SURFACE ORGANOMETALLIC CHEMISTRY - PHYSISORPTION AND THERMAL-DECOMPOSITION OF IR4(CO)12 ON SILICA

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 (phi > 2-mu) of Ir4(CO)12, unevenly distributed on the surface. By thermal treatment in vacuum at 100-degrees-C the complete sublimation of Ir4(CO)12 occurs. By heating under Ar or O2 at 100-degrees-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-degrees-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-degrees-C or at lower temperatures in H-2. The adsorption of CO at 100-degrees-C leads to disruption of large metallic particles. This surface process is enhanced by a preliminary study under O2 at 25-degrees-C.