TEMPERATURE, MEDIUM, METALS AND LIGAND STRUCTURE EFFECTS ON THE STABILITY OF THE METAL-COMPLEXES OF CERTAIN SCHIFF-BASE LIGANDS DERIVED FROM NINHYDRIN AND ISATIN WITH SOME SUBTITUTED-HYDRAZINES

Stability constants of Ni-II, Co-II, Cd-II and Mn-II complexes with so me Schiff base ligands of isatin-semi- and -thiosemicarbazones, isatin -S-methylhydrazine carbodithioate and ninhydrin-semi- and -thiosemicar bazones have been determined potentiometrically in different ratios of aquo-organic solvent media (ethanol, acetone, dioxane, tetrahydrofura n, dimethylformamide) at ionic strength mu = 0.04 mol dm(-3) (KCl) and different temperatures. The acid dissociation constants of the ligand s have been also determined under identical conditions, The results ar e discussed in terms of the molecular structure of the ligands, the so lvent characteristics as well as the nature of central metal ion, The stability constant values increase with increasing organic solvent in the reaction medium and decrease at higher temperatures, Thermodynamic functions have been evaluated and discussed.