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 KC l and 50% (v/v) ethanol-water mixture. Also, the stepwise stability constan ts 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 co mplexes follow the sequence: Th4+ > UO22+ > Ce3+ > La3+ > Mn2+ < Co2+ < Ni2+ < Cu2+ > Zn2The thermodynamic parameters (Delta G, Delta H and Delta S) for AHMPP and i ts complexes were evaluated and discussed. The dissociation process is nons pontaneous, endothermic and entropically unfavourable. The formation of the metal complexes has been found to be spontaneous, exothermic or endothermi c (depends on the metal) and entropically favourable. The stoichiometries o f these complexes were determined conductometrically indicating the formati on of 1.1 and 1:2 (metal:ligand) complexes.