Utilisation of in situ formed cyano-bridged coordination polymers as precursors of supported Ir–Ni alloy nanoparticles with precisely controlled compositions and sizes†

Ir–Ni alloys supported on SiO₂ have been reported to show high catalytic activity for styrene hydrogenation; however, precise control of compositions and sizes of the Ir–Ni alloys is difficult when conventional metal salts are used as precursors. Furthermore, the concomitant formation of unalloyed Ni nanoparticles disturbs quantitative discussion about Ir–Ni alloy compositions. We report herein a preparation method of Ir–Ni alloys with precisely controlled compositions on SiO₂ using Ni(NO₃)₂ and an Ir complex possessing CN⁻ ligands, [Ir(CN)₆]³⁻ or [Ir(ppy)₂(CN)₂]⁻ (ppy = 2-phenylpyridine), as precursors. The in situ formation of cyano-bridged coordination polymers involving Ir and Ni promotes the formation of Ir–Ni alloys, whose compositions are virtually the same as expected from the amounts of Ir and Ni used for the preparation, after heat treatment under H₂. The use of [Ir(ppy)₂(CN)₂]⁻ as the precursor resulted in the formation of smaller Ir–Ni alloy particles than those with [Ir(CN)₆]³⁻ related to the structures of the formed coordination polymers.