coordinate with M(II) ions in bi and monodentate approach through C(4)O, N(3) and imidazole ring N(3) atoms respectively. The thermogravimetric analysis shows the dehydration, decomposition and thermal stability of mixed ligand complexes. XRD and SEM patterns show sharp crystalline peaks with homogeneous morphology. In vitro antimicrobial activities of free ligands (A & B) and their metal complexes were screened against some pathogenic strains by well diffusion technique. Absorption and gel electrophoresis experiments on the interaction of mixed ligand complexes with DNA suggest that all the complexes can bind as well as cleave the DNA by intercalation between chromophores and DNA base pairs. In addition, in vitro antioxidant activities were tested by DPPH free radical scavenging model.

Spectrophotometric and pH-metric studies on Pb(II), Cd(II), Al(III) and Cu(II) complexes of paracetamol and ascorbic acid

Spectrophotometric and pH-metric studies of the aqueous binary and mixed ligand complexes of Pb(II), Cd(II), Al(III) and Cu(II) were carried out with ascorbic acid and paracetamol. The study was conducted at an ionic strength of 0.15 mol dm-3 and a temperature of 37.0 ± 0.2 oC. The protonation constants of the free ligands and the stability constants of the binary and mixed ligand complexes were determined using pH titration data. Proton dissociation of free ligands and complex formation were also qualitatively confirmed with UV data. The stabilities of mixed ligand complexes were quantitatively compared with those of the corresponding single ligand complexes in terms of Δlog K. Aluminium formed the most stable binary complex; Al (paracetamol)2, with a high overall stability constant (log β2 = 16.74). The stable mixed ligand complexes; Pb (ascorbic acid) (paracetamol), Cd (ascorbic acid)(paracetamol) and Cu (ascorbic acid) (paracetamol) were observed with positive Δlog K values showing the ability of using them in less harmful chelation therapy of these metals. Further, the results revealed that the bioavailability of both ligands will be lower for a metal intoxicated person. J.Natn.Sci.Foundation Sri Lanka 2013 41 (4): 337-344 DOI: http://dx.doi.org/10.4038/jnsfsr.v41i4.6253

Features of Formation of Mixed-Ligand Complexes of Aluminum Tetraphenylporphine

Formation of extra complexes of aluminum tetraphenylporphine was studied by spectrophotometric titration. The effect of the nature of acido ligands on the stability of mixed-ligand complexes of aluminum tetraphenylporphine was determined. The stability constant (log Kst) of sterically unstrained complexes (Cl)Al(L)TPP and (OH)Al(L)TPP increases linearly with increasing basicity of the extra ligand (log KBH+); in the case of sterically distorted complexes (OAc)Al(L)TPP and (Acac)Al(L)TPP changes in log Kst and log KBH+ vary in the same direction. The geometries and energy characteristics of six-coordinate complexes of aluminum porphyrins were calculated quantum-chemically. The calculated enthalpies and Gibbs energies of formation of the complexes are consistent with the experiment. The possibility of the bidentate coordination of acetate and acetylacetonate in the porphyrin extra complexes was proved.

Potentiometrische Untersuchung der Bildungsgleichgewichte von bin�ren und tern�ren Komplexen von Kobalt(II) mit Adenosin-5?-mono-, -di- und -triphosphat und einigen biologisch bedeutenden polybasischen Sauerstoffs�uren

Potentiometric equilibrium measurements have been made for the interaction of adenosine-5′-mono-,-di-, and -triphosphate, and Co(II) with biologically important secondary ligands (malic, maleic, succinic, tartaric, citric, and oxalic acid). The formation of various 1:1:1 mixed ligand complexes inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP and the secondary ligand acids have been refined with a computer program. In some systems, the ternary complexes are found to be more stable than the corresponding binary ones. In some ternary systems studied, interligand interactions or some cooperativity between the coordinate ligands, possibly H bond formation, have been found to be most effective in deciding the stability of the complexes formed in solution. Stabilities of mixed ligand complexes increase in the orderAMP maleic > tartaric > malic > citric > oxalic acid.

Tern�re Komplexe in L�sung. Vergleich der Koordinationstendenz einiger biologisch wichtiger zwitterionischer Puffer an bin�re Komplexe von Cu(II) und Adenosin-5?-mono-, -5?-di- und-5?-triphosphat

Potentiometric equilibrium measurements have been made at 25.0±0.1 °C and ionic strengthI=0.1 mol dm−3 KNO3 for the interaction of adenosine 5′-mono-, 5′-di-, and 5′-triphosphate (AMP,ADP andATP) and Cu(II) with biologically important secondary ligand zwitterionic buffers (N,N-bis-(2-hydroxyethyl)-2-aminoethanesulphonic acid (BES), N-tris-(hydroxymethyl)-methyl-2-aminoethanesulphonic acid (TES), N,N-bis-(2-hydroxyethyl)-glycine (Bicine) andtris-(hydroxymethyl)-methylaminopropane sulphonic acid (TAPS)) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP, and secondary ligands have been refined with the SUPERQUAD computer program. Negative and positive Δ logK values were obtained for the ternary systems studied. In some Cu(II) ternary systems studied the interligand interactions or some cooperativity between the coordinate ligands, possibly H bond formation, has been found to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increase in the orderAMP Bicine>TES>BES.

