Stability Constants of Some Polydentate Ligands with Nickel(II) by Spectrophotometric Titration

The polydentate macrocyclic ligands, 1,4,7,10-tetraazacyclododecane (L-1), 1,4,8,11-tetra (2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane (L-2); and acyclicpolydentate ligands; 3-(2-aminocyclohexylamino)-2-(2-aminocyclohexylaminomethyl) propionic acid (L-3), 4,7,10-triazatridecane dinitrile trihydrochloride (L-4), 2, 2'-(1,2-diyl)bis(methylazanediyl)diethanol (L-5) and 1,1'-(ethane-1,2-diylbis((2-aminoethyl) azanediyl)) dipropan -2-ol, (L-6) were prepared and their structures were investigated by FTIR, NMR and MS. The stability constants of the nickel (II) complexes with these ligands were determined by spectrophotometric titration using a diode array UV-VIS spectrophotometer equipped with peristaltic pump and pH meter. The values of the stability constants are discussed in terms of the open chain or cyclic nature of the ligands. The effect of pendant group on the stability of the complexes is discussed.