Volumes of Activation for the Base Hydrolysis of [Rh(NH₃)₅X]²⁺ Complex Ions

Abstract

The pressure dependencies of the rates of base hydrolysis of [Rh(NH₃)₅X]²⁺ were measured at 313.2 K and μ1M, where X = Cl^-, Br^-, I^- and NO₃^-, in the range 1-1500 bar. The respective Δν^‡_exp values are 19.3 ± 0.9, 20.2 ± 0.5, 20.4 ± 0.5 and 22.3 ± 0.9cm³ mol^-1. The partial molar volumes of these complexes, as well as those of other relevant pentaamminerhodium(III) complexes, were also determined. The volume data are discussed in terms of the conventional dissociative conjugate base mechanism. The Δν^‡_exp for the aquation of [Rh(NH₃)₅NO₃]²⁺ was found to be -6.9 ± 0.4cm³ mol^-1 at 313.2K, [H⁺] 0.005M and μ0.1 M. An I mechanism is favoured for this process.