Ternary complexes of iron(III) with 1, 2-bis(2-hydroxybenzamido)ethane, thiocyanate and sulphur(IV): A kinetic study.

Abstract

The kinetics of anation of (diaqua)(1,2-bis(2-hydroxybenzamido)iron(III) by NCS¯ and S^IV (HSO₃¯ and SO₃^2- ) are reported at 25°C, <i>I= </i>0.5 mol dm^-3 in 20% (v/v) MeOH + H₂O medium. The formation of the monothiocyanato complex, Fe(L)(OH₂)(NCS), is reversible. The monosulphito complex, Fe(L)(OH₂)(SO₃)¯ is formed via the reaction of the diaqua complex with H SO_3¯ and SO₃^{2 -} ; dissoc iation of the sulphito complex to the reactants has not been observed. Ion-pairing of the diaqua complex with SO₃^{2 -} (but not with HSO_3¯) has been identified kinetically and resulted in the reduced reactivity of SO₃^{2 -}in comparison to HSO_3¯. The results are consistent with the dissociative mode of activation for the aqua ligand substitution of Fe(L)(OH₂)₂⁺. It has been found that there is no significant labilising action of the coordinated phenoxide and amide functions of the primary ligand (L^2-) on the aqua ligand replacement reaction at iron(III) center.