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

摘要

The kinetics of anation of (diaqua)(1,2-bis(2-hydroxybenzamido)iron(III) by NCS~- and S~(IV) (HSO_3~- and SO_3~(2-)) are reported at 25 deg C, I = 0.5 mol dm~(-3) in 20% (v/v) MeOH + H_2O medium. The formation of the monothiocyanato complex, Fe(L)(OH_2)(NCS), is reversible. The monosulphito complex, Fe(L)(OH_2)(SO_3)~- is formed via the reaction of the diaqua complex with HSO_3~- and SO_3~(2-); dissociation of the sulphito complex to the reactants has not been observed. Ion-pairing of the diaqua complex with SO_3~(2-) (but not with HSO_3~-) has been identified kinetically and resulted in the reduced reactivity of SO_3~(2-) in comparison to HSO_3~-. The results are consistent with the dissociative mode of activation for the aqua ligand substitution of Fe(L)(OH_2)_2~+. It has been found that there is no significant labilising action of the coordinated phenoxide and amide function of the primary ligand (L~(2-)) on the aqua ligand replacement reaction at iron(III) center.