Potentiometric and Thermodynamic Studies of Some Schiff-Base Derivatives of 4-Aminoantipyrine and Their Metal Complexes

• Main Authors: A. A. El-Bindary, A. Z. El-Sonbati, M. A. Diab, M. K. Abd El-Kader
• Format: Article
• Language: English
• Published: Hindawi Limited 2013-01-01
• Series: Journal of Chemistry
• Online Access: http://dx.doi.org/10.1155/2013/682186

The proton-ligand dissociation constant of 4-(4-amino-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-ylideneamino)-phenol () and 4-(4-amino-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-ylideneamino)-benzoic acid () and metal-ligand stability constants of their complexes with metal ions (Mn2+, Co2+, Ni2+, and Cu2+) 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 (, , and ) 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.