Pb122-:: Plumbaspherene

Although Si or Ge is not known to form empty cage clusters such as the fullerenes, we recently found a unique 12-atom icosahedral tin cluster, Sn-12(2-) ( stannaspherene). Here we report photoelectron spectroscopy and theoretical evidence that Pb-12(2-) is also a highly stable icosahedral cage cluster and bonded by four delocalized radial pi bonds and nine delocalized on-sphere sigma bonds from the 6p orbitals of the Pb atoms. Following Sn-12(2-), we coin a name, plumbaspherene, for the highly stable and nearly spherical Pb-12(2-) cluster, which is expected to be stable in solution and the solid state. Plumbaspherene has a diameter of similar to 6.3 angstrom with an empty interior volume large enough to host most transition metal atoms, affording a new class of endohedral clusters.