Effect of Excess of Secondary Ligand on Speciation and Stability in Some Ternary Complexes

Abstract

Stability constant of ternary complexes of type MAL where M = Ni(II) and Cu(II) and A = diamine (ethylene diamine, 1,2-diaminopropane, 1,3-diaminopropane, o-, m- or p-phenylenediamine) and L = salicylic acid, have been determined by potentiometric method in aqueous medium at 30 ± 0.1ºC at 0.2 M ionic strength under nitrogen atmosphere. Ratio of metal to primary ligand and secondary ligand is maintained at 1 : 1 : 1.5, 1 : 1 : 2 and 1 : 1 : 2.5 and compared. Stability of ternary complexes affected by concentration of secondary ligand along with other parameters like D log K_T, structure and basicity of primary and secondary ligand, steric factors, chelation, etc. Species distribution diagrams also reflect the effect of concentration of secondary ligand on percentage distribution of various species. FORTRAN-IV Program has been used for calculation and for pruning species like MAL, MAL₂, MA₂L, MAL₂H₂ etc., in equilibrium conditions.