Stability constants and Thermodynamic Parameters of Mixed Ligand Chelates of Ni(II) with 5-Phenylazo-8-Quinolinol and 5-(4-Substituted Phenylazo)-8-Quinolinols in the Presence of O,O; O, N and N, N-Donor Ligands in 50% Dioxane-Water Medium

Abstract

The equilibria involved in the formation of ternary chelates of Ni(II) with different ligands in presence of N, O donor ligands such as 5-phenylazo- 8-quinolinol (PAZOX), 5-(4-methoxyphenylazo)-8-quinolinol (MPAZOX), 5-(4-tolyl phenylazo)-8-quinolinol (TPAZOX) and 5-(4-nitro phenylazo)-8-quinolinol (NPAZOX) have been studied by pH titration technique at 30º ± 1ºC and μ = 0.10 M (KNO₃) in 50% dioxane-water medium. The ligands used were (i) glycine (Gly); alanine (ala) (N,O-donors); (ii) catechol (cat); oxalic acid (oxa) (O, O-donors); (iii) 1,10-phenanthroline (1,10-phen), 2,2-bipyridyl (2,2-bipy) (N,N donors). The overall stability constants of ternary chelates are discussed in light of basicity of ligands, nature of donor atoms, metal-ligand d_π–p_π interactions denticity and statistical aspects. The formation constants of mixed ligand complexes have been studied at 20º, 30º, 40º, and 50ºC at constant (0.10 M) ionic strength.