M8(μ8-E′)(μ4-E)6L8 Species Centered and Hexacapped by Main-Group Atoms

The bonding in main-group atom-centered hexacapped transition-metal cubic clusters M8(μ8-E′)(μ4-E)6L8 has been analyzed by means of density functional theory (DFT) calculations. Although only one example of such compounds has been characterized so far, DFT results indicate that it should be possible for other members of this family to be synthesized. As for their metal-centered parents, there are several “magic” electron numbers that are able to satisfy the closed-shell requirement for such species, depending on the nature of the metal and the capping ligands. The most probable cluster valence electron counts that imply significant M–M bonding are 120 and 122. The former value is favored when E′ is an early main-group element while the latter value is favored when E′ is a late main-group element. Owing to the high connectivity between the atoms, such a regular cubic architecture may also be observed with open-shell electron configurations, as observed for the 119-cluster-valence-electron cluster Ni8(μ8-As)(μ4-As)6(PPh3)8.