K2[Ir(OH)6]: an isolable platform intermediate for the refining of complex chloroiridate mixtures to synthetically useful Ir(iii) coordination complexes.

A holistic approach to iridium recycling is the synthesis of technologically useful iridium(iii) coordination complexes from complex aqueous waste streams. Simple, chloride-free complexes such as Ir(acac)3 are precursors for a variety of important applications: as homogeneous pre-catalysts, precursors to IrO x nanoparticles, and molecular sources for iridium thin films. However, their synthesis from the major refinery intermediate [NH4]2[IrCl6] is typified by harsh reaction conditions and moderate yields. We now show that a key platform intermediate for such complexes, K2[Ir(OH)6], can be reliably isolated as a crystalline, compositionally pure, material from both [IrCl6]2- salt precursors and crude refinery chloroiridate solutions, as optimized using the convenient analytical reporters of cyclic voltammetry and ultraviolet-visible spectroscopy. K2[Ir(OH)6] is shown to be a platform intermediate for the formation of iridium(iii) coordination complexes, demonstrated by mild, selective and high yielding routes to known Ir(acac)3, cis- and trans-K[Ir(oxalate)2(H2O)2], and new K3[Ir(citrate)2]. The reliable isolation of K2[Ir(OH)6] from refinery streams opens up opportunities for iridium recycling by the synthesis of industrially important, but compositionally simple, Ir(iii) complexes.