: A Ligand - Free Intermetalloid Cluster

One of the most important aspects of metal clusters is that they provide a window into the rather ill-defined area of chemistry that lies between isolated molecular species and solid-state compounds with extended structures. Small, cage-like clusters have been relatively well studied and are found to generally follow established rules for electron counting and isolobal relationships. Their structures and bonding are fairly well understood and can be rationalized within the context of these rules. However, this is not the case for large clusters with high nuclearities (more than 12 atoms) and dimensions beyond that of the nanometer. These species lack such a cohesive foundation, and furthermore, many of them seem to disobey traditional electron-counting rules, which ultimately makes the discussion of their structure and bonding very difficult. In addition, only a handful of such clusters have been structurally characterized, most of them limited to the field of precious-metal cluster chemistry. This scarcity is all the more valid for main-group-element species, for which the first example, [Al77{N(SiMe3)2}20] 2 , was isolated by Schn/ckel and co-workers only a few years ago. These authors coined the term metalloid cluster for such species in which the metal–metal contacts in the cluster outnumber the metal–ligand contacts, and in which the cluster atoms exhibit close packing, as in bulk metals. More species have been discovered since, and the cluster chemistry of Group 13 has been enriched by the isolation of species with Aln (n= 7, 12, 14, 50, 69) and Gam (m= 9, 10, 19, 22, 24, 26, 84) metal cores. Similarly, large metal-centered clusters of Group 14 elements have also been extensively studied in recent years. The synthetic approach towards these species involves reactions of nine-atom deltahedral clusters of Group 14 elements, known as Zintl ions, with various transition-metal complexes. Some of the species isolated by this route are: [Ni(Ni@Ge9)2] 4 , [Pd2@Ge18] 4 , [Ni2Sn17] 4 , [Ni@ Pb10] 2 , [Pt@Pb12] 2 , and a single cluster of a Group 15 element, [As@Ni12@As20] 3 . These species are also metalloid clusters, although, as they involve more than one metal, they may be more appropriately referred to as intermetalloid