Stability Constants Of Metal Complexes Research Articles

Stability constants of 5-carboxyuracil and 5-carboxy-2-thiouracil with some metal ions

The stability constants of metal complexes formed between Cu 2+ , Zn 2+ , Hg 2+ , UO 2+ 2 , VO 2+ , Ni 2+ , Co 2+ and Fe 3+ metal ions with 5-carboxyuracil and 5-carboxy-2-thiouracil were determined by potentiometric titration technique. Calvin-Bjerrum pH titration method us modified by Irving-Rossotti was used to calculate the proton-ligand stability constants (log K H 1 , log K H 2 ) and metal-ligand stability constants (log β n ) values in aqueous, 80: 20% (v/v) water-ethanol and water-DMSO media at 15 °C temperature and constant ionic strength of 0.1 M NaCl. The correlation between log β n values and various parameters relating to ligand as well as metal are discussed. The negative ΔG 0 values indicate that complex formation is spontaneous one.

Chemical speciation and computer modelling studies on interaction of an antioxidant 7 ,8-dihydroxy-4-methylcoumarin with bivalent metal ions

The stability constants of bivalent metal complexes with 7,8-dihydroxy-4-methylcoumarin, an antioxidant are reported. The variation of stability constant with different ionic strengths, temperatures, percentage of solvents, dielectric constants have been studied by potentiometric estimation of H + ions in the solution. The n and pL values, thermodynamic parameters ΔG, AH and AS have been evaluated at 25 ± 0.5 °C. The values of δ min were also evaluated. Species distribution curves are plotted to visualize the nature of 1: 1 and 1: 2 complexation equilibria at different H + ions concentration.

Critical Evaluation of Stability Constants of Metal Complexes of Complexones for Biomedical and Environmental Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

3,3,3-Trifluoro-N′-(3-trifluoromethylphenyl)-1,2-propanediamine and its N-mono-and N,N-dicarboxyethyl derivatives: synthesis, protolytic and complexation properties

3,3,3-Trifluoro-N′-(3-trifluoromethylphenyl)-1,2-propanediamine (5) was synthesized by the reaction of 2-diazo-1,1,1-trifluoro-3-nitropropane or 3,3,3-trifluoro-1-nitropropene with 3-aminobenzotrifluoride followed by the reduction of the nitro group. The Michael 1,4-addition of diamine 5 to acrylic acid occurs only at the N(1) atom and affords N-mono-or N,N-dicarboxyethyl derivatives 6 and 7, depending on the reactant ratio. Protolytic equilibria 5–7 in aqueous solutions were studied by pH-potentiometry and UV spectroscopy. Only the aliphatic amino group can be protonated in an aqueous solution, while the aromatic amino group remains unprotonated even in 12 M HCl. The stability constants of transition metal (Cu2+, Ni2+, Zn2+) complexes with ligands 5–7 were determined by pH-potentiometric titration. The stability of the complexes and selectivity of the ligands toward Cu2+ ions increase with an increase in the number of N-carboxyethyl groups.

Critical Evaluation of Stability Constants of Metal Complexes of Complexones for Biomedical and Environmental Applications (IUPAC Technical Report)

Article Critical Evaluation of Stability Constants of Metal Complexes of Complexones for Biomedical and Environmental Applications (IUPAC Technical Report) was published on November 1, 2005 in the journal Chemistry International (volume 27, issue 6).

Critical evaluation of stability constants of metal complexes of complexones for biomedical and environmental applications* (IUPAC Technical Report)

Abstract Available experimental data on stability constants of proton (hydron) and metal complexes for seven complexones of particular biomedical and environmental interest: iminodiacetic acid [2,2'-azanediyldiacetic acid, IDA], (methylimino)diacetic acid [2,2'-(methylazanediyl)diacetic acid, MIDA]; 2,2',2'',2'''-{[(carboxymethyl)azanediyl]bis[(ethane-1,2-diyl)nitrilo]}tetraacetic acid (DTPA), 3,6,9,12-tetrakis(carboxymethyl)-3,6,9,12-tetraazatetradecanedioic acid (TTHA); 2,2',2''-(1,4,7-triazonane-1,4,7-triyl)triacetic acid (NOTA); 2,2',2'',2'''-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA); 2,2',2'',2'''-(1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl)tetraacetic acid (TETA), published in 1945-2000, have been critically evaluated. Some typical errors in stability constant measurements for particular complexones are summarized. Higher quality data are selected and presented as “Recommended” or “Provisional”.

