Potentiometric and thermodynamic studies of some schiff-base derivatives of 4-aminoantipyrine and their metal complexes

Abstract

The proton-ligand dissociation constant of 4-(4-amino-1,5-dimethyl-2- phenyl-1,2-dihydro-pyrazol-3-ylideneamino)-phenol (L1) and 4-(4-amino-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-ylideneamino)-benzoic acid (L2) and metal-ligand stability constants of their complexes with metal ions (Mn2+, Co2+, Ni2+, and Cu 2+) have been determined potentiometrically in 0.1 mol·dm -3 KCl and 10% (by volume) ethanol-water mixture and at 298, 308, and 318 K. The stability constants of the formed complexes increase in the order Mn2+, Co2+, Ni2+, and Cu2+. The effect of temperature was studied, and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were derived and discussed. The dissociation process is nonspontaneous, endothermic, and entropically unfavourable. The formation of the metal complexes has been found to be spontaneous, endothermic, and entropically favourable. © 2013 A. A. El-Bindary et al.