Kinetics and thermodynamics of the intramolecular isomerization of [Fe(SCH3(CO)3]4

Ann Mueting, Bruce M. Mattson

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Abstract

The kinetics and thermodynamics of the isomerization of syn- and anti-[Fe(SCH3)(CO3)]2 were investigated over the temperature range 40-70°C in chloroform and other solvents. In chloroform the thermodynamic parameters for the isomerization syn → anti are ΔH = 1.4 ± 1.1 kcal/mol, ΔS = 6.0 ± 2.6 cal/mol°K, ΔG298 = -0.4 ± 1.9 kcal/mol. The kinetic parameters for the same reaction are ΔH‡ = 28.4 ± 1.4 kcal/mol, ΔS‡ = 27.9 ± 4.2 cal/mol°K, and ΔG‡298 = 21.1 ± 2.6 kcal/mol. The isomerization is first order in both direction and probably involves FeS bond rupture and reformation. The equilibrium constant, Kχ = [anti]/[syn] varies from 1.89 ± 0.22 at 40°C to 2.26 ± 0.18 at 70°C. The rate of isomerization increases with solvent polarity hexane <toluene <CH3CN <CHCl3).

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