Speciation of iridium(IV) in hydrochloric acid medium by means of capillary zone electrophoresis and spectrophotometry

Speciation of iridium(IV) [Ir(IV)] in hydrochloric acid solutions at different proton concentrations (between 1 and 10(-3) M) has been studied using capillary zone electrophoresis and spectrophotometry in order to determine the number of species that are formed during the aquation and hydrolysis of the hexachloro complex of Ir(IV). The formation of more than seven species was found. The presence of [IrCl6](2-), [Ir(H2O)Cl-5](-) and [Ir(OH)Cl-5](2-) species of Ir(IV) and [Ir(H2O)Cl-5](2-) and [Ir(OH)Cl-5](3-) of Ir(III) give the best explanation of the obtained results. The formation of other species detected in solution can be explained by the formation of dimers of the aquated species by the formation of hydroxo bridges. A spontaneous reduction of Ir(IV) to Ir(III) has been proved in all the solution studied. The extension of this process increases at higher pH values. Other peaks that appear in the electropherograms are associated to the formation of dimers of the aquated species by means of hydroxo bridges. (C) 1999 Elsevier Science B.V. All rights reserved.