Impregnation of Fe3(CO)12 on Cab-O-Sil has been studied by ir spectroscopy, Mössbauer spectroscopy, and mass spectrometry. Isotope exchange between CO ligands of the impregnated sample and gas phase CO molecules was also investigated. On impregnation, two types of interaction can be distinguished: (i) interaction of the type FeCO...HOSi and CO...HOSi, shown by the shift to lower and higher ir frequencies for bridged and for terminal CO, respectively, and (ii) interaction between the metal framework and the support revealed in the oxidation of iron to form very small iron oxide particles. On impregnation a small amount of CO is evolved as a result of the interaction. CO exchange occurs faster with alumina-supported clusters than with silica-supported samples. On decomposition up to 370 K, the metal framework is retained and the cluster structure can be partly restored in a CO atmosphere. Above 420 K, Fe3(CO)12 is decomposed to form Fe2+ oxide on the surface. A possible mechanism for impregnation is discussed in terms of electron donation from the support oxygen to the iron d-bands as a result of which the metal-carbon bond strength is influenced. On decomposition the metallic iron interacts with the support OH groups causing oxidation and Fe2+ formation.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry