The acid-catalysed hydrolysis of the azidopentammine complexes of chromium(III), cobalt(III), and rhodium(III)

Abstract

The acid-catalysed hydrolysis of the ions [M(NH₃)₅N₃]²⁺(where M = Co, Cr and Rh) in aqueous sulphuric acid at various temperatures has been studied. In each case a limiting rate of hydrolysis was observed and the apparent pK_a values of the complexes were deduced. The activation energies for the hydrolyses of the completely protonated species have been evaluated. The activation energy for the chromium system is appreciably lower than that for the Group VIII metal systems, which is attributed to the weaker chromium–nitrogen bond as compared with, e.g. the cobalt–nitrogen bond. The difference in rate of reaction between the complexes of cobalt and rhodium is much smaller than in the case of basic hydrolysis. A unimolecular mechanism is proposed for these acid-catalysed hydrolyses.