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

A A El-Bindary,A Z El-Sonbati,M K Abd El-Kader,M A Diab

doi:10.1155/2013/682186

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 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 (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.

Highlights

Schiff-base coordination complexes have attracted great attention over the past decades due to their facile syntheses, their wide application, and the accessibility of diverse structural modi cations, and to their biological modeling applications, catalysis, design of molecular ferromagnets, and materials chemistry [1,2,3,4,5,6]
It is well known that N atoms play a key role in the coordination of metals at the active sites of numerous metallobiomolecules [7]. e Schiff bases of 4-aminoantipyrine and their coordination complexes have been extensively investigated because of their biological, clinical, pharmacological, analytical and material applications [8,9,10,11]
In continuation of earlier work [14,15,16,17,18], we report here the dissociation constant of 4-(4-amino-1,5-dimethyl-2-phenyl1,2-dihydro-pyrazol-3-ylideneamino)-phenol (L1) and 4-(4amino-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-ylideneamino)-benzoic acid (L2) and the stability constants of their complexes with Mn2+, Co2+, Ni2+, and Cu2+ at different temperatures

Summary

Introduction

Schiff-base coordination complexes have attracted great attention over the past decades due to their facile syntheses, their wide application, and the accessibility of diverse structural modi cations, and to their biological modeling applications, catalysis, design of molecular ferromagnets, and materials chemistry [1,2,3,4,5,6]. T 2: ermodynamic functions for the dissociation of ligand (L2) in 10% (by volume) ethanol-water mixture and 0.1 mol ⋅ dm−3 KCl at different temperatures.

Results

Conclusion