Protonation thermodynamics of 1,10-phenanthroline in aqueous solution. Salt effects and weak complex formation

Abstract

The protonation of 1,10-phenanthroline has been studied potentiometrically in different aqueous salt media (LiCl, NaCl, KCl, Me4NCl, Et4NI, MgCl2, CaCl2, SrCl2, and BaCl2) in the ionic strength range 0≤1≤1 M. This ligand forms two protonated species, [H(phen)]+ and [H(phen)2]+; the monoligand species shows protonation constants strongly dependent on the medium. Medium effects were explained by the formation of some weak species: [H(phen)Cl]0, [M(phen)]2+ (M=alkaline earth metal cations). Formation thermodynamic parameters are reported.