Polarographic study of mixed ligand complexes of Pb(II) with carboxylate ions and imidazole

Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart^2?), malonate (mal^2?) and citrate (citr^3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO₃) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β₁₁ = 4.19; with mal^2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)₂] and [Pb(mal)₂(im)]^2? with stability constants log β₁₁ = 4.3, log β₁₂ = 7.3 and log β₂₁ = 5.5 respectively are formed. With citr^3? and im a single mixed species, [Pb(citr)(im)]^? with stability constant log β₁₁ = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed.     

Synthesis,characterization and fluorescence spectra of mixed ligand Zn(II), Cd(II) and Hg(II) complexes with 1,10-phenanthroline-5,6-dione ligand

The novel mixed ligand complexes [M(bpy)(phen-dione)](PF₆)₂ (M?=?Zn(II), Cd(II) and Hg(II), bpy?=?2,2^′-bipyridine and phen-dione?=?1,10-phenanthroline-5,6-dione) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and electronic absorption spectroscopies. The ν(C=O) of coordinated phen-dione in these complexes are very similar to the free phen-dione ligand showing that phen-dione is not coordinated to metal ion from its C=O sites. Absorption spectra of the complexes show two absorption bands for intraligand transitions. These absorption bands show dependence to the dielectric constant of solvent. These complexes exhibit an intensive fluorescence band around 535?nm in DMF when the excitation wavelength is 260?nm at room temperature. The fluorescence intensity of these complexes is larger than that of the free ligand.     

A study of mixed ligand complexes using differential pulse polarography

Differential pulse polarography was used to study the mixed ligand complexes of trimethylenediamine (TMDA) and oxalate (OX) with Cd(II) at constant ionic strength (μ = 1, NaNO₃) at 25°C. It has been found that the reduction of complexes is reversible and diffusion-controlled. Three mixed complexes, [Cd(TMDA)(OX)], [Cd(TMDA)(OX)₂]^2? and [Cd(TMDA)₂(OX)], are formed. Their overall stability constants are: log β₁₁ = 6.78, log β₁₂ = 7.53 and log β₂₁ = 8.20, respectively.     

Electrochemical Study of the Mixed Ligand Complexes of Co(II) and Ni(II) with Acetylsalicylic Acid and Nicotinamide

The interaction of acetylsalicylic acid (aspirin, aspH) and nicotinamide (NA) with Co(II) and Ni(II) ions was investigated using square-wave and cyclic voltammetry techniques. In the presence of Ni(II)/Co(II),nicotinamide gave new peaks at -0.85V and soh.12 V, corresponding to the reduction of Ni(II)-nicotinamide(log β_1:2 =5.97) and Co(II)-nicotinamide (log β_1:2 =5.19) complexes, respectively. In the presence of Ni(II)/Co(II), acetylsalicylic acid gave new peaks at -0.91V and -1.19 V, respectively, corresponding to the reductionof Ni(II)-salicylate (log β_1:2 =8.48) and Co(II)-salicylate (log β_1:2 =8.14) complexes. In the presence of nicotinamide, Ni(II)-salicylate and Co(II)-salicylate form mixed ligand complexes, reducing at -0.78V (log β_1:2:2 =9.68) and -1.14V (log β_1:2:2 =8.64), respectively.     

Trace metal speciation in sea water — a paper electrophoretic approach

Stability constants of individual trace metal complexes form the basis for calculations predicting the distribution of trace metal species in complexing media, such as sea water. In this study, the electrophoretic mobility of radiotracer ²¹⁰Pb is measured as a function of ligand concentration in chloride and sulfate solutions of constant ionic strength and temperature. A theoretically-derived expression, relating mobility to ligand concentration and complex stability constants, is fitted by the method of least squares to the experimental data to obtain estimates of the conditional stability constants of lead(II) chloro and sulfato complexes at 23°C and ionic strength 0.7 i.e., under conditions resembling those of ocean water. The values obtained are: log β₁ = 0.999 ± 0.014, log β₂ = 1.037± 0.032, log β₃ = 1.250 ± 0.015 for lead(II) chloro complexes, and log β₁ = 1.048 ± 0.015 and log β₂ = 1.183 ± 0.025 for lead(II) sulfato complexes. Experiments with eight other metal ions [Au(III), Bi(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), and Po(IV)] and with sea water as electrolyte indicate the general applicability of the method.     

