Comparative formation constants for complexes of copper, nickel, and silver with some substituted pyridines

Abstract

Formation constants for metal complexes of Cu(II), Ni(II), and Ag(I) with some substituted pyridine ligands were determined in a nitrate salt solution of the ligand (0.5 F KNO3 + 0.1 F HL) at 25 °C by pH measurement. The linear relationship shown by a logarithmic plot of the formation constant versus the basicity of the ligands characterizes qualitatively the dΠ → pπ-bonding capacity for each metal ion. The 2-substituents, such as —CH3 and —NH2, on these pyridine ligands have a very profound steric effect upon the stabilities of Cu(II) and Ni(II) complexes, but have no such effect upon that of Ag(I) complexes. An explanation is given which may be useful in selecting analytical reagents.