Iron-Iridium Mixed-Metal Carbonyl Clusters: A Mössbauer Study of the Structure and of the Adsorption of [Fe2Ir2(CO)12]2- on MgO

193Ir and 57Fe Mo ssbauer spectroscopy was used to investigate the structure of the [Fe2 Ir2(CO)12]2& cluster compound and the adsorption of this cluster on hydrated MgO. Supported samples were prepared by impregnation of the magnesia with solutions of [Et4N]2[Fe2 Ir2(CO)12] in acetone. The Mo ssbauer and FT-IR spectra of the MgO-supported cluster confirm that the bimetallic carbonyl is molecularly physisorbed onto MgO without undergoing any trans- formation or decomposition. The easy solvent extraction of the intact cluster from the oxide surface excludes ion pairing between the cluster anion and the Mg2+ surface sites. Mo ssbauer spectra are in agreement with the refined struc- ture of the molecular cluster and the temperature dependence of the 57Fe Mo ssbauer spectra above 80 K is consistent with the low degree of interaction of the cluster with the support. This technique, therefore, appears to be promis- ing in order to infer structural information when X-ray determination fails.