POTENTIOMETRIC AND QUANTUM CHEMICAL STUDIES OF SOME METAL COMPLEXES WITH 2- (4-AMINO-1,5-DIMETHYL-2-PHENYL-1,2-DIHYDRO-PYRAZOL-3-YLIDENEAMINO)PHENOL
Abstract
Stability constants of Ni2+, Cu2+ and Pd2+ metal complexes with 2-(4-amino-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-ylideneamino)phenol (APP) have been determined using a pH metric titration technique in 0.1 M KCl and 20 % (v/v) ethanol-water mixture. The sequence of stability constants is: Cu2+ > Pd2+ > Ni2+. The dissociation constants pKiH of APP and the stability constants log Ki values of their complexes were determined at 298, 308 and 318 K. The corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were derived and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavourable. The formation of the metal complexes has been found to be endothermic and entropically favourable. Quantum chemical calculation gives a good correlation between the experimental and theoretical calculation where, the sequence of stability of metal complexes 1:2 arranged as Cu+2 > Ni+2 > Pd+2 as a result of values of energy gap between EHOMO and ELUMO. On the other hand, for complexes 1:1 for the same metals the sequence of stability arranged as Cu+2 > Pd+2 > Ni+2 according to values of the energy gap.
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