Abstract
A new 3methyl1phenyl4arylazo5pyrazolone and 1, 3diphenyl4arylazo5pyrazolone have been synthesized and characterized by elemental analysis, IR, mass and 1H NMR spectra. The acid dissociation constants (pKa values) of the investigated ligands were determined potentiometrically and spectrophotometrically. The stability constants of the transition metal ions (VO2+, Cr3+, Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) with the investigated ligands were determined potentiometrically at different ionic strengths (0.167, 0.1, 0.05 and 0.025 M) NaCl at 25oC and different temperature (25, 30, 35, and 45oC). The values of stability constants were found to decrease with increasing ionic strengths and temperature. The stoichiometries were studied using spectrophotometric and conductimetric methods, the results indicate the existence of 1:1 and 1:2 (M:L) metal:ligand species. The relationships between the stability constants of the complexes, ionization constants of the ligands have been discussed and correlated. The thermodynamic parameters (?G, ?H and ?S) and the thermodynamic stability constants for all of the investigated complexes were determined potentiometrically.
Highlights
Pyrazolone and azopyrazolone compounds are widely used as analytical reagents, they are capable of forming chelates with a number of metal cations [1,2], the formation of which is accompanied by change in color, pH, conductivity, and absorption spectra [3]
Water used was bidistilled water; distillation process was carried out using both of condensation process and ion exchange technique. 10-3 M of azopyrazolone solutions were prepared by dissolving a known mass of the azo compound in a proper volume of ethanol. 10-3 M solution of the metal ion in 0.1 M hydrochloric acid (HCl) was prepared by dissolving the appropriate weight of the corresponding metal chlorides of Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and VOSO4·3H2O in a proper volume of 0.1 M HCl to prevent the hydrolysis of the metal salt solutions
The mean values of nnHH for the investigated ligands (L1-L6) at different pH values were calculated from the titration curves of solutions 1 and 2 by employing the relationship derived by Irving and Rossotti [17]
Summary
Pyrazolone and azopyrazolone compounds are widely used as analytical reagents, they are capable of forming chelates with a number of metal cations [1,2], the formation of which is accompanied by change in color, pH, conductivity, and absorption spectra [3]. The azo-derivatives of 5-pyrazolones as well as their metal complexes have wide applications in dye industry as well as analytical reagents for determination of trace metals and it is predicted to have some medical and biological applications [5,6]. The present paper deals with the determination of the stability constants of the binary complexes of VO2+, Cr3+, Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ metal ions with the investigated ligands (L1-L6) in the presence of 0.167, 0.1, 0.05 and 0.025 M at 25oC. The molar ratio of the metal ions to ligands [M]/[L] were studied spectrophotometrically using molar-ratio and continuous variation methods and were determined using conductimetric titrations in aqueous ethanolic solutions (40% v/v)
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