Multiple-decker sandwich compounds

The most unusual geometries among these types of clusters are clearly the multiple-decker sandwich structures observed for vanadium ion-benzene clusters Vn(C6H6)+ [142, 151-157]. One interesting finding is that early transition metals all appear to form sandwich compounds with benzene but for the late metals the benzene adducts coat a central metal cluster [158]. 

There has been considerable interest in the synthesis of polymers such as structure (6) in which aromatic rings and metal atoms alternate, due to the possibility of building extended electron-delocalized organometallic polymer chains. However, such a multiple decker polymer has not yet been synthesized, and only a few triple decker-sandwich compounds such as tris( 5-cyclopentadienyl)dinickel cation and tris-(cyclooctatetraene)dititanium dianion have been reported10. ... 

Several examples illustrate how organometallic molecules are strikingly different from those encountered in classical inorganic and organic chemistry. Ligands1 of cyclic delocalized n systems (e.g., benzene or cyclopentadienyl) can team up with metal atoms to form sandwich compounds with a metal sandwiched between them. Sometimes atoms of other elements, such as phosphorus or sulfur, can be included as well. Examples of these double- and multiple-decker sandwich... 

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