Spectrophotometric study of complex formations between 1-(2-pyridylazo)-2-naphthol (PAN) and some metal ions in organic solvents and the determination of thermodynamic parameters

The complexation reactions between Ni2+, Co2+ and Zn2+ metal ions with PAN in methanol (MeOH), acetonitrile (AN) and dimethyl sulfoxide (DMSO) were studied using a spectrophotometric method. The stability constants of the resulting complexes were determined from computer fitting absorbance mole-ratio data. The results revealed that the stability constants of complexes are varying in order of Ni2+ < Zn2+ < Co2+ for all solvents. The values of the thermodynamic parameters (ΔH°, ΔS° and ΔG°) for complexation reactions were obtained from the temperature dependence of the stability constants.

The complexation reactions between Ni2+, Co2+ and Zn2+ metal ions with PAN in methanol (MeOH), acetonitrile (AN) and dimethyl sulfoxide (DMSO) were studied using a spectrophotometric method. The stability constants of the resulting complexes were determined from computer fitting absorbance mole-ratio data. The results revealed that the stability constants of complexs are varying in order of Ni2+ < Zn2+ < Co2+ for all solvents. The values of the thermodynamic parameters (ΔH°, ΔS° and ΔG°) for complexation reactions were obtained from the temperature dependence of the stability constants.In order to have a better understanding of thermodynamics of the complexation reactions between the above metal ions and ligand, it is useful to determine the contribution of enthalpy and entropy of the reactions. The ΔH° and ΔS° values in all solvents were determined from the temperature dependence of the formation constants by applying a linear least squares analysis according to the Van’t Hoff equation. For example, the Van’t Hoff plots of log Kf vs. 1/T for all metal-PAN complexes in MeOH solution are shown in below figure.Figure optionsDownload as PowerPoint slideResearch highlights
► The complexation reactions between Ni2+, Co2+ and Zn2+ metal ions with PAN in methanol (MeOH), acetonitrile (AN) and dimethyl sulfoxide (DMSO) were studied using a spectrophotometric method.
► The stability constants of the resulting complexes were determined from computer fitting absorbance mole-ratio data.
► The values of the thermodynamic parameters (ΔH°, ΔS° and ΔG°) for complexation reactions were obtained from the temperature dependence of the stability constants.