Formation and Stability of Co(II), Ni(II), Cu(II) and Zn(II) Complexes of Pyridoxal Semicarbazone and Pyridoxal Thiosemicarbazone in Solution

The formation and stability of Pyridoxal semicarbazone (PLSC) and Pyridoxal thiosemicarbazone (PLTSC) Schiff base ligand (L) complexes of Co(II), Ni(II), Cu(II) and Zn(II) have been investigated by Irving-Rossotti pH-metric titration technique, at 30 ± 1°C and an ionic strength of 0.1M KNO₃ in 70% v/v DMF-H₂O medium. The acid dissociation constants (pK_a) of the ligands and the stability constants of the metal complexes formed in solution were determined. The results indicate the formation of 1:1(ML) and 1:2(ML₂) complexes in solution. The order of stability of the metal complexes with respect to the metal ions follows the Irwing - william's natural order, Co(II), Ni(II), Cu(II) > Zn(II).