pi complexes: This subset of the database focuses on organometallic species that involve "pi" complexes--delocalized bonds involving a central atom and one or more ligand that interacts through a pi-orbital system. There some pretty interesting compounds here. Not all are cyclopentadienyl complexes, although those are most common. Can you find the complexes involving benzene or cyclooctatetraene? What is the charge on the cyclooctatetraenyl ligand? Why?