Effect of Schiff bases on stabilities of copper(II) complexes

Some substituted Schiff bases viz., cyano acetyl benzalidene hydrazone (CABH), cyano-acetyl salicylidene hydrazone (CASH) and cyanoacetyl 3:5 diiodo salicylidene hydrazone (CAISH) have been synthesized and the effect of substitution in the ligand molecule on stabilities of Cu(II) complexes has been studied. The metal ligand ratio was found to be 1:1 conductometrically following job's method. The stabilities of the complexes have been determined by Bjerrum-Calvin pH titration technique. The log k(H) values of these ligands were found to be 9.24 (CABH), 9,10 (CASH) and 10.15 (CAISH). The order of stabilities of Cu(II) complexes with these ligands has been found to be Cu-CABH > Cu-CASH > Cu-CAISH which has been explained on the basis of pi electron delocalization possible in the ligand molecules.