Ternary complexes of nickel(II) withAMP,ADP andATP as primary ligands and some biologically important polybasic oxygen acids as secondary ligands

Potentiometric equilibrium measurements have been made at 25±0.1 °C (μ=0.1 mol dm−3 KNO3) for the interaction of adenosine-5′-mono-, -di-, and-triphosphate (AMP,ADP, andATP) and Ni(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP and secondary ligand acid, have been refined with SUPERQUAD computer program. In some systems Δ logK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. H-bond formation seems to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increases in the orderAMP maleic>tartaric>malic>citric>oxalic acid.

Ternary complexes in solution. Comparison of the coordination tendency of some polybasic oxygen acids toward the binary complexes of Cu(II) andAMP,ADP orATP

Potentiometric equilibrium measurements have been made at 25±0.1°C (μ=0.1 mol dm−3 KNO3) for the interaction of adenosine-5′-mono-, -di- and -triphosphate (AMP,ADP andATP) and Cu(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP, and secondary ligand acid, have been refined with the SUPERQUAD computer program. In some systems ΔlogK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. In some Cu(II) ternary systems the interligand interactions between the coordinate ligands, possibly H bond formation, have been found to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increase in the orderAMP maleic > tartaric > malic > citric > oxalic acid.

Stabilities of mixed ligand complexes of Cu(II) with ligands coordinating through O and N : ESR studies

Mixed ligand complexes of Cu(II) with 8-hydroxy-quinolinate (Hy) as one ligand and acetylacetonate (ac.ac) or salicylaldehydate (Sal) as the second ligand have been prepared in reaction mixtures of Cu(Hy)2 + Cu(ac.ac)2 and Cu(Hy)2 + Cu(Sal)2 in chloroform. Ligand hyperfine structures and the minimum ESR linewidth associated withm = − 3/2 hyperfine component have been used to detect and identify the mixed ligand complexes. The ligands in these complexes coordinate through O or N. The constantsK associated with the ligand exchange equilibriums are ~ 2 at −20°C and are close to the value expected from the empirical relation obtained in an earlier work from a study of Cu(II) complexes in which S also participates in the coordination.

Effect of the varying ?-accepting properties of someortho-substituted benzoic acids on the stability of mixed-ligand complexes also containing quinizarin and thorium(IV)

The mixed-ligand complexes of thorium(IV) with quinizarin (quin) and as a second ligand,L, salicyclic acid (sa), thiosalicylic acid (tsa) or anthranilic acid (ant) were studied potentiometrically in 40% (v/v) ethanol-water medium [I=100 mmol dm−3 (KNO3), 25±0.1 °C]. The equilibria existing in solutions were demonstrated and the ternary stability constants of the 1:1:1 Th-quin-L-complexes were characterized. All of these biligand complexes are considerably more stable than the corresponding monoligand ones. In addition, the relatively most stable ternary complex is formed withant which is the best π-acceptor. The order of stability of the ternary complexes is in accordance with the calculated π-charge densities of the varying ligating group in the ligandL. The values of the equilibrium constants (log units) for the reaction: Th(quin)2+ThL2⇌2Th(quin)(L) are 2.47 (0.13), 2.60 (0.3) and 4.25 (0.86) for Th(quin)(tsa), Th(quin)(sa) and Th(quin)(ant), respectively. The constants given in parentheses correspond to Δ logKTh (= logKTh(quin)(L)Th(quin) — logKThLTh).

Influence of electrostatic effect on the stability of mixed-ligand complexes: Uranyl-complexone-phenol/phenolic acid ternary systems

The formation constants (logKMALMA) of the complexes of the type (UO2.A.L] (whereA = IMDA, NTA or EDTA;L = catechol, resorcinol, phloroglucinol, pyrogallol, β-resorcylic acid or protocatechuic acid) have been determined potentiometrically at 25°C and ionic strength,I = 0·2 (mol dm−3, NaClO4) using the Irving-Rossotti approach. The formation constants of the binary complexes (logKKMAKM) have been found to lie in the sequence IMDA NTA > EDTA. due to the electrostatic effect.

Ternary complexes in solution. 31. Effect of the varying .pi.-accepting properties of several bipyridyl-like ligands on the stability of mixed-ligand complexes also containing pyrocatecholate and cobalt(II), nickel(II), copper(II), or zinc(II)

Ternary complexes in solution. 31. Effect of the varying .pi.-accepting properties of several bipyridyl-like ligands on the stability of mixed-ligand complexes also containing pyrocatecholate and cobalt(II), nickel(II), copper(II), or zinc(II)

Solvent effects on the stability of mixed ligand complexes

The effect of solvents on the equilibrium MX 4 2− + Y − ⇋ MYX 3 2− + X −, where M = Cd 2+ or Hg 2+ and X and Y = Cl −, Br −, I −, or CN −, has been studied by quantitative Raman spectrophotometry. This technique, employing LiClO 4 as internal reference, permits the direct determination of the decrease in concentration of the tetrahedral MX 4 2− due to the formation of MYX 3 2−. The fraction [1 − α( MX 4 2−)] is thus a direct measure of the solvent effect on the mixed complex stability. It is shown that bulk solvent properties are not relevant, and only solvent molecules in the immediate vicinity of the anionic complex have an effect on its stability. Selective solvation in this second coordination sphere is exhibited by several solvents, and water is not always the preferred solvent.

Spectrophotometric determination of the stabilities of mixed ligand complexes of mercury(II)-methylthymol blue with thiocyanate, bromide and chloride

Spectrophotometric determination of the stabilities of mixed ligand complexes of mercury(II)-methylthymol blue with thiocyanate, bromide and chloride