Thermodynamic studies of some complexes of 2-benzoylpyridine 4-phenyl-3-thiosemicarbazone

The stability constants of the Co(II), Ni(II), Cu(II) and Zn(II) complexes with 2-benzoylpyridine 4-phenyl-3-thiosemicarbazone were determined using a spectrophotometric method at different temperatures (25, 30, 35 and 40 +/- 0.1 degrees C) and ionic strengths (0.05, 0.01 and 0.20 M KNO3) in 50 % (v/v) aqueous ethanol. Plots of thermodynamic stability constants at zero ionic strength (ln K degrees) versus T-1 gave linear curves and Delta H degrees and Delta S degrees were also calculated from these plots. Moreover, the changes in free energy for each metal-ligand system were calculated from the following equation. Delta G degrees = -RT ln K degrees.