Mixed-ligand complexes of zinc(II), cobalt(II) and cadmium(II) with sulfur, nitrogen and oxygen ligands. Analysis of the solid state structure and solution behavior. Implications for metal ion substitution in alcohol dehydrogenase

In this paper we characterize new, mixed ligand complexes of zinc(II), cobalt(II) and cadmium(II) with tri-tert-butoxysilanethiolate and 2-(2′-hydroxyethyl)pyridine ligands. Due to the chelating versus non-chelating behavior of 2-(2′-hydroxyethyl)pyridine ligand we have obtained an interesting structural variety in the studied system. The presented coordination patterns together with the results of NMR studies have been used to illustrate a rapid chemical exchange undergoing in methanolic solutions of zinc(II) and cadmium(II) complexes. UV-Vis spectra of cobalt(II) species have also evidenced an exchange in the case of cobalt(II) complex. The relative strength of hydrogen bond formed by hydroxyl group bonded to Zn(II), Co(II) or Cd(II) was evaluated by analysis of structural parameters and position of the OH stretching vibrations in the FT-IR spectra of the complexes in solid state. The data were compared with the activity of zinc (native) alcohol dehydrogenase and alcohol dehydrogenase substituted with cobalt and cadmium ions. The enthalpies of proton abstraction in zinc and cobalt complexes were calculated and found to be very similar. The attempt to apply zinc tri-tert-butoxysilanethiolate as a catalyst in the biomimetic reaction of reduction of N-benzylnicotinamide chloride by ethanol was unsuccessful.     

Investigation of DNA Binding Interaction of Newly Synthesized Nickel(II) and Palladium(II) Complexes Containing Ferrocenyl Schiff Base Ligand

New complexes of nickel(II) and palladium(II) were synthesized using the ferrocenyl imine ligand, which was formed by the condensation of 2‐aminothiophenol and acetylferrocene. This bidentate Schiff base ligand was coordinated to the metal ions through the NS donor atoms. Monomeric complexes of nickel(II) and palladium(II) were synthesized by the reactions of the Schiff base ligand with nickel(II) and palladium(II) chloride in a 2:1 M ratio. In these complexes, the thiol group was deprotonated and coordinated to the metals. The molar conductivity values of the complexes in DMSO showed the presence of non‐electrolyte species. The fluorescence characteristics of the Schiff base ligand and its complexes were studied in DMSO. The synthesized complexes were characterized by FT‐IR, ¹H NMR, UV–vis spectroscopy, elemental analysis, and conductometry. Furthermore, the binding interactions of the complexes with DNA were investigated by electronic absorption spectroscopy, and the intrinsic binding constant (K _b) was calculated. Moreover, viscosity and melting temperature (T _m) were investigated in order to further explore the nature of interactions between the complexes and DNA.     

Formation of Zinc(II) and Cadmium(II) Complexes with Pyridine Oxime Ligands in Aqueous Solution

Complex formation equilibria involving pyridine-2-carboxaldehyde oxime (1), 1-(2-pyridinyl)ethanone oxime (2) and 6-methylpyridine-2-carboxaldehyde oxime (3), HL, with zinc(II) and cadmium(II) ions were studied in aqueous 0.1 M NaCl solution at 25° C by potentiometric titrations with a glass electrode. Experimental data were analysed with the least-squares computer program SUPERQUAD to determine the complexes formed and their stability constants. With Ligands 1 and 2 the sets of complexes for Zn(II) and Cd(II) are essentially the same, mono- and dinuclear oxime complexes and their deprotonated/hydrolysed products H_pM_q(HL)^2q+p _r. Owing to the steric requirements of the 6-methyl group, sets of complexes formed with 3 are distinctly different. For zinc(II), only dinuclear oximato species H_pZn₂(HL)^4q+p ₂ ( p = ? 2, ? 3, ? 4) are found, while for the larger cadmium(II) ion mononuclear oximato species CdL⁺ and CdL₂ are detected in addition to the dinuclear complex H_pCd₂(HL)^4q+p ₂ ( p = ? 3).     

Potentiometric study of Cd(II) and Pb(II) complexation with two high molecular weight poly(acrylic acids); comparison with Cu(II) and Ni(II)

The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×10⁵ and 3×10⁶) was investigated in dilute aqueous solution (NaNO₃ 0.1 mol l⁻¹; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA₂ complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) . It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)β₁₀₂ was found to be close to 7.0) and allowed the formation of the predominant PbA₂ species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed.     

