Heikki Saarinen

Complexation of [S,S] and mixed stereoisomers of N,N′-ethylenediaminedisuccinic acid (EDDS) with Fe(III), Cu(II), Zn(II) and Mn(II) ions in aqueous solution

The protonation and complex formation equilibria of N,N′-ethylenediaminedisuccinic acid (EDDS) in the isomeric form [S,S] and a mixture of EDDS isomers (25% [S,S], 50% [R,S], 25% [R,R]) with Fe(III), Cu(II), Zn(II) and Mn(II) have been studied in aqueous 0.1 M NaCl solution at 25 °C by potentiometric titrations. The calculations were carried out with the computer program SUPERQUAD.

Studies on biodegradable chelating ligands: complexation of iminodisuccinic acid (ISA) with Cu(II), Zn(II), Mn(II) and Fe(III) ions in aqueous solution

In a search for biodegradable chelating ligands for industrial applications, study was made of the protonation and complex formation equilibria of iminodisuccinic acid (ISA) as a mixture of two of its stereoisomers (50% [S,S] and 50% [R,S]) with Cu(II), Zn(II), Mn(II) and Fe(III) ions in aqueous 0.1 M NaCl solution by potentiometric titration at 25 °C. The model of the complexation and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metals the complex formation was dominated by stable MLn − 4 complexes. Biodegradable and of low nitrogen content, ISA was found to be a good chelating agent in pulp bleaching.

Formation of Trinuclear Copper(II) Complexes with Three Pyridine Oxime Ligands in Aqueous Solution

Abstract The protonation and complex formation equilibria of pyridine-2-carboxaldehyde oxime (1), 1-(2-pyridinyl)elhanone oxime (2) and 6-methylpyridine-2-carboxaldehyde oxime (3), HL, with copper(II) ion were studied in aqueous 0.1 M NaCl solution at 25°C by potentiometric titrations with the use of a glass electrode. Application of the least-squares computer program SUPERQUAD to the experimental data indicated that the following complex species are formed: Cu(HL)2 +, CuL+ (ligand 1), Cu(HL)2 2 + (ligands 1 and 3), Cu(HL)L+ CuL2, Cu3L3OH2+ and Cu3L3O + (or Cu3L3(OH)2 +, ligands 1 and 2). The trinuclear complex Cu3L3OH2 + most probably has a triangular Cu3OH central core. In 1:1 molar ratio of ligand to Cu2+ the trimer exists as the predominating complex around pH 4–6 and gives way to the next deprotonated trimer as the pH is increased.

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 HpMq(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 HpZn2(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 HpCd2(HL)4q+p 2 ( p = − 3).

Equilibrium and structural studies of copper(II) and nickel(II) complexes with pyridine-2,6-diamidoxime in aqueous solution

The complex formation equilibria of copper(II) and nickel(II) with pyridine-2,6-amidoxime (H2L) were studied in aqueous 0.1 M NaCl solution at 25°C by potentiometric titrations with use of a glass electrode. Experimental data were analyzed with the least-squares computer program SUPERQUAD to determine the complexes formed and their stability constants. The best model included both metal ions in the mononuclear complexes M(H2L)2+, , M(H2L)HL+ and M(HL)2 and with nickel(II) also the complexes Ni(HL)L− and . The structure of the crystallized complex with the formula [Ni(HL)2]·4H2O was determined by X-ray diffraction. The crystal structure is orthorhombic, space group pbcn with a = 12.601(3), b = 9.3990(19), c = 17.195(3) Å, α = β = γ = 90° and Z = 4.

Complexation of N-tris[(1,2-dicarboxyethoxy)ethyl]amine with Ca(II), Mn(II), Cu(II) and Zn(II) in aqueous solution

In a search for environmentally friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of N-tris[(1,2-dicarboxyethoxy)ethyl]amine (TCA6) with Ca(II), Mn(II), Cu(II) and Zn(II) ions in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. A model for complexation and stability constants of the complexes were determined. With all of the metals, complex formation was dominated by ML4−. Comparison of TCA6 and six other chelating agents showed TCA6 to be suitable for applications where strong calcium binding is essential.

Formation of cobalt(II) complexes with five pyridine oximes in aqueous solution

Complex formation equilibria of cobalt(II) with pyridine-2-carboxamidoxime (1), pyridine-2-acetamidoxime (2), pyridine-2-aldoxime (3), 1-(2-pyridinyl)ethanone oxime (4) and 6-methylpyridine-2-aldoxime (5) were studied in 0.1 M NaCl solution at 25°C by potentiometric titrations with use of 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 1−4 Co(II) forms mono, bis and (except for 2) tris complexes of the type and deprotonated/hydrolyzed products of the bis and tris complexes, Co(HL)L+ and Co(HL)2L+. The deprotonated complexes have a low spin structure (t 2 g 6 e g ) and are readily oxidized after the easy loss of the sole e g electron. Their formation with increasing pH involves slow attainment of equilibrium in the pH range 3−5. Only with ligand 3 could studies be continued to pH 8−10 by using very low cobalt(II) ion concentrations. There, CoL2 is formed quantitatively, while complexes Co(HL)L2 and could not be observed. Ligand 1 also forms the complex Co2(HL)2H2L5+ and ligand 2 the complex Co(H2L)3+ with the positively charged ligand (H2L+). Ligand 5 forms the complexes Co(HL)2+, CoL2, Co2L2OH+, and Co2L3OH mainly in the pH range 6−10. The stabilities of these complexes and also their oxidation reactions are reduced by the steric requirements of the 6-methyl groups of the ligand.