Kinetics and mechanism of the aquation of the trinuclear cation, [mu(3)-oxo-triaqua-hexakis(acetato)tris(iron(III))](+) in perchloric acid media

摘要

The aquation of the title complex cation in aqueous perchloric acid proceeded via two steps, both postulated to be the proton attack on the oxygen atom which binds the acetate ligand to the metal centre, followed by Fe-O bond cleavage. This was followed by rapid decomposition to produce aqueous iron(III) and acetate ions. The first-order rate constants for the first and second steps at 25 degrees C are: k(1) (4.16 +/- 0.58) x 10(-2) s(-1) and k(2) = (2.09 +/- 0.42) x 10(-3) s(-1), respectively, and their corresponding activation parameters are Delta H-1(double dagger), 22.2 +/- 11.6 kJ mol(-1), Delta S-1(double dagger) = -197 +/- 5 J K-1 mol(-1), Delta H-1(double dagger) = 40.2 +/- 3.8 kJ mol(-1), Delta S-1(double dagger) = - 161 +/- 13 J K-1 mol(-1). The spontaneous hydrolysis rate constants for the first and second steps were also determined at 25 degrees C and ionic strength of mol dm(-3) and they are k(0) (3.10 +/- 0.82) x 10(-3) s(-1) and k(0)' = (2.65 +/- 0.68) x 10(-4) s(-1), respectively. The corresponding activation parameters 0 are Delta H-0(double dagger) = 32.5 +/- 5.5 kJ mol(-1), Delta S-0(double dagger) 184 +/- 18 J K-1 mol(-1); Delta H-0(double dagger) = 39.0 +/- 2.6 kJ mol(-1), Delta S-0(double dagger) 182 +/- 8 J K-1 mol(-1). (c) 2005 Elsevier B.V. All rights reserved.