Synthesis and Characterization of Ni(II), Cu(II), Zn(II) and Cd(II) Complexes of a New Vic-Dioxime Ligand

In this study, 1,2-dihydroxyimino-3,7-di-aza-9,10-O-α-methyl benzal decane (LH₂) was synthesized starting from 1,2-O-α-methyl benzal-4-aza-7-amino heptane (RNH₂) and antichloroglyoxime. With this ligand, complexes were synthesized using Ni(II) and Cu(II) salts with a metal:ligand ratio of 1:2. However, the reaction of the ligand with salts of Zn(II) and Cd(II) gave products with metal:ligand ratio of 1:1. Structures of the ligand and its complexes are proposed based on elemental analyses, IR, ¹³C- and ¹H-NMR spectra, magnetic susceptibility measurements and thermogravimetric analyses (TGA).     

Hg(II), Tl(III), Cu(I), and Pd(II) Complexes with 2,2'-Diphenyl-4,4'-Bithiazole (DPBTZ), Syntheses and X-Ray Crystal Structure of [Hg(DPBTZ)(SCN)2]

Reaction of the ligand 2,2′-diphenyl-4,4′-bithiazole (DPBTZ) with Hg(SCN)₂, Tl(NO₃)₃, CuCl, and PdCl₂ gives complexes with stoichiometry [Hg(DPBTZ)(SCN)₂], [Tl(DPBTZ)(NO₃)₃], [Cu(DPBTZ)(H₂O)Cl]_, and [Pd(DPBTZ)Cl₂]. The new complexes were characterized by elemental analyses and infrared spectroscopy. The crystal structure of [Hg(DPBTZ)(SCN)₂] determined by X-ray crystallography. The Hg atom in the title monomeric complex, (2,2′-diphenyl-4,4′-bithiazole)mercury(II)bisthiocyanate, [Hg(C₁₈H₁₂N₂S₂)(SCN)₂], is four-coordinate having an irregular tetrahedral geometry composed of two S atoms of thiocyanate ions [Hg-S 2.4025(15) and 2.4073(15) Å] and two N atoms of 2,2′-diphenyl-4,4′-bithiazole ligand [Hg-N 2.411(4) and 2.459(4) Å]. The bond angle S(3)-Hg(1)-S(4) of 147.46(5)° has the greatest derivation from ideal tetrahedral geometry. Intermolecular interaction between Hg(1) and two S atoms of two neighboring molecules, 3.9318(15) and 3.9640(18) Å, make the Hg(1) distort from a tetrahedron to a disordered octahedron. The attempts for preparation complexes of Tl(I), Pb(II), Bi(III), Cd(II) ions with 2,2′-diphenyl-4,4′-bithiazole ligand were not successful and also the attempts for preparation complexes of 4,4′,5,5′-tetraphenyl-2,2′-bithizole ligand with Cu(II), Ni(II), Co(II), Co(III), Mn(II), Mn(III), Fe(II), Fe(III), Cr(III), Zn(II), Tl(III), Pb(II), Hg(II), Cu(I), Pd(II) were not successful. This point can be regarded as the initial electron withdrawing of phenyl rings and also their spatial steric effects.     

Complexation of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid with Cd(II), Hg(II) and Pb(II) ions in aqueous solution

The persistence of widely used chelating agents EDTA and DTPA in nature has been of concern and there is a need for ligands to replace them. In a search for environmentally friendly metal chelating ligands for industrial applications, complex formation equilibria of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA6) with Cd(II), Hg(II) and Pb(II) in aqueous 0.1 M NaNO₃ solution were studied at 25°C by potentiometric titration. Complexation was modeled and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metal ions, stable ML^4? complexes dominated the complex formation. The stabilities of Cd(II), Hg(II) and Pb(II) chelates of BCA6 are remarkably lower than those of EDTA and DTPA. Environmental advantages of the use of BCA6 instead of EDTA and DTPA are better biodegradability and lower nitrogen content with a possibility to save chemicals and process steps in pulp bleaching.     

Study of the Complexation of Pb(II) with meso‐2,3‐ Dimercaptosuccinic Acid (DMSA) and 2,3‐Dimercapto‐1‐propanesulfonic acid (DMPS) Using a Bismuth‐Bulk Rotating Disk Electrode

For the first time, the suitability of bismuth bulk rotating disk electrode (BiB‐RDE) for the study of metal complexation has been tested. Cyclic (CV) and differential pulse (DPV) voltammetry have been used to study the complexation of Pb(II) with two of the most effective chelating agents for the treatment of Pb(II) poisoning (meso‐2,3‐dimercaptosuccinic acid, DMSA, and 2,3‐dimercapto‐1‐propanesulfonic acid, DMPS). Multivariate curve resolution has been applied to voltammetric data to obtain the stoichiometries and stability constants of the complexes formed. In both systems, the ML₂ complex was predominant, with log β₂ values of 10.13 and 8.80 for DMSA‐Pb(II) and DMPS‐Pb(II), respectively.     

