Ladder Oxygenation of Group VIII Metal Clusters and the Formation of Metalloxocubes M 13 O 8 .

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 Rh n ± ( n = 3-30) and find that Rh 3,4 O 4 + , Rh 5-7 O 6 + , and Rh 8-13 O 8 + always dominate the mass distributions showing size-dependent ladder oxygenation which is closely associated with the O-binding modes. While the Rh 8-13 O 8 + clusters display a μ 3 -O binding mode (hollow site adsorption), Rh 3-4 O 4 + and Rh 5-7 O 6 + favor the μ 2 -O binding mode (edge-site adsorption) or a mixture of the two modes. The μ 3 -O binding mode is inclined to yield a cubic Rh 13 O 8 , while the μ 2 -O binding mode gives rise to oxygen-bridge protection for the metal clusters. Such ladder oxidation was also observed for Pt n + , Fe n + , Co n + , and Ni n + clusters. We propose a three-dimensional diagram for the oxidation states and O-binding modes of metals, and highlight the metalloxocubes M 13 O 8 + for cluster-genetic materials.