Surface organometallic chemistry: physisorption and thermal decomposition of Ir4(CO)12 on silica

Abstract

The surface reactivity of Ir₄(CO)₁₂ supported on silica has been investigated by means of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed decomposition techniques. The initial stage of physisorption from a solution results in the deposition of large crystallites (ϕ > 2µ) of Ir₄(CO)₁₂, unevenly distributed on the surface. By thermal treatment in vacuum at 100 °C the complete sublimation of Ir₄(CO)₁₂ occurs. By heating under Ar or O₂ at 100 °C a disaggregation of the crystallites to single Ir₄(CO)₁₂ units evenly distributed on the surface is observed. Admission of water vapour at 25 °C promotes a high surface mobility of the Ir₄(CO)₁₂ units towards reaggregation. The formation of metallic particles is achieved by thermal decomposition of well dispersed Ir₄(CO)₁₂ in Ar at 150–200 °C or at lower temperatures in H₂. The adsorption of CO at 100 °C leads to disruption of large metallic particles. This surface process is enhanced by a preliminary study under O₂ at 25 °C.