Ternary complexes of Co(II), Ni(II), Cu(II) with N-(2-acetamido)iminodiacetic acid (disodium salt, Na2ADA) and some bi- or tricarboxylic aliphatic acids (succinic, malic, tartaric and citric, H2L or H3L) were prepared. The structure of the complexes was determined by elemental and thermal analyses, IR and electronic spectra as well as conductivity measurements. The general formulas [M(ADA) (L) (H2O)]Na2 (H2O) and [M(ADA) (L)]Na3 (H2O) are deduced for the secondary ligand bi- and tricarboxylate aliphatic acid anions, respectively. An octahedral structure is suggested for the Co(II) and Ni(II) complexes, while a tetragonally distorted structure is proposed for the Cu(II) complexes. Stability constant of the different binary and ternary complexes formed in such system were determined at 25°C and μ=0.1 mol dm-3 KNO3 using the pH-titrimetric technique. It is deduced that the mixed complex is more stable than the corresponding binary aliphatic acid anion complex. The order of stability of the binary or mixed ligand complexes in terms of nature of aliphatic bi- and tricarboxylate anions and metal ion is examined and discussed.

Ternary complexes of Co(II), Ni(II), Cu(II) with N-(2-acetamido)iminodiacetic acid (disodium salt, Na2ADA) and some bi- or tricarboxylic aliphatic acids (succinic, malic, tartaric and citric, H2L or H3L) were prepared. The structure of the complexes was determined by elemental and thermal analyses, IR and electronic spectra as well as conductivity measurements. The general formulas [M(ADA) (L) (H2O)]Na2 (H2O) and [M(ADA) (L)]Na3 (H2O) are deduced for the secondary ligand bi- and tricarboxylate aliphatic acid anions, respectively. An octahedral structure is suggested for the Co(II) and Ni(II) complexes, while a tetragonally distorted structure is proposed for the Cu(II) complexes. Stability constant of the different binary and ternary complexes formed in such system were determined at 25°C and μ=0.1 mol dm-3 KNO3 using the pH-titrimetric technique. It is deduced that the mixed complex is more stable than the corresponding binary aliphatic acid anion complex. The order of stability of the binary or mixed ligand complexes in terms of nature of aliphatic bi- and tricarboxylate anions and metal ion is examined and discussed.

The visible electronic spectral behaviour of Eriochrome Black T, in a number of organic solvents of different characteristics has been examined. It was concluded that the dye exists in solution in basic solvents (based on their autoprotolysis constant, pKs) in an azo hydrazone tautomeric equilibrium, while in acetone, acetonitrile and DMSO it exists mainly in the azo form. In DMF and other basic solvent solutions, the dye exhibits an acid-base equilibrium of the type H2In HIn2− + H+. The proportional concentration of the base form (HIn2−), as well as the relative tautomerisation, are largely dependent upon the concentration of Erio T, the basicity of the solvent and the tendency of the base and/or the hydrazone form to be stabilized by H-bonding interaction with the solvent molecules. The compound was found to aggregate in water and hydroxylic solvents. The bands displayed by the differents forms of the compound have been assigned to an electronic transition involving the whole molecule with an appreciable charge transfer character.

The visible electronic spectral behaviour of Eriochrome Black T, in a number of organic solvents of different characteristics has been examined. It was concluded that the dye exists in solution in basic solvents (based on their autoprotolysis constant, pKs) in an azo hydrazone tautomeric equilibrium, while in acetone, acetonitrile and DMSO it exists mainly in the azo form. In DMF and other basic solvent solutions, the dye exhibits an acid-base equilibrium of the type H2In HIn2− + H+. The proportional concentration of the base form (HIn2−), as well as the relative tautomerisation, are largely dependent upon the concentration of Erio T, the basicity of the solvent and the tendency of the base and/or the hydrazone form to be stabilized by H-bonding interaction with the solvent molecules. The compound was found to aggregate in water and hydroxylic solvents. The bands displayed by the differents forms of the compound have been assigned to an electronic transition involving the whole molecule with an appreciable charge transfer character.