Kinetic Studies of Fast Equilibrium by Means of High-performance Liquid Chromatography. V. Stepwise Complex Formation of the Nickel(II) Ion with 2,2′-Bipyridine and 1,10-Phenanthroline

The stepwise complex formation of the nickel(II) ion (M2+) with 2,2′-bipyridine(bpy) and 1,10-phenanthroline(phen) (Mn−12++L2+ with Kn=[MLn2+]/[MLn−12+][L], where n=1–3), has been investigated by means of high-performance liquid chromatography. Peaks of the labile partially ligand substituted complexes, ML2+ and ML22+, have appeared on chromatograms, along with peaks of the ML32+ and excess free ligands, on reverse phase ion-pair chromatography using sodium dodecyl sulfate in acidic media. Each labile species has been found to be eluted without any noticeable change, such as ligand addition, dissociation, or disproportionation, during chromatography. Thus, the chromatograms obtained have directly indicated the equilibrium concentrations of each species in the solutions prior to chromatography. The stepwise complex formation constants of nickel(II) with bpy or phen have been determined by means of high-performance liquid chromatography.