Synthesis, Characterization and Stability Constants of Polynuclear Metal Complexes

Unsymmetric tridentate ligands, 4-methyl-2,6-di(4-methyliminomethyl)phenol (HL1), 4-(t-butyl)-2,6-di(4-methylphenyliminomethyl)phenol (HL2), 2,6-di(4-bromophenyliminomethyl)-4-methylphenol (HL3), 2,6-di(4-bromophenyliminomethyl)-4-(t-butyl)phenol (HL4), 2,6-di(4-hydroxyphenyliminomethyl)-4-methylphenol (HL5) and 4-(t-butyl)-2,6-di(4-hydroxyphenyliminomethyl)phenol (HL6), and their binuclear CuII, CoII and NiII complexes were synthesized and characterized by elemental analysis, FT-IR, u.v.-vis spectrometry magnetic moments, 1H(13C)-n.m.r. and mass spectral data. Also, the electrical conductivities of the complexes have been measured using 10-3 M solutions in MeCN. The complexes are weak electrolytes. In the electronic spectra of the complexes of the HL1-HL6 ligands, the 480-410 nm band has been determined as the charge-transfer band. While the HL5 and HL6 ligands have five potential donor atoms, other ligands have only three. Protonation constants of the ligands have been studied in dioxan-water mixtures. In addition, the antimicrobial properties of the ligands and their metal complexes have been studied:Bacillus megaterium, Micrococcus luteus, Corynebavterium xenosis, Enterococcus faecalis, bacteria and Saccoramyces cerevisia, yeast. The keto-enol tautomeric equilibria of the ligands have been investigated in polar and non-polar solvents.

Alkali Metal Complexation. Binding Properties of cone and partial-cone Calix[4]arenes Bearing a Mixed (O2, O2') Donor Set (O = Phosphine Oxide; O' = Amide or Ester)

The stability constants of alkali metal complexes obtained from the followingO-substituted calix[4]arenes were determined by UV/Vis spectroscopy inmethanol at 20°C: 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene(cone-1), 25,27-syn-26,28-anti-5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene (paco-1),5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonylmethoxy-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene(cone-2) and25,27-syn-26,28-anti-5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonylmethoxy-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene(paco-2). All ligands form 1:1 complexes with alkali metal cations. The amide-containing calixarenes were found to be more efficient for alkali metalcomplexation than those bearing ester substituents. While sodium ions are selectivelycomplexed by the two mixed amide-(phosphine oxide) calixarenes, the twoester-containing isomers cone-2 and paco-2 turned out to be selective towards potassium and rubidium ions, respectively. With allfour ligands the lowest stability constants were found for the lithium andcesium ions.

Oxidation of mercury microelectrodes in complexing media in the presence and absence of supporting electrolyte:: Formation of thiocyanate complexes

Normal pulse- and staircase-voltammetric oxidation of a mercury microelectrode in thiocyanate media both with and without supporting electrolyte was investigated. An equation describing the normal pulse voltammetric limiting currents flowing through a nearly spherical segment microelectrode was developed theoretically and verified experimentally. The diffusion coefficients of mercury(II) complexes containing different numbers of the thiocyanate anions were determined. A general time-dependent digital simulation scheme was developed for calculating the current for the oxidation of mercury(0) in the presence of ligands and excess supporting electrolyte and for any pulse voltammetric technique. The time-dependent mass balance equation recently developed for a system, in which diffusion coefficients of reactant and products are different, was applied. A brief review was given on the standard potentials of various mercury systems available in the literature. A general procedure for the evaluation of the stability constants of metal complexes based on the shape of the voltammograms was described and applied to the case of thiocyanato complexes of Hg(II). The stability constant results agreed well with those of Nyman and Alberts [Anal. Chem. 32 (1960) 207]. Also discussed was the determination of the formation constant β 1 for Hg(SCN) +.