A new amino alcohol NpyNimineNamineOalcohol-donor ligand: coordination toward zinc(II) and cadmium(II) halides and enantioselective products

In the present work a new ligand, 2-(2-(phenyl(pyridin-2-yl)methyleneamino)ethylamino)ethanol (L), and its Zn(II) and Cd(II) complexes, [Zn(L)Br₂] (1), [Cd(L)Br₂] (2) and [Cd(L)I₂] (3), have been synthesized and characterized by elemental analysis, FT-IR, Raman and ¹H NMR spectroscopies as well as X-ray crystallography. All complexes are isostructural and their metal ions have distorted square pyramidal geometry with an MN₃X₂ (X: Br, I) environment. During the complexation process, the amine group of the ligand becomes a chiral center. In the solid-state, an R-configuration was observed in all three complexes. Furthermore, the molecules form intermolecular C–H?O, C–H?X and O–H?X (X: Br, I) hydrogen bonds in the solid-state.     

Cu(II), Zn(II), AND Pb(II) STABILITY CONSTANTS OF CYCLAM AMPHIPHILES

Abstract

1-Hexadecyl-1,4,8,11-tetraazacyclotetradecane (hexadecyl cyclam) and 1-(3,7,11,15-tetramethyl) hexadecyl-1,4,8,11-tetraazacyclotetradecane (tetramethylhexadecyl cyclam) have been synthesized and their deprotonation and ligand-metal formation constants, K, determined for Cu(II), Zn(II) and Pb(II). The coupling of a long hydrocarbon chain to a ring nitrogen decreased the general ability of the cyclam ring to complex with metal ions. The greatest effect appeared to be for Cu(II) decreasing from a pK of 27 for cyclam to about 17. The titrations were fitted by HYPERQUAD and the concentrations of the intermediate complexes obtained as a function of pH. Metal-ligand complexes LMH₂ ⁴⁺, LMH₂₊ and LM₂₊ can coexist through a wide pH range. We have also calculated a composite metal-binding constant, K′, to reflect more accurately the overall ability of these ligands to bind a metal at any particular pH. K′, which is 14.6 for (hexadecyl cyclam)-Cu(II), is constructed from the concentrations of all the metal-chelated species at pH = 7. Generally, K′ is much lower than K.     

Mononuclear and homobinuclear cobalt(II), nickel(II) and copper(II) complexes with mono and bis-azocompounds derived from 2,7-dihydroxynaphthalene and anthranilic acid or o-aminophenol

Two new series of mononuclear and homobinuclear Co(II), Ni(II) and Cu(II) complexes with mono- and bis-azo compounds derived from 2,7-dihydroxynaphthalene and anthranilic acid or o-aminophenol are prepared and characterized by elemental and thermal analyses, conductance, IR, electronic, ESR spectra and magnetic moment measurements. The ligand field splitting parameters and Racah constant are calculated. The spectral and magnetic results obtained are utilized to determine the geometries around the metal(II) ion. The geometry of the complex formed depends on the structure of the ligand and the type of metal(II) ion. The mode of bonding of the ligand with the metal ions is deduced from IR spectra.     

Zinc(II), Cadmium(II), Mercury(II), and Lead(II) Complexes of N-Carboxymethyl-D,L-threonine in Aqueous Solution

The formation of complexes of Zn(II), Cd(II), Hg(II), and Pb(II) and N-carboxymethyl-D,L-threonine (H₂CMT, H₂L) in aqueous solutions has been studied by spectrophotometric and potentiometric methods. The complexation model for each system has been established by the HYPERQUAD program from the potentiometric data. Three different behaviors are found: ML₂H, MLH, ML, MLOH, and ML₂ complexes are formed by Zn(II) and Cd(II) ions, ML₂H, ML, MLOH, and ML₂ are formed by Hg(II) ion, and only 1/1 complexes MLH, ML, and MLOH are formed by the Pb(II) ion. The formation constants determined for all these complexes allow simulation of experimental titration curves with good agreement. The speciation of multimetal systems with H₂CMT shows that this compound is a good and selective ligand at low pH for the Hg(II) ion.     

