Radiation chemistry of Na3IrCl6 solutions: Catalysed H2 formation by radicals and postirradiation reduction of IrCl3-6 by propanol-2

1-Hydroxy-1-methyl ethyl radicals produced in the irradiation of Na₃IrCl₆ solutions containing propanol-2 and acetone react very slowly with the IrCl^3-₆ anion (k of the order 100 M^-1 s^-1). The product of the reaction is a compound which reacts very efficiently with the radicals and thereby catalyses the formation of hydrogen. This compound is supposed to be an iridium hydride. No iridium is produced at small Na₃IrCl₆ concentrations and a maximum H₂ yield of 3.7 H₂/100 eV is observed at concentrations of IrCl^3-₆ between 2 and 5 times 10^-4 M. At higher concentrations, iridium metal starts to be formed. A faster formation of iridium occurs in solutions of Na₃IrCl₆(>10^-3 M) containing only propanol-2 as additive. In these solutions, the reduction of IrCl^3-₆ takes place thermally after initiation with λ radiation (some 10⁴ rads). The postirradiation effect is inhibited by O₂, N₂O, CH₃I, CH₂CHCN, H₂ and CO. A mechanism for the reduction of IrCl^3-₆ by propanol-2 is proposed, in which an Ir^I complex produced by radiation acts as the catalyst.