Solution equilibrium studies on complex formation by biological metal ions with 3- and 5- aldehydosalicylic acids and their aniline schiff base mixed ligands.

Equilibrium study on the mixed ligands complex formation of transition metal ions (M2+ = Cu, Zn, Ni, Co ) with 3-aldehydosalicylic acid (3ASA) and 5-aldehydosalicylic acid (5ASA) form variety of binary and mixed – ligand complexes with Cu(II), Zn(II), Ni(II) and Co(II). The mixed ligand complexes dominate the pH range of biological relevance. Formation constants of the proton-ligand and metal-ligand complexes at 30oC in 50% (v/v) water-ethanol medium, at ionic strength I= 0.1 mol/dm3, were determined employing Calvin Bjerrum titration technique as adopted by Irving and Rossotti. The order of stability constants were found and are in agreement with Irving-Williams order. The changes of colour during titration have been studied with related to stepwise formation constants of different complex species in solution for separate ligand titrations and mixed-ligand titrations. The complex formation equilibriums were elucidated by analyzing the speciation curves and correlated with the mode of coordination of the ligands.