Ladder Oxygenation of Group VIII Metal Clusters and the Formation of Metalloxocubes M13O8+

Abstract

The diversity of valence and bonding of transition metals makes their oxidation processes perplexing at reduced sizes. Here we report a comprehensive study on the oxidation reactions of rhodium clusters Rhn± (n = 3-30) and find that Rh3,4O4+, Rh5-7O6+, and Rh8-13O8+ always dominate the mass distributions showing size-dependent ladder oxygenation which is closely associated with the O-binding modes. While the Rh8-13O8+ clusters display a μ3-O binding mode (hollow site adsorption), Rh3-4O4+ and Rh5-7O6+ favor the μ2-O binding mode (edge-site adsorption) or a mixture of the two modes. The μ3-O binding mode is inclined to yield a cubic Rh13O8, while the μ2-O binding mode gives rise to oxygen-bridge protection for the metal clusters. Such ladder oxidation was also observed for Ptn+, Fen+, Con+, and Nin+ clusters. We propose a three-dimensional diagram for the oxidation states and O-binding modes of metals, and highlight the metalloxocubes M13O8+ for cluster-genetic materials.