MECHANISTIC INFORMATION FROM THE EFFECT OF PRESSURE ON THE KINETICS OF SOME ANATION REACTIONS OF AQUOPENTAAMMINECOBALT(III), AQUOPENTAAMMINERHODIUM(III), AND AQUOPENTAAMMINECHROMIUM(III) IONS IN ACIDIC AQUEOUS-SOLUTION

The anations of Co(NH3)5OH23+ by Cl- SO42-, Rh(NH3)5OH23+ by Cl-, and Cr(NH3)5OH23+ by NCS- studied in acidic aqueous solution as a function of nucleophile concentration and pressure up to 1.5 kbar. No kinetic evidence for the participation of ion pairs could be found. The volumes of activation for the anation reactions are +1.4 ± 0.8 (μ = 2 M, 60 °C), +2.3 ± 1.8 (μ = 2 M, 60 °C), +3.0 ± 0.7 (μ = 2 M, 60 °C), and -4.9 ± 0.6 cm3 mol-1 (μ= 1 M, 50 °C), respectively. These values were used in conjunction with the volumes of activation for the corresponding aquation reactions to estimate the overall volume changes incurred in the reactions. The latter could then be compared with independently obtained values of Δ. The results are discussed in terms of an interchange mechanism and compared with data reported in the literature. © 1979, American Chemical Society. All rights reserved.