Oxidation reaction of [Ni(1,4,7-triazacyclononane)_2]~(2+) by [Fe(O-phenanthroline)_3]~(3+) in aqueous acidic solution at elevated pressures:determination of the activation and reaction volumes for the Ni(III)/(II) couple

摘要

The reaction volume corresponding to the self-exchange process of the [Ni(tacn)_2]~(3+/2+) couple was determined in aqueous acidic solution.Theoretical equations on the basis of the Mean Spherical Approximation were proposed for the estimation of reaction volumes for M~(n+/(n-1)+) couples in solution,and the calculated reaction volumes were compared with the experimentally estimated values.The activation volume for the [Ni(tacn)_2]~(3+/2+) couple was determined in the acidic condition from the cross reaction of [Ni(tacn)_2]~(2+) and [Fe(O-phen)_3]~(3+) at elevated pressures.The agreement of the experimentally estimated activation volume for the [Ni(tacn)_2]~(3+2+) couple,-8.2+-2.4 cm~3 mol~(-1),with the theoretically calculated value,-7.5 cm~3 mol~(-1),within the allowed uncertainty (+-1 cm~3 mol~(-1)) indicates that the electron self-exchange reaction of this redox couple obeys the Marcusian behavior in aqueous acidic solution.