Thermodynamics of Substituted Pyrazolone : VI. Potentiometric and Conductometric Studies of Complexes of Some Transition Metals with 4-(4-Acetophenyl)hydrazono-3-methyl-1-phenyl-2-pyrazolin-5-one

The dissociation constant of 4-(4-acetophenyl)hydrazono-3-methyl-1-phenyl-2-pyrazolin-5-one (AHMPP) has been determined potentiometrically in 0.1 M KCl and 50% (v/v) ethanol-water mixture. Also, the stepwise stability constants of the formed complexes of Mn2+, Co2+, Ni2+, Cu2+, Zn2+, La3+, Ce3+, UO2+2 and Th4+ with AHMPP have been determined. The stability of the formed complexes follow the sequence: Th4+ UO2+2 Ce3+ La3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ The thermodynamic parameters (deltaG, delta H and deltaS) for AHPP and its complexes were evaluated and discussed. The dissociation process is nonspontaneous, endothermic and entropically unfavourable. The formation of the metal complexes has been found to be spontaneous, exothermic or endothermic (depends on the metal) and entropically favourable. The stoichiometries of these complexes were determined conductometrically indicating the formation of 1:1 and 1:2 (etal:ligand) complexes.