Determination of protonation- and metal complex stability constants for a chelating monomer and its immobilized in polymer resin

An improved method is described for the calculation of complex stability constants for metal–ligand complexes considering ligands immobilized in resin phase. The applicability of it has been proved for N′-benzylethylene diamine N, N, N′-triacetic acid monomer (BEDTA) and for the ion exchange resin developed in the authors laboratory immobilizing this with styrene divinyl benzene. Calcium and magnesium metal ion complexes were investigated. Electrochemical and flame photometric measurements were used to collect equilibrium concentration data. The procedure worked out included the measurement of the quantity of resin bound water. Using these and the other experimentally gathered values and the improved way of calculation metal ligand complex stability constants were determined in aqueous media. Ion exchange chromatographic separation of calcium and magnesium ions was performed with a resin containing column for separation and optimized eluent.

Synthesis, Physico‐Chemical Characterization, and Stability Constants of Metal Complexes of Pyridine‐2‐carbaldehyde Thiosemicarbazone

The synthesis, physico‐chemical properties and complexes with transition element cations of pyridine‐2‐carbaldehyde thiosemicarbazone (L) are reported. The synthesis and structural analysis of L, its complexes with MCl2 (M = Mn(II), Zn(II), Cd(II)) and MıCl3 (Mı = Cr(III), Co(III)) salts are reported. Their general formulas are [M(L)3]Cl3 · 3H2O [M = Cr(III) and Co(III)], [M(L)(H2O)Cl]Cl [M = Zn(II) and Mn(II)] and [Cd(L)Cl2)] · H2O. Mn(II), Zn(II), Cd(II) complexes with a metal‐ligand ratio 1:1 and Cr(III), Co(III) complexes with a metal‐ligand ratio 1:3 have been prepared. Molecular structures of these complexes were identified using elemental analyses, FT‐IR UV‐Vis, thermogravimetric (TGA) and conductivity techniques. The structure, along with other physico‐chemical studies, establishes that the complexes of L, except for the cobalt complex, are low‐spin. Spectroscopic analysis shows that the transition metal complexes have octahedral or tetrahedral geometry. For the Cr(III) and Co(III) complexes octahedral geometry is proposed, and the Zn(II), Cd(II) and Mn(II) complexes are proposed to be of tetrahedral geometry. The stability constants of the Zn(II) and Mn(II) complexes were determined by the Job method. The stability constants of the Zn(II) and Mn(II) complexes were found to be 8.77 × 104 M–1 and 6.40 × 105 M–1, respectively. The increase in stability constants follows the order of Zn(II) > Mn(II) and this increase is in agreement with the Irving‐Williams series.

Interaction of actinide ions with [NaP5W30O110]14- and [P2W18O62]6-

Abstract Stability constants (log b101) of Th4+, UO2 2+, NpO2 + and Am3+ with [NaP5W30O110]14- were determined by solvent extraction (m = 0.1M NaCl) and found to be 6.18±0.07, 3.80±0.06, 2.98±0.04, and 5.85±0.05, respectively. The order of stability constants: Th4+>Am3+>UO2 2+>NpO2 + is due to electrostatic repulsion between the actinyl oxygens and oxygens on the polyoxometalate surface. The order of stability constants for metal complexes with [P2W18O62]6- is Th4+>UO2 2+>Eu3+>NpO2 + because the steric repulsion between actinyl oxygens and oxygens on polyoxometalate are less important. Enthalpies of complexation were measured by calorimetric titration of Th4+, UO2 2+, Nd3+ with [NaP5W30O110]14- and [P2W18O62]6-. The results indicate that the conformation and charge distribution of the microscopic surface structures are important factors in the formation of pseudocolloids.

Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids II. Tb 3+, Yb 3+ and Gd 3+ complexes in weakly alkaline conditions

The conditional stability constants for tracer concentrations of Tb(III), Yb(III), and Gd(III) with three soil humic acids, three soil fulvic acids and a fulvic acid from weathered coal were determined at pH 9.0–9.1 (these values are similar to those in calcareous soils) in the presence of NaHCO 3 by using the anion exchange method. It was found that 1 : 1 and 1 : 2 complexes were simultaneously formed in the weakly alkaline conditions. The conditional stability constants of these 1 : 1 and 1 : 2 complexes were calculated from the distribution coefficients of rare earth elements at various concentrations of humate or fulvate. The stability constants indicate the very high stability of trivalent Tb 3+, Yb 3+ and Gd 3+ complexes with humic substances in weakly alkaline conditions. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in the presence of NaHCO 3 by using an anion exchange method were discussed. The conditional stability constants of these 1 : 1 and 1 : 2 complexes were compared in this paper. It was found that stabilities of Tb 3+ 1 : 1 and 1 : 2 complexes with humic acid are greater than the corresponding ones with fulvic acid from the same soil. In addition, the effect of the presence of Ca 2+ as a competitor on the stabilities of 1 : 1 and 1 : 2 complexes of Yb was examined and no pronounced change of stabilities of 1 : 1 complex was found, even though Ca 2+ is in a 10 3 excess to Yb 3+.

Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids—Part I: Eu 3+ and Am 3+ complexes in weakly acidic conditions

The conditional stability constants for tracer concentrations of Eu(III) and Am(III) with a red earth humic acid (REHA), a red earth fulvic acid (REFA) and a fulvic acid from weathered coal (WFA) were determined at pH 5.2–6.4 (such values are similar to those in non-calcareous soils) in the presence of HAc/NaAc or NaNO 3 by using the cation exchange method. It was found that 1 : 1 complexes were predominately formed in weakly acidic conditions. The total exchangeable proton capacities and the degrees of dissociation of these humic substances were determined by using a potentiometric titration method. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in weakly acidic conditions by using the cation exchange method were discussed. The conditional stability constants of 1 : 1 complexes obtained in this paper were compared with the literature data of Am(III) determined by using the ion exchange method and the solvent extraction method and with the stability constants of 1 : 1 complexes of UO 2 2+ and Th 4+ with the same soil humic substances. These results indicate the great stability of bivalent UO 2 2+, trivalent Eu 3+, Am 3+ and tetravalent Th 4+ complexes with humic and fulvic acids in weakly acidic conditions.

Recent advances in the histochemical staining of heavy metals by means of chelating agents, with special reference to cadmium.

This review discusses the way of improving the sensitivity and specificity of chelating agents used for the histochemical demonstration of trace amounts of heavy metals in cells and tissues. In the search for a more sensitive and specific agent, various chelating agents have been prepared and their staining properties for various metals examined. Of those developed 1-(2-benzothiazolylazo)-2-naphthol (BTAN), 2-(8-quinolylazo)-4,5-(diphenyl)imidazole (QAI), and 2-(5-bromo-2-pridylazo)-5-(diethylamino)phenol (BrPADAP) were far superior to conventional staining agents in staining sensitivity. This was particularly so for staining cadmium. When modifying chelating agents to increase staining sensitivity, hydrophobicity of the agent molecules, selection of substituent groups, and the position of the groups added to the agent molecules must be taken into consideration. The most frequently mentioned factors in a staining mechanism are complex-tissue attractive forces, and recent studies have made it clear that weak interactions, such as hydrogen bonds and hydrophobic interactions, contribute significantly. The Hansch pi values were a useful indication of the hydrophobicity of metal staining agents. The published values for stability constants of metal complexes were found to be unreliable guides for choosing a masking agent to block interfering metals. The polyphosphates, aminopolycarboxylic acids, and alkylamines were among the most useful masking agents for metal staining from a practical standpoint.

Graphical methods of determination of stability constants of metal complexes using spectrophotometric and ion-selective electrode measurement data: cobalt(II)-PAR complex

A new heterogeneous Co I I -ion selective electrode has been developed and its characteristics have been studied. Using the electrode the stability constant of the complexes formed by Co I I -ion with 4-(2-pyridylazo)resorcinol (PAR) has been determined (log β 2 = 19.75) involving a graphical method. Stability constant of 1: 2 complexes, determined by the ion-selective electrode (log β 2 = 19.75) agrees well with the value (log β 2 = 19.6) determined by spectrophotometric method.

Critical evaluation of stability constants of phosphonic acids (IUPAC Technical Report)

Abstract Available experimental data on stability constants of proton and metal complexes for 10 phosphonic acids [methylphosphonic acid, 1-hydroxyethane-1,1-diylbisphosphonic acid, dichloromethylenebisphosphonic acid, amino-methanephosphonic acid, N-(phosphonomethyl)glycine, imino-N,N-bis(methylenephosphonic acid), N-methylamino-N,N-bis(methylenephosphonic acid), nitrilotris(methylenephosphonic acid), 1,2-diaminoethane-N,N,N´,N´-tetrakis-(methylenephosphonic acid), and diethylenetriamine-N,N,N´,N´´,N´´-pentakis-(methylenephosphonic acid)], published in 1950­1997, have been critically evaluated. For the latter phosphonate, all the data are rejected, as well as protonation constants [HL]/[H][L] for three other ligands. Higher-quality data are selected and presented as "Recommended" and "Provisional".

