PROTONATION THERMODYNAMICS OF 1,10-PHENANTHROLINE IN AQUEOUS-SOLUTION- SALT EFFECTS AND WEAK COMPLEX-FORMATION

The protonation of 1,10-phenanthroline has been studied potentiometric ally in different aqueous salt media (LiCl, NaCl, KCl, Me(4)NCl, Et(4) NI, MgCl2, CaCl2, SrCl2, and BaCl2) in the ionic strength range 0 less than or equal to I less than or equal to 1 M. This ligand forms two p rotonated species, [H(phen)](+) and [H(phen)(2)](+); the monoligand sp ecies shows protonation constants strongly dependent on the medium. Me dium effects were explained by the formation of some weak species: [H( phen)Cl](0), [M(phen)](2+) (M = alkaline earth metal cations). Formati on thermodynamic parameters are reported.