Structure and behaviour of Ru3(CO)12 supported on inorganic oxide surfaces, studied by EXAFS, infrared spectroscopy and temperature-programmed decomposition

Abstract

The structure and behaviour of Ru₃(CO)₁₂ supported on inorganic oxides such as V₂O₅, SiO₂, TiO₂, Al₂O₃, K-Al₂O₃, MgO and MnO₂ have been studied by means of EXAFS, IR and TPD. Ru₃(CO)₁₂ was physisorbed on V₂O₅, SiO₂, and TiO₂, whereas [Ru₃(CO)₁₀(µ-H)(µ-O)] and [HRu₃(CO)₁₁]^– were formed on Al₂O₃ and the basic supports MgO and K-doped Al₂O₃, respectively, by the reaction of Ru₃(CO)₁₂ with the surface OH groups. Although [HRu₃(CO)₁₁]^– was observed with MnO₂, most of Ru₃(CO)₁₂ was oxidized on this surface. By the thermal decomposition of the supported clusters on V₂O₅ and SiO₂, Ru metal and coordinatively unsaturated Ru₃(CO)₆ were formed, respectively, where no Ru—O bonding was observed by EXAFS. In contrast to these surfaces, on TiO₂[Ru₃(CO)₆] was bonded to the surface oxygens to form [Ru₃(CO)₆(µ-OTi)₃] with a Ru—O distance of 0.219 nm and an Ru–Ru distance of 0.275 nm. Similar structures, with different bond distances, were suggested for Ru₃ clusters on K-Al₂O₃ and MgO. The monomeric Ru twin carbonyls [Ru(CO)₂(OAl)₂] which have the direct Ru—O bond of 0.218 nm in a bidentate form were formed on Al₂O₃. On the MnO₂ surface, Ru oxide having Ru—O bonds of 0.200 nm was formed. The monomeric [Ru(CO)₂(OAl)₂] exhibited CO stretching at 2080 and 2030 cm^–1. [Ru₃(CO)₆(µ-OTi)₃] with a Ru–Ru distance of 0.275 nm showed peaks at 2081 and 2009 cm^–1, while [Ru₃(CO)₆(µ-OZ)₃](Z = Mg or Al) with the Ru–Ru distance of 0.271 nm showed peaks at 2040–2050 cm^–1 and 1959–1975 cm^–1. Peaks at 2067 and 2010 cm^–1 were observed with [Ru^o₃(CO)₆] on SiO₂ with no direct chemical bonding to SiO₂ surfaces. The different structures of the Ru twin carbonyl species produced on the various oxide surfaces are discussed in terms of the acidity or basicity of metal oxides and the strength of the support metal–oxygen bond.