Determination of complex stabilities with nearly insoluble host molecules: cucurbit[5]uril, decamethylcucurbit[5]uril and cucurbit[6]uril as ligands for the complexation of some multicharged cations in aqueous solution

A new experimental method has been developed to determine the stability constants of metal complexes of nearly insoluble ligands in homogeneous solution. Cucurbit[5]uril, decamethylcucurbit[5]uril and cucurbit[6]uril are used as ligands for the complexation of doubly and triply charged transition metal cations in aqueous solution. The total concentration of the ligand in solution increases due to complex formation. Different experimental methods have been tested for the determination of the total ligand concentration in solution. The measurement of the total organic carbon content can be used to study complex formation quantitatively. The sensitivity of NMR spectroscopy is not sufficient. UV–VIS spectrophotometry is also not suitable because, the maximum absorbance of the ligands used is below 220 nm. Of the metals studied the most stable complex was formed by Cd(II) and cucurbit[6]uril. The stability constants of the complexes formed with cucurbit[5]uril are of the same order of magnitude as the complexes with cucurbit[6]uril. No stability constants can be calculated from the measurements of the total organic carbon content in the case of decamethylcucurbit[5]uril due to a decrease of this value in the presence of the metal salts. The solubilities of the complexes formed in this case are lower than that of the pure ligand.

Potentiometric titration study of two novel polydenate ligands and investigations of their complexes

Two novel linear polyamine ligands, N,N'-bis-(2-(N''-2-hydroxyl-5-bromobenzyl)aminoethyl) malondiamide (L1) and N,N'-bis-(3-(N''-2-hydroxyl-5-bromobenzyl)aminopropyl) malondiamide (L2), have been synthesized and fully characterized by elemental analysis (1H NMR and IR spectroscopy) (Fig. 1). The binding ability of ligands L1 and L2 to metal ions such as Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II) has been investigated by the potentiometric method in 1,4-dioxane–water (v/v = 15:100) and KNO3 (0.1 mol dm–3) at 25.0°C. In view of the linear structures of L1 and L2, binuclear metal complexes can be formed in solution by controlling Cu(II)-5-substituted o-phenanthroline (Rphen, R = CH3, H, Cl, NO2):L to a 2:1 molar ratio, whereas the mononuclear metal complexes form at molar ratio M(II):L of 1:1, where M(II) is Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II). The stability constants of metal complexes have been determined and further discussed. In addition, two manganic complexes have been synthesized and IR and electronic spectra showed their coordination nature.Key words: linear polyamine ligand, 5-substituted o-phenanthroline, mononuclear and binuclear metal complex, stability, spectrum.

Direct Quantification of Metal‐Organic Interactions by Size‐Exclusion Chromatography (SEC) and Inductively Coupled Plasma Mass Spectrometry (ICP‐MS)

AbstractMetal speciation significantly influences the geochemical cycling of trace metals and can control metal bioavailability and toxicity. Advanced analytical techniques have been applied to address some difficulties encountered in identifying metal organic species. In this method, size‐exclusion chromatography (SEC) was directly coupled with inductively coupled plasma mass spectrometry (ICP‐MS) to determine conditional stability constants of metal complexes with strong organic ligands in competitive equilibration experiments. Molecular size calibration of the column was performed with polystyrenesulfonate standards and the effects of hydrophobic interactions on the column were determined. Metal concentrations corresponding to different organic fractions were measured directly, in the SEC column effluent, by ICP‐MS. The method was validated with well‐defined organic ligands in ligand competition studies with a single metal and a binary metal mixture. The distribution of metal‐ligand species determined analytically was shown to correspond to the calculated equilibrium speciation. Model studies using metal complexes with weaker organic ligands demonstrated that the technique is subject to kinetic limitations since labile metal‐organic complexes can dissociate during chromatographic separation. Nonetheless, the kinetic window of the method should be appropriate for the strong ligands postulated to control metal speciation in natural waters.