Equilibria in complexes of N-heterocyclic molecules. Part 13. The racemization and dissociation of some tris(1,10-phenanthroline) and tris(2,2′-bipyridyl) complexes of iron-(II) and -(III)

Abstract

The racemization and dissociation of [Fe(phen)₃]³⁺, together wrth the racemization of [Fe(phen)₃]²⁺ and [Fe(bipy)₃]³⁺, have been followed kinetically in aqueous acid solutions containing HCl, H₂SO₄, or HNO₃, up to 100% acid concentration. The rates of racemization and dissociation of [FeL₃]³⁺[L = 1,10-phenanthroline(phen) or 2,2′-bipyridyl(bipy)] are zero in 100% H₂SO₄, and the racemization of [Fe(phen)₃]²⁺ reaches a limiting rate in ca. 11.0 mol dm^–3 HCl. The kinetics of dissociation of [Fe(bipy)₃]³⁺ are quite different from other reported complexes and a maximum rate is attained at ca, 3.0 mol dm^–3 H₂SO₄. On the basis of the observations and previously reported data, a new mechanism for racemization and dissociation is proposed.