THE INTERACTION OF 2-AMINO-2-HYDROXYMETHYL-1,3-PROPANEDIOL WITH COBALT(II) AND MANGANESE(II) IONS

Abstract

The stepwise complex formation between 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) with Co(II) and Mn(II) was studied by potentiometry at constant ionic strength 2.0 M (NaClO₄) and T = (25.0 ± 0.1)°C, from pH measurements. Data of average ligand number (Bjerrum's function) were obtained from such measurements followed by integration to obtain Leden's function, F ₀(L). Graphical treatment and matrix solution of simultaneous equations have shown two overall stability constants of mononuclear stepwise complexes for the Mn(II)/TRIS system (β₁ = (5.04 ± 0.02) M^?1 and β₂ = (5.4 ± 0.5) M^?2) and three for the Co(II)/TRIS system (β₁ = (1.67 ± 0.02) × 10² M^?1, β₂ = (7.01 ± 0.05) × 10³ M^?2 and β₃ = (2.4 ± 0.4) × 10⁴ M^?3). Slow spontaneous oxidation of Co(II) solutions by dissolved oxygen, accelerated by S(IV), occurs in a buffer solution TRIS/HTRIS⁺ 0.010/0.030 M, with a synergistic effect of Mn(II).     

Synthesis and Properties of Complexes of Lead(II), Cadmium(II), and Zinc(II) with N-Phosphonomethylglycine

Summary.  Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C₃H₆O₅NPPb, C₃H₆O₅NPCdċ2H₂O, and C₃H₆O₅NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was determined. Thermal, diffractometric, and IR spectrophotometric analyses were carried out. It was found that the metal is bonded to glyphosate through the oxygen atoms of the carboxylic and phosphonate groups; metal-nitrogen binding is absent in the above compounds. Studying the complexing behaviour in solution by UV spectrophotometry pointed out that a complex of the composition Pb(II) : NPMG=1:1 with an absorption band at 232 nm is formed. Its stability constant as determined by Job’s method is logK=5.9±0.1. Using potentiometric techniques, the dissociation constant of N-phosphonomethylglycine and the stability constants of its complexes with cadmium (II) and zinc (II) were determined. Received June 30, 1999/Accepted July 21, 1999.     

Synthesis, crystal structure, spectroscopic and photoluminescence studies of manganese(II), cobalt(II), cadmium(II), zinc(II) and copper(II) complexes with a pyrazole derived Schiff base ligand

Varying coordination modes of the Schiff base ligand H₂L [5-methyl-1-H-pyrazole-3-carboxylic acid (1-pyridin-2-yl-ethylidene)-hydrazide] towards different metal centers are reported with the syntheses and characterization of four mononuclear Mn(II), Co(II), Cd(II) and Zn(II) complexes, [Mn(H₂L)(H₂O)₂](ClO₄)₂(MeOH) (1), [Co(H₂L)(NCS)₂] (2), [Cd(H₂L)(H₂O)₂](ClO₄)₂ (3) and [Zn(H₂L)(H₂O)₂](ClO₄)₂ (4), and a binuclear Cu(II) complex, [Cu₂(L)₂](ClO₄)₂ (5). In the complexes 1-4 the neutral ligand serves as a 3N,2O donor where the pyridine ring N, two azomethine N and two carbohydrazine oxygen atoms are coordinatively active, leaving the pyrazole-N atoms inactive. In the case of complex 5, each ligand molecule behaves as a 4N,O donor utilizing the pyridine N, one azomethine N, the nitrogen atom proximal to the azomethine of the remaining pendant arm and one pyrazole-N atom to one metal center and the carbohydrazide oxygen atom to the second metal center. The complexes 1-4 are pentagonal bipyramidal in geometry. In each case, the ligand molecule spans the equatorial plane while the apical positions are occupied by water molecules in 1, 3 and 4 and two N bonded thiocyanate ions in 2. In complex 5, the two Cu(II) centers have almost square pyramidal geometry (τ = 0.05 for Cu1 and 0.013 for Cu2). Four N atoms from a ligand molecule form the basal plane and the carbohydrazide oxygen atom of a second ligand molecule sits in the apex of the square pyramid. All the complexes have been X-ray crystallographically characterized. The Zn(II) and Cd(II) complexes show considerable fluorescence emission while the remaining complexes and the ligand molecule are fluorescent silent.