Site Preference Effects in Heterometallic Clusters

In organometallic chemistry new and versatile synthetic routes have been developed for isolating heterometallic ligated cluster compounds with up to 44 metal atoms. Naked mixed metal clusters with size ranges of 10–50 Å are of importance in catalytic processes and smaller naked heterometallic clusters have been isolated in molecular beam experiments. These rather different areas raise common problems concerning the relative dispositions of the two types of metal atoms. In this review a general analysis of site preference effects derived from molecular orbital perturbation theory methods is developed. For naked clusters the site preferences are controlled primarily by the relative strengths of the metal—metal bonds, with the metal that forms stronger metal—metal bonds occupying interstitial or high connectivity sites. For ligated clusters these effects are important but the relative strengths of the metal—ligand bonds can also